Reaction Types and Rates: a full term of science

Ten ready-to-teach lessons for Year 10 Chemical sciences. Print this pack and the term is prepared: every lesson comes with a step-by-step plan, the questions to ask, a student worksheet, cut-out cards, a class sheet or exit tickets, an assessment kit and worked answers.

Start here: five minutes to Monday

1. Skim the term at a glance on the next page.
2. Print the lesson you need. Each lesson is three A4 sheets: plan, worksheet, and cards, a class sheet or tickets.
3. Gather the few items under “You need” on the plan. Most come from the classroom or the science prep room.
4. Open the free interactive unit on your board or projector. Every plan tells you which picture to show and when.
5. Teach straight from the plan. Timings, talk prompts, misconceptions and worked answers are all on the one page.

For any Year 10 science teacher

The pack suits a chemistry specialist and a teacher working outside their own subject alike: each plan explains the idea in plain words, lists the misconceptions students bring, and gives worked answers. The big idea of the term has two halves. Many reactions follow one of three patterns, so their products can be predicted; and every reaction runs at a rate set by how often particles collide with enough energy, which temperature, concentration, surface area and catalysts all change.

Two ways to run each lesson

Every lesson works as one 60-minute block, or as two 30-minute sessions; the split point is marked in every plan. Look ahead: Lessons 7 to 9 use effervescent tablets, dried yeast and 3% hydrogen peroxide from a supermarket or pharmacy.

Safety and care in one look

Safety glasses for every practical; nobody looks straight at burning magnesium. Lift the delivery tube out of the limewater before taking the heat away. Use small volumes of the acids and salt solutions, and wash hands. Warm water stays below 50 °C.

The term at a glance

One lesson a week for a term. Each lesson stands on the ones before it, so run them in order where you can.

How the sequence builds

Lesson 1 meets the three patterns, and Lessons 2 to 4 see each one at the bench. Lesson 5 uses the patterns to predict products. Lesson 6 turns to speed and measures a rate, so that Lessons 7 to 9 can test what changes it: temperature, concentration and surface area, and catalysts. Lesson 10 brings both halves together.

Curriculum links (Australian Curriculum V9)

The whole term teaches the Science Understanding descriptor AC9S10U07 quoted on the cover. The lessons also work these Science Inquiry descriptors:

Assessment in this pack

• Every plan ends with “Answers and look-fors”: what meeting the idea sounds like in a Year 10 voice, with working.
• The assessment sheet near the front has a class observation checklist and a three-level rubric.
• Lesson 10 is the summative pair: the marble chip task, plus the “Show what we know” check.

Materials for the whole term

One gathering session covers all ten lessons, and most of it is already in the science prep room. Two things are worth doing ahead: make up the four strengths of hydrochloric acid for Lesson 8, and buy effervescent tablets, dried yeast and 3% hydrogen peroxide for Lessons 7 to 9.

The one-trip list

• From the prep room: Bunsen burners, tongs, test tubes, delivery tubes, spotting tiles, the metals, the salt solutions, copper carbonate, limewater, marble chips, hydrochloric acid, balances, manganese dioxide.
• From the classroom: scissors, timers, rulers and calculators.
• From a supermarket or pharmacy: effervescent vitamin C tablets, dried yeast, 3% hydrogen peroxide and detergent.

Safety and care in one look

• Safety glasses for every practical. Hot foil and test tubes are held in tongs or a holder, pointing away from people.
• Take the delivery tube out of the limewater before taking the heat away, so the limewater cannot be sucked back.
• Small volumes of acid and salt solutions; wash hands afterwards. Warm water no hotter than 50 °C. Manganese dioxide is for the teacher only.

Assessment without extra work

The term assesses itself. Every lesson plan ends with worked answers and look-fors, and Lesson 10 is the summative pair: the task, in which students name four reactions, plan a rate investigation and compare small and large marble chips from their gas readings, and the final check. This sheet is the place to note what you see along the way.

The three levels

Class observation checklist

A tick a lesson is plenty; the Lesson 10 task and check fill the gaps.

Word wall cards

Cut out the cards and build the wall as the words arrive: reactant, product, synthesis, decomposition, displacement, word equation and symbol equation in Lesson 1; conservation of mass in Lesson 2; thermal decomposition in Lesson 3; reactivity series in Lesson 4; rate of reaction and gradient in Lesson 6; collision theory and activation energy in Lesson 7; concentration and surface area in Lesson 8; catalyst and enzyme in Lesson 9.

