Question

When zinc reacts with hydrochloric acid, it produces hydrogen gas. As the reaction proceeds, why does the rate of production of hydrogen gas decrease? (3 points)

The concentration of hydrogen gas decreases.

The concentration of the reactants decreases.

The hydrogen gas formed inhibits the reaction.

The hydrogen gas also reacts with the zinc metal.

Answer 1

The answer is B. The concentration of the reactants decreases.
In the reaction of zinc with hydrochloric acid, hydrogen gas and zinc chloride are formed:
Zn(s)+2HCl(aq)→ZnCl2(aq)+H2(g)Zn(s)+2HCl(aq)→ZnCl2(aq)+H2(g)
As the reaction proceeds, the concentration of the reactants (zinc and hydrochloric acid) decreases because they are being consumed to produce the products (zinc chloride and hydrogen gas). This decrease in reactant concentration over time leads to a decrease in the reaction rate, according to the rate law which states that the rate of a reaction is directly proportional to the concentration of the reactants.
The other options are not correct:
A. The concentration of hydrogen gas actually increases as the reaction proceeds, because it is a product of the reaction.
C. There is no evidence to suggest that the hydrogen gas formed would inhibit the reaction. In fact, it usually escapes from the reaction vessel as it is formed (since it's a gas), and therefore doesn't remain in the reaction environment to inhibit the reaction.
D. In this reaction, hydrogen gas does not react with the zinc metal. It is a product of the reaction, not a reactant.