A reaction is of first order when — Chemical Kinetics Chemistry Question

💡 Solution & Explanation

I need to explain what defines a first-order reaction, but I notice the options (A, B, D, etc.) aren't provided in your question. Let me give you the key characteristic: **A reaction is first-order when:** The rate of reaction is directly proportional to the **concentration of one reactant raised to the power of 1**. **Mathematically:** $$\text{Rate} = k[A]^1 = k[A]$$ where $k$ is the rate constant and $[A]$ is the concentration of the reactant. **Key features of first-order reactions:** 1. **Half-life is constant** — independent of initial concentration 2. **Integrated rate law:** $\ln[A] = \ln[A]_0 - kt$ (linear plot: $\ln[A]$ vs $t$) 3. **Rate depends on concentration** — doubling $[A]$ doubles the rate 4. **Units of $k$:** $\text{s}^{-1}$ or $\text{min}^{-1}$ **Common examples:** Radioactive decay, decomposition of $N_2O_5$, reactions like $A \rightarrow B$ Without seeing option C specifically, the correct answer typically states that **the rate is proportional to the first power of concentration** or **the rate law exponent is 1** or **half-life is independent of initial concentration**. If you can share the answer choices, I can explain why C is correct and why others are wrong.