3.1.5 Kinetics Flashcards
What does collision theory state?
For a chemical reaction to take place, particles must collide with each other with sufficient energy.
What happens if collisions are unsuccessful?
A chemical reaction will not take place.
What is collision frequency?
The number of collisions per unit time.
What happens when collision frequency increases?
The number of particles that collide with energy greater than or equal to the activation energy increases, so the rate of reaction increases.
What is activation energy?
The minimum energy requirement in order for a chemical reaction to take place.
What is needed for a successful collision to take place?
Particles must collide with energy that is greater than or equal to the activation energy.
Why do most collisions not lead to a reaction?
Because particles do not collide with energy that is greater than or equal to the activation energy.
What is a catalyst?
A substance that increases the rate of a chemical reaction without being used up.
How do catalysts increase the rate of reaction?
By providing an alternative reaction pathway with a lower activation energy.
What is the rate of reaction?
The speed at which a chemical reaction takes place.
What is rate of reaction measured in?
Moldm^-3 s^-1
How do you find the rate of reaction at a point on a curve?
Draw a tangent to the point and the gradient of the tangent is equal to the rate of reaction at that point.
How does increasing the temperature affect the rate of reaction?
It increases the rate of reaction
Why does increased temperature increase the rate of reaction?
At higher temperatures, the particles have more kinetic energy, so are moving faster. This means they collide more frequently. A higher number of collisions increases the proportion of particles that collide with energy greater than or equal to the activation energy. This increases the rate of reaction.
How does increased concentration of reactants affect the rate of reaction?
Increases the rate of reaction
Why does increased concentration of reactants increase the rate of reaction?
Increasing the concentration of reactants will increase the rate of reaction, as there is a greater number of reactant particles per unit volume. This means there will be more frequent successful collisions, which increases the chance of particles colliding with energy greater than or equal to the activation energy.
How does increased pressure affect the rate of reaction in a gaseous reaction?
Increases the rate of reaction
Why does increasing the pressure of a gaseous reaction increase the rate of reaction?
When the pressure is increased, there are more particles per unit volume. This means there will be more frequent successful collisions, which increases the chance of particles colliding with energy greater than or equal to the activation energy. Therefore the rate of reaction increases.
How does increased surface area affect the rate of reaction?
Increased rate of reaction
Why does increasing the surface area increase the rate of reaction?
When the surface area increases, there are more reactant particles exposed and therefore available to react. Therefore, there will be more frequent collisions between reactants. This increases the chance of particles colliding with energy greater than or equal to the activation energy, which increases the rate of the reaction.
What do Maxwell-Boltzmann curves show?
The distribution of energies of molecules at a certain temperature in a gas.
This is because there is variation in the energies of the particles in a gas.
What is the most probable energy?
The energy that the most number of molecules have
What is the average energy?
The mean energy of all of the molecules in the gas
What does the area under the curve represent in maxwell-Boltzmann curve?
The number of moelcules
What happens to energy in a collision?
It is transferred from one molecule to another
Why is the maxwell-Boltzmann curve asymptotic?
It does not touch the x-axis as there is no maximum energy
Why does the maxwell-Boltzmann curve start at the origin?
Because 0 particles have 0 kinetic energy.
What happens to a maxwell-Boltzmann curve if temperature increases?
It flattens and shifts to the right
The most probable energy and and average energy increase
There are more molecules with energy greater than or equal to the activation energy.
This shows that the rate of reaction increases.
What is a homogenous catalyst?
When the catalyst and the reactants are in the same phase.
What is a heterogenous catalyst?
When the catalyst and the reactants are in different phases.
What is a phase?
When the substances are chemically uniform. It means the same as ‘state’ in most cases, but thee are some exceptions eg. Water and oil are in different liquid phases.
Explain why a catalyst lowering the activation energy increases the rate of reaction?
A lower activation energy means that a greater proportion of molecules in the reaction mixture have energy that is greater than or equal to the activation energy.
This means the rate of the catalysed reaction is increased, compared to the uncatalysed reaction.
How can catalysts use intermediates?
Sometimes, to lower the activation energy, catalysts form a reactive intermediate, which means that there will be two transition states.
The transition states have a lower activation energy to reach than the original reaction pathway.
This means a greater proportion of molecules have energy that is greater than or equal to the activation energy, which increases the rate of reaction.
What is a transition state?
The stage during a chemical reaction where bonds are constantly broken and reformed.
