Which of these describes the rate of this chemical reaction?

H2 + Cl2 → 2 HCl

a. an increase in the concentration of HCl and H2 with time

b. an increase in the concentration of HCl with time

c. an increase in H2 and Cl2 with time

d. a decrease in HCl and Cl2 with time

b. an increase in concentration of HCl with time.

Explanation:

The measurement of reaction rate is simply based on the dissapearance of a reactant or appearance of a product with increasing reaction time.

For this kind of chemical reaction, the rate would increase if the concentration of the reactants increase.

The reactants are made up of gaseous particles, for gases reacting, the rate of the reaction is directly proportional to concentration. The concentration of a gaseous system is also directly proportional to the pressure and we can use pressure in place of concentration.

For this reaction, we don't know the order of reaction of the reactants. This would not make the gaseous reactants suitable to monitor the rate of the reaction.

Since it is only the appearance of the product we are sure of, we simply monitor the concentration of the product to determine the rate.