Energy In, Energy Out
Some reactions warm your hands and some turn ice-cold. Sort exothermic from endothermic, read the energy story off a reaction profile, and, for Higher tier, weigh the energy of bonds broken against bonds made.
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Every reaction moves energy 🔥
Every chemical reaction transfers energy. Some reactions **release** energy and **warm** their surroundings; others **take in** energy and **cool** them. This module looks at **exothermic** and **endothermic** reactions, how to read a **reaction profile**, and, for Higher tier, how the energy of **bonds** decides the balance.
The language of energy 🔑
Four ideas run through the topic:
Which way does the heat go? 🌡️
In an EXOTHERMIC reaction, what happens to the temperature of the surroundings?
- It rises, because energy is released to the surroundings
- It falls, because energy is taken in from the surroundings
- It stays exactly the same throughout
- It rises and falls in equal amounts
Match each reaction to its energy change 🔗
- Combustion
- Thermal decomposition
- Neutralisation
- Photosynthesis
- Releases heat as a fuel burns, warming the surroundings
- Takes in heat to break a compound apart
- Gives out energy as an acid and an alkali react
- Absorbs light energy to build glucose in plants
Energy out or energy in? ⚖️
Reactions fall into two groups by their energy transfer. Both can be shown on a reaction profile.
Which are exothermic? ✅
Select the TWO reactions that are EXOTHERMIC.
- Burning methane as a fuel
- Neutralising an acid with an alkali
- Heating limestone to break it down
- Dissolving ammonium nitrate in a cold pack
Reading a reaction profile ⛰️
A **reaction profile** plots energy against the progress of a reaction. The **reactants** start on the left and the **products** end on the right. In an **exothermic** reaction the products sit **lower** than the reactants, so energy is given out; in an **endothermic** reaction they sit **higher**, so energy is taken in. The barrier between them is the **activation energy**, the minimum energy the reactants must gain before they can react.
Complete the summary 🧩
A reaction that gives out energy and warms its surroundings is _____, while one that takes in energy and cools them is _____. On a reaction profile, the products of an exothermic reaction are _____ than the reactants. The energy barrier the reactants must climb is the _____ energy. Breaking bonds takes in energy, while _____ bonds gives energy out.
Plot the reaction profile 📈
An interactive activity.
Bonds broken and made 🧮
An interactive activity.
Bonds and energy 🔬
Which statement about the bonds in a reaction is correct?
- Breaking bonds takes in energy, and making bonds releases energy
- Breaking bonds releases energy, and making bonds takes it in
- Both breaking and making bonds release energy
- Bonds have nothing to do with a reaction's energy
Spot the true statements 🖍️
An interactive activity.
Explain the energy change ✍️
An interactive activity.