What is the definition of collision theory ?

Collision theory states that for a reaction to occur, particles must collide with the correct orientation and with energy equal to or greater than the activation energy .

An effective collision requires particles to collide with the correct .......... AND with energy equal to or greater than the .......... .

An effective collision requires particles to collide with the correct orientation AND with energy equal to or greater than the activation energy .

True or False? All collisions between reactant particles result in a chemical reaction.

False. Only effective collisions cause a reaction. Particles must collide with the correct orientation and with sufficient energy (≥ E a ). Ineffective collisions result in particles bouncing off each other.

What is the activation energy ( E a )?

An Activation energy is the minimum energy that colliding particles must possess for a reaction to occur. Only collisions with energy ≥ E a are effective.

Is the activation energy relatively larger or smaller in endothermic reactions compared to exothermic reactions? Explain why.

The E a is relatively larger in endothermic reactions. In endothermic reactions, reactants are lower in energy than products, so particles must overcome a larger energy barrier to reach the transition state.

A catalyst increases the rate of reaction by providing an alternative .......... with a .......... activation energy, without being .......... in the reaction.

A catalyst increases the rate of reaction by providing an alternative reaction pathway with a lower activation energy, without being consumed in the reaction.

What is collision frequency and how does it affect the rate of reaction?

Collision frequency is the number of collisions per unit time . As collision frequency increases, more particles can collide with energy ≥ E a , so the rate of reaction increases.

What is the rate of reaction ?

A Rate of reaction is the speed at which a chemical reaction takes place, measured as the change in concentration of reactant or product per unit time. Units: mol dm -3 s -1 .

The rate of reaction can be calculated using: rate = .......... ÷ .......... . The units of rate are .......... .

The rate of reaction can be calculated using: rate = change in concentration ÷ time . The units of rate are mol dm -3 s -1 .

True or False? The rate of reaction remains constant throughout the reaction.

False. The rate of reaction changes as the reaction proceeds. As reactants are used up, the concentration of reactants decreases, so the rate decreases over time.

How can you find the rate of reaction at a specific point during a reaction from a concentration-time graph?

Draw a tangent to the concentration-time curve at that point. The gradient of the tangent (change in concentration ÷ change in time) gives the rate at that moment.

True or False? On a rate-concentration graph, if the rate is directly proportional to concentration, the graph is a straight line through the origin.

True. A straight line through the origin shows a directly proportional relationship. Doubling the concentration doubles the rate.

As a reaction proceeds, the concentration of reactants .......... and the concentration of products .......... . This causes the gradient of the concentration-time curve to become .......... .

As a reaction proceeds, the concentration of reactants decreases and the concentration of products increases . This causes the gradient of the concentration-time curve to become shallower .

What must be kept constant when measuring the rate of reaction to ensure a fair experiment?

Temperature must be kept constant. A change in temperature changes the rate of reaction independently, which would invalidate results.

What is a Maxwell-Boltzmann distribution curve ?

A Gibbs free energy change is a thermodynamic quantity (ΔG) that determines whether a process is spontaneous. ΔG = ΔH − TΔS; the process is spontaneous when ΔG < 0.

True or False? On a Maxwell-Boltzmann distribution curve, increasing temperature shifts the peak to the right and the curve becomes taller.

False. Increasing temperature shifts the peak to the right but the curve becomes flatter (lower peak). The total area under the curve remains the same as it represents the total number of particles.

On a Maxwell-Boltzmann curve, only particles with energy equal to or greater than the .......... can undergo an .......... collision. At higher temperatures, a .......... proportion of particles exceed this threshold.

On a Maxwell-Boltzmann curve, only particles with energy equal to or greater than the activation energy can undergo an effective collision. At higher temperatures, a greater proportion of particles exceed this threshold.

Give two reasons why increasing temperature increases the rate of reaction, as shown by the Maxwell-Boltzmann curve.

Particles move faster, so collision frequency increases. A greater proportion of particles have energy ≥ E a , so more collisions are successful.

Which effect of temperature has the larger impact on reaction rate: increased collision frequency or increased proportion of particles above E a ?

The increase in the proportion of particles with energy ≥ E a has the larger effect on reaction rate — the change in collision frequency alone would not account for the observed rate increase.

The area under a Maxwell-Boltzmann curve to the .......... of the activation energy represents the fraction of particles that .......... react at that temperature. This area .......... when temperature increases.

The area under a Maxwell-Boltzmann curve to the right of the activation energy represents the fraction of particles that can react at that temperature. This area increases when temperature increases.

Explain how increasing temperature affects the rate of reaction .

Increasing temperature increases the rate of reaction in two ways: particles move faster so collision frequency increases, and a greater proportion of particles have energy ≥ E a so more collisions are successful.

