Equilibria yr 2

Question 1

What is kc?

Answer 1

the equilibrium constant

Question 2

What is the equation for kc for the reaction 2A + B = 2C + D

Answer 2

kc = [C]^2 [D]/ [A]^2 [B]

Question 3

How do you calculate the units for kc?

Answer 3

same as you would for K in rate equation = cancel units in equation

Question 4

What does homogeneous mean?

Answer 4

all products and reactants are in the same state

Question 5

What does heterogeneous mean?

Answer 5

not all products and reactants are in the same state

Question 6

What do you do if a substance in an equation is hetergeneous to the other substances in terms of writing the kc equation?

Answer 6

ignore it - not in kc equation

A(g) + B(s) = C(g) + D(g)

kc = [C] [D] / [A]

Question 7

What 2 states are not included in the kc equation?

Answer 7

solids and pure liquids (water)

Question 8

Why do you not include solids or pure liquids in the kc equation?

Answer 8

their concs remain constant

Question 9

How can you work out the equilibrium concs?

Answer 9

ICE
Initial no. of mol
change in no of mol ( moles after reaction happened)
equilibrium no of mol / vol

Question 10

What is the total pressure?

Answer 10

the total pressure in a reaction is the sum of all partial pressures of the individual gases

Question 11

What is a mole fraction?

Answer 11

a mole fraction is the proportion (fraction) of a gas in a gas mixture

Question 12

How do you calculate the mole fraction of a gas?

Answer 12

mole fraction of a gas = number of moles of gas/ tot number of moles in the gas mixture

or partial press of gas/ total pressure of mixture

Question 13

How do you calculate partial pressure?

Answer 13

partial pressure = mole fraction x total pressure in a mixture

Question 14

What is kp?

Answer 14

pressure equilibrium constant

Question 15

What is used in the Kp equation instead of concs?

Answer 15

partial pressures of gases raised to the power of moles

Question 16

What are the units for partial pressure?

Answer 16

KPa

Question 17

What do you do when writing a Kp equation for a heterogeneous reaction?

Answer 17

only include gas substances
ignore solids, liquids and (aq)

Question 18

What type of equilibria will Le chats principle only work in?

Answer 18

homogeneous equilibria

Question 19

What happens to equilibria when you increase pressure?

Answer 19

equilibria will shift to the side of reaction that has fewer moles of gas

Question 20

What happens to equilibria when increasing temperature?

Answer 20

shifts to the endothermic direction

Question 21

What is the effect of temperature on the value of Kp?

Answer 21

if temp causes equil, to shift to right = kp increases
it temp causes eqil. to shift to left = kp decreases

Question 22

How does pressure affect Kp?

Answer 22

changes pressure does not affect the value of Kp

Question 23

What affect does adding a catalyst have on Kp and Kc?

Answer 23

no effect on the value of Kp and Kc = it speeds up the rate at which equilibrium is established

Question 24

What are the affects of changing temp on kc?

Answer 24

temp change causes equil to shift to right = Kc increases
temp change causes equil to shift to left = kc decreases

Question 25

What is the affect of changing concs on the value of Kc?

Answer 25

value of Kc is unaffected

Question 26

What is equilibrium?

Answer 26

a reversible reaction in a close system is at equilibrium when the forward and back rates are equal

Question 27

What are 3 methods for measuring the change in conc?

Answer 27

change in absorption of light - if substance is coloured
change in pH - acid/ alkali
titration

Question 28

What does a larger kc and kp value mean?

Answer 28

the equilibrium is further shifted to the right

Question 29

What happens to the value of kc increasing temp of a exothermic reaction?

Answer 29

equil shifts to left
kc decreases

Question 30

What happens to the value of kc increasing temp of a endothermic reaction?

Answer 30

equil shifts to the right
kc increases