Question

A reaction is said to be of zero order if the rate is entirely independent of the concentration of the reactants. Answer if true or false.

Answer 1

Hint: A reaction is said to be of zero order if the sum of the powers of concentration of reactants in the rate law expression is equal to zero. This means that the rate of the reaction will become independent of the concentration of the reactants.

Complete answer:
Reactions in which the rate of reaction remains independent of the initial concentration of the reactant are said to be zero. These reactions are relatively not common but they can occur under special conditions. There are some enzyme catalysed reactions and reactions which occur on the metal surfaces which can be categorized in the reactions with the second order.
Some examples of the reactions are:
(i)${H_2}(g) + C{l_2}(g) \to 2HCl(g)$
(ii) Reaction between acetone and bromine.
Now, coming to the mathematical expression of the zero order reaction, we have:
$A \to \ Product $
Initial (t=0) a , 0
Final (t=t sec) (a-x), x
Now, writing the mathematical expression of the rate law of zero order reaction, we have:
$Rate = k{[A]^0}$
The differential form:
$ - \dfrac{{dA}}{{dt}} = k{[A]^0}$
The expression in terms of dissociated moles and rate constant will become:
$x = kt = {[A]_0} - {[A]_t}$
The expression of half-life can be deduced as:
$t = {t_{{\raise0.5ex\hbox{$\scriptstyle 1$}
\kern-0.1em/\kern-0.15em
\lower0.25ex\hbox{$\scriptstyle 2$}}}},x = \dfrac{a}{2}$
${t_{{\raise0.5ex\hbox{$\scriptstyle 1$}
\kern-0.1em/\kern-0.15em
\lower0.25ex\hbox{$\scriptstyle 2$}}}} = \dfrac{a}{{2k}}$ , where $a = $ Initial concentration of the reactants
Thus, the statement is true. Hence, we can clearly state that a reaction is said to be of zero order if the rate is entirely independent of the concentration of the reactants.

Note:
The unit of the rate constant for a zero order reaction is equal to $mol{L^{ - 1}}{\sec ^{ - 1}}$ and the same is also the unit for the rate of the reaction. The half-life of a reaction is the time period in which half of the amount of initial reactants is consumed.