Question

In the diagram, the black line represents the concentration of a reactant and the green line represents the concentration of a product.
Which statement best describes the reaction rate?



A. The product maintains an constant concentration in the first half of the reaction.


B. At the end of the reaction, both product and reactants are of a constant concentration.


C. The reactants maintain an constant concentration in the first half of the reaction.


D. At the end of the reaction, both product and reactants are of an equal concentration.

I think is A. Please correct me if I am wrong. Thank you!

Answer 1

Answer:

B. At the end of the reaction, both product and reactants are of a constant concentration.

Explanation:

• Option A and C are similar as they both refer to constant concentration of product and reactant respectively in first half. As in the graph, the concentration of reactant and product changes (concentration of reactant decreases and concentration of product increase) with time in the first half$^{*}$ of the reaction. This made both A and C option wrong.
• Option D is also wrong as at the end of reaction$^{**}$ the line of concentration of product and reactant do not coincide which means they are not equal.
• Option B is correct as we take the end of reaction at the point where the concentration of reactant and product won't change much or become constant

$^{*}$first half time is the when concentration of reactant reduces to 50% of initial concentration which you can nearly assume on or before the point of intersection of both the concentration graphs.

$^{**}$end of reaction is the time when the reaction completes which is theoretically infinite but generally we take end of the reaction as the time when the slope of concentration curve becomes nearly zero or the time when change in concentration of reactant and product is negligible.