Dear families

This term in science, Year 10 studies chemical reactions in two ways: the patterns that let chemists predict what a reaction will make, and the factors that decide how fast it goes.

Along the way your student will turn copper black in a flame, heat green copper carbonate until it gives off carbon dioxide, rank four metals by watching them push each other out of solution, time tablets fizzing in warm and cold water, and make foam from hydrogen peroxide and yeast.

Try this at home

• Drop half an effervescent tablet into cold water and half into warm water at the same time. Which finishes first?
• Compare a whole sugar cube and a spoonful of loose sugar stirred into water. Which dissolves faster, and why?
• Look for rust on an old tool or bike: iron, oxygen and water have combined into a new substance.
• Ask why food lasts longer in the fridge, and why bread with yeast rises faster in a warm place.

What to ask your scientist

• What are the three patterns of reaction, and how do you tell them apart?
• Why does a more reactive metal push a less reactive one out of a solution?
• What has to happen when particles collide for a reaction to take place?
• What is a catalyst, and where are catalysts used?

A small note on safety: practical work this term uses Bunsen burners, dilute acids and salt solutions, always with safety glasses and small amounts. The household hydrogen peroxide is the mild 3% kind.

Warm regards,

The Year 10 science team

Printed from the free seegongsik Reaction Types and Rates teaching pack · seegongsik.com/au/y10/chemical/AC9S10U07/pack

Three patterns

A great many reactions follow one of three shapes. In synthesis, two or more reactants combine into one product, A + B → AB, as when magnesium burns in air to make magnesium oxide. In decomposition, one compound splits into simpler products, AB → A + B, as when heat breaks copper carbonate into copper oxide and carbon dioxide. In displacement, an element takes the place of another inside a compound, A + BC → AC + B, as when an iron nail in copper sulfate solution comes out coated with copper. Once students can see the shape of an equation, they can sort reactions, spot one that is another run backwards, and later predict products. Today they sort twelve reactions, each with its equation and where it happens.

We are learning to

• describe the patterns of synthesis, decomposition and displacement reactions,
• classify a reaction from its word or symbol equation,
• pick out the reactants and the products in an equation.

Success criteria

• I can sort reactions into the three patterns and explain each choice.
• I can write the general form of each pattern with letters.

You need

• the reaction cards (third sheet), one set per pair, with scissors,
• the worksheet (next sheet), one per student; a rusty nail and a new one, or photos of each.

Lesson flow (about 60 minutes)

Running two half-sessions instead? Do the nails, the board and Part A in Session A, and the cards, Part C and the debate in Session B.

Watch for these ideas

• “Two products means decomposition.” Count the reactants too: magnesium in acid has two of each, and an element swaps places.
• “Burning is a different kind of reaction.” Magnesium or carbon burning in oxygen is also synthesis: two reactants, one product.
• “The number in front changes the substance.” It counts the particles; the formula, and so the substance, stays the same.

Make it easier, make it bigger

• Easier: sort the cards by their equations with the lower line folded under, then unfold to check against the places.
• Bigger: methane burns as CH₄ + 2O₂ → CO₂ + 2H₂O. Why does it fit none of the three patterns?

Answers and look-fors

• Part A: synthesis A + B → AB: two or more reactants combine into one product; decomposition AB → A + B: one compound splits into simpler products; displacement A + BC → AC + B: an element takes the place of another in a compound.
• Part B: synthesis C, E, F, I, K; decomposition A, D, J, L; displacement B, G, H.
• Part C: 1. Cards D and I: salt split by electricity is decomposition, and sodium burning in chlorine is synthesis. 2. An element, magnesium, takes the place of hydrogen in the acid, and hydrogen comes out on its own. 3. Answers vary; for example carbon + oxygen → carbon dioxide, water → hydrogen + oxygen, zinc + copper sulfate → zinc sulfate + copper.
• Bigger: there are two reactants and two products, but no element is set free; both products are new compounds.

Three patterns

A. Three shapes

B. Sort the reaction cards

Write the letters of the cards under each pattern.

C. Questions

Which pattern?

Cut out the three headings and the twelve cards. Sort each reaction under its pattern.

Teacher note: the answer letters are in the plan. The three piles are different sizes.

Building up

In a synthesis reaction the reactants combine, and the product holds every atom they brought. Heated in air, copper combines with oxygen to make black copper oxide: 2Cu + O₂ → 2CuO. Fold the copper into a closed envelope first and only the outside turns black, because the air cannot reach the inside: the oxygen comes from the air. Magnesium burns with a dazzling white flame to make white magnesium oxide: 2Mg + O₂ → 2MgO. The product is heavier than the metal, because it has gained the mass of the oxygen; no atoms are made or lost. In magnesium oxide every 24 g of magnesium joins 16 g of oxygen, so a graph of the oxygen against the magnesium is a straight line, and one result in the example class is clearly off it.

