Energy in Chemistry
Energy changes in reactions
Energy and reactions
Many chemical reactions involve energy changes. Some release energy to the surroundings, while others absorb energy from the surroundings.
Exothermic and endothermic
An exothermic process releases energy, often as heat. An endothermic process absorbs energy. In symbols, you can think of exothermic as energy leaving the system and endothermic as energy entering it.
Energy change comparison
Exothermic
- Releases energy
- Surroundings may warm up
- Examples include combustion
Endothermic
- Absorbs energy
- Surroundings may cool down
- Examples include some dissolving and decomposition
Activation energy
Even reactions that release energy often need a small input of energy to start. This minimum starting energy is called activation energy.
A reaction that absorbs energy is called:
Endothermic reactions absorb energy from their surroundings.
Correct answer: Endothermic
What is activation energy?
Many reactions need a small energy input before they can proceed.
Correct answer: The minimum energy needed to start a reaction
What usually happens to the surroundings in an exothermic reaction?
Exothermic reactions release energy, often warming the surroundings.
Correct answer: They may warm up
Real-world example
Combustion, such as burning wood or fuel, is a familiar exothermic process.