The relative rate expression relates rates of change of species by their stoichiometric coefficients.

The relative rate expression relates rates of change of species by their stoichiometric coefficients.

• A. It is independent of stoichiometry
• B. It uses equilibrium constants
• C. It relates the rates of change of different species by their stoichiometric coefficients
• D. It depends only on temperature

Answer: (C)

During a reaction, the changes in concentrations of all species are tied to the same underlying rate of progress, scaled by their stoichiometric coefficients. If the reaction is aA + bB → cC + dD and the rate of reaction is r, then the concentration changes satisfy d[A]/dt = -a r, d[B]/dt = -b r, d[C]/dt = c r, and d[D]/dt = d r. Dividing each by its coefficient gives -1/a d[A]/dt = -1/b d[B]/dt = 1/c d[C]/dt = 1/d d[D]/dt = r. This is the relative rate expression: it shows how fast each species is changing relative to the same progress variable, with the stoichiometric coefficients setting the scale. The actual value of r depends on temperature through the rate constant, but the proportionality among the species’ rates is dictated by the coefficients, not by equilibrium constants. Equilibrium constants describe the balance at equilibrium, not the instantaneous rates, and temperature alone sets the rate constant, not the ratio of rate changes.

During a reaction, the changes in concentrations of all species are tied to the same underlying rate of progress, scaled by their stoichiometric coefficients. If the reaction is aA + bB → cC + dD and the rate of reaction is r, then the concentration changes satisfy d[A]/dt = -a r, d[B]/dt = -b r, d[C]/dt = c r, and d[D]/dt = d r. Dividing each by its coefficient gives -1/a d[A]/dt = -1/b d[B]/dt = 1/c d[C]/dt = 1/d d[D]/dt = r. This is the relative rate expression: it shows how fast each species is changing relative to the same progress variable, with the stoichiometric coefficients setting the scale. The actual value of r depends on temperature through the rate constant, but the proportionality among the species’ rates is dictated by the coefficients, not by equilibrium constants. Equilibrium constants describe the balance at equilibrium, not the instantaneous rates, and temperature alone sets the rate constant, not the ratio of rate changes.