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# What goes in, what comes out?

Years 9 and 10 Chemistry · Equations and conservation of mass

<!-- Speaker note: Students identify reactants and products, explain that products are new substances with different properties, and write word equations that include every product (AC9S9U07, nodes 1 and 3). About 28 minutes (Engage and Explore 7 min · Explain 10 min · Practise 5 min · Evaluate 3 min · Typical adds 4 min, Wider about 4 min). -->

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## Today

**We are learning to** in a chemical reaction the reactants are used up and new substances, the products, are made. A word equation names them: reactants → products. It must include every product (burning a fuel makes water as well as carbon dioxide), but it shows no amounts or atoms.

- I can name the reactants and products of a reaction.
- I can write a word equation that includes every product.
- I can say what a word equation shows and does not show.

<!-- Speaker note: Before class: A concept tutorial for introducing or revising the idea; it does not replace doing the reactions (magnesium ribbon, zinc in copper sulfate, acid on marble chips). Set the width with `?width=minimum`, `typical` (default) or `wider`. One lesson for two nodes: reactants and products (node 1) and word equations (node 3). It comes before Where do the atoms go? (node 2), so students name substances before they follow atoms. Neither is a hinge node; node 3 asks for practice, so there is a Practise step. The prediction targets the usual error: leaving water out of a combustion equation (and forgetting oxygen as a reactant). Board notes: the science board shows molecules as rigid particles. Magnesium oxide and sodium chloride are drawn as small particles too, although they are really giant lattices of ions; say so if asked. Heat given out shows as faster particles. -->

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## Why it matters

> A gas stove burns methane with a blue flame. Hold a cold spoon above it and drops of water appear. Where did the water come from?

<!-- Speaker note: You know the signs of a chemical change: a new substance is made. This lesson names what goes in and what comes out. -->

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<span style="background:#dbeafe; color:#1a1a1a; border:1.5px solid #3b82f6; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">💬 Discussion</span>

## Engage: predict

**Methane (natural gas) burns in air. Which word equation names everything that goes in and comes out?**

- methane + oxygen → carbon dioxide + water
- methane + oxygen → smoke + heat
- methane + oxygen → carbon dioxide
- methane → carbon dioxide + water

<!-- Speaker note: What happens: methane + oxygen → carbon dioxide + water. Methane contains carbon and hydrogen: the carbon ends up in carbon dioxide and the hydrogen in water (the drops on the cold spoon). Oxygen from the air is a reactant too. Heat is energy given out, not a substance, so it is not in the equation. Take two or three predictions before anyone runs it. -->

<!-- Speaker note: Teacher: tally the four options. 'Carbon dioxide only' and 'smoke and heat' are the ones to discuss. -->

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## Explore it

{{embed: https://studio.learningwaypoints.com/tutorials/_playground-science/index.html?id=deck%2Fscience%2Fchemistry-9-10%2Fword-equations%2Fstep-2&code=widget%3A+reaction%0Ashow%3A+CH4+x6%2C+O2+x12%0Areact%3A+CH4+%2B+2+O2+-%3E+CO2+%2B+2+H2O%0Aea%3A+1.5%0Arelease%3A+1%0Acaption%3A+Methane+burning+in+oxygen.%0A}}

[Open this step in the tutorial](https://studio.learningwaypoints.com/tutorials/science/chemistry-9-10/word-equations/?full=step-2#step-2)

<!-- Speaker note: Watch the counts beside the board. Which substances go down? Which new ones appear? -->

<!-- Speaker note: Teacher: ask which counts went down (reactants) and which appeared (products). -->

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## What happened?

* methane + oxygen → carbon dioxide + water. Methane contains carbon and hydrogen: the carbon ends up in carbon dioxide and the hydrogen in water (the drops on the cold spoon). Oxygen from the air is a reactant too. Heat is energy given out, not a substance, so it is not in the equation.

