Activation energy (Ea)

Definition

Activation energy (Ea) is the minimum amount of energy required for a chemical reaction to occur. It determines the rate at which reactants transform into products.

5 Must Know Facts For Your Next Test

1. Activation energy is often represented by the symbol $E_a$ and measured in joules (J) or kilojoules per mole (kJ/mol).
2. A higher activation energy means a slower reaction rate, while a lower activation energy indicates a faster reaction rate.
3. Catalysts lower the activation energy of a reaction without being consumed in the process.
4. The Arrhenius equation, $k = A e^{-E_a/RT}$, relates the rate constant $k$ to the activation energy $E_a$, where $R$ is the gas constant and $T$ is temperature in Kelvin.
5. Activation energy can be determined experimentally by measuring how reaction rates change with temperature.

Review Questions

• What role does activation energy play in chemical reactions?
• How does a catalyst affect activation energy?
• Describe how you would determine activation energy using experimental data.

Related terms

Catalyst:

A substance that increases the rate of a chemical reaction by lowering its activation energy without being consumed.

Arrhenius Equation:

$k = A e^{-E_a/RT}$; an equation that shows how the rate constant ($k$) of a reaction depends on temperature ($T$) and activation energy ($E_a$).

Transition State:

A high-energy state during a chemical reaction where old bonds are breaking and new bonds are forming.