UNIT OVERVIEW

Every time you light a match, digest your breakfast, or use a hand warmer, energy is being transformed. This unit explains the energy changes that happen during chemical reactions.

You already know that atoms bond together to form molecules. But why do some reactions release heat while others feel cold? The answers lie in the energy stored within chemical bonds.

What you will learn:

• How energy is stored in chemical bonds and released or absorbed during reactions
• The difference between exothermic and endothermic reactions
• What activation energy is and why all reactions need it
• How to read and draw energy diagrams (potential energy diagrams)
• How to calculate enthalpy changes using bond energies
• How catalysts change activation energy

Real-Life Applications:

1. Hand warmers and cold packs — Instant heat packs contain iron powder that releases heat when it reacts with oxygen. Cold packs contain ammonium nitrate that absorbs heat when dissolved in water.

2. Cooking and combustion — When you braai meat over a fire, the burning charcoal releases energy as heat and light.