What's the relationship between enthalpy change and bond breaking/forming?

Enthalpy change is directly related to the energy required to break bonds and the energy released when bonds are formed.

In a chemical reaction, bonds in the reactants are broken and new bonds are formed in the products. The enthalpy change of a reaction, denoted as ΔH, is the difference between the energy absorbed to break the bonds in the reactants and the energy released when new bonds are formed in the products.

When a bond is broken, energy is absorbed from the surroundings, this is an endothermic process. The energy required to break a bond is known as bond dissociation energy or bond enthalpy. It is always a positive value as it corresponds to the minimum energy required to disassemble a molecule of a substance into its constituent atoms.

On the other hand, when a bond is formed, energy is released to the surroundings, this is an exothermic process. The energy released when new bonds are formed is also referred to as bond enthalpy, but it is a negative value as energy is being released.

The overall enthalpy change of a reaction (ΔH) is calculated by subtracting the total energy released when bonds are formed in the products from the total energy absorbed to break the bonds in the reactants. If the energy required to break the bonds is greater than the energy released when new bonds are formed, the reaction is endothermic and ΔH is positive. Conversely, if the energy released when new bonds are formed is greater than the energy required to break the bonds, the reaction is exothermic and ΔH is negative.

In summary, the enthalpy change in a chemical reaction is a measure of the difference in energy between bond breaking and bond forming. It provides valuable information about the energy changes that occur during a reaction, which can be used to predict whether a reaction is likely to occur spontaneously or not. Understanding the relationship between enthalpy change and bond breaking/forming is fundamental to the study of chemical reactions in IB Chemistry.