True or False? Increasing temperature only increases the rate of reaction because particles collide more frequently.

False. Increasing temperature also increases the proportion of particles with energy ≥ E a . This second effect is more significant than the increase in collision frequency alone.

At higher temperatures, particles have greater .......... energy, so they move .......... and collide .......... . A higher proportion of collisions are successful because more particles have energy ≥ .......... .

At higher temperatures, particles have greater kinetic energy, so they move faster and collide more frequently . A higher proportion of collisions are successful because more particles have energy ≥ E a .

Why does a small increase in temperature cause a large increase in reaction rate?

Even a small temperature rise significantly increases the proportion of particles with energy ≥ E a . This disproportionately large increase in successful collisions causes a large rise in rate.

When temperature increases, both the number of collisions and the .......... of those collisions increase. The total effect is a significant .......... in the rate of reaction.

When temperature increases, both the number of collisions and the proportion of successful outcomes of those collisions increase. The total effect is a significant increase in the rate of reaction.

True or False? Decreasing temperature decreases the rate of reaction because fewer particles exceed the activation energy.

True. At lower temperatures, fewer particles have energy ≥ E a , so fewer collisions are effective. Both collision frequency and the proportion of successful collisions decrease.

The minimum energy that colliding particles must possess for a collision to result in a chemical reaction. Denoted E a , it represents the energy barrier that must be overcome.

How does increasing concentration affect the rate of reaction?

Increasing concentration increases the number of particles in a given volume. This increases collision frequency , leading to more successful collisions and a higher rate of reaction .

Increasing the pressure of a gas reaction has the same effect as increasing .......... . It forces gas molecules into a .......... volume, increasing .......... frequency and therefore the rate.

Increasing the pressure of a gas reaction has the same effect as increasing concentration . It forces gas molecules into a smaller volume, increasing collision frequency and therefore the rate.

True or False? Increasing pressure increases the rate of reaction for reactions involving only solids.

False. Changes in pressure only affect reactions involving gases . Increasing pressure increases the concentration of gas molecules, raising collision frequency. Solids are not affected by pressure changes.

Explain why a more concentrated solution reacts faster than a dilute one.

A more concentrated solution contains more particles per unit volume . This increases the collision frequency , so more effective collisions occur per second, raising the rate of reaction.

Increasing concentration or pressure does not change the .......... of individual particles. The increase in rate is due entirely to increased .......... .

Increasing concentration or pressure does not change the energy of individual particles. The increase in rate is due entirely to increased collision frequency .

True or False? Doubling the concentration of a reactant always doubles the rate of reaction.

False. Doubling concentration increases collision frequency, which increases rate — but whether the rate doubles depends on the order of reaction with respect to that reactant, which must be determined experimentally.

The number of collisions between reacting particles per unit time. Increasing concentration or pressure raises collision frequency, increasing the rate of reaction.

What is a catalyst and how does it increase reaction rate?

A catalyst increases the rate of a reaction by providing an alternative reaction pathway with a lower activation energy , without being consumed in the reaction.

True or False? On a Maxwell-Boltzmann distribution curve, a catalyst shifts the curve to the right, meaning more particles have higher energies.

False. A catalyst does not change the energy distribution of particles or the shape of the Maxwell-Boltzmann curve. It lowers E a , so a greater proportion of the existing particles have sufficient energy to react.

A homogeneous catalyst is in the .......... phase as the reactants, while a heterogeneous catalyst is in a .......... phase. An example of a heterogeneous catalyst is a .......... used with gaseous reactants.

A homogeneous catalyst is in the same phase as the reactants, while a heterogeneous catalyst is in a different phase. An example of a heterogeneous catalyst is a solid used with gaseous reactants.

On a Maxwell-Boltzmann curve with a catalyst present, what does the shaded area to the right of the new (lower) E a represent?

The shaded area represents the proportion of particles with energy ≥ the new E a . This area is larger than the uncatalysed area, showing more particles can now react effectively.

By lowering the activation energy, a catalyst increases the proportion of particles that have .......... energy for an effective collision. This increases the rate of reaction without altering the .......... of the reaction.

By lowering the activation energy, a catalyst increases the proportion of particles that have sufficient energy for an effective collision. This increases the rate of reaction without altering the enthalpy change of the reaction.

True or False? A catalyst is used up during a chemical reaction.

False. A catalyst is not consumed in the reaction. It provides an alternative pathway with lower E a and can be recovered unchanged at the end of the reaction.

Heterogeneous catalyst

A catalyst that is in a different phase from the reactants — for example, a solid catalyst used in a reaction involving gaseous or aqueous reactants.

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Kinetics (AQA A Level Chemistry): Flashcards

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FrontCollision Theory
What is the definition of collision theory?