<!-- Speaker note: Reveal after running. Ask who predicted it, and what made them think so. -->

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<span style="background:#dcfce7; color:#1a1a1a; border:1.5px solid #22c55e; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">✅ Check</span>

## Reactants and products

**methane + oxygen → carbon dioxide + water. Reactant or product?**

Groups: Reactant · Product

methane · oxygen · carbon dioxide · water

* Answer: methane → Reactant; oxygen → Reactant; carbon dioxide → Product; water → Product

<!-- Speaker note:  -->

<!-- Speaker note: Teacher: the reactant and product sort and the 'what it leaves out' question are the success criteria. -->

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## The arrow

**What does the arrow in a word equation mean?**

- Is mixed with
- Reacts to make
- Equals: the two sides are the same substances

* Answer: Reacts to make

<!-- Speaker note: Reactants → products: read the arrow as 'react to make'. -->

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## New substances

**Why are carbon dioxide and water counted as new substances, and not just methane and oxygen in a new shape?**

- They have different properties: methane burns and water puts fires out
- They are heavier
- They are gases

* Answer: They have different properties: methane burns and water puts fires out

<!-- Speaker note: A product is a new substance with its own properties. The atoms are the same; how they are joined is different (next lesson). -->

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<span style="background:#dcfce7; color:#1a1a1a; border:1.5px solid #22c55e; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">✅ Check</span>

## Signs of a reaction

**Is it a sign that a chemical reaction has made a new product?**

Groups: Sign of a reaction · Not on its own

Bubbles of a new gas · A colour change in a mixture · A solid forming when two clear solutions mix · Ice melting into water · Sugar disappearing in tea

* Answer: Bubbles of a new gas → Sign of a reaction; A colour change in a mixture → Sign of a reaction; A solid forming when two clear solutions mix → Sign of a reaction; Ice melting into water → Not on its own; Sugar disappearing in tea → Not on its own

<!-- Speaker note:  -->

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## What it leaves out

**What does a word equation NOT tell you?**

- How many particles of each substance react, or which atoms they contain
- Which substances react
- Which substances are made

* Answer: How many particles of each substance react, or which atoms they contain

<!-- Speaker note: Word equations name the substances only. Formulas and balanced equations (two lessons on) show the atoms and amounts. -->

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## Magnesium

**Magnesium burns in oxygen with a bright white flame, leaving white magnesium oxide.**

- magnesium + oxygen → light
- magnesium + oxygen → magnesium oxide
- magnesium oxide → magnesium + oxygen
- magnesium → magnesium oxide

* Answer: magnesium + oxygen → magnesium oxide

<!-- Speaker note: magnesium + oxygen → magnesium oxide. -->

<!-- Speaker note: Teacher: four reactions with the same check: every reactant, every product. -->

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## Neutralisation

**Hydrochloric acid neutralises sodium hydroxide, making salt (sodium chloride) and water.**

- hydrochloric acid + sodium hydroxide → sodium chloride
- hydrochloric acid + sodium hydroxide → water
- sodium chloride + water → hydrochloric acid + sodium hydroxide
- hydrochloric acid + sodium hydroxide → sodium chloride + water

* Answer: hydrochloric acid + sodium hydroxide → sodium chloride + water

<!-- Speaker note: acid + base → salt + water. -->

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## Displacement

**A zinc strip is put in blue copper sulfate solution. Copper forms on the zinc, and zinc sulfate is left in solution.**

- zinc + copper sulfate → zinc sulfate + copper
- zinc + copper → zinc sulfate
- zinc + copper sulfate → copper
- zinc sulfate + copper → zinc + copper sulfate

* Answer: zinc + copper sulfate → zinc sulfate + copper

<!-- Speaker note: Zinc takes the place of copper: zinc + copper sulfate → zinc sulfate + copper. -->

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## Fizzing marble

**Hydrochloric acid is added to marble chips (calcium carbonate). It fizzes. The products are calcium chloride, water and carbon dioxide.**

- calcium carbonate + hydrochloric acid → calcium chloride + carbon dioxide
- calcium carbonate + hydrochloric acid → carbon dioxide
- calcium carbonate → calcium chloride + water + carbon dioxide
- calcium carbonate + hydrochloric acid → calcium chloride + water + carbon dioxide

* Answer: calcium carbonate + hydrochloric acid → calcium chloride + water + carbon dioxide

<!-- Speaker note: Acid + carbonate → salt + water + carbon dioxide (the fizz). -->

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## Elaborate: magnesium burning

