Coordinate diagrams in general describe changes in energy as a reaction transpir
ID: 1010664 • Letter: C
Question
Coordinate diagrams in general describe changes in energy as a reaction transpires. It may be useful to plot on a coordinate diagram (a reaction coordinate, in this case).You have a start point (the reactants) and an end point (the products) connected by a single reaction arrow. This is a one-step elementary reaction, in which two "stable" states (reactants and products) are connected by a pathway passing through a single, high energy state or "transition state." In column 1, a box represents your reactants. In column 2, a box represents the transition state. In column 3, a box represents your products. Choose the coordinate diagram that makes sure that all states are at sensible energies relative to one another!
Explanation / Answer
The first co-ordinate diagram is the correct one where the transition state is at a higher energy than the reactants and the products have lower energy than the products. A system is stable when it has the minimum potential energy. A reaction occurs in the first place to minimize the potential energy of the system. Hence, the products can never be at a higher energy than the reactants, such a reaction will never occur spontaneously. Thus, the products must always be at a lower energy than the reactants. This straightaway eliminates the second diagram where the products have higher energy than the reactants.
We are now left to decide between the first and third diagrams where the products have lower energy than the reactants. However, observe in the third diagram, the transition state has the lowest energy. If such is the case, then the transition state will be the most stable and the conversion of transition state to product will never occur. This eliminates the third diagram. In general, the transition state has a higher energy than the reactants and is less stable than the reactants. Thus the transition state quickly converts itself into the more stable products (having the lowest energy).
Thus, the first diagram gives the correct energies of the states relative to each other.