Practice Activation Energy in Chemistry

Use these practice problems to test your method after reviewing the concept explanation and worked examples.

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Quick Recap

The minimum kinetic energy that reactant particles must possess upon collision in order to break existing bonds and initiate a chemical reaction, represented as the.

The 'hill' reactants must climb over before the reaction can proceed.

Showing a random 20 of 50 problems.

Example 1

medium
An endothermic reaction has ฮ”H=+40โ€‰kJ/mol\Delta H = +40\,\text{kJ/mol} and reverse Ea=25โ€‰kJ/molE_a = 25\,\text{kJ/mol}. Find the forward EaE_a.

Example 2

easy
Does a catalyst raise or lower the activation energy?

Example 3

medium
On an energy diagram, Reaction A has Ea=50โ€‰kJ/molE_a = 50\,\text{kJ/mol} and Reaction B has Ea=120โ€‰kJ/molE_a = 120\,\text{kJ/mol}. Both occur at the same temperature. Which reaction is faster and why?

Example 4

easy
A spark ignites a fuel-air mixture. What is the spark providing?

Example 5

challenge
A reaction has A=5.0ร—1012โ€‰sโˆ’1A = 5.0\times 10^{12}\,\text{s}^{-1} and Ea=90โ€‰kJ/molE_a = 90\,\text{kJ/mol}. Estimate kk at 400โ€‰K400\,\text{K}. Use R=8.314โ€‰J/(mol\cdotpK)R = 8.314\,\text{J/(molยทK)}.

Example 6

medium
Why does milk spoil more slowly when refrigerated?

Example 7

easy
Name the high-energy intermediate at the top of an energy diagram peak.

Example 8

medium
A reaction has Ea=65E_a = 65 kJ and ฮ”H=+25\Delta H = +25 kJ (endothermic). Are the products above or below the reactants, and by how much?

Example 9

easy
Does a catalyst change the activation energy of a reaction? How?

Example 10

medium
How does activation energy explain why food spoils faster at room temperature than in a fridge?

Example 11

medium
Hydrogen and oxygen can coexist at room temperature without reacting. Why?

Example 12

easy
Explain why a match must be struck before it ignites, even though combustion is exothermic.

Example 13

hard
Using the two-point Arrhenius form, if kk doubles when T rises from 300โ€‰K300\,\text{K} to 310โ€‰K310\,\text{K}, estimate EaE_a. Use R=8.314โ€‰J/(mol\cdotpK)R = 8.314\,\text{J/(molยทK)}.

Example 14

easy
Why must reactant particles collide with at least the activation energy to react?

Example 15

easy
Do exothermic reactions have an activation energy?

Example 16

easy
What units are typically used to express activation energy?

Example 17

hard
Reaction A: Ea=50E_a = 50, ฮ”H=โˆ’10\Delta H = -10. Reaction B: Ea=50E_a = 50, ฮ”H=โˆ’60\Delta H = -60. Compare forward rates (assume similar AA factors).

Example 18

easy
What is activation energy?

Example 19

easy
Is activation energy the same as the overall energy change ฮ”H\Delta H?

Example 20

hard
Enzyme catalase lowers EaE_a for H2O2\text{H}_2\text{O}_2 decomposition from 7575 to 8โ€‰kJ/mol8\,\text{kJ/mol}. By approximately what factor does kk increase at 310โ€‰K310\,\text{K}? Use RTโ‰ˆ2.58โ€‰kJ/molRT \approx 2.58\,\text{kJ/mol}.
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