Ch19 Equilibrium

Question 1

What factors must be true for a chemical system to be in dynamic equilibrium?

Answer 1

• if the concn of R + P remain constant
• rates of forward + reverse reactions are equal
• it needs to be a closed system

Question 2

What is Le Chatelier’s Principle:

Answer 2

Le Chatelier’s Principle states…….:
When a system in dynamic equilibrium is subjected to external change, the position of equilibrium will shift to minimise effect of that change.

Question 3

What is the general Kc equation:

Answer 3

Question 4

What is a homogenous equilibrium:

Answer 4

Homogenous eqm = all species in same physical state

Kc expression contains concn of all species

Question 5

What is a heterogenous equilibrium:

Answer 5

Heterogenous eqm = species in different physical states

Kc expression only contains species in (g) or (aq) as concentrations of (s) and (l) are constant.

Question 6

What do the different Kc values represent?

Answer 6

• Kc > 1 = product favoured eqm
• Kc < 1 reactant favoured eqm

Question 7

What is the rule for units in Kc calculations?

Answer 7

Positive indices come before negative indices

Question 8

RICE TABLES SHEET

Question 9

What is the Kp constant used for?

Answer 9

• reactions only involving gases
• partial pressure is used instead of concn in eqm expression
• partial pressure is proportional to concn

Question 10

Explain how to calculate mole fractions:

Answer 10

Question 11

Explain how to calculate partial pressure:

Answer 11

Question 12

What three factors does Le Chatlier propose affect eqm?

Answer 12

• If concn of species increase, eqm shifts in direction that reduces concn
• If pressure increases, eqm position shifts towards side with gaseous moles
• If temp increases, eqm position shifts in endothermic direction
• If temp decreases, eqm shifts in exothermic direction

Question 13

What three factors does Le Chatlier propose affect eqm?

Answer 13

• If concn of species increase, eqm shifts in direction that reduces concn
• If pressure increases, eqm position shifts towards side with gaseous moles
• If temp increases, eqm position shifts in endothermic direction
• If temp decreases, eqm shifts in exothermic direction

Question 14

What do these values of k mean for the position of eqm:
* K = 1
* K = 100
* K = 1x10-2

Answer 14

• K = 1- indicates eqm halfway between R +P
• K = 100 - indicates eqm well in favour of P
• K = 1x10-2 - indicates eqm well in favour of R

Question 15

What happens to k at constant temp but other factors changing (conc, pressure, catalyst) and what happens to k if temp changes,

Answer 15

• At constant temp, k is constant, does NOT change despite changes to concn, pressure, prescence of catalyst
• If temp is changed, k does change value.

Question 16

Explain how temp affects value of k when the forward reaction is:
* exothermic
* endothermic

Answer 16

Forward reaction = exothermic
* k decreases with increase in temp
* increase in temp decreases eqm yield of products
* position is shifted towards products

Forward reaction = endothermic
* k increases with temp increase
* increase in temp increase eqm yield of products
* shifts eqm towards products

Question 17

How does a change in concentration affect the value of Kc

Answer 17

Question 18

How does a change in pressure affect Kp constant:

Answer 18

Question 19

How does a catalyst affect eqm constants (Kc, Kp)

Answer 19

• eqm constants Kc and Kp are unaffected by presence of catalyst
• Catalysts affect rate of chemical reactions, not position of eqm
• catalysts speed up both forward and reverse reactions equally
• eqm is reached quicker, but eqm position NOT changed.