Read the Passage carefully and answer the Questions. Kinetic studies not only help us to determine the rate of a chemical reaction but also describe the conditions by which the reaction rates can be altered. The factors such as concentration, temperature, pressure and catalyst affect the rate of a reaction. The speed of a reaction or the rate of a reaction can be defined as the change in concentration of a reactant or product in unit time. Rate = $k [A]^x [B]^y$ Here k is the rate constant $x + y$ gives the overall order of a reaction, whereas x and y represent the order with respect to the reactants A and B, respectively. |
Table: Initial rate of formation of $NO_2$
Based on the above observations, the rate of formation of $NO_2$ can be represented as |
Rate of reaction = $k[NO]^2 [O_2]$ Rate of reaction = $k[NO][O_2]^2$ Rate of reaction = $k[NO]^2 [O_2]^2$ Rate of reaction = $k[NO][O_2]$ |
Rate of reaction = $k[NO]^2 [O_2]$ |
The correct answer is Option (1) → Rate of reaction = $k[NO]^2 [O_2]$ The rate of formation of $\text{NO}_2$ can be represented by the general rate law: $\text{Rate} = k[\text{NO}]^x[\text{O}_2]^y$ where $x$ and $y$ are the reaction orders with respect to $\text{NO}$ and $\text{O}_2$, respectively. We determine $x$ and $y$ using the method of initial rates. 1. Determine the Order with Respect to $\text{NO}$ ($x$) We compare experiments where the concentration of $\text{O}_2$ is held constant (Experiments 1 and 2). $\frac{\text{Rate}_2}{\text{Rate}_1} = \frac{k[\text{NO}]_2^x[\text{O}_2]_2^y}{k[\text{NO}]_1^x[\text{O}_2]_1^y}$ $\frac{0.384}{0.096} = \left(\frac{0.60}{0.30}\right)^x \left(\frac{0.30}{0.30}\right)^y$ $4 = (2)^x$ $\mathbf{x = 2}$ The reaction is second order with respect to $\text{NO}$. 2. Determine the Order with Respect to $\text{O}_2$ ($y$) We compare experiments where the concentration of $\text{NO}$ is held constant (Experiments 1 and 3). $\frac{\text{Rate}_3}{\text{Rate}_1} = \frac{k[\text{NO}]_3^x[\text{O}_2]_3^y}{k[\text{NO}]_1^x[\text{O}_2]_1^y}$ $\frac{0.192}{0.096} = \left(\frac{0.30}{0.30}\right)^x \left(\frac{0.60}{0.30}\right)^y$ $2 = (2)^y$ $\mathbf{y = 1}$ The reaction is first order with respect to $\text{O}_2$. 3. Write the Rate Law Substituting the orders ($x=2$ and $y=1$) into the general rate law: $\text{Rate of reaction} = k[\text{NO}]^2[\text{O}_2]$ The correct option is: $\text{Rate of reaction} = k[\text{NO}]^2[\text{O}_2]$ |