Question

Which of the following correctly describes how rate laws are determined?
Rate laws can be determined from the coefficients of balanced equations.
The rate law for an elementary step can only be determined from unimolecular reactions.
The rate law for the overall reaction is always determined by the rate law of the fastest step.
Rate laws are determined through experimentation.

Answer 1

To answer this question, we must go through a process of elimination.

A. This is only true for elementary reactions; It does not apply to all.
B. This is not only applicable to unimolecular but to bimolecular and so on and so forth.
C. The contrary is true. The slowest reaction would be the basis because it is the rate-limiting step.
D. This is true.

The answer is D.

Answer 2

Answer: Rate laws are determined through experimentation.

Explanation:

Elementary reactions are reactions which takes place in single step. For elementary reactions the order is same as the stoichiometric coefficients.

For a complex reaction, the rate is determined by the slowest step.

Rate law says that rate of a reaction is directly proportional to the concentration of the reactants each raised to a stoichiometric coefficient determined experimentally called as order.

$Rate=k[A]^x[B]^y$

k= rate constant

x = order with respect to A

y = order with respect to AB

n = x+y = Total order