Select the correct answer.
In this reaction, what effect does a change in the concentration of substances have on the reverse reaction rate?
[tex]CaCO_3(s) \rightleftharpoons CaO(g)+CO_2(g)[/tex]
A. The rate of the reverse reaction increases with an increase in the concentration of [tex]CaCO _3(s)[/tex].
B. The rate of the reverse reaction increases with an increase in the concentration of [tex]CaO (g)[/tex] and [tex]CO _2(g)[/tex].
C. The rate of the reverse reaction decreases with a decrease in the concentration of [tex]CaCO _3(s)[/tex].
D. The rate of the reverse reaction decreases with an increase in the concentration of [tex]CaO (g)[/tex] and [tex]CO _2(g)[/tex]
E. The rate of the reverse reaction increases with a decrease in the concentration of [tex]CaO (g)[/tex] and [tex]CO _2(g)[/tex].
Answer (1)
The reverse reaction is C a O ( g ) + C O 2 ( g ) → C a C O 3 ( s ) .
The rate law for the reverse reaction is R a t e = k [ C a O ] [ C O 2 ] .
Increasing the concentration of C a O and C O 2 increases the rate of the reverse reaction.
The correct answer is B: The rate of the reverse reaction increases with an increase in the concentration of C a O ( g ) and C O 2 ( g ) . B
Explanation
Analyzing the Reaction The given reaction is a reversible reaction: C a C O 3 ( s ) ⇌ C a O ( g ) + C O 2 ( g ) We are asked to determine the effect of changing the concentration of the substances on the rate of the reverse reaction. The reverse reaction is: C a O ( g ) + C O 2 ( g ) → C a C O 3 ( s )
Identifying Factors Affecting Reaction Rate The rate of the reverse reaction depends on the concentration of the reactants in the reverse reaction, which are C a O ( g ) and C O 2 ( g ) . The concentration of solids like C a C O 3 ( s ) does not affect the reaction rate because the concentration of a solid is constant.
Writing the Rate Law The rate law for the reverse reaction can be written as: R a t e = k [ C a O ] [ C O 2 ] where k is the rate constant, [ C a O ] is the concentration of C a O , and [ C O 2 ] is the concentration of C O 2 .
Determining the Effect of Concentration Changes From the rate law, we can see that:
If the concentration of C a O and C O 2 increases, the rate of the reverse reaction increases.
If the concentration of C a O and C O 2 decreases, the rate of the reverse reaction decreases.
Changing the concentration of C a C O 3 ( s ) has no effect on the rate of the reverse reaction because it is a solid.
Selecting the Correct Answer Based on the analysis, the correct answer is: B. The rate of the reverse reaction increases with an increase in the concentration of C a O ( g ) and C O 2 ( g ) .
Examples
Consider a scenario where limestone ( C a C O 3 ) is heated to produce lime ( C a O ) and carbon dioxide ( C O 2 ). If we increase the concentration of lime and carbon dioxide in the environment, the reverse reaction will be favored, leading to the reformation of limestone. This principle is crucial in industrial processes where controlling the concentration of reactants and products can shift the equilibrium to optimize the yield of desired substances. Understanding this helps in designing efficient chemical reactors and managing waste products effectively.
