Exothermic and endothermic reactions and catalysts

In a nutshell

Exothermic reactions release energy into the surrounding whereas endothermic reactions absorb energy from the surroundings. Catalysts are substances which increase the rate of reactions.

Energy

Energy cannot be created or destroyed, therefore the amount of energy in this universe will always be constant. Chemicals store energy.

In chemical reactions, sometimes chemicals absorb energy from the surrounding and sometimes they release energy into the surrounding; the energy transferred is usually in the form of heat.

Exothermic reactions

Definition

Exothermic reactions are reactions in which energy is transferred from the chemicals to the surrounding. Exothermic reactions increase the temperature of the surroundings.

Science; Chemical reactions; KS3 Year 7; Exothermic and endothermic reactions and catalysts

Examples

Combustion and neutralisation reactions are examples of exothermic reactions. Self-heating cans of food contain chemicals that undergo exothermic reactions to release heat and warm the food.

Science; Chemical reactions; KS3 Year 7; Exothermic and endothermic reactions and catalysts

Combustion of fossil fuels is an exothermic process as energy is released.

Endothermic reactions

Definition

Endothermic reactions are reactions in which chemicals absorb energy from the surroundings. Endothermic reactions decrease the temperature of the surroundings.

Science; Chemical reactions; KS3 Year 7; Exothermic and endothermic reactions and catalysts

There are fewer examples of endothermic reactions.

Examples

Decomposition reactions are examples of endothermic reactions and heat needs to be supplied for them to take place.

Injury packs involves endothermic reactions. Once the pack is snapped, endothermic reactions take place inside the pack which absorbs heat and make the pack feel cold. This can help with swelling.

Catalysts

Definition

Catalysts are substances which speed up the rate of reaction. Catalysts do not change or get used up reactions, therefore they are not included in equations.

Different reactions require different catalysts. Enzymes are catalysts which exist in nature.

Example

Lactase enzymes help break down lactose molecules in our body.