Question 1

What does the Arrhenius equation describe?

Accepted Answer

The Arrhenius equation is k = A exp(-Eₐ/RT), where k is the rate constant, A is the frequency factor, Eₐ is activation energy, R is the gas constant, and T is absolute temperature in kelvin. It connects reaction-rate behaviour with the activation-energy threshold.

Question 2

How is activation energy calculated from two rate constants?

Accepted Answer

Use Eₐ = R ln(k₂/k₁)/(1/T₁ - 1/T₂). Both temperatures must be in kelvin, and k₁ and k₂ must be positive rate constants for the same reaction. The result is first obtained in J mol⁻¹ and can be divided by 1000 to report kJ mol⁻¹.

Question 3

Why does the rate constant increase when temperature rises?

Accepted Answer

For positive Eₐ, increasing T makes RT larger, so the exponent -Eₐ/RT becomes less negative. The exponential factor therefore increases. If A and Eₐ remain unchanged, the rate constant k also increases.

Question 4

What are the slope and intercept of an ln k versus 1/T plot?

Accepted Answer

Taking the natural logarithm gives ln k = ln A - (Eₐ/R)(1/T). Therefore, the slope is -Eₐ/R and the vertical intercept is ln A. Reading this line as having a positive slope reverses the sign and is incorrect.

Question 5

How does a catalyst affect activation energy and equilibrium?

Accepted Answer

A catalyst provides an alternative reaction path with a lower activation-energy threshold, allowing the rate to increase. It helps the reaction reach equilibrium faster but does not change the equilibrium position.

Arrhenius & the Activation-Energy Landscape

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