3.15 - kinetics & 3.16 - equilibrium

Question 1

What is the definition of activation energy?

Answer 1

The minimum energy required for reactant particles to collide and the reaction occurring

Question 2

Why do not all reactions occur

Answer 2

• not enough activation energy
• reactants not in the right orientation

Question 3

What is the effect of concentration and pressure on ROR?

Answer 3

• more particles in a given volume
• more frequent successful collisions
• ROR increases

Question 4

What is the definition of a catalyst?

Answer 4

a substance that increases the rate of a chemical reaction without being changed in chemical composition or amount

Question 5

How do catalysts work?

Answer 5

by providing an alternative reaction route of lower activation energy.

Question 6

What are the conditions of an equilibrium ?

Answer 6

• rate of forward and backwards reactions are equal
• concentrations of reactants and products are not changing

Question 7

What is Le Chatelier’s principle?

Answer 7

When a factor is changed an equilibrium will shift to oppose that change

Question 8

How does a catalyst effect the yield of a reaction?

Answer 8

No effect

Question 9

How does pressure effect yield?

Answer 9

Increased pressure = increased yield

Question 10

How does temperature effect yield?

Answer 10

Increased temperature = decreased yield

Question 11

Affect on Yield - pressure (model answer) 3 marks

Answer 11

• the yield increases/decreases
• because there are more/less moles on the left/right
• therefore equilibrium shifts to oppose the increase/decrease

Question 12

Affect on Yield - temperature (model answer) 3 marks

Answer 12

• the yield increases/decreases
• because the forwards/backwards reaction is exo/endothermic
• therefore equilibrium shifts right/left to oppose the increase/decrease in temperature

Question 13

How do you know if a reaction is exothermic or endothermic

Answer 13

Exothermic: forward enthalpy change is -
Endothermic: forward enthalpy change is +

Question 14

How does pressure effect how the equilibrium shifts

Answer 14

DECREASE pressure:
Equilibrium will shift to side with LESS moles

INCREASE pressure:
Equilibrium will shift to side with MORE moles

Question 15

What factors effect Kc and Kp

Answer 15

ONLY temperature not pressure or catalyst

Question 16

What’s the effect of a catalyst on Kp

Answer 16

No effect because it increases the rate of forwards and backwards reaction equally

Question 17

How does adding more reactant effect Kp

Answer 17

No effect

Question 18

Why might a catalyst become less efficient if there are impurities

Answer 18

Impurities may block the active sites

Question 19

What happens to yield if pressure is changed but there are equal moles on both sides

Answer 19

Equal moles of gas in products and reactants so there is no change in yield

Question 20

Why does the total volume of a mixture not need to be measured to allow a correct Kc value to be calculated

Answer 20

There are equal number of moles on each side of the equation

Question 21

What does the area under a maxwell Boltzmann curve represent

Answer 21

Total number of particles

Question 22

Why does a catalyst increase ROR

Answer 22

• lower activation energy means more particles will have energy greater than the activation energy

Question 23

What is the impact of pressure used in an industrial process

Answer 23

• increasing pressure may give a higher yield and faster ROR
• but expensive to produce due to higher energy costs and may be dangerous
• after a certain point the increase in yield is minimal (when the curve starts to flatten)

Question 24

What is the impact of temperature used in an industrial process

Answer 24

• low temperatures may give a higher yield
• but slow ROR therefore the optimum temp needs to be a compromise between the ROR and yield

Question 25

What increases Kp and Kc

Answer 25

• if the equilibrium shifts right resulting in more products
  ** ONLY TEMPERATURE **

Question 26

If the equation has been halved then how do you calculate Kp and its units from it

Answer 26

Square root Kp
Halve units

Question 27

How would you work out total pressure if you have mole fractions and a Kp value

Answer 27

• insert mole fractions into the Kp expression instead of pp’s
• multiply Kp by what’s on the bottom
• flip the expression

Question 28

In an ICE table are the products or reactants + or -

Answer 28

Reactants (left) are -
Products (right) are +