Energy Changes: Temperature Changes

Energy changes are responsible for temperature changes in a chemical reaction.
An exothermic reaction is one that releases energy, usually in the form of heat, causing the temperature of the surroundings to rise. Examples include combustion reactions and many oxidation reactions.
An endothermic reaction on the other hand absorbs energy, usually from the surroundings, which leads to a drop in temperature. Examples of endothermic reactions include photosynthesis and the thermal decomposition of calcium carbonate in making cement.
The term energy ‘given out’ refers to exothermic reactions and ‘taken in’ refers to endothermic reactions. This is how energy change affects temperature.
The energy change in a chemical reaction can be calculated by measuring the temperature change in the reactions. This is accomplished by subtracting the final temperature from the initial temperature.
Factors affecting the temperature change include: the amounts of reactants used, the surface area of any solid reactants, the concentrations of any solutions used and the temperature at which the reaction is carried out.
Bond breaking is an endothermic process (absorbs energy), while bond formation is an exothermic process (releases energy). In reactions where the energy released when new bonds are formed is greater than the energy absorbed to break the old bonds, the overall reaction is exothermic.
In cases where the energy needed to break the bonds is greater than the energy released when new bonds are formed, the overall reaction is endothermic.
The temperature change in a solution can also be used to calculate the enthalpy change of a reaction.
Enthalpy change, symbolised as ∆H, is the amount of heat energy absorbed or evoked at constant pressure by a system in a chemical reaction. It’s given in joules (J).
It’s important to remember that any energy change in a chemical reaction is due to the difference in energy between the products and reactants, not the actual amounts of substances involved in the reaction.
Energy diagrams can be used to help visualise the energy changes and temperature changes that occur in a reaction. These diagrams represent the energy levels of the reactants and products, and show the energy input required to break bonds and the energy released when new bonds are formed.