--- title: "What kind of reaction is it?" subtitle: "Years 9 and 10 Chemistry · Reaction rates · Lesson 14" --- # What kind of reaction is it? **Name:** {{field-24}} **Date:** {{field-15}} **Class:** {{field-15}} > **Key question:** Drop an iron nail into blue copper sulfate solution and it comes out coated in copper, while the blue slowly fades. Iron has pushed copper out of its compound. :::teacher-note **In one sentence:** Students identify synthesis, decomposition and displacement reactions by their patterns, use reactivity to predict whether a displacement happens, and classify unfamiliar reactions and predict products (AC9S10U07, nodes 1 to 4). **Students should be able to say:** I can recognise synthesis, decomposition and displacement reactions from their patterns. I can predict the products of a displacement reaction using reactivity. I can classify a reaction I haven't seen before. **Width:** the unmarked parts are the floor every student does (Engage, Explore, Explain, Evaluate). Typical and Wider sections add contexts, not difficulty. Students work in the online tutorial alongside this sheet. ::: ## Engage :::keep-together **An iron nail is put in copper sulfate solution. Iron is more reactive than copper. What happens?** ☐ The copper sulfate turns into iron ☐ Nothing: metals don't react with solutions ☐ The iron and copper mix to make an alloy ☐ Iron takes copper's place: iron sulfate forms and copper coats the nail My prediction, and why: {{lines-3}} ::: :::teacher-note **What happens:** Iron takes copper's place: iron + copper sulfate → iron sulfate + copper. The more reactive metal displaces the less reactive one from its compound. That is a displacement reaction. ::: ## Explore Try it on the board in the tutorial. Was your prediction right? What was different? {{lines-2}} ## Explain: spotting the pattern :::keep-together ### Three patterns **Match each pattern to its name.** A. Displacement B. Decomposition C. Synthesis {{columns 60% 40%}} {{rows 1}} | Part | Letter | |---|---| | `A + B → AB` | | | `AB → A + B` | | | `A + BC → AC + B` | | ::: :::teacher-note **Answer:** A + B → AB → C. Synthesis; AB → A + B → B. Decomposition; A + BC → AC + B → A. Displacement Join, break apart, swap. ::: :::keep-together ### Classify them **Which kind of reaction is it?** Groups: Synthesis, Decomposition, Displacement - iron + sulfur → iron sulfide: {{field-15}} - 2H₂ + O₂ → 2H₂O: {{field-15}} - calcium carbonate → calcium oxide + carbon dioxide: {{field-15}} - 2H₂O → 2H₂ + O₂ (electricity passed through water): {{field-15}} - magnesium + copper sulfate → magnesium sulfate + copper: {{field-15}} - chlorine + sodium bromide → sodium chloride + bromine: {{field-15}} ::: :::teacher-note **Answer:** iron + sulfur → iron sulfide → Synthesis; 2H₂ + O₂ → 2H₂O → Synthesis; calcium carbonate → calcium oxide + carbon dioxide → Decomposition; 2H₂O → 2H₂ + O₂ (electricity passed through water) → Decomposition; magnesium + copper sulfate → magnesium sulfate + copper → Displacement; chlorine + sodium bromide → sodium chloride + bromine → Displacement ::: :::keep-together ### Predict the products **Zinc is more reactive than copper. What are the products of zinc + copper sulfate?** ☐ Copper zinc + sulfate ☐ Zinc copper sulfate ☐ No reaction ☐ Zinc sulfate + copper ::: :::teacher-note **Answer:** Zinc sulfate + copper The more reactive metal (zinc) takes the less reactive one's place: zinc + copper sulfate → zinc sulfate + copper. ::: :::keep-together ### The other way round **Copper is put into zinc sulfate solution. What happens?** ☐ Nothing: copper is less reactive, so it can't displace zinc ☐ The copper dissolves ☐ Copper sulfate and zinc form ::: :::teacher-note **Answer:** Nothing: copper is less reactive, so it can't displace zinc Reactivity decides whether a displacement happens. ::: :::keep-together ### Synthesis product **Aluminium burns in oxygen. It is a synthesis reaction (A + B → AB). What is the product?