Second order description?

Second order description?

• A. Rate is independent of concentration.
• B. Rate is proportional to the cube of the concentration.
• C. Rate is proportional to the square of the concentration.
• D. Rate is directly proportional to concentration.

Answer: (D)

The main idea here is how the rate depends on concentration, which is described by the rate law. The order of reaction tells you how sensitive the rate is to changes in concentration. If the rate is directly proportional to the concentration, the rate law has a linear dependence: rate = k[A]. That is a first-order dependence in that reactant. The other options describe different kinds of dependence: rate independent of concentration means zero order; rate proportional to the square of the concentration means second order (for a single reactant); rate proportional to the cube of the concentration means third order. Since the statement in question expresses a simple linear relationship between rate and concentration, that linear dependence is the best description among the choices.

The main idea here is how the rate depends on concentration, which is described by the rate law. The order of reaction tells you how sensitive the rate is to changes in concentration. If the rate is directly proportional to the concentration, the rate law has a linear dependence: rate = k[A]. That is a first-order dependence in that reactant.

The other options describe different kinds of dependence: rate independent of concentration means zero order; rate proportional to the square of the concentration means second order (for a single reactant); rate proportional to the cube of the concentration means third order. Since the statement in question expresses a simple linear relationship between rate and concentration, that linear dependence is the best description among the choices.