Energy Changes

Question 1

What is an Exothermic reaction?
What is an Endothermic reaction?

Answer 1

Exothermic:
- A reaction in which energy is transferred from the substance TO the surroundings (this can be seen in a temperature increace)
- Most chemical reactions are exothermic. (e.g, combustion, neutralisation)

Endothermic
- A reaction in which energy is transferred from the surroundings TO the substance. (energy is taken in, this can be seen in a decreace in temperature)
- Only a few chemical reactions are endothermic, (e.g, thermal decomposition)

Question 2

What is activation energy?
How is this represented in an energy profile?

Answer 2

The minimum amount of energy that a chemical needs in order to react

This is represented in an energy profile as the gap between the reactants and the peak of the curve

Question 3

When bonds are broken, does this release or require energy?
When bonds are made, does this release or require energy?

And is this exothermic or endothermic as a result?

Answer 3

Breaking bonds - Requires energy (endothermic)
Making bonds - Releases energy (exothermic)