---
marp: true
theme: default
html: true
---

# Where does the heat go?

Year 7 Chemistry · Particle theory

<!-- Speaker note: Students explain changes of state with particle theory, identify energy input or output for each, and explain the flat parts of a heating or cooling curve (AC9S7U05, node 4). About 24 minutes (Engage and Explore 6 min · Explain 11 min · Evaluate 3 min · Typical adds 3 min, Wider about 2 min). -->

---

## Today

**We are learning to** melting and boiling need energy put in: the particles move faster and pull free of each other. Freezing and condensing give energy out. While a substance is changing state, its temperature stays the same, because the energy goes into separating the particles, not speeding them up.

- I can say whether energy goes in or out when a substance melts, boils, freezes or condenses.
- I can explain a change of state using particles.
- I can explain why the temperature stays the same while a substance changes state.

<!-- Speaker note: Before class: A concept tutorial for introducing or revising the idea; a real heating curve (ice in a beaker with a thermometer and a timer) is the best partner. Set the width with `?width=minimum`, `typical` (default) or `wider`. It follows Why can you squash air but not water? and comes before Pure substance or mixture? Not a hinge node, but the plateau surprises almost everyone: students expect heating always to raise the temperature. The prediction tests that. Board notes: the particle board changes state at 0 °C and 100 °C without showing the plateau (the slider sets the temperature directly); the heating curve on the graph board shows it. The curve is idealised: real ones curve at the corners, and the boiling plateau is longer than the melting one because boiling needs more energy. Teacher: In your own words: the labelled heating curve is the evidence. -->

<style scoped>pre, marp-pre { font-size: 0.5em; line-height: 1.25; } section { font-size: 27px; }</style>

---

## Why it matters

> A pot of water on the stove climbs to 100 °C and then stops, even with the gas still on full. Where is all that heat going?

<!-- Speaker note: You know how particles are arranged in solids, liquids and gases. This lesson asks what energy does when one changes into another. -->

---

<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

**A pot of water is boiling on a stove. The stove stays on full. What does a thermometer in the water show over the next five minutes?**

- It drops, because the water is turning to steam
- It keeps rising
- It goes up and down
- It stays at about 100 °C

<!-- Speaker note: What happens: It stays at about 100 °C. The energy from the stove is going into separating the water particles so they escape as steam, not into making them move faster, so the temperature stays the same until the water has all boiled away. Take two or three predictions before anyone runs it. -->

<!-- Speaker note: Teacher: tally the predictions. 'It keeps rising' is the idea the curve challenges. -->

---

<span style="background:#fef3c7; color:#1a1a1a; border:1.5px solid #f59e0b; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">✍️ Activity</span>

## Explore it

{{embed: https://studio.learningwaypoints.com/tutorials/_playground-science/index.html?id=deck%2Fscience%2Fchemistry%2Fheating-curve%2Fstep-2&code=widget%3A+heat%0A}}

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

<!-- Speaker note: Drag the temperature slider and watch the particles. Where does the heat go? -->

<!-- Speaker note: Teacher: ask what the particles were doing just as the ice turned to water. -->

<style scoped>pre, marp-pre { font-size: 0.5em; line-height: 1.25; } section { font-size: 25px; }</style>

---

<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>

## What happened?

* It stays at about 100 °C. The energy from the stove is going into separating the water particles so they escape as steam, not into making them move faster, so the temperature stays the same until the water has all boiled away.

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

---

<span style="background:#fef3c7; color:#1a1a1a; border:1.5px solid #f59e0b; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">✍️ Activity</span>

## Explain: energy in, energy out

{{embed: https://studio.learningwaypoints.com/tutorials/_playground-board/index.html?id=deck%2Fscience%2Fchemistry%2Fheating-curve%2Fstep-3&code=widget%3A+graph%0Aaxes%3A+Time+heating+%28min%29%2C+Temperature+%28%C2%B0C%29%0Ax%3A+0%2C+80%0Ay%3A+-20%2C+120%0Agrid%3A+10%2C+20%0Aseries+Water%3A+0%2C-20%3B+1%2C0%3B+9%2C0%3B+19%2C100%3B+73%2C100%3B+74%2C115%0Acursor+R%3A+1%0A&fresh=1}}

