Question

Units of average rate of reaction is:

• A. sec${}^{-1}$
• B. mole sec${}^{-1}$
• C. mole dm${}^{-3}$ sec${}^{-1}$
• D. unitless

Answer 1

The correct option is C mole dm${}^{-3}$ sec${}^{-1}$

The change in molar concentration of either reactants or products in unit time is called as average rate.

Let ‘Δc’ is the decrease in concentration of reactants in a small interval of time ‘Δt’ then:

$-\frac{\Delta c}{\Delta t}$ is the average rate with respect to reactant concentration(negative sign is used to make the rate positive, since the concentration of reactants decreases with time)

If ‘Δx’ is the increase in concentration of products in a small interval of time ‘Δt’ then:

$\frac{\Delta x}{\Delta t}$ is average rate with respect to product concentration ( positive sign is used since there is increase in the concentration of products during the reaction )

So the unit is Concentration divided by time scale.So, C is the answer.