We are learning to

• describe synthesis reactions between metals and oxygen,
• use conservation of mass to work out the mass of a reactant,
• spot an odd result on a graph and suggest what caused it.

Success criteria

• I can explain why only the outside of my copper envelope turned black.
• I can work out the mass of oxygen that joined the magnesium, and explain the odd result.

You need

• for each group: a 3 cm square of copper foil, tongs, a Bunsen burner on a heatproof mat, safety glasses,
• for the teacher: a 3 cm strip of magnesium ribbon and tongs; the worksheet (next sheet), one per student; the exit tickets (third sheet), cut into four.

Lesson flow (about 60 minutes)

Running two half-sessions instead? Do the magnesium, the board and the envelopes in Session A, and Parts B and C and the ticket in Session B.

Watch for these ideas

• “Burning destroys matter, so the product is lighter.” A metal that burns gains oxygen, so its product is heavier.
• “The black is soot from the flame.” The inside sat in the same flame and stayed shiny: the black formed only where air could reach.
• “An odd result can just be crossed out.” Say why it is odd and what may have caused it, then leave it out of the line.

Make it easier, make it bigger

• Easier: work out the oxygen for group 1 together: mass of the oxide − mass of the magnesium.
• Bigger: what mass of magnesium oxide would 1.2 g of magnesium make?

Answers and look-fors

• Part A: the outside turns black (copper oxide) and the inside stays shiny: the black forms only where oxygen from the air reaches the copper.
• Part B: oxygen 0.08, 0.11, 0.16, 0.15, 0.23 g. All but group 4 sit on a straight line through the origin with a gradient of about 0.67.
• Part C: 1. Oxygen from the air combined with the magnesium, adding its mass. 2. Group 4: too little oxygen for its magnesium; some white smoke of magnesium oxide escaped when the lid was lifted, or not all of the magnesium reacted. 3. 2Mg + O₂ → 2MgO; synthesis, because two reactants make one product.
• Exit ticket: 1. Copper + oxygen → copper oxide (2Cu + O₂ → 2CuO). 2. 3.0 − 1.8 = 1.2 g. 3. Two reactants combine into one product.
• Bigger: 1.2 × 40 ÷ 24 = 2.0 g.

Building up

A. The copper envelope

B. An example class: magnesium in a crucible

Each group heated magnesium in a crucible, lifting the lid now and then, and weighed the white oxide. These are example results.

C. Questions

Exit tickets

Breaking down

Decomposition needs energy to break bonds, most often heat (thermal decomposition) or an electric current. Heated, green copper(II) carbonate turns black as it breaks into copper oxide and carbon dioxide: CuCO₃ → CuO + CO₂. The gas turns limewater milky, the test for carbon dioxide. The solid left behind is lighter by exactly the mass of gas that escaped, so mass is conserved once the gas is counted. Every sample that is heated until nothing more changes loses the same share of its mass, about 35.6%, because the formula fixes how much of the compound leaves as carbon dioxide. Students heat copper carbonate and test the gas, then work through an example class in which one group stopped heating too soon.

We are learning to

• describe thermal decomposition, and test a gas for carbon dioxide,
• use conservation of mass to find the mass of a gas given off,
• calculate a percentage change in mass and use it to judge results.

Success criteria

• I can explain why the solid gets lighter, and where the mass went.
• I can calculate the percentage of mass lost and find the group that stopped too soon.

You need

• for each group: half a spatula of copper(II) carbonate, a test tube with a bung and delivery tube, a second test tube a third full of limewater, a test tube holder, a Bunsen burner on a heatproof mat, a balance, safety glasses,
• the worksheet (next sheet), one per student, and the class results sheet (third sheet), on the board or a bench.

Lesson flow (about 60 minutes)

Running two half-sessions instead? Do the powders, the board and the heating in Session A, and Parts B and C and the class sheet in Session B.

Watch for these ideas

• “The powder burned.” Nothing joined it: it broke apart, and one product left as a gas.
• “Mass was lost, so conservation of mass is wrong.” The missing mass left as carbon dioxide; count the gas and nothing is lost.
• “Milky limewater shows that a gas was made.” It is the test for carbon dioxide only.

