3.1 Equilibrium Constant

Question 1

What is equilibrium?

Answer 1

moles of reactants and product are constant, rate of forward reaction = rate of reverse reaction
** dynamic - forward and reverse reactions still occur

Question 2

What is the equilibrium constant?

Answer 2

relationship between pressures or concentrations of the reactants and products, K

Question 3

What are equilibrium constants dependent on?

Answer 3

temperature
–> temperature change = equilibrium constant change
**effect is different depending on reaction is endo or exo and temp inc or dec

Question 4

What is homogenous equilibrium?

Answer 4

all components are in the same phase

Question 5

What is heterogenous equilibrium?

Answer 5

components are in different phases

Question 6

Which components are considered for K value?

Answer 6

gaseous and not solid

Question 7

What is the general form of equilibrium constant using concentrations?

Answer 7

K = [C]^c[D]^d/[A]^a[B]^b

Question 8

Why are solid or solvent concentrations not considered for finding K value?

Answer 8

concentrations of solvent/solids are considered constant or equal to 1

Question 9

How does the K value change when the reaction is reversed?

Answer 9

1/K

Question 10

How does the K value change when the reaction is multiplied? divided?

Answer 10

K^(number multiplied)

ex. reaction x 2 = K^2

K^1/(number mutiplied)
ex. reaction x 3 = K^1/3

Question 11

How does the K value change when you combine equilibria (add reactions)

Answer 11

K(new) = K1 x K2

Question 12

What does it mean if K is greater than 1?

Answer 12

K=products/reactants

so: products>reactants

favours products = equilibrium lies towards the right/products side = at equilibrium, there are more products than reactants

Question 13

What does it mean if K is less than 1?

Answer 13

K = products/reactants

so: reactants>products

favours reactants=equilibrium lies towards the left/reactants side = at equilibrium, there are more reactants than products

Question 14

Why must only M (mol/L) and atm be used in K calculations?

Answer 14

equilibrium constants are actually given in terms of activity for species in a solution and fugacity for gas-phase species) which are related to concentration and partial pressure respectively, but don’t have units
– activity is approximated as concentrations in M units
– fugacity is approximated as partial pressure in atm

Question 15

What is the reaction quotient?

Answer 15

same as equation equilibrium constant but allows for calculating whether the system is at equilibrium and what direction it needs to go to get to equilibrium
–> concentrations and partial pressures of reactants and products are not necessarily at equilibrium

Question 16

What happens when Q = K?

Q>K?

Q<K?

Answer 16

Q=K –> system is at equilibrium

Q>K –> too many products - must shift left

Q<K –> too many reactants - must shift right

Question 17

What happens to the equilibrium constant when temperature, pressure or reactant/products are added?

Answer 17

shifts position of equilibrium to a new value and the concentrations/pressures at equilibrium will be different

Question 18

What is Le Chatelier’s Principle?

Answer 18

If a chemical system at equilibrium is disturbed by a change in temperature, pressure or the concentration of a participant in the equilibrium, the equilibrium will shift in such a way to minimize the disturbance

Question 19

What is the impact of concentration change on equilibrium?

Answer 19

adding or removing reactants or products cause the reaction to shift left or right to reestablish equilibrium

Question 20

What is the impact of total pressure change on equilibrium?

Answer 20

shift left or right: pressure of a species is directly proportional to the number ormolus of that species

Question 21

How can the pressure of a system of gases be disturbed?

Answer 21

changing volume of system:

increasing volume = decrease pressure of each gas = reaction proceeds in the direction that produces more moles of gas to increase pressure again

decreasing volume = increase procession = reaction proceeds in direction that will produce fewer moles of gas

Question 22

What occurs when an inert gas (one that doesn’t readily react) is added to gaseous equilibrium system?

Answer 22

increase in total pressure but no change in partial pressure of reactant and product gases = no change in equilibrium position

Question 23

Does volume change impact only solid and liquid equilibriums (no gas)?

Answer 23

No

Question 24

When does volume has no effect in a gaseous equilibrium system?

Answer 24

when number of moles is equal on both sides

Question 25

Does K change when volume, concentrations or pressure is changed?

Answer 25

no! only temperature changes K value

Question 26

How can enthalpy be written in a reaction?

Answer 26

endothermic = +∆H = reactant = heat/temp of surroundings decrease
exothermic = -∆H = product = heat/temp of surroundings increase

Question 27

In an exothermic reaction what occurs when heat is added/temperature increased?

Answer 27

analogous to adding product:

equilibrium shifts left and produces more reactant, decreases K value

Question 28

In an exothermic reaction what occurs when heat is removed/temperature decreased?

Answer 28

analogous to removing product:

equilibrium shift right and produces more product, increases K value

Question 29

In an endothermic reaction what occurs when heat is added/temperature increased?

Answer 29

analogous to adding reactant:

equilibrium shift right and produces more product, increase K value (num)

Question 30

In an endothermic reaction, what occurs when heat is removed/temperature decreased?

Answer 30

analogous to removing reactant:

equilibrium shift left and produces more reactant, decreases K value (denom)

Question 31

What happens to equilibrium when ∆Gº is positive (>0)?

Answer 31

equilibrium lies to the left/reactant side and K is small

Question 32

What happens to equilibrium when ∆Gº is negative (<0)?

Answer 32

equilibrium lies to the right/product side and K is large

Question 33

What happens to equilibrium when ∆Gº = 0?

Answer 33

K = 1

Question 34

What is the relationship between free energy under nonstandard and standard condition (∆G and ∆Gº)?

Answer 34

∆G = ∆Gº + R T lnQ

where Q is the reaction quotient

when Q = K at equilibrium and ∆G = 0:

∆Gº = -R T lnK

Question 35

What is the relationship between ∆Gº and K?

Answer 35

∆Gº = - R T lnK

∆Gº = J/mol
R = 8.314 J/mol*K
T = 298.15 K
K = equilibrium constant

Question 36

How can you find equilibrium constant at different temperatures?

Answer 36

lnK = -∆Hº/RT + ∆Sº/R

because enthalpy and entropy do not vary much over temperature range of reaction

Question 37

What is van’t Hoff’s Equation? What is it used for?

Answer 37

determine K values at different temperatures or find temperature to carry out reaction for certain K:

lnK2/K1 = ∆Hº/R(1/T1 - 1/T2)