Energy Changes in Chemistry

Energy Changes in Chemistry

• A chemical reaction may either absorb energy or release energy, and these reactions are respectively referred to as endothermic reactions or exothermic reactions.
• The energy referred to in these reactions is often predominantly thermal energy, manifesting as a change in temperature.

Endothermic Reactions

• In an endothermic reaction, the products have more energy than the reactants.
• The energy difference is absorbed from the surroundings, resulting in a cooling effect.
• Examples of endothermic reactions include evaporation of water, dissolving certain salts in water, and photosynthesis in plants.
• The generic equation for an endothermic reaction can be represented as: Reactants + Energy -> Products.

Exothermic Reactions

• In an exothermic reaction, the reactants have more energy than the products.
• This energy difference is released into the surroundings, often observed as an increase in temperature.
• Common examples of exothermic reactions include combustion reactions and neutralisation reactions. The rusting of iron is also an exothermic process.
• The generic equation for an exothermic reaction is: Reactants -> Products + Energy.

Energy Profile Diagrams

• Energy changes in chemical reactions can be represented visually using energy profile diagrams.
• In these diagrams, the energy of the system is plotted against the reaction progress.
• For an exothermic reaction, the energy level decreases as the reaction progresses, while it increases for an endothermic reaction.

Activation Energy

• The activation energy is the minimum amount of energy that reactants must possess for a chemical reaction to occur.
• It can be visualised as the peak of the energy profile diagram, representing the energy barrier to be crossed in the reaction.
• Catalysts work by reducing the activation energy for a reaction, thereby increasing the rate of reaction.

Applications of Energy Changes

• Understanding and controlling energy changes in chemical reactions are important in many industries and for various applications - such as chemical manufacturing, energy generation, healthcare and agriculture.
• For instance, exothermic reactions are exploited in hand warmers and self-heating cans, while endothermic reactions are utilised in instant cold packs used for injuries.