Which statement best describes the final form of the relative rate expression?

Which statement best describes the final form of the relative rate expression?

• A. It is the square of the rate constant
• B. It is the integrated form of the rate law
• C. It applies only to first-order reactions
• D. It relates the rate of appearance or disappearance of a species to its stoichiometric coefficient

Answer: (D)

The relative rate expression ties the rate of the reaction to how fast each species changes, scaled by its stoichiometric coefficient. For a general equation aA + bB → cC + dD, the rate is defined so that the same value describes the disappearance of reactants and the appearance of products when each change is divided by its coefficient: v = -(1/a) d[A]/dt = -(1/b) d[B]/dt = (1/c) d[C]/dt = (1/d) d[D]/dt. This shows that the rate of appearance or disappearance of a given species is directly linked to its stoichiometric coefficient and the overall reaction rate. The other statements don’t capture this relationship: it isn’t simply the square of a rate constant, it isn’t an integrated form, and it isn’t restricted to first-order reactions.

The relative rate expression ties the rate of the reaction to how fast each species changes, scaled by its stoichiometric coefficient. For a general equation aA + bB → cC + dD, the rate is defined so that the same value describes the disappearance of reactants and the appearance of products when each change is divided by its coefficient: v = -(1/a) d[A]/dt = -(1/b) d[B]/dt = (1/c) d[C]/dt = (1/d) d[D]/dt. This shows that the rate of appearance or disappearance of a given species is directly linked to its stoichiometric coefficient and the overall reaction rate. The other statements don’t capture this relationship: it isn’t simply the square of a rate constant, it isn’t an integrated form, and it isn’t restricted to first-order reactions.