Question

The graph shows the volume of a gaseous product formed during two trials of a reaction. A different concentration of reactant was used during each trial, whereas the other factors were kept constant.
Which of the following statements explains which trial has a lower concentration of the reactant?

A: Trial 1, because the average rate of the reaction is lower.
B: Trial 1, because this reaction lasted for a longer duration than Trial 2.
C: Trial 2, because this reaction was initially fast and later slowed down.
D: Trial 2, because the volume of product formed per unit time was higher.

Answer 1

A: Trial 1, because the average rate of the reaction is lower.

The rate of reaction is the speed with which reactants are converted into products. It is also the rate at which reactants disappear and products appear.  The higher the rate of reaction, the greater the amount of product formed in a reaction.

If we look at the graph, we will realize that trial 1 produces a lesser amount of product than trial 2. This implies that the  average rate of the reaction in trial 1 is lower than in trial 2.

Lower average rate of reaction implies lower concentration of the reactants since the rate of reaction depends on the concentration of reactants.

Hence trial 1 has a lower concentration of reactants because the average rate of the reaction is lower.

Answer 2

The correct option is option A: Trial 1, because the average rate of the reaction is lower

The average rate of reaction increases as the concentration of reactants increases;

The rate of reaction increases as the concentration of reactants increases because the number moles of the reaction particles increases resulting in increased collisions among the reacting particles followed by an increase in the number of effective collisions to form the total possible number of the product at a shorter time which shows a higher reaction rate.

The higher the reaction rate, the steeper the slope of the graph of the Amount of Products to Time produced and, from the given graph, Trial 2 has a higher average rate of reaction and given that other factors were kept constant, a higher concentration of reaction, while, Trial 1 that has a gentler slope of Amount of Product to Time has a lower concentration of the reactant, and therefore, the average rate of reaction in Trial 1, is lower

Therefore, the statement that explains which trial has a lower concentration of the reactant is option A, Trial 1, because the average rate of the reaction is lower