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Cards in this collection (41)

What is the definition of collision theory?
Collision theory states that for a reaction to occur, particles must collide with the correct orientation and with energy equal to or greater than the activation energy.
An effective collision requires particles to collide with the correct .......... AND with energy equal to or greater than the .......... .
An effective collision requires particles to collide with the correct orientation AND with energy equal to or greater than the activation energy.
True or False?
All collisions between reactant particles result in a chemical reaction.
False.
Only effective collisions cause a reaction. Particles must collide with the correct orientation and with sufficient energy (≥ E_a). Ineffective collisions result in particles bouncing off each other.
What is the activation energy (E_a)?
An Activation energy is the minimum energy that colliding particles must possess for a reaction to occur. Only collisions with energy ≥ E_a are effective.
Is the activation energy relatively larger or smaller in endothermic reactions compared to exothermic reactions? Explain why.
The E_a is relatively larger in endothermic reactions.
In endothermic reactions, reactants are lower in energy than products, so particles must overcome a larger energy barrier to reach the transition state.
A catalyst increases the rate of reaction by providing an alternative .......... with a .......... activation energy, without being .......... in the reaction.
A catalyst increases the rate of reaction by providing an alternative reaction pathway with a lower activation energy, without being consumed in the reaction.
What is collision frequency and how does it affect the rate of reaction?
Collision frequency is the number of collisions per unit time.
As collision frequency increases, more particles can collide with energy ≥ E_a, so the rate of reaction increases.
What is the rate of reaction?
A Rate of reaction is the speed at which a chemical reaction takes place, measured as the change in concentration of reactant or product per unit time. Units: mol dm^-3 s^-1.
The rate of reaction can be calculated using: rate = .......... ÷ .......... . The units of rate are .......... .
The rate of reaction can be calculated using: rate = change in concentration ÷ time. The units of rate are mol dm^-3 s^-1.
True or False?
The rate of reaction remains constant throughout the reaction.
False.
The rate of reaction changes as the reaction proceeds. As reactants are used up, the concentration of reactants decreases, so the rate decreases over time.
How can you find the rate of reaction at a specific point during a reaction from a concentration-time graph?
Draw a tangent to the concentration-time curve at that point.
The gradient of the tangent (change in concentration ÷ change in time) gives the rate at that moment.
True or False?
On a rate-concentration graph, if the rate is directly proportional to concentration, the graph is a straight line through the origin.
True.
A straight line through the origin shows a directly proportional relationship. Doubling the concentration doubles the rate.
As a reaction proceeds, the concentration of reactants .......... and the concentration of products .......... . This causes the gradient of the concentration-time curve to become .......... .
As a reaction proceeds, the concentration of reactants decreases and the concentration of products increases. This causes the gradient of the concentration-time curve to become shallower.
What must be kept constant when measuring the rate of reaction to ensure a fair experiment?
Temperature must be kept constant. A change in temperature changes the rate of reaction independently, which would invalidate results.
What is a Maxwell-Boltzmann distribution curve?
A Gibbs free energy change is a thermodynamic quantity (ΔG) that determines whether a process is spontaneous. ΔG = ΔH − TΔS; the process is spontaneous when ΔG < 0.
True or False?
On a Maxwell-Boltzmann distribution curve, increasing temperature shifts the peak to the right and the curve becomes taller.
False.
Increasing temperature shifts the peak to the right but the curve becomes flatter (lower peak). The total area under the curve remains the same as it represents the total number of particles.
On a Maxwell-Boltzmann curve, only particles with energy equal to or greater than the .......... can undergo an .......... collision. At higher temperatures, a .......... proportion of particles exceed this threshold.
On a Maxwell-Boltzmann curve, only particles with energy equal to or greater than the activation energy can undergo an effective collision. At higher temperatures, a greater proportion of particles exceed this threshold.
Give two reasons why increasing temperature increases the rate of reaction, as shown by the Maxwell-Boltzmann curve.
1. Particles move faster, so collision frequency increases.
2. A greater proportion of particles have energy ≥ E_a, so more collisions are successful.
Which effect of temperature has the larger impact on reaction rate: increased collision frequency or increased proportion of particles above E_a?
The increase in the proportion of particles with energy ≥ E_a has the larger effect on reaction rate — the change in collision frequency alone would not account for the observed rate increase.
The area under a Maxwell-Boltzmann curve to the .......... of the activation energy represents the fraction of particles that .......... react at that temperature. This area .......... when temperature increases.
The area under a Maxwell-Boltzmann curve to the right of the activation energy represents the fraction of particles that can react at that temperature. This area increases when temperature increases.
Explain how increasing temperature affects the rate of reaction.
Increasing temperature increases the rate of reaction in two ways: particles move faster so collision frequency increases, and a greater proportion of particles have energy ≥ E_a so more collisions are successful.
