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Chemical Energetics | IGCSE Chemistry (0620)

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CS-991 · Module I-5

5 · Chemical Energetics

Cambridge IGCSE Chemistry 0620 · Core + Supplement · 2026–2028
Quick Revision
🔥 Exothermic/Endothermic📈 Energy Profiles⚖️ Bond Energy

5.1 Exothermic and Endothermic Reactions

Exothermic reactions release energy to the surroundings (temperature increases) — e.g. combustion, neutralization.

Endothermic reactions absorb energy from the surroundings (temperature decreases) — e.g. thermal decomposition, dissolving certain salts.

🎥 Video lectures for this sub-topic — coming soon
Q1: In an exothermic reaction, the temperature of the surroundings:
a) Increases b) Decreases c) Stays the same d) Cannot be determined
Show Answer
✅ a) Increases
Q2: Thermal decomposition is an example of a(n):
a) Exothermic reaction b) Endothermic reaction c) Neutral reaction d) Reversible reaction only
Show Answer
✅ b) Endothermic reaction

5.2 Energy Profile Diagrams and Bond Energy

In an exothermic reaction, products end up at a lower energy level than reactants (energy released). In an endothermic reaction, products end up at a higher energy level (energy absorbed).

Activation energy is the minimum energy needed for a reaction to start — the "hump" at the start of the energy profile, for both exo and endothermic reactions.

Overall energy change = energy absorbed breaking bonds in reactants − energy released forming bonds in products. Breaking bonds is always endothermic; forming bonds is always exothermic.

🎥 Video lectures for this sub-topic — coming soon
Q1: Breaking chemical bonds is always:
a) Exothermic b) Endothermic c) Neither d) Depends on the bond
Show Answer
✅ b) Endothermic (requires energy)
Q2: Activation energy is best described as:
a) The total energy released in a reaction b) The minimum energy needed to start a reaction c) The energy of the products only d) Always zero for exothermic reactions
Show Answer
✅ b) The minimum energy needed to start a reaction
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