Make it easier, make it bigger

• Easier: work out the mass lost and the percentage for group 1 of the example class together.
• Bigger: zinc carbonate breaks down the same way when heated. Write its word equation, and predict what the limewater will do.

Answers and look-fors

• Part A: the green powder turns black and the limewater turns milky, so the gas is carbon dioxide; a fully heated sample loses about 35.6% of its mass.
• Part B: mass lost 0.36, 0.53, 0.71, 0.75, 1.07 g; percentage lost 36%, 35.3%, 35.5%, 30%, 35.7%. Group 4 lost only 30%.
• Part C: 1. Carbon dioxide gas escaped through the delivery tube. 2. Group 4: it stopped heating before all the carbonate had broken down, so some green powder was left. 3. CuCO₃ → CuO + CO₂; decomposition, because one reactant makes two products.
• Bigger: zinc carbonate → zinc oxide + carbon dioxide; the limewater turns milky.

Breaking down

A. Our copper carbonate

Lift the delivery tube out of the limewater before you turn off the burner.

B. An example class

Percentage lost = mass lost ÷ mass before × 100. These are example results.

C. Questions

Class results: copper carbonate

Each group adds its masses and its percentage lost. Do the percentages agree? Which groups had green powder left?

The formula says about 35.6% should leave as carbon dioxide. Why might a result be a little higher, or lower?

Swapping partners

A more reactive metal pushes a less reactive metal out of its compounds. Drop zinc into blue copper sulfate solution and a brown coat of copper grows on the zinc while the blue colour fades: Zn + CuSO₄ → ZnSO₄ + Cu. Put copper into zinc sulfate solution and nothing happens. Students test four metals in solutions of the others’ salts and count how many each one displaces. The counts put the metals in order, from most to least reactive: magnesium, zinc, iron, copper. That order is a reactivity series, and it predicts reactions nobody in the room has tried.

We are learning to

• describe what happens in a metal displacement reaction,
• build a reactivity series from our results,
• use a reactivity series to predict whether a displacement will happen.

Success criteria

• I can explain each of my results with the reactivity of the two metals.
• I can predict whether one metal will displace another from a solution.

You need

• for each group: a spotting tile; small pieces of magnesium ribbon, zinc, iron and copper, rubbed clean with sandpaper; dropper bottles of magnesium, zinc, iron(II) and copper(II) sulfate solutions; safety glasses,
• the worksheet (next sheet), one per student, and the exit tickets (third sheet), cut into four.

Lesson flow (about 60 minutes)

Running two half-sessions instead? Do the test tube, the board and the spotting tiles in Session A, and Parts B and C and the ticket in Session B.

Watch for these ideas

• “A solution reacts with any metal.” Only a metal more reactive than the one in the solution displaces it.
• “The coating is dirt or rust.” It is the displaced metal: copper is pink-brown, zinc and iron dark grey.
• “Nothing after a minute means no reaction.” Some are slow, such as zinc in iron(II) sulfate; give the tile ten minutes.

Make it easier, make it bigger

• Easier: give the series first, and ask students to tick the wells where they expect a reaction before they begin.
• Bigger: silver is below copper in the series. What would you see if copper wire were left in silver nitrate solution?

Answers and look-fors

• Part A: zinc in copper(II) sulfate yes, zinc in magnesium sulfate no, zinc in iron(II) sulfate yes; copper in magnesium sulfate no, copper in iron(II) sulfate no, copper in zinc sulfate no; magnesium in copper(II) sulfate yes, magnesium in iron(II) sulfate yes, magnesium in zinc sulfate yes; iron in copper(II) sulfate yes, iron in magnesium sulfate no, iron in zinc sulfate no.
• Part B: magnesium 3, zinc 2, iron 1, copper 0, so the series is magnesium, zinc, iron, copper, most reactive first.
• Part C: 1. Zinc + copper sulfate → zinc sulfate + copper; Zn + CuSO₄ → ZnSO₄ + Cu. 2. No: iron is less reactive than magnesium, so it cannot push magnesium out. 3. Copper: it is the least reactive, so it does not react with the water or with what is dissolved in it.
• Exit ticket: 1. No: zinc is less reactive than magnesium. 2. Yes: magnesium + iron(II) sulfate → magnesium sulfate + iron. 3. A list of metals in order from the most to the least reactive.
• Bigger: silver crystals grow on the wire, and the solution slowly turns blue as copper goes into it.

Swapping partners

A. Metals in solutions

After ten minutes, write yes and what you saw (a coating, a colour change), or no if nothing happened.

