Energy Changes: Endothermic Reactions

Understanding Endothermic Reactions

Endothermic reactions are those that absorb energy from the surroundings, typically in the form of heat.
During such reactions, the energy required to break bonds in the reactants is greater than the energy released when new bonds form in the products.
The temperature of the surroundings decreases during endothermic reactions, as energy is sucked into the reaction.
Photosynthesis in plants (converting light energy, carbon dioxide and water into glucose and oxygen) and the process of dissolving certain salts in water are examples of endothermic reactions.

Energy Changes in Endothermic Reactions

The energy difference between reactants and products in a chemical reaction is represented as ΔH, where ΔH = energy of bonds broken - energy of bonds formed.
For endothermic reactions, ΔH will be positive, signifying that energy is absorbed from the surroundings.
The energy level diagram of an endothermic reaction shows that the energy of products is higher than that of the reactants.

Measuring Energy Change

To measure the energy change in a reaction, use a calorimeter – a setup that determines the heat absorbed or released by a solution to understand the energy involved in the reaction.
The quantity of heat determined experimentally is used to calculate the enthalpy change, ΔH.

Applications of Endothermic Reactions

Cold packs (used to treat injuries) utilise the principle of endothermic reactions to absorb heat and thus provide a cooling effect.
The process of photosynthesis in plants, which is vital for the continued existence of life on earth, is an example of an endothermic reaction.

Factors Affecting Endothermic Reactions

Factors such as temperature, surface area, concentration, and the presence of a catalyst can affect the rate at which an endothermic reaction occurs.
Increasing temperature, surface area, or concentration, or the addition of a catalyst, generally speeds up the reaction rate.
However, unlike exothermic reactions, increasing the temperature in an endothermic reaction not only increases the reaction rate but can also provide the necessary energy for the reaction to take place.