Question

Due today!

The diagram shows the potential energy changes for a reaction pathway.

A curved lined graph is shown. The y axis of the graph has the title Potential Energy. The x axis of the graph has the title Reaction Pathway. The graph curve begins at a lower level and ends at a slightly higher level. A vertical line labeled A, starting from the x axis till the beginning of the graph line is shown. A vertical line labeled B, starting from where the line labeled A ended, till the uppermost hump in the graph curve is shown. Another vertical line labeled C is shown from starting from the x axis till the point where the graph curve ends.

Part 1: Describe how you can determine the total change in enthalpy and activation energy from the diagram, and if each is positive or negative.

Part 2: Describe how the curve will look if the reaction was exothermic. Be sure to mention changes in the potential energies of the reactants and products and the sign changes of the enthalpy.

Answer 1

The total change in enthalpy can be determined by looking at the vertical distance between the starting point (reactants) and the ending point (products).

If the reaction is exothermic, the curve would start at a higher potential energy (on the y-axis) for the reactants and end at a lower potential energy for the products.

The sign of activation energy depends on the convention used. If it's defined as the energy required to go from reactants to the transition state, it would be positive. If defined as the energy released when going from reactants to the transition state, it would be negative.

If the reaction is exothermic, the curve would start at a higher potential energy (on the y-axis) for the reactants and end at a lower potential energy for the products. This is because in an exothermic reaction, energy is released, leading to a decrease in potential energy. The curve would slope downward from left to right.