B. Build the series

C. Questions

Exit tickets

Predicting products

Knowing the pattern lets students write the products before anyone runs the reaction. In synthesis the elements join into one compound named from both, with the second name ending in -ide: zinc + oxygen → zinc oxide. When a metal carbonate decomposes on heating, the products are the metal oxide and carbon dioxide. In displacement the more reactive metal swaps into the compound and the other metal comes out, magnesium + copper sulfate → magnesium sulfate + copper, but only if the incoming metal is higher in the reactivity series; otherwise there is no reaction. Students finish six reactions, then match six everyday reactions to their word equations and name the pattern of each.

We are learning to

• predict the products of a reaction from its pattern,
• write word equations, naming simple compounds from their elements,
• recognise the three patterns in everyday reactions.

Success criteria

• I can predict the products of a synthesis, a decomposition and a displacement.
• I can tell when there will be no reaction, and say why.

You need

• the everyday cards (third sheet), one set per pair, with scissors; the reactivity series from Lesson 4 on the board,
• the worksheet (next sheet), one per student.

Lesson flow (about 60 minutes)

Running two half-sessions instead? Do the naming, the board and Part A in Session A, and the cards and Part C in Session B.

Watch for these ideas

• “The compound is magnesium oxygen.” A compound of two elements ends in -ide: oxide, chloride, sulfide.
• “Any metal swaps into any compound.” Only into a compound of a less reactive metal; otherwise write no reaction.
• “Rust is made by burning iron.” Rusting is a slow synthesis that needs oxygen and water together.

Make it easier, make it bigger

• Easier: tell students the pattern of each reaction in Part A, so they only write the products.
• Bigger: 100 g of calcium carbonate is heated in a lime kiln and 56 g of calcium oxide is left. Name the other product and find its mass.

Answers and look-fors

• Part A: zinc + oxygen: synthesis, zinc oxide; zinc carbonate, heated: decomposition, zinc oxide + carbon dioxide; magnesium + copper sulfate: displacement, magnesium sulfate + copper; copper + zinc sulfate: no reaction, as copper is less reactive than zinc; sodium + chlorine: synthesis, sodium chloride; water, with an electric current: decomposition, hydrogen + oxygen.
• Part B: G with A decomposition; D with J decomposition; E with L synthesis; B with H synthesis; K with F displacement; I with C displacement.
• Part C: 1. Copper is below zinc in the series, so it cannot push zinc out. 2. Zinc carbonate → zinc oxide + carbon dioxide; bubble the gas through limewater, which turns milky. 3. (a) potassium chloride; (b) magnesium sulfate + zinc; (c) copper oxide + carbon dioxide.
• Bigger: carbon dioxide; 100 − 56 = 44 g, since mass is conserved.

Predicting products

A. Finish the reactions

Name the pattern and write the products. If there is no reaction, write no reaction and say why.

B. Everyday pairs

Match each everyday reaction to its word equation. Write the letters and the pattern.

C. Questions

Everyday reactions

Cut out the twelve cards. Six describe something you might see; six are word equations. Match each pair.

Teacher note: the pairs are in the plan. Every card has exactly one partner.

Measuring rate

The rate of a reaction is how quickly the reactants are used up or the products are made. When marble chips (calcium carbonate) react with hydrochloric acid, carbon dioxide escapes, so a flask on a balance gets lighter: CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂. Weighed every 30 seconds, the mass lost makes a curve that is steep at first and flattens as the acid is used up. The average rate over any stretch is the change in mass divided by the time, which is the gradient of the curve. Students run the reaction on a balance, graph the example readings, and compare the rate at the start with the rate at the end.

We are learning to

• measure the rate of a reaction by following a change over time,
• draw and describe a graph of mass lost against time,
• calculate an average rate from a graph, with its unit.

Success criteria

• I can explain why the curve is steep at the start and flat at the end.
• I can calculate the average rate over one minute, in grams per second.

You need

• for each group: a conical flask, about 10 g of marble chips, 50 mL of 1 mol/L hydrochloric acid, a cotton wool plug, a top-pan balance, a timer, safety glasses,
• the worksheet (next sheet), one per student, and the exit tickets (third sheet), cut into four.

Lesson flow (about 60 minutes)

Running two half-sessions instead? Do the question, the board and the weighing in Session A, and the graph, Part C and the ticket in Session B.

Watch for these ideas

• “Rate is how much product you get.” Rate is how fast it is made: an amount each second.
• “It stopped because the chips ran out.” Here the acid runs out first, and some chips are left at the end.
• “The rate is the same all the way.” The gradient falls as the acid is used up; the rate is highest at the start.

