Question

For the reaction $A2+B+C\to AC+AB$ it is that tripling the concentration of $A$ triples the rate, doubling the concentration of $C$ doubles the rate and doubling the concentration$B$ has no effect?
(i) What is rate law?
(ii) Why does the change in the concentration of $B$ have no effect?

Answer 1

Rate of reaction is directly proportional to concentration of reactant as concentration increases there will be more number of collisions of that reactant in a specific time and therefore, rate of reaction increases.

Complete step by step solution
Rate law defines the rate of reaction in terms of molar concentration of reactants reacting raised to some power. This is also known as rate equation or rate expression. In other words, a mathematical relationship obtained by relating the rate of reaction with concentration of reactant.
$A+B\to C+D$
then, Rate = $k[A]m[b]n$
where $k$= rate constant
$[A]$and $[B]$ represents the concentration of reactants
$m$and $n$ represents order of reaction w.r.t reactants $[A]$and $[B]$
According to question,
Rate law= $k[A2][C]$
Explantation: Rate law is not dependent on concentration of $[B]$ because the change in concentration of $[B]$ has no effect. There is no change in the concentration of $[B]$as it is not participating in the reaction due to which it is not responsible for the formation of the product or does not react with other reactants. It only acts as a medium to alter the rate of reaction.
On tripling the concentration of$[A]$, the rate of reaction becomes triples because it has power 1.
On doubling the concentration of$[C]$, the rate of reaction doubles because it has power 1

Additional information:
Rate of reaction can be determined by using the formula
Rate = $\dfrac{\Delta [C]}{\Delta t}$ where numerator represents the change in product concentration and denominator represents change in time
Rate of reaction mainly depends on four factors: concentration of reactants, temperature, surface area and catalyst. The order of reaction may be defined as power dependence of rate on concentration of all the reactants.

Note: Molecularity determines the number of reactant molecules taking part in the elementary reaction whereas order defines the sum of the exponents to which the concentration term in rate law is raised.