** ☐ aluminium and oxygen, mixed together ☐ aluminium oxide and water ☐ aluminium oxide ::: :::teacher-note **Answer:** aluminium oxide Two substances join into one: aluminium + oxygen → aluminium oxide. ::: :::keep-together ### Heating copper carbonate **Green copper carbonate powder is heated strongly. It turns black (copper oxide) and gives off carbon dioxide. Which kind of reaction is it, and what drives it?** ☐ Synthesis: the copper carbonate joins with the heat ☐ Decomposition, driven by heat: one compound breaks into two simpler substances ☐ Displacement: carbon dioxide takes copper's place ::: :::teacher-note **Answer:** Decomposition, driven by heat: one compound breaks into two simpler substances copper carbonate → copper oxide + carbon dioxide. Many decompositions need energy put in: heat, as here and for limestone, or electricity, as for splitting water. ::: :::keep-together ### Swapping partners **In some reactions two compounds swap partners (AB + CD → AD + CB): a double displacement. Neutralisation is one. What are the products of hydrochloric acid + sodium hydroxide?** ☐ sodium hydroxide chloride ☐ sodium chloride + hydrogen ☐ sodium chloride + water ::: :::teacher-note **Answer:** sodium chloride + water Sodium and hydrogen swap partners: sodium chloride and water (H + OH). acid + base → salt + water. A precipitation, where two solutions make a solid, swaps partners in the same way. ::: :::typical ## Elaborate: the other way round :::keep-together **On this board, copper is mixed with zinc oxide. Watch it for a while. Why does no reaction happen?** ☐ There isn't enough copper ☐ Copper is less reactive than zinc, so it can't take the oxygen from zinc ☐ The temperature is too low ::: :::teacher-note **Answer:** Copper is less reactive than zinc, so it can't take the oxygen from zinc A displacement goes only from more reactive to less reactive. The reactivity series (potassium, sodium, calcium, magnesium, aluminium, zinc, iron, copper, silver, gold) predicts which way. ::: ::: :::wider ## Elaborate: making useful things :::keep-together ### Iron from rock **In a blast furnace, carbon takes oxygen from iron oxide: iron oxide + carbon → iron + carbon dioxide. Which kind of reaction is this, and why does it work?** ☐ Displacement: carbon is more reactive than iron, so it takes the oxygen ☐ Synthesis: iron and carbon join ☐ Decomposition: iron oxide breaks apart on its own ::: :::teacher-note **Answer:** Displacement: carbon is more reactive than iron, so it takes the oxygen Metals less reactive than carbon (zinc, iron, copper) are extracted from their ores this way. ::: :::keep-together ### Lime from limestone **Builders heat limestone (calcium carbonate) to make lime (calcium oxide) for cement. Which kind of reaction is this?** ☐ Synthesis ☐ Decomposition ☐ Displacement ::: :::teacher-note **Answer:** Decomposition calcium carbonate → calcium oxide + carbon dioxide. Cement making releases a lot of carbon dioxide for this reason. ::: ::: ## Evaluate: look back Write one sentence: "At first I thought… Now I think… because…" **Revision summary** - **Synthesis**: substances join into one (A + B → AB), such as magnesium burning. - **Decomposition**: one substance breaks into simpler ones (AB → A + B), such as hydrogen peroxide → water + oxygen, often with heat or electricity. - **Displacement**: a more reactive element takes a less reactive one's place (A + BC → AC + B). It doesn't happen the other way round. In a **double displacement** two compounds swap partners (AB + CD → AD + CB), as in neutralisation: acid + base → salt + water. - Spot the pattern to classify a reaction and predict its products. ## Exit ticket :::keep-together **Classify magnesium + zinc sulfate → magnesium sulfate + zinc, and say why it happens.** {{lines-3}} ::: :::teacher-note **Answer:** Displacement: magnesium is more reactive than zinc, so it takes zinc's place. :::