Chemistry/Chapter 8: Energetics
8.1 Energy in Chemical Reactions
**Chemical energetics** is the study of energy changes in chemical reactions
Explanation level
This topic explains how energy is involved in chemical reactions — why some reactions release energy and others absorb it.
Definition
Chemical energetics is the study of energy changes in chemical reactions.
Simple explanation: Chemical energetics is about the heat (energy) that is absorbed or released during chemical reactions.
Main Idea
Energy in the form of heat is developed or absorbed as a result of a chemical reaction. This is because in a chemical reaction:
- Old bonds are broken → energy is consumed.
- New bonds are formed → energy is released.
If the energy released in forming bonds is greater than the energy expended in breaking bonds, there is a net release of chemical energy.
On the other hand, energy is absorbed when the energy expended in breaking a bond is greater than the energy released in forming the bond.
Thus, during chemical reactions, energy is exchanged with the surroundings.
Simple explanation: Breaking bonds needs energy; making bonds releases energy. The net effect decides whether the reaction releases or absorbs energy.
Core Concept
Bond Breaking and Bond Making
| Process | Energy Change |
|---|---|
| Breaking bonds | Energy is absorbed (consumed) |
| Forming bonds | Energy is released |
Net energy change:
Δ H = Energy absorbed in breaking bonds - Energy released in forming bonds
Two Types of Reactions
| Type | Energy Change | ΔH Sign |
|---|---|---|
| Exothermic | Releases heat | Negative (−) |
| Endothermic | Absorbs heat | Positive (+) |
Simple explanation: Exothermic = heat out; endothermic = heat in.
Detailed Explanation
Why Energy Changes Occur
Every process in this universe — whether in living cells, test tubes, atmosphere, or water — involves a change in energy.
- Some processes release energy.
- Others require energy.
- Produce new raw materials such as iron, steel, copper, aluminium, etc.
- Transform raw materials into useful products such as trains, trucks, cars, buildings, bridges, and many other objects.
Simple explanation: Energy changes are everywhere — from the food we digest to the fuels we burn.
Bond Breaking and Bond Making
Breaking bonds always consumes energy — you have to put energy in to pull atoms apart.
Forming bonds always releases energy — when atoms come together, they give out energy.
The balance between these two decides whether the reaction is exothermic or endothermic.
Simple explanation: It's like a business: you "spend" energy to break bonds and "earn" energy when new bonds form. If you earn more than you spend, the reaction releases energy (exothermic). If you spend more than you earn, the reaction absorbs energy (endothermic).
Net Energy Release or Absorption
- More energy is released in forming new bonds than is absorbed in breaking old bonds.
- Net release of energy → exothermic reaction.
- More energy is absorbed in breaking old bonds than is released in forming new bonds.
- Net absorption of energy → endothermic reaction.
Did you understand this topic?
Your answer is saved with your learning record. It does not mark the topic as mastered.
Same supplied content as this Notes page (shared canonical source).