1.5 Kinetics

Question 1

What is a reaction rate?

Answer 1

Change in concentration (or amount) of reactant or product over time

Question 2

State the formula for a rate of reaction

Answer 2

Question 3

Name the 2 conditions needed for particles to react with one another when they collide

Answer 3

• Collide in right direction
  
  • Need to be facing each other in right way
• Collide with certain minimum amount of kinetic energy

Question 4

What is meant by activation energy?

Answer 4

Minimum (amount of kinetic) energy needed for a reaction to occur

Question 5

Why do particles need a minimum amount of kinetic energy for them to react?

Answer 5

Need to have this much energy to break their bonds & start reaction

Question 6

Molecules in gas don’t all have the…

Answer 6

same amount of energy

Question 7

What does a Maxwell-Boltzmann distribution show?

Answer 7

Number of molecules in a gas with different kinetic energies

Question 8

Draw a Maxwell–Boltzmann distribution

Answer 8

• (y axis) %/fraction of particles/molecules/atoms
• (x axis) energy

Question 9

Maxwell–Boltzmann Distribution

What does the peak of the curve represent?

Answer 9

Question 10

Maxwell–Boltzmann Distribution

Where is the mean (average) energy of all molecules on the curve? Label it on your curve.

Answer 10

Question 11

Maxwell–Boltzmann Distribution

At what speed are most molecules moving at?

Answer 11

Question 12

Maxwell–Boltzmann Distribution

Shade the area where there’s molecules that can react

Answer 12

Question 13

What is the area under a Maxwell–Boltzmann distribution curve equal to?

Answer 13

Total number of molecules

Question 14

Why does the Maxwell–Boltzmann distribution curve start at (0,0)?

Answer 14

Because no molecules have 0 energy

Question 15

Describe the effect of temperature on reaction rate

Answer 15

• ↑ temp of reaction = particles have more kinetic energy ∴ move faster
• Greater proportion of molecules E ≥ E_a & able to react (have at least activation energy)
• More frequent successful collisions in given time
  
  • Another reason why ↑ temp = reaction faster

Question 16

Describe and illustrate the effect of an increase in temperature on Maxwell–Boltzmann distribution curve

Answer 16

Changes shape of Maxwell–Boltzmann distribution curve → shifts to the right

Question 17

Why does a small increase in temperature create a large increase in reaction rate? (2)

Answer 17

• Many more molcules have E ≥ E_a (energy greater than the activation energy)
• Far more successful collisions per second

Question 18

Describe the effect of concentration on reaction rates

Answer 18

• ↑ concentration of reactants in solution = particles will be closer together
• Closer = collide more often
• Collisions occurring more frequently = more chances to react
• Explains why ↑ concentration = ↑ reaction rate

Question 19

Describe the effect of pressure on reaction rates

Answer 19

• Gas particles closer together
• ↑ collsion frequencies = reaction rate ↑

Question 20

What is a catalyst?

Answer 20

• Substance that increases the rate of reaction by providing an alternative reaction pathway with lower activation energy
• Catalyst is chemically unchanged by end of the reaction

Question 21

Catalysts take part in reactions but…

Answer 21

are remade at end

Question 22

Draw a Maxwell–Boltzmann distribution showing the effect of a catalyst work

Answer 22

Question 23

Describe how you can measure reaction rates

Answer 23

Measure how fast reactants are used up or how fast products are formed

Question 24

Name 3 ways to measure reaction rates

Answer 24

1. Timing how long a precipitate takes to form
2. Measuring a decrease in mass
3. Measuring the volume of gas given off

Question 25

Measuring reaction rates Describe "measuring a decrease in mass"

Answer 25

1. When one or more products is gas = measure rate of formation using mass balance 2. As gas given off, mass of reaction mixture decreases 3. Method is accurate & easy to do * Usually done in fume cupboard

Question 26

Measuring reaction rates Describe "measuring the volume of gas given off"

Answer 26

1. Uses gas syringe to measure volume of gas being produced 2. Use it when 1 or more products is gas 3. Method is accurate