Class-X-Endothermic & Exothermic Reactions

Endothermic Reactions

An endothermic reaction is any chemical reaction that absorbs heat from its environment. The absorbed energy provides the activation energy for the reaction to occur. A hallmark of this type of reaction is that it feels cold.

Expressed in a chemical equation: Reactants + Energy → Products.

• Photosynthesis (chlorophyll is used to react to carbon dioxide plus water plus energy to make glucose and oxygen)
• Dissolving ammonium chloride in water
• Mixing water and ammonium nitrate
• Mixing water with potassium chloride
• Reacting ethanoic acid with sodium carbonate
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Exothermic Reactions

An exothermic reaction is a chemical reaction that releases energy through light or heat. It is the opposite of an endothermic reaction.

Expressed in a chemical equation: Reactants → Products + Energy.

Examples of Exothermic Reactions

Any combustion reaction.
A neutralization reaction.
Rusting of iron (rust steel wool with vinegar).
The thermit reaction.
Reaction between water and calcium chloride.

Thermit Reaction
The reaction of iron (III) oxide (Fe2O3) with aluminium is used to join railway tracks or cracked machine parts. This reaction is known as the thermit reaction. These displacement reactions are highly exothermic. The amount of heat evolved is so large that the metals are produced in the molten state.

Fe2O3 (s) + 2Al (s) → 2Fe (l) + Al2O3 (s) + Heat