Which of the following is not an example of first order reaction?

Question

Accepted Answer

Option 4 is the correct answer because it represents a reaction that is not a first-order reaction. Let's analyze each option to understand why Option 4 is the correct choice:

1. **Option 1: $C_{2}H_{4}(g)+H_{2}(g)ightarrow C_{2}H_{6}(g)$**

This reaction is a bimolecular reaction involving two reactants, ethylene ($C_{2}H_{4}$) and hydrogen ($H_{2}$). The rate of this reaction depends on the concentration of both reactants, making it a second-order reaction overall. Therefore, it is not a first-order reaction.

2. **Option 2: ${}_{88}^{226}Raightarrow{}_{2}^{4}He+{}_{86}^{222}Rn$**

This is a radioactive decay process, which is a classic example of a first-order reaction. The rate of radioactive decay depends only on the concentration of the radioactive isotope (${}_{88}^{226}Ra$) and is independent of any other substances. Thus, this is a first-order reaction.

3. **Option 3: $N_{2}O_{5}(g)ightarrow N_{2}O_{4}(g)+\frac{1}{2}O_{2}(g)$**

The decomposition of $N_{2}O_{5}$ is a first-order reaction. The rate of this reaction depends solely on the concentration of $N_{2}O_{5}$, making it a first-order reaction.

4. **Option 4: $2NH_{3}(g)\xrightarrow[	ext{Pt Catalyst}]{1130 K} N_{2}(g)+3H_{2}(g)$**

This reaction is the decomposition of ammonia ($NH_{3}$) in the presence of a platinum catalyst at high temperature. It is a catalytic reaction that involves the breaking of bonds in $NH_{3}$ and the formation of $N_{2}$ and $H_{2}$. The rate of this reaction is not solely dependent on the concentration of a single reactant, as it involves multiple steps and the presence of a catalyst. Therefore, it is not a first-order reaction.

In conclusion, Option 4 is the correct answer because it represents a reaction that does not follow first-order kinetics, unlike the other options which are examples of first-order reactions.