Question

Give the unit of rate of reaction.
A) Molar
B) Second
C) second/molar
D) Molar/second

Answer 1

Hint: The rate of reaction is the speed of the chemical reaction at which it proceeds to form the products. The rate of reaction is determined by calculating the difference in the concentration for the given time.

Complete answer:
So in the question, it is asked to write the unit of the reaction. So first we should know what the rate of the reaction is. So as said above the rate is the speed with which the chemical reaction is proceeding. The rate of the chemical reaction often expresses the amount of change or concentration change with respect to the time. Either it is expressed as the rate at which the product is formed at the unit time or the reactants that are being consumed for the unit time. So we can say that, rate of equation = change in concentration
Change in time
Hence,\[rate\text{ }of\text{ }reaction=\dfrac{\Delta C}{\Delta t}\]
Concentration term is expressed in molarity (M) i.e. moles per litre (mol/L)
And time is expressed in seconds
Give the units in the equation for rate of reaction, we will get the unit for the rate of reaction.
\[rate\text{ }of\text{ }reaction=\dfrac{moles/L}{\text{seconds}}=\dfrac{Molar}{\text{seconds}}\] \[rate\text{ }of\text{ }reaction=\dfrac{moles/L}{\text{seconds}}=\dfrac{Molar}{\text{seconds}}\]
Molar is that quantity equal to the number of moles in one litre of the solution.

So the unit of rate of reaction is molar/seconds and the correct option for the question is option ( D).

Note: For a reaction say,
$C+3D\to E$
Rate of the reaction is expressed as rate of appearance of the products in a chemical reaction,
$rate=\dfrac{\Delta \left[ E \right]}{\Delta t}$ $rate=\dfrac{\Delta \left[ E \right]}{\Delta t}$
As the change in the concentration of the product with respect to time.
We can also write rate equation in terms of reactants which is,
$rate=-\dfrac{1}{3}\dfrac{\Delta \left[ D \right]}{\Delta t}=-\dfrac{\Delta \left[ C \right]}{\Delta t}$. But for experimental conditions the rate of the equation depends on many factors like catalyst, temperature, concentration of reactants, products etc.
Hence we can write the expression for the equation say,
$aA+bB\to cC+dD$
$rate=k{{\left[ A \right]}^{x}}{{\left[ B \right]}^{y}}$ $rate=k{{\left[ A \right]}^{x}}{{\left[ B \right]}^{y}}$,
K is the rate constant
In this reaction x and y will not always be the stoichiometric coefficients a and b of the reactants.