States of Matter
Where does the energy go when you heat something? Sometimes into temperature, sometimes into breaking bonds. Explore internal energy, heat capacity, latent heat and the tell-tale flat sections of a heating curve.
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States of Matter 🌡️
Heat a block of ice and it warms up, melts, warms again, then boils. But the energy you supply does not always raise the **temperature** — sometimes it does something else entirely. To follow it, meet **internal energy**, **heat capacity** and **latent heat**.
Internal energy 🔋
The **internal energy** of a substance is the **total** energy stored by its particles: • their **kinetic** energy (from moving/vibrating), plus • their **potential** energy (from the bonds and spacing between them). Heating a substance transfers energy to this internal store.
Temperature or state 🔥
The energy you add does one of two things: • Raise the **temperature** — the particles gain **kinetic** energy and move faster. • Change the **state** — the energy breaks the bonds between particles (**potential** energy). During this the **temperature stays the same**.
Melting temperature
While a pure substance is melting, what happens to its temperature?
- It stays constant — the energy breaks bonds rather than raising the temperature
- It rises steadily
- It falls
- It rises then falls
Specific heat capacity ♨️
To RAISE the temperature, the energy needed is: **ΔE = m c Δθ** (energy = mass × specific heat capacity × temperature change). The **specific heat capacity (c)** is the energy needed to raise **1 kg** of the substance by **1 °C**. Water's is high, which is why it takes a lot of energy to boil a kettle.
Heating calculation
An interactive activity.
Latent heat 💧
To CHANGE the state (with no temperature change), the energy needed is: **E = m L** (energy = mass × specific latent heat). The **specific latent heat (L)** is the energy to change the state of **1 kg** of a substance. This is the energy that goes into breaking bonds while the temperature stays constant.
Melting calculation
An interactive activity.
Match each term to its meaning
- Internal energy
- Specific heat capacity
- Specific latent heat
- A change of state
- The total kinetic and potential energy of the particles
- Energy to raise 1 kg by 1 °C
- Energy to change the state of 1 kg (no temperature change)
- Happens at constant temperature
The heating curve 📈
Plot **temperature against time** as you heat a substance steadily and you get a **heating curve**. It **rises** while the temperature climbs, but goes **flat** whenever the substance is **changing state** — once at the melting point, once at the boiling point. The flat bits are the give-away.
Plot the melting point
An interactive activity.
Read the flat section
On a graph of temperature against time, what does a FLAT (horizontal) section show?
- The substance is changing state, e.g. melting or boiling
- The substance is cooling down
- The heater has been switched off
- The temperature is rising fastest
Order the experiment
An interactive activity.
The heating rules
Heating a substance can raise its temperature or change its _____. During a change of state, the temperature stays _____. The energy to raise 1 kg of a substance by 1 °C is its specific heat _____.