Make it easier, make it bigger

• Easier: give the rates for the first and the last minute, and ask which is bigger and why.
• Bigger: draw a tangent to the curve at 60 s and use its gradient to find the rate at that moment.

Answers and look-fors

• Part A: results vary; the mass lost rises quickly, then more slowly, then levels off.
• Part B: a smooth curve through the points, steep at first and levelling off near 1.45 g.
• Part C: 1. Fastest at the start, when there are the most acid particles to collide with the chips; it slows as the acid is used up. 2. First minute: 0.73 ÷ 60 ≈ 0.012 g/s; last minute: (1.45 − 1.4) ÷ 60 ≈ 0.0008 g/s. 3. It lets carbon dioxide out but stops acid spray escaping, so only the gas’s mass is lost.
• Exit ticket: 1. 40 ÷ 20 = 2 cm³/s. 2. Rising steeply at first, then levelling off. 3. A reactant is being used up, so collisions become less frequent.
• Bigger: about 0.009 g/s, between the rates of the intervals either side of 60 s.

Measuring rate

A. Our flask

B. Example readings

C. Questions

Exit tickets

Temperature

Particles react only when they collide with at least a certain amount of energy, the activation energy. This is collision theory. Heating makes particles move faster, so they collide a little more often and, far more importantly, a bigger share of the collisions carry enough energy to react. So reactions speed up as the temperature rises. In an effervescent tablet, an acid and a carbonate sit side by side as dry powders; water lets their particles meet, and the fizz is the carbon dioxide they make. Students time half a tablet in water at five temperatures, from fridge-cold to warm, and turn each time into a rate.

We are learning to

• explain reaction rates with collision theory and activation energy,
• investigate how temperature affects the rate of a reaction,
• turn times into rates and graph them.

Success criteria

• I can explain, with collision theory, why the tablet fizzes faster in warm water.
• I can turn a time into a rate and graph rate against temperature.

You need

• for each group: effervescent vitamin C tablets cut in half, a 250 mL beaker, a measuring cylinder, a thermometer, a timer,
• cold water from a fridge and warm water mixed from a kettle, no hotter than 50 °C; the worksheet (next sheet), one per student, and the class results sheet (third sheet), on the board or a bench.

Lesson flow (about 60 minutes)

Running two half-sessions instead? Do the beakers, the board and the timing in Session A, and the rates, Part C and the class means in Session B.

Watch for these ideas

• “Heat makes the particles bigger.” They move faster; their size does not change.
• “Heating only makes particles collide more often.” It does, a little; mostly it makes more of the collisions energetic enough.
• “The tablet is only dissolving.” The fizz is carbon dioxide made by a reaction between an acid and a carbonate.

Make it easier, make it bigger

• Easier: use three temperatures instead of five, and give the rate for the first one.
• Bigger: use collision theory to explain why food keeps longer in a fridge, and longer still in a freezer.

Answers and look-fors

• Part A: results vary; the time should fall as the water gets warmer.
• Part B: rates 10 °C 0.013, 20 °C 0.018, 30 °C 0.025, 40 °C 0.033, 50 °C 0.043 per second; the rate rises with temperature, more steeply at the warm end.
• Part C: 1. As the temperature rises, the time falls and the rate rises. 2. The particles move faster, so they collide more often, and more of the collisions have at least the activation energy. 3. About 35 s, between the times at 30 and 40 °C.
• Bigger: in the cold, particles in food and in the microbes that spoil it move more slowly, so fewer collisions succeed; frozen, fewer still.

Temperature

A. Our tablets

Half a tablet each time, in 100 mL of water. Warm water no hotter than 50 °C.

B. Example results

Rate = 1 ÷ time, in “per second”. These are example results.

C. Questions

Class results: tablets at five temperatures

Each group adds its times, in seconds, under the temperature it measured nearest. Work out the class mean at the end.

Where the spread is widest, what might have differed between groups?

Concentration and surface area

Concentration is how many particles of a substance are packed into a given volume. In a stronger acid there are more acid particles in every millilitre, so they hit the magnesium more often and the ribbon disappears sooner; in this reaction, doubling the strength roughly doubles the rate. Surface area works in the same way for solids: only particles on the surface can be hit, so breaking a tablet into pieces, or crushing it to powder, exposes more particles and the reaction finishes sooner. Neither change gives a single collision more energy. Both make collisions more frequent. Students time magnesium in four strengths of acid, and half tablets in one piece, in four pieces and as a powder.