[Open this step in the tutorial](https://studio.learningwaypoints.com/tutorials/science/chemistry/heating-curve/?full=step-3#step-3)

<!-- Speaker note: What this step is for: Reading a real heating curve, sorting the changes by energy in or out, then explaining a flat part of the curve with particles, is the node's success criterion. -->

<!-- Speaker note: Teacher: the energy in/out sort and the flat-part question are the success criteria. -->

<style scoped>pre, marp-pre { font-size: 0.5em; line-height: 1.25; } section { font-size: 25px; }</style>

---

<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>

## In or out

**Does the substance take energy in, or give energy out?**

Groups: Energy in · Energy out

Melting (solid to liquid) · Boiling or evaporating (liquid to gas) · Freezing (liquid to solid) · Condensing (gas to liquid)

* Answer: Melting (solid to liquid) → Energy in; Boiling or evaporating (liquid to gas) → Energy in; Freezing (liquid to solid) → Energy out; Condensing (gas to liquid) → Energy out

<!-- Speaker note:  -->

---

<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 flat part

**On the heating curve, the line is flat from 1 to 9 minutes. What is happening?**

- Nothing: the stove was turned off
- The water is boiling
- The ice is melting: energy goes into freeing the particles from their fixed places, so the temperature doesn't rise

* Answer: The ice is melting: energy goes into freeing the particles from their fixed places, so the temperature doesn't rise

<!-- Speaker note: During a change of state, the energy goes into overcoming the attraction between particles, not into making them move faster, so the temperature stays constant. -->

<style scoped>pre, marp-pre { font-size: 0.5em; line-height: 1.25; } section { font-size: 26px; }</style>

---

<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 second flat part

**At what temperature (°C) is the second flat part of water's heating curve?**

* Answer: 100

<!-- Speaker note: 100 °C: water's boiling point (at sea level). The first flat part, at 0 °C, is its melting point. -->

---

<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>

## Why boiling takes longer

**The curve is drawn to scale: the stove gives the same energy every minute. Why is the flat part at 100 °C about seven times longer than the one at 0 °C?**

- The stove gives less energy once the water is hot
- Boiling pulls the particles completely apart, which takes far more energy than loosening them from their fixed places
- Steam is lighter than ice, so it takes longer to make

* Answer: Boiling pulls the particles completely apart, which takes far more energy than loosening them from their fixed places

<!-- Speaker note: Melting only frees the particles to slide past each other. Boiling has to pull them far apart against their attraction, so it needs about seven times as much energy (2260 kJ for each kilogram, against 334 kJ to melt it). -->

<style scoped>pre, marp-pre { font-size: 0.5em; line-height: 1.25; } section { font-size: 24px; }</style>

---

<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>

## Before melting

**What does adding energy do to the particles in a solid, before it melts?**

- They start to leave the solid straight away
- They get bigger
- They vibrate faster, so the temperature rises

* Answer: They vibrate faster, so the temperature rises

<!-- Speaker note: Temperature is a measure of how fast the particles move on average. Energy in, faster particles, higher temperature, until a change of state begins. -->

---

<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>

## What the particles do

**What happens to the particles in each change of state?**

| | |
|---|---|
| `Melting` | A. Gas particles slow down and are pulled close together into a liquid, giving out energy |
| `Freezing` | B. Particles slow down and settle into fixed places, giving out energy |
| `Evaporating` | C. Fast particles at the surface pull free of the others and escape as a gas |
| `Condensing` | D. Particles vibrate hard enough to break free of their fixed places and start sliding past each other |

* Answer: Melting → D. Particles vibrate hard enough to break free of their fixed places and start sliding past each other; Freezing → B. Particles slow down and settle into fixed places, giving out energy; Evaporating → C. Fast particles at the surface pull free of the others and escape as a gas; Condensing → A. Gas particles slow down and are pulled close together into a liquid, giving out energy

<!-- Speaker note: Energy in frees the particles from each other's attraction; energy out lets the attraction pull them back together. -->

