Define activation energy .

An activation energy ( E a ) is the minimum energy that reactant particles must possess for a collision to be effective and a chemical reaction to occur.

Why is the activation energy relatively larger for endothermic reactions than for exothermic reactions?

In endothermic reactions, the products are at a higher energy level than the reactants. The activation energy ( E a ) is the energy needed to reach the transition state above the reactants, so E a tends to be larger for endothermic reactions than for exothermic ones, where the products lie at lower energy than the reactants.

Define Boltzmann distribution curve .

A Boltzmann distribution curve is a graph showing the distribution of energies among molecules in a sample at a given temperature. The area under the curve to the right of E a represents molecules with enough energy to react.

True or False? At a given temperature, most molecules in a sample have energies close to or greater than the activation energy.

False. Only a small proportion of molecules have energies equal to or greater than E a . Most molecules have intermediate energies and the curve peaks well below E a for most reactions.

When temperature increases, the Boltzmann distribution curve .......... and its peak shifts to the .......... , indicating a greater proportion of molecules with energy above E a .

When temperature increases, the Boltzmann distribution curve flattens and its peak shifts to the right , indicating a greater proportion of molecules with energy above E a .

Give two reasons why increasing temperature increases the rate of a chemical reaction.

Particles move faster, so collision frequency increases, giving more effective collisions per unit time. A greater proportion of molecules have kinetic energy exceeding E a , so a higher fraction of collisions are successful.

True or False? The increase in collision frequency is the main reason why rate increases with temperature.

False. The greater proportion of molecules exceeding E a has a larger effect on rate than the increase in collision frequency alone.

On a Boltzmann distribution curve, how is the effect of increasing temperature shown, and what does this indicate about the rate of reaction?

The curve flattens and the peak moves to higher energy . The area under the curve to the right of E a increases , showing more molecules have sufficient energy to react and the rate of reaction increases.

For a collision to be effective, particles must collide in the correct .......... and possess energy equal to or greater than the .......... .

For a collision to be effective, particles must collide in the correct orientation and possess energy equal to or greater than the activation energy .

A LevelChemistryCambridge (CIE)Flashcards8. Reaction KineticsEffect of Temperature on Reaction Rates & the Concept of Activation Energy

Effect of Temperature on Reaction Rates & the Concept of Activation Energy (Cambridge (CIE) A Level Chemistry): Flashcards

Exam code: 9701

1/9

0Still learning

Know0

FrontActivation Energy & Boltzmann Distribution Curves
Define activation energy.

Was this flashcard helpful?

Cards in this collection (9)

Define activation energy.
An activation energy (E_a) is the minimum energy that reactant particles must possess for a collision to be effective and a chemical reaction to occur.
Why is the activation energy relatively larger for endothermic reactions than for exothermic reactions?
In endothermic reactions, the products are at a higher energy level than the reactants. The activation energy (E_a) is the energy needed to reach the transition state above the reactants, so E_a tends to be larger for endothermic reactions than for exothermic ones, where the products lie at lower energy than the reactants.
Define Boltzmann distribution curve.
A Boltzmann distribution curve is a graph showing the distribution of energies among molecules in a sample at a given temperature. The area under the curve to the right of E_a represents molecules with enough energy to react.
True or False?
At a given temperature, most molecules in a sample have energies close to or greater than the activation energy.
False.
Only a small proportion of molecules have energies equal to or greater than E_a. Most molecules have intermediate energies and the curve peaks well below E_a for most reactions.
When temperature increases, the Boltzmann distribution curve .......... and its peak shifts to the .......... , indicating a greater proportion of molecules with energy above E_a.
When temperature increases, the Boltzmann distribution curve flattens and its peak shifts to the right, indicating a greater proportion of molecules with energy above E_a.
Give two reasons why increasing temperature increases the rate of a chemical reaction.
1. Particles move faster, so collision frequency increases, giving more effective collisions per unit time.
2. A greater proportion of molecules have kinetic energy exceeding E_a, so a higher fraction of collisions are successful.
True or False?
The increase in collision frequency is the main reason why rate increases with temperature.
False.
The greater proportion of molecules exceeding E_a has a larger effect on rate than the increase in collision frequency alone.
On a Boltzmann distribution curve, how is the effect of increasing temperature shown, and what does this indicate about the rate of reaction?
The curve flattens and the peak moves to higher energy. The area under the curve to the right of E_a increases, showing more molecules have sufficient energy to react and the rate of reaction increases.
For a collision to be effective, particles must collide in the correct .......... and possess energy equal to or greater than the .......... .
For a collision to be effective, particles must collide in the correct orientation and possess energy equal to or greater than the activation energy.

Sign up to unlock flashcards

By signing up you agree to our Terms and Privacy Policy

Previous:Rate of ReactionNext:Homogeneous & Heterogeneous Catalysts

More Revision Notes you might like