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The energy change of a reaction is influenced by bond energies, reaction conditions, and the nature of reactants.
The energy change in a chemical reaction, also known as the enthalpy change, is primarily determined by the bond energies of the reactants and products. Bond energy is the amount of energy required to break a bond between two atoms, or the energy released when a bond is formed. If more energy is required to break the bonds in the reactants than is released when the new bonds are formed in the products, the reaction is endothermic and the energy change is positive. Conversely, if less energy is required to break the bonds than is released when new ones are formed, the reaction is exothermic and the energy change is negative.
The conditions under which a reaction takes place can also affect the energy change. Factors such as temperature, pressure, and the presence of a catalyst can all influence the rate of a reaction and thus the energy change. For example, increasing the temperature generally increases the rate of reaction, which can lead to a greater energy change. Similarly, a catalyst can lower the activation energy required for a reaction to occur, potentially altering the energy change.
Lastly, the nature of the reactants themselves can influence the energy change. Different substances have different bond energies, so the specific reactants involved in a reaction will determine the total energy required to break the bonds and the energy released when new bonds are formed. Additionally, the physical state of the reactants (solid, liquid, or gas) can affect the energy change, as different states require different amounts of energy to change. For instance, reactions involving gases often have larger energy changes than those involving solids or liquids.
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