Unit 4- Equilibria

Question 1

What is a dynamic equilibrium?

Answer 1

• When events occur to maintain an equilibrium in a closed container

Question 2

What is the general equilibrium constant for the standard reaction aA + bB –> cC + dD

Answer 2

K_c=([C]^c x [D]^d)/ ([A]^a x [B]^b)

Question 3

What does the equilibrium constant represent?

Answer 3

The relationship between the molar concentrations of the reactants and products

Question 4

What is a homogenous equilibria?

Answer 4

When the reactants and products are in the same phase e.g. water or liquid

Question 5

What is a heterogenous equilibria?

Answer 5

when the states of the products and reactants differ

Question 6

When an equilibrium constant is used, other than concentration , what can be used?

Answer 6

partial pressure

Question 7

What is the partial pressure?

Answer 7

the pressure that the gas would have if the gas occupied the volume alone

Question 8

How to calculate partial pressure?

Answer 8

(Number of moles of the substance/total moles in the mixture) x total pressure

Question 9

How to calculate total pressure?

Answer 9

The sum of the partial pressure

Question 10

What is different in a heterogenous equilibria for the constant?

Answer 10

Substances in the solid state are not considered as their concentrations is always constant

Question 11

What is formula for the Partition constant? and where does it apply?

Answer 11

• For immisicible liquids
• K_part = Concentration in liquid/concentration in water
• e.g. when iodine is added to water and hexane
• K_{part =}[I] in hexane/ [I] in water

Question 12

What is the link between the entropy of a system and the equilibrium constant?

Answer 12

Delta S = RlnK where K can be K_{c or p} and R the gas constant

Question 13

What does a change in temperature in the equilibria affect?

Answer 13

• S_surroundings
• S_surroundings = -H/T
• Change in T affects S_surroundings
• Affects S_total as S_total = S_surroundings + S_system

Question 14

What does the equilibrium constant measure?

Answer 14

How far a reaction goes to completion

Question 15

If the value of the equilibrium constant is greater than 1x10¹⁰ , what does this represent?

Answer 15

The reaction has gone nearly to completion. Only small amount of reactant left

Question 16

If the value of K is 1, what does this mean?

Answer 16

Concentration of reactants and products is roughly the same at equilibrium

Question 17

If the value of K is smaller than 1x10^-10, what does this mean?

Answer 17

The reaction hardly occurs, small amount of products formed

Question 18

How does the size of the equilibrium constant affect the shift in equilibrium?

Answer 18

• Large K –> shifts right due to more products and less reactants
• Small K–> shifts left due to more reactants and less products

Question 19

Does the equilibrium constant affect rate?

Answer 19

no, no effect