Equilibria

Question 1

What does dynamic equilibrium mean?

Answer 1

Rate of forward reaction = rate of backward reaction

Question 2

Explain Le Chatelier’s principle

Answer 2

If a system at equilibrium is disturbed, the equilibrium moves in the direction that reduces the disturbance

Question 3

Changing what factors can alter the position of equilibrium?

Answer 3

• Concentration of reactants or products
• Pressure
• Temperature

Question 4

What effect would increasing the temp have on the position of the equilibrium?
CH4 + H2O = CO + 3H2 +210 kJmol-1

Answer 4

The equilibrium positions shifts to the right

Question 5

What effect would increasing pressure have on the position of equilibrium?
CH4 + H2O = CO + 3H2 +210 kJmol-1

Answer 5

Shifts to the left

Question 6

Suggest and explain why an industrial chemist may use high pressure for the production of hydrogen?
CH4 + H2O = CO + 3H2 +210 kJmol-1

Answer 6

• High pressure increases the collision frequency thus increases rate of reaction
• This is a compromise pressure between an economically viable rate of reaction and a slightly lower yield of hydrogen

Question 7

What effect does a catalyst have on the position of the equilibrium?

Answer 7

No effect because it affects rate of forward and backward reaction equally

Question 8

What condition affects the value of Kc?

Answer 8

Temperature

Question 9

What does Kc being greater or less than 1 suggest for the position of equilibrium?

Answer 9

Kc > 1 shifts to right
Kc < 1 shifts to left

Question 10

What effect does decreasing the temperature in an endothermic reaction have on Kc?

Answer 10

Kc decreases

Question 11

What effect does increasing temperature on an endothermic reaction have on Kc?

Answer 11

Kc increases

Question 12

What effect does decreasing the temperature of an exothermic reaction have on Kc?

Answer 12

Kc increases

Question 13

What 2 conditions needs to be met for a collision to be effective?

Answer 13

1. The particles need to collide with the correct orientation
2. The particles have sufficient energy to overcome Ea barrier

Question 14

How does increasing conc affect the rate of reaction?

Answer 14

• An increase in conc increases the number of particles in the same volume
• The particles are closer together so collide more frequently

Question 15

How does increasing pressure of a gas affect the rate of reaction?

Answer 15

• The conc of gas molecules increase as the same number of gas molecules occupy a smaller volume
• The gas molecules are closer together and collide more frequently leading to more effective collisions

Question 16

What are 2 methods that can be used to determine the rate of reaction of a gas?

Answer 16

1. Monitoring the volume of gas produced at regular intervals through gas collection
2. Monitoring the loss of mass of reactants using a balance

Question 17

What is the method for monitoring the production of gas using gas collection of hydrogen peroxide?

Answer 17

1. Add hydrogen peroxide to a conical flask
2. Measure the initial gas in the measuring cylinder
3. Add manganese dioxide, catalyst, to the conical flask and put the bung on
4. Measure the gas produced at regular intervals until no more gas is produced

Question 18

What is the method to monitoring the loss of mass of reactants using a balance?

Answer 18

1. Add calcium carbonate and HCl to a flask on a balance
2. The mass of the flask is recorded initially and at regular intervals

Question 19

What is a homogeneous catalyst?

Answer 19

Has the same physical state as the reactants?

Question 20

What is a heterogeneous catalsyt?

Answer 20

Has a different physical state from the reactants

Question 20

Using boltzmann distribution, what effect does an increase in temp have on molecules?

Answer 20

• The graph is stretched over a greater range of energy values
• More molecules have an energy greater than or equal to the Ea, so a greater proportion of collisions
• The peak is lower and shifted to the right

Question 21

Using boltzmann distribution, what effect does a catalst have on molecules?

Answer 21

• A catalst provides an alternative route with a lower Ea
• The Ea is reduced so now a greater proportion of molecules can overcome the Ea

Question 22

What is the equation for the haber process?

Answer 22

N2 + 3H2 -> 2NH3

Question 23

State the temperature and pressure that are used in the Haber process

Answer 23

100 atm
500 degrees

Question 24

Why are the conditions in the Haber process a compromise between rate and equilibrium?

Answer 24

• Increased pressure because there are molecules on the LHS
• Increased temp increases rate because more molecules have more energy
• Increased pressure increases rate as molecules are more concentrated
• Increased temp pushes equilibrium to the left as forward reaction is exothermic
• If temp too high, low yield
• If temp too low, slow rate

Question 25

Use collision theory to explain the changes in the rate of reaction as it proceeds

Answer 25

• Concentration decreases gradually
• Rate of collision decreases
• Reaction stops when all of one reagent is used up

Question 26

Suggest 2 ways in which the use of catalysts help chemical companies to make their processes more sustainable

Answer 26

• Not used up so better atom economy
• Less CO2 emitted so less harmful toxins in the environment

Question 27

What is homogeneous equilibria?

Answer 27

• Kc expression written as normal
• All species are in the same state

Question 28

What is heterogeneous equilibria?

Answer 28

• Species are in different states
• Don’t include solids and liquids

Question 29

What type of bracket is used for partial pressure?

Answer 29

(X)

Question 30

How do you calculate partial pressure continuing from an ICE table?

Answer 30

1. Add all equilibrium moles
2. Divide mole/total moles
3. Multiple by sum of partial pressures

Question 31

What is the equation for (CH3COOH)2 (g) ⇌ 2CH3COOH (g)

Answer 31

kP = p((CH3COOH2))/p(CH3COOH)2