Which statement best describes how temperature and activation energy affect the rate of a chemical reaction?

• A. Activation energy does not affect the reaction rate, only temperature does.
• B. Increasing temperature increases the reaction rate, while a higher activation energy decreases the reaction rate.
• C. Increasing temperature and increasing activation energy both increase the reaction rate.
• D. Decreasing temperature and decreasing activation energy both decrease the reaction rate.

Answer: (B)

Verified step by step guidance

1. Understand that the rate of a chemical reaction depends on how often and how energetically reactant molecules collide, which is influenced by temperature and activation energy.
2. Recall the Arrhenius equation, which relates the rate constant \(k\) to temperature \(T\) and activation energy \(E_a\): \[k = A \times e^{-\frac{E_a}{RT}}\] where \(A\) is the frequency factor, \(R\) is the gas constant, and \(T\) is the temperature in kelvin.
3. Analyze the effect of temperature: as \(T\) increases, the exponential term \(e^{-\frac{E_a}{RT}}\) becomes larger because the denominator increases, making the negative exponent smaller in magnitude, thus increasing \(k\) and speeding up the reaction.
4. Analyze the effect of activation energy: as \(E_a\) increases, the exponent \(-\frac{E_a}{RT}\) becomes more negative, decreasing the value of the exponential term and thus decreasing the rate constant \(k\), which slows down the reaction.
5. Combine these insights to conclude that increasing temperature increases the reaction rate, while increasing activation energy decreases the reaction rate.