True or False?
Increasing temperature only increases the rate of reaction because particles collide more frequently.
False.
Increasing temperature also increases the proportion of particles with energy ≥ E_a. This second effect is more significant than the increase in collision frequency alone.
At higher temperatures, particles have greater .......... energy, so they move .......... and collide .......... . A higher proportion of collisions are successful because more particles have energy ≥ .......... .
At higher temperatures, particles have greater kinetic energy, so they move faster and collide more frequently. A higher proportion of collisions are successful because more particles have energy ≥ E_a.
Why does a small increase in temperature cause a large increase in reaction rate?
Even a small temperature rise significantly increases the proportion of particles with energy ≥ E_a. This disproportionately large increase in successful collisions causes a large rise in rate.
When temperature increases, both the number of collisions and the .......... of those collisions increase. The total effect is a significant .......... in the rate of reaction.
When temperature increases, both the number of collisions and the proportion of successful outcomes of those collisions increase. The total effect is a significant increase in the rate of reaction.
True or False?
Decreasing temperature decreases the rate of reaction because fewer particles exceed the activation energy.
True.
At lower temperatures, fewer particles have energy ≥ E_a, so fewer collisions are effective. Both collision frequency and the proportion of successful collisions decrease.
Activation energy
The minimum energy that colliding particles must possess for a collision to result in a chemical reaction. Denoted E_a, it represents the energy barrier that must be overcome.
How does increasing concentration affect the rate of reaction?
Increasing concentration increases the number of particles in a given volume. This increases collision frequency, leading to more successful collisions and a higher rate of reaction.
Increasing the pressure of a gas reaction has the same effect as increasing .......... . It forces gas molecules into a .......... volume, increasing .......... frequency and therefore the rate.
Increasing the pressure of a gas reaction has the same effect as increasing concentration. It forces gas molecules into a smaller volume, increasing collision frequency and therefore the rate.
True or False?
Increasing pressure increases the rate of reaction for reactions involving only solids.
False.
Changes in pressure only affect reactions involving gases. Increasing pressure increases the concentration of gas molecules, raising collision frequency. Solids are not affected by pressure changes.
Explain why a more concentrated solution reacts faster than a dilute one.
A more concentrated solution contains more particles per unit volume.
This increases the collision frequency, so more effective collisions occur per second, raising the rate of reaction.
Increasing concentration or pressure does not change the .......... of individual particles. The increase in rate is due entirely to increased .......... .
Increasing concentration or pressure does not change the energy of individual particles. The increase in rate is due entirely to increased collision frequency.
True or False?
Doubling the concentration of a reactant always doubles the rate of reaction.
False.
Doubling concentration increases collision frequency, which increases rate — but whether the rate doubles depends on the order of reaction with respect to that reactant, which must be determined experimentally.
Collision frequency
The number of collisions between reacting particles per unit time. Increasing concentration or pressure raises collision frequency, increasing the rate of reaction.
What is a catalyst and how does it increase reaction rate?
A catalyst increases the rate of a reaction by providing an alternative reaction pathway with a lower activation energy, without being consumed in the reaction.
True or False?
On a Maxwell-Boltzmann distribution curve, a catalyst shifts the curve to the right, meaning more particles have higher energies.
False.
A catalyst does not change the energy distribution of particles or the shape of the Maxwell-Boltzmann curve. It lowers E_a, so a greater proportion of the existing particles have sufficient energy to react.
A homogeneous catalyst is in the .......... phase as the reactants, while a heterogeneous catalyst is in a .......... phase. An example of a heterogeneous catalyst is a .......... used with gaseous reactants.
A homogeneous catalyst is in the same phase as the reactants, while a heterogeneous catalyst is in a different phase. An example of a heterogeneous catalyst is a solid used with gaseous reactants.
On a Maxwell-Boltzmann curve with a catalyst present, what does the shaded area to the right of the new (lower) E_a represent?
The shaded area represents the proportion of particles with energy ≥ the new E_a.
This area is larger than the uncatalysed area, showing more particles can now react effectively.
By lowering the activation energy, a catalyst increases the proportion of particles that have .......... energy for an effective collision. This increases the rate of reaction without altering the .......... of the reaction.
By lowering the activation energy, a catalyst increases the proportion of particles that have sufficient energy for an effective collision. This increases the rate of reaction without altering the enthalpy change of the reaction.
True or False?
A catalyst is used up during a chemical reaction.
False.
A catalyst is not consumed in the reaction. It provides an alternative pathway with lower E_a and can be recovered unchanged at the end of the reaction.
Heterogeneous catalyst
A catalyst that is in a different phase from the reactants — for example, a solid catalyst used in a reaction involving gaseous or aqueous reactants.

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