Question

Consider the following hypothetical reaction: $$ \mathrm{X}+\mathrm{Y} \longrightarrow \text { Products } \quad \Delta H=-75 \mathrm{~kJ} $$ Draw a reaction-energy diagram for the reaction if the activation energy is \(32 \mathrm{~kJ}\).

Short answer

Question: Draw and label a reaction-energy diagram for the hypothetical reaction X + Y -> Products, given an activation energy of 32 kJ and an enthalpy change of -75 kJ. Describe the energy changes occurring during the reaction.

Step-by-step solution

Understand the reaction-energy diagram

A reaction-energy diagram shows the energy profile of a chemical reaction. It typically consists of a y-axis representing potential energy (in kJ) and an x-axis that represents the reaction path or progress. The diagram will show the energy state of reactants, intermediates, transition states, and products involved in the reaction.

Prepare the diagram

Begin by drawing the axes for the diagram. Label the y-axis "Potential energy (kJ)" and the x-axis "Reaction progress".

Plot the reactants and products

On the y-axis, mark the initial energy state of the reactants, let's say at y = 0. Then, plot a point for the initial energy of the reactants (X + Y) somewhere along the x-axis. Next, use the given enthalpy change (-75 kJ) to determine the final energy state of the products. Since the enthalpy change is negative, the products will have a lower potential energy than the reactants (75 kJ lower in this case). Plot the final energy state of the products along the x-axis, 75 kJ below the energy level of the reactants.

Determine and plot the transition state

The activation energy (32 kJ) represents the energy barrier that must be overcome for the reaction to occur, which corresponds to the highest potential energy along the reaction path. Since we have the reactants at the initial energy level, add the activation energy to the energy level of the reactants. That will give the energy level of the transition state. Plot the transition state on the diagram.

Draw the energy profile

Now that we have the energy levels for reactants, products, and the transition state, we can connect them to create the energy profile for the reaction. Draw a curved line from the initial energy state (reactants) that goes up to the transition state and then descends to the final energy state (products). This curve represents the energy changes that occur during the reaction.

Label the diagram

Finally, label the important parts of the diagram: the energy levels of reactants, products, transition state, the activation energy, and the enthalpy change. This will help make the diagram easier to understand and interpret. You should now have a complete reaction-energy diagram for the given reaction with the activation energy of 32 kJ and enthalpy change of -75 kJ.