Kinetics - Unit 1, Section 5

Question 1

what is the rate of a reaction?

Answer 1

the change in the amount of a reactant or product over time.

it describes how fast a reaction is happening.

Question 2

Collision theory

Answer 2

says that a reaction won’t take place between 2 particles unless they collide in the right direction (facing each other) and they collide with at least a certain minimum amount of kinetic energy.

Question 3

Activation energy

Answer 3

the minimum amount of kinetic energy particles need to react.

this much energy is needed to break the bonds within reactant particles to start the reaction.

reactions with low activation energies happen easily, whereas reactions with high activation energies don’t.

you need to give the particles extra energy by heating them.

Question 4

Maxwell-Boltzmann Distribution

Answer 4

• where a graph is plotted with the numbers of molecules in a gas with different kinetic energies.
• it is a theoretical model that has been developed to explain scientific observations.

Question 5

Maxwell-Boltzmann Distribution Labels

Answer 5

• x-axis = kinetic energy
• y-axis = number of molecules
• the curve starts at (0,0) because no molecules have 0 energy
• the peak of the curve represents the most likely energy of any single molecule
• the mean energy of all the molecules is a bit to the right of the peak
• most molecules are moving at moderate speeds so their energies are in the middle
• some molecules have more than the activation energy. These are the only ones that can react.
• the area under the curve is equal to the total number of molecules

Question 6

the effect of temperature on reaction rate

Answer 6

if you increase the temperature of a gas, the molecules will on average have more kinetic energy and will move faster. A greater proportion of molecules will have at least the activation energy and be able to react.

this pushes the Maxwell-Boltzmann curve to the right. The total number of molecules is still the same so the area under the curve must be the same.

Because the molecules are moving faster, they will collide more often which is why temperature increase can increase the rate of reaction.

Question 7

the effect of concentration/pressure on reaction rate

Answer 7

if you increase the concentration/pressure of reactants in a solution or volume, the particles will on average be closer together. This means that collisions will be more frequent and therefore there are more chances for the particles to react.

Question 8

what is a catalyst?

Answer 8

increases the rate of reaction by providing an alternative reaction pathway with a lower activation energy.

the catalyst is chemically unchanged at the end of a reaction.

only need a little bit of catalyst to catalyse a huge amount of stuff.

certain catalysts are used for certain reactions

they save lots of money in industrial processes

Question 9

how do catalysts work?

Answer 9

catalysts lower the activation energy, meaning there are more particles with enough energy to react when they collide. it does this by allowing the reaction to go via a different route, so in a set amount of time, more particles react.

the maxwell-boltzmann curve is unchanged with a catalyst present.

Question 10

calculating reaction rates

Answer 10

rate of reaction = amount of reactant used or product formed/time