The Rate Equation

X + Y → Z

The rate law of the above reaction is:

rate = k [X]a [Y]b

k is a constant determined by the reaction and conditions. The values of a and b are determined by varying the concentrations of X and Y. For example, if the concentration of X is doubled while the concentration of Y is constant, and the rate quadrupl es, then a must equal two. Likewise, if in a separate experiment the concentration of Y doubles and the concentration of X stays the same, and the rate does not change, than b must equal zero. Thus it appears that two molecules of X and no molecules of Y are involved in the rate-limiting step.

For substitution and elimination reactions, the values of a and b are zero or one. The sum of a and b is the reaction order. Substitution and elimination reactions have orders of one and two.

	Created by HappyOwl over 10 years ago

Third Year MCAT Note on MCAT Chemistry Review: Organic Chemistry, created by HappyOwl on 20/05/2014.