1.6 Chemical Equilibria

Question 1

What is a closed system?

Answer 1

No chemicals can get in or out during a reaction

Question 2

What are the features of a dynamic system?

Answer 2

Closed
Forwards and backwards reactions are happening at the same time

Question 3

What are the features of a reaction at equilibrium?

Answer 3

Rate of forwards reaction is equal to backwards reaction
Concentration of reactants and products remain the same

Question 4

What factors effect equilibrium?

Answer 4

Temperature
Concentration
Pressure (only in gases)

Question 5

What affect does a catalyst have on equilibrium?

Answer 5

Speed up rate but does not influence equilibrium

Question 6

What is Le Chateliers principle?

Answer 6

Position of equilibrium will shift to oppose a change

Question 7

What is the effect of changing the temperature of a reaction?

Answer 7

• Depends on whether it is endo or exothermic
• If forward reaction is exothermic it will shift to left
• If forward reaction is endothermic it will shift to right

Question 8

What is the effect of increasingthe pressure/concentration?

Answer 8

Moves the equilibrium to the side with the lowest number of moles

Question 9

What is the effect of increasing pressure if moles are equal on both sides?

Answer 9

Pressure has no effect

Question 10

What is the way to obtain the greatest yield from the Haber process?

Answer 10

• High pressure
• Low temperature
• High Concentration
• Remove NH3 as it’s produced

Question 11

What are the compromised conditions for the Haber process?

Answer 11

• Lower pressure 200 atm
• Higher temperature of 450c to maintain a fast enough reaction
• Iron catalyst (allows for lower temperature)

Question 12

What is a Homogenous equilibrium?

Answer 12

• All reactants and products are in the same state

Question 13

What is a heterogenous equilibrium?

Answer 13

• More than one state is present

Question 14

What is not included in an equilibrium constant reaction?

Answer 14

• Solids and pure liquids

Question 15

What is the equilibrium constant?

Answer 15

aA + bB >< cC + dD

Question 16

What is the equilibrium law equation?

Answer 16

Kc= [C] ^c + [D] ^d
———————
[A]^a + [B] ^b

(Concentrations of)

Question 17

How are units of Kc calculated?

Answer 17

Using the same formula for calculating the values but inputting the concentrations units e.g (moldm^-3 x moldm^-3)

Question 18

What is the definition of equilibrium constant?

Answer 18

Constant for a particular reaction at a particular temperature in solution (moldm^-3)

Question 19

When does equilibrium constant change?

Answer 19

ONLY WHEN TEMPERATURE CHANGES

Question 20

What does a Kc value over 1 mean?

Answer 20

Forward reaction dominates

Question 21

How do you calculate equilibrium quantities?

Answer 21

Initial moles - Change in moles

Question 22

Why is (Br or Cl) added to swimming pools when it’s toxic?

Answer 22

Usually a Hydroxide is added which reacts with H+ ions
Equilibrium will shift to oppose decrease in H+ ions increasing yield of less toxic stuff
Leaves only a small amount of toxic halogen which will kill bacteria but not people