Video Transcript
Consider the following reaction: CuSO4 solid plus five H2O liquid are in equilibrium with CuSO4⋅5H2O solid. What is the enthalpy change for the backward reaction according to the data provided in the energy pathway diagram?
To answer this question, we must determine the enthalpy change for the backward reaction of the given reversible reaction process. We’ve been provided with an energy pathway diagram. An energy pathway diagram shows the potential energy over the course of a reaction. The potential energy of the reactants is shown on the left, and the potential energy of the products is shown on the right.
From this, we can see that this energy pathway diagram describes the forward reaction. In order for the reactants to turn into the products, energy must first be supplied to the system. This is the energy required to break the bonds between the atoms or ions. In this case, this represents the energy required to break the ionic bonds between the copper and sulfate ions. Then, energy will be released as bonds are formed to create the products. The net change in energy over the course of the reaction is the change in enthalpy.
We could also say that the change in enthalpy is the difference between the energy of the products and the energy of the reactants. For the forward reaction, the change in enthalpy is negative 67 kilojoules per mole. The negative sign indicates that there is a net release of energy during the reaction.
With this information regarding the forward reaction, let’s consider the backward reaction. In the backward reaction, the reactants and products are switched, but they still have the same potential energies. Energy must be supplied in order for the bonds in the reactants to be broken. Energy is released to form the bonds in the products. The net change in energy is the change in enthalpy. The enthalpy change of the backward reaction will have the same magnitude as the enthalpy change of the forward reaction but the opposite sign. This is true for all reversible reactions.
The change in enthalpy of this backward reaction is positive because species with a low potential energy are being converted into species with a high potential energy. So over the course of the reaction, there is a net increase in the energy of the system.
In conclusion, we have determined that the enthalpy change for the backward reaction is positive 67 kilojoules per mole.