{{embed: https://studio.learningwaypoints.com/tutorials/_playground-science/index.html?id=deck%2Fscience%2Fchemistry-9-10%2Fword-equations%2Fstep-5&code=widget%3A+reaction%0Ashow%3A+Mg+x12%2C+O2+x6%0Areact%3A+2+Mg+%2B+O2+-%3E+2+MgO%0Aea%3A+1.5%0Arelease%3A+1%0Acaption%3A+Magnesium+burning+in+oxygen.%0A}}

[Open this step in the tutorial](https://studio.learningwaypoints.com/tutorials/science/chemistry-9-10/word-equations/?full=step-5#step-5)

<!-- Speaker note: What this step is for: A second reaction on the board, with a metal and a single product, checks that students can name reactants and products from what they see. -->

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<span style="background:#dcfce7; color:#1a1a1a; border:1.5px solid #22c55e; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">✅ Check</span>

## The heavier ash

**The white ash after burning magnesium is heavier than the magnesium ribbon was. Why?**

- Oxygen from the air joined the magnesium to make magnesium oxide
- Burning makes new atoms
- The ash soaks up water

* Answer: Oxygen from the air joined the magnesium to make magnesium oxide

<!-- Speaker note: The word equation shows it: magnesium + oxygen → magnesium oxide. The product contains the oxygen as well. -->

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## Elaborate: why sodium hides

{{embed: https://studio.learningwaypoints.com/tutorials/_playground-science/index.html?id=deck%2Fscience%2Fchemistry-9-10%2Fword-equations%2Fstep-6&code=widget%3A+reaction%0Ashow%3A+Na+x12%2C+Cl2+x6%0Areact%3A+2+Na+%2B+Cl2+-%3E+2+NaCl%0Aea%3A+1.2%0Arelease%3A+1%0Acaption%3A+Sodium+reacting+with+chlorine.%0A}}

[Open this step in the tutorial](https://studio.learningwaypoints.com/tutorials/science/chemistry-9-10/word-equations/?full=step-6#step-6)

<!-- Speaker note: What this step is for: Reactive elements are found in nature as products of reactions, which explains why ores and salts, not pure metals, are what we mine. -->

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## Sodium in nature

**Sodium is never found as a pure metal in nature, but there is plenty of sodium chloride in seawater. Why?**

- Sodium dissolves in seawater as a metal
- Sodium is a rare element
- Sodium reacts so readily that any sodium has long since reacted, leaving it in compounds

* Answer: Sodium reacts so readily that any sodium has long since reacted, leaving it in compounds

<!-- Speaker note: Reactive elements end up as products. Getting sodium (or iron, or aluminium) back as the element takes another reaction, and usually a lot of energy. -->

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## Evaluate: look back

Write one sentence: "At first I thought… Now I think… because…"

**Revision summary**

- In a chemical reaction the **reactants** are used up and new substances, the **products**, are made. Products have different properties.
- A **word equation** names them: reactants → products. Read the arrow as "react to make".
- Include every reactant and product: burning a fuel that contains hydrogen makes water as well as carbon dioxide; oxygen from the air is a reactant.
- Heat and light are energy, not substances, so they are not in the equation.
- A word equation shows no amounts and no atoms: formulas and balanced equations do.

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<span style="background:#dcfce7; color:#1a1a1a; border:1.5px solid #22c55e; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">✅ Check</span>

## Exit ticket

**Iron reacts with oxygen and water to make rust (hydrated iron oxide). Write the word equation and label the reactants and products.**

* iron + oxygen + water → hydrated iron oxide (rust). Reactants: iron, oxygen, water. Product: hydrated iron oxide.

<!-- Speaker note: Students answer on paper or a mini whiteboard before the reveal. Anyone who cannot answer needs the main idea again next lesson. Where this leads: Next: Where do the atoms go? (node 2) follows the atoms through the same burning methane; then balancing (node 4) adds the formulas and amounts that word equations leave out. In class: magnesium ribbon burning (weigh the crucible before and after), zinc in copper sulfate, acid on marble chips with limewater. The progression's Wider also suggests First Nations processes that make toxic plants safe to eat; many of these combine physical steps (grinding, leaching in water) with chemical ones, so check the chemistry with local sources and community guidance before writing equations for them. -->