Difference Between Exothermic and Endothermic Reactions

In Chemistry, chemical reactions involve the breaking and making of bonds. Depending on whether heat energy is released or absorbed during this process, reactions are classified as Exothermic or Endothermic.

Question (Click to Flip)

Differentiate between exothermic and endothermic reactions.

Answer

Exothermic reactions release heat energy into the surroundings, making them hotter (e.g., burning coal). Endothermic reactions absorb heat energy from the surroundings, making them cooler (e.g., melting ice).

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Key Facts

Exothermic: Releases heat (Exo = Exit). Surroundings get hot.

Endothermic: Absorbs heat (Endo = Enter). Surroundings get cold.

Combustion: Always Exothermic.

Decomposition: Usually Endothermic (requires heat to break bonds).

1. Exothermic Reaction

Definition: A chemical reaction that releases heat (or energy) into its surroundings.
Temperature Effect: The surroundings (like the test tube or the air) become hotter.
Examples:
1. Burning of wood or coal (Combustion).
2. Respiration in our bodies.
3. Mixing water with quicklime (CaO).

2. Endothermic Reaction

Definition: A chemical reaction that absorbs heat (or energy) from its surroundings to proceed.
Temperature Effect: The surroundings become cooler.
Examples:
1. Photosynthesis in plants (absorbs sunlight).
2. Melting of ice.
3. Thermal decomposition (like heating limestone CaCO₃ to break it down).

Summary Comparison

Feature	Exothermic	Endothermic
Heat Energy	Released	Absorbed
Surroundings	Feel Hotter	Feel Cooler
Energy Level	Reactants have more energy than Products	Products have more energy than Reactants
Sign of ΔH	Negative (-)	Positive (+)

Questions and Answers

Differentiate between exothermic and endothermic reactions.+

Is respiration an exothermic or endothermic reaction?+

Respiration is an exothermic reaction because it breaks down glucose in our cells to release energy that our body uses.

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