Question

Compound A can be converted to either B or C. The energy diagrams for both processes are drawn on the graph below.

1. Label each reaction as endothermic or exothermic.
2. Which reaction is faster?
3. Which reaction generates the product lower in energy?
4. Which points on the graphs correspond to transition states?
5. Label the energy of activation for each reaction.
6. Label the $\mathbf{∆}{\mathbf{H}}^{\mathbf{°}}$ for each reaction.

Short answer

Answer

1. The reaction A to B is endothermic and reaction A to C is exothermic.
2. The reaction that involves a lower activation energy barrier will be faster and hence in the given case, the reaction A to C is faster.
3. Reaction A to C generates a product lower in energy.
4. The points which have high energy (i.e., the points D and E) corresponds to the transition states.
5. Labeled in the energy diagram
6. Labeled in the energy diagram

Step-by-step solution

Step-by-Step SolutionStep 1: Exothermic and Endothermic reactions

The reactions that liberate energy/heat are termed exothermic and the ones that absorb heat are termed endothermic reactions.

• The reactions that have a positive $∆{\mathrm{H}}^{°}$(i.e., the reactions in which the energy of products is higher than the energy of the reactants) are endothermic.
• The reactions that have a negative $∆{\mathrm{H}}^{°}$(i.e., the reactions in which the energy of products is lower than that of the reactants) are exothermic.

Transition state and activation energy

In an energy profile diagram, the peak (high energy point) that lies between the reactants and the products is referred to as the transition state.

The energy barrier between the reactant and product species is referred to as the activation energy of the reaction.

Energy diagrams

Energy diagram of the given reactions

The reaction A to B is endothermic and reaction A to C is exothermic.