<style scoped>pre, marp-pre { font-size: 0.5em; line-height: 1.25; } section { font-size: 16px; }</style>

---

<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>

## Mix it up

**Looking back at states of matter: a small jar of gas is opened in the middle of a large, sealed room. A few minutes later, where are its particles?**

- Mostly on the floor
- Spread through the whole room
- Mostly at the top of the room
- Still in a clump where the jar was

* Answer: Spread through the whole room

<!-- Speaker note: Gas particles move fast in every direction and barely attract each other, so they spread to fill the room. What this step is for: Gas particles moving fast in every direction is what the heating curve builds on: energy in makes particles move faster and spread. -->

<style scoped>pre, marp-pre { font-size: 0.5em; line-height: 1.25; } section { font-size: 27px; }</style>

---

<span style="background:#fef3c7; color:#1a1a1a; border:1.5px solid #f59e0b; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">✍️ Activity</span>

## Elaborate: a cooling curve

{{embed: https://studio.learningwaypoints.com/tutorials/_playground-board/index.html?id=deck%2Fscience%2Fchemistry%2Fheating-curve%2Fstep-5&code=widget%3A+graph%0Aaxes%3A+Time+cooling+%28min%29%2C+Temperature+%28%C2%B0C%29%0Ax%3A+0%2C+20%0Ay%3A+0%2C+100%0Agrid%3A+2%2C+20%0Aseries+Stearic%3A+0%2C90%3B+4%2C69%3B+12%2C69%3B+20%2C30%0Acursor+R%3A+1%0A&fresh=1}}

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

<!-- Speaker note: What this step is for: Reading a cooling curve applies the same idea in reverse: a flat part while the substance freezes and gives out energy. -->

<style scoped>pre, marp-pre { font-size: 0.5em; line-height: 1.25; } section { font-size: 25px; }</style>

---

<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>

## Why it stays flat

**Why does the stearic acid's temperature stay at 69 °C for 8 minutes while it freezes?**

- As particles settle into fixed places they give out energy, which keeps the temperature steady
- The thermometer stopped working
- The room warms the wax

* Answer: As particles settle into fixed places they give out energy, which keeps the temperature steady

<!-- Speaker note: Freezing gives energy out. Until every particle has settled, that energy balances what is lost to the room. -->

<style scoped>pre, marp-pre { font-size: 0.5em; line-height: 1.25; } section { font-size: 28px; }</style>

---

<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>

## Elaborate: sweating

**Why does sweating cool you down, even on a hot day?**

- Sweat is colder than your body
- Evaporating sweat takes energy in, and it takes it from your skin
- The wind blows the heat away

* Answer: Evaporating sweat takes energy in, and it takes it from your skin

<!-- Speaker note: Changing liquid to gas needs energy. The fastest particles escape from the sweat, carrying energy away from your skin. What this step is for: Evaporation taking energy from the skin connects 'energy in for a change of state' to everyday cooling. -->

---

## Evaluate: look back

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

**Revision summary**

- Melting, boiling and evaporating take **energy in**; freezing and condensing give **energy out**.
- Adding energy to a substance makes its particles move faster (the temperature rises), until it reaches a change of state.
- During a change of state the temperature stays the same: the energy goes into separating the particles (or comes out as they settle).
- A **heating curve** shows this as flat parts at the melting and boiling points.

<style scoped>pre, marp-pre { font-size: 0.5em; line-height: 1.25; } section { font-size: 24px; }</style>

---

<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

**Water vapour condenses on a cold window. Is energy taken in or given out, and what are the particles doing?**

* Given out. The water particles slow down and come close together, forming a liquid on the glass.

<!-- 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: Pure substance or mixture? (AC9S7U06). Particle theory's scope and limits (node 5) is a short lesson. In class: a heating curve for ice or a cooling curve for stearic acid, with data loggers if you have them. Candle wax is a mixture, so it freezes over a range of temperatures, not at one: use it to show what a mixture's curve looks like. The water curve on the board is to scale for steady heating (1 kg: 42 kJ to warm the ice, 334 kJ to melt, 418 kJ to warm the water, 2260 kJ to boil); a real pot loses some heat, so times vary. -->