Question

The rate of a reaction expressed in terms of change in concentration of reactants at two different times, that is the average rate in terms of reactants, can be written as ?

• A. $\frac{x_2-x_1}{t_2-t_1}$
• B. $+$$\Delta x$$/$$\Delta t$
• C. $-$$\frac{x_2-x_1}{t_2-t_1}$
• D. $-$$\Delta x$$/$$\Delta t$

Answer 1

Answer: (C), (D)

The correct options are
C $-$$\frac{x_2-x_1}{t_2-t_1}$
D $-$$\Delta x$$/$$\Delta t$

The concentration of reactants decreases over a time interval, unlike products. If $x_2$ and $x_1$ are the concentrations at time $t_2$ and $t_1$, $x_2$ is smaller than $x_1$. Hence the average rate of the reaction will be $-$$\frac{x_2-x_1}{t_2-t_1}$ or it can also be written as $-$$\Delta x$$/$$\Delta t$. The negative sign is given in front of the formula so that the rate becomes a positive quantity.