We are learning to

• investigate how concentration and surface area affect the rate of a reaction,
• explain both effects with collision theory,
• decide from a graph whether two quantities are in proportion.

Success criteria

• I can explain why the ribbon disappears sooner in stronger acid.
• I can explain why a powder reacts faster than a lump of the same mass.

You need

• for each group: four 1 cm lengths of magnesium ribbon; four test tubes in a rack, each with 10 mL of hydrochloric acid made up by the teacher at 0.5, 1.0, 1.5 and 2.0 mol/L; half tablets as in Lesson 7; a timer; safety glasses; no flames nearby,
• the worksheet (next sheet), one per student, and the exit tickets (third sheet), cut into four.

Lesson flow (about 60 minutes)

Running two half-sessions instead? Do the sugar, the board and the acids in Session A, and the tablets, the graph and Part D in Session B.

Watch for these ideas

• “Stronger acid particles hit harder.” There are more of them in each millilitre; each collision is no more energetic.
• “A powder reacts faster because it has more mass.” The mass is the same; more of it is on the surface.
• “Double the strength always doubles the rate exactly.” Roughly, in this reaction; results scatter, and not every reaction behaves so.

Make it easier, make it bigger

• Easier: give the example rates, so students only plot them and describe the line.
• Bigger: a campfire is lit with small twigs, not a log. Use surface area and collision theory to explain why.

Answers and look-fors

• Part A: example rates 0.5 mol/L 0.0083, 1 mol/L 0.0172, 1.5 mol/L 0.0250, 2 mol/L 0.0323 per second; our times should fall as the acid gets stronger.
• Part B: the example times fall from 62 to 41 to 24 s as the pieces get smaller.
• Part C: the points lie close to a straight line through the origin.
• Part D: 1. More acid particles in each millilitre, so more collisions with the magnesium each second. 2. Only surface particles can be hit; smaller pieces put more particles on the surface, so there are more collisions each second. 3. Yes, roughly: the points are close to a straight line through the origin, and doubling the strength from 0.5 to 1.0 mol/L about doubles the rate.
• Exit ticket: 1. More particles in each millilitre, so more frequent collisions. 2. More particles on the surface to be hit. 3. Temperature.
• Bigger: twigs expose far more surface to the air than a log, so far more collisions with oxygen happen each second.

Concentration and surface area

A. Four strengths of acid

1 cm of magnesium ribbon in 10 mL of acid. Rate = 1 ÷ time. The example times come from another class.

B. One piece, four pieces, powder

C. Graph the example rates

D. Questions

Exit tickets

Catalysts

A catalyst speeds up a reaction without being used up. It gives the reaction a different route with a lower activation energy, so more collisions have enough energy to succeed at the same temperature. Hydrogen peroxide slowly breaks down into water and oxygen: 2H₂O₂ → 2H₂O + O₂. Add dried yeast, which holds an enzyme (a catalyst made by living things), and the oxygen pours out; with a drop of detergent it builds a tower of foam. Sand, another powder, does nothing, so the effect comes from the catalyst and not from adding any solid. The teacher shows that manganese dioxide works too, and that it is all still there at the end. Catalysts make most of the chemicals industry produces, and the catalytic converter in a car’s exhaust cleans the gases.

We are learning to

• describe what a catalyst does, and how we know it is not used up,
• explain the effect of a catalyst with collision theory and activation energy,
• use a control to show that an effect comes from the variable we changed.

Success criteria

• I can explain why the yeast speeds up the reaction and the sand does not.
• I can sketch how a catalyst lowers the activation energy.

You need

• for each group: 20 mL of 3% hydrogen peroxide for each test, a 100 mL measuring cylinder standing in a tray, detergent, dried yeast, sand, a balance, a ruler, a timer, safety glasses,
• for the teacher: manganese dioxide and a glowing splint; the worksheet (next sheet), one per student, and the class results sheet (third sheet), on the board or a bench.

Lesson flow (about 60 minutes)

Running two half-sessions instead? Do the bottle, the board and the foam towers in Session A, and Parts B and C and the examples in Session B.

Watch for these ideas

• “The catalyst gets used up.” The manganese dioxide weighed 0.50 g before and 0.50 g after.
• “A catalyst gives the particles more energy.” It lowers the energy a collision needs.
• “Any powder would do.” The sand made no foam: the effect comes from the catalyst, not the powder.

Make it easier, make it bigger

• Easier: run the yeast test at the front as a demonstration, then groups test the sand and nothing.
• Bigger: enzymes work best near body temperature. Predict, without testing, how yeast would do in hydrogen peroxide at 70 °C.

