Chapter 16, Problem 75A

Interpretation Introduction

Interpretation:

To evaluate the validity of the given statement.

Concept introduction:

In a chemical reaction, the reactants are written on the left side of the equation and the product is written on the right side.

The average rate of a reaction can be given by the formula,

Average reaction rate $\text{=}-\frac{\text{Δ}\left[\text{reactant}\right]}{\text{Δt}}$

Here, $\text{Δ}\left[\text{reactant}\right]$ = change in the concentration of the reactant

Answer to Problem 75A

The statement “You can determine the rate law for a chemical reaction by examining the mole ratio of reactants in the balanced equation” is only valid for a one-step reaction but is not valid for complex reactions.

Explanation of Solution

We can determine the rate law for a chemical reaction by examining the mole ratio of reactants in the balanced equation.

For a reaction, $a\text{A}+b\text{B}\to \text{products}$, the rate can be given as,

$\text{rate=}k{\left[\text{A}\right]}^m{\left[\text{B}\right]}^n$

Here, [A] is the concentration of reactant A and [B] is the concentration of reactant B and k is the rate constant and the exponents m and n signify the order of the corresponding reactant.

For a one-step reaction, the reaction coefficients a and bis equal to their corresponding orders for each reactant, i.e., m=a and n=b.

For a reaction that does not include just one-step, the orders are not possible to determine alone using the mole ratio of the reactant coefficients. The order has to be determined experimentally.

So, we can conclude that, the statement “You can determine the rate law for a chemical reaction by examining the mole ratio of reactants in the balanced equation” is only valid for a one-step reaction but is not valid for complex reactions.

Conclusion

The rate law for a chemical reaction can be examined by using the mole ratio of reactants in the balanced equation for a one-step reaction.