Answers and look-fors

• Part A (example): nothing 0 cm; 0.5 g of sand 0 cm; 0.5 g of dried yeast 9 cm; 1.0 g of dried yeast 16 cm; 0.5 g of manganese dioxide (teacher only) 14 cm.
• Part B: two hills with the same start and end; the hill with the catalyst is lower. The products sit below the reactants, as the reaction gives out energy.
• Part C: 1. It is a control: it shows that adding a powder alone makes no foam. 2. The enzyme lowers the activation energy, so more collisions succeed each second. 3. Weigh it before and after; it was still 0.50 g. 4. Oxygen.
• Bigger: little or no foam: heat changes the shape of the enzyme, so it stops working as a catalyst.

Catalysts

A. Foam towers

20 mL of 3% hydrogen peroxide and a drop of detergent each time. Measure the foam after 60 s.

The teacher weighed the manganese dioxide before (0.50 g), then filtered, dried and weighed it again afterwards (0.50 g).

B. Lower the hill

Sketch energy against the progress of the reaction: one hill without a catalyst and one with. Label the activation energy.

C. Questions

Class results: foam towers

Each group adds its foam heights after 60 s, in centimetres. Which results agree? Do any groups disagree about the sand?

Foam from the sand would suggest the cylinder was not rinsed after a yeast test. Why?

Show what we know

The term comes together. In the task, students name the pattern of four reactions, then plan a fair test of whether the size of marble chips changes the rate of their reaction with acid. Last, they graph example gas readings for small and large chips of the same mass, compare the starting rates, and explain the difference with collision theory. Then they sit the eight-question final check, and the class plays the unit quiz as a game on the board.

We are learning to

• classify reactions and predict their products,
• plan a fair test of a factor that affects the rate,
• compare rates from graphs and explain them with collision theory.

Success criteria

• I can plan a fair test and name its variables.
• I can compare two curves and explain why one reaction is faster.

You need

• the task (next sheet) and the final check (third sheet), one each per student; rulers and two coloured pencils,
• the interactive unit open on the board for the quiz; mini whiteboards if you have them.

Lesson flow (about 60 minutes)

Running two half-sessions instead? Do the warm-up and the task in Session A, and the final check and the quiz in Session B.

Watch for these ideas

• Students who name variables loosely, such as “the chips”: the independent variable is the size of the chips, the dependent the gas made.
• Students who think the large chips make less gas: the same mass makes the same total; it only takes longer.
• Students who say smaller chips have more particles: the same mass has the same particles, but more of them are on the surface.

Make it easier, make it bigger

• Easier: give the three kinds of variable as headings, each with one example filled in.
• Bigger: on the same axes, sketch the curve you would expect for the small chips in warmer acid.

Answers and look-fors

• Task: 1. 2Ca + O₂ → 2CaO: synthesis; Mg + CuSO₄ → MgSO₄ + Cu: displacement; ZnCO₃ → ZnO + CO₂: decomposition; 2Al + 3CuCl₂ → 2AlCl₃ + 3Cu: displacement. 2. For example: smaller chips react faster because they have more surface area. 3. Independent: the size of the chips; dependent: the volume of gas made every 20 s; controlled: the mass of chips, the volume and strength of the acid, and the temperature. 4. Small: 30 ÷ 20 = 1.5 cm³/s; large: 14 ÷ 20 = 0.7 cm³/s. 5. The small chips have more surface, so more acid particles hit them each second. 6. The same mass of chips makes the same total gas, 60 cm³; the large chips just take longer to get there.
• Final check: 1. decomposition. 2. No: copper is below zinc in the reactivity series, so it cannot push zinc out. 3. it has more surface for collisions. 4. Magnesium oxide; synthesis. 5. In the cold, particles move more slowly, so they collide less often and fewer collisions have enough energy; the reactions that spoil food slow down. 6. lowers the energy a collision needs. 7. 24 ÷ 30 = 0.8 cm³/s. 8. The reactants are used up, so there are fewer particles to collide and collisions happen less often.
• Bigger: steeper at the start, levelling off sooner, at the same final volume.
• Mark the task against the rubric in the assessment kit; the check covers both halves of the term.

Marble chips, and four reactions

Part 1. Name the pattern

1. Write synthesis, decomposition or displacement beside each reaction.

Part 2. Plan a fair test

Does the size of marble chips change the rate of their reaction with hydrochloric acid?

Part 3. Small chips and large chips

The same mass of chips in the same acid, the gas collected in a syringe. These are example results.

Show what we know