CHEMICAL EQUILIBRIUM

Question 1

Kc

Answer 1

Equilibrium concentration (units: mol/L)

Question 2

Kp

Answer 2

Equilibrium pressure (units: bar)

Question 3

Which equilibrium constant do I use?

Answer 3

K/Keq always refer to Kc. If asked SPECIFICALLY for Kp then use that

Question 4

Relating Kc & Kp formula

Answer 4

Kc = Kp (RT)^-∆n

Question 5

Equilibrium constant equation format

Answer 5

[Products]/[Reactants] but DO NOT include pure liquids or solids, only solutions and gas

Question 6

If equation is all gas phase

Answer 6

Use Kp and find pressure

Question 7

If equation has gas and aq phase

Answer 7

Use Kc cause aq is present

Question 8

Homogenous equilibria

Answer 8

Reaction with all the same phase (Kc/Kp)

Question 9

Heterogenous equilibria

Answer 9

Reaction with more than one phase (activity a)

Question 10

Activity (a)

Answer 10

Used in heterogenous equilibria that is unites and measures effective concentration relative to standard state

Question 11

Standard states (3)

Answer 11

1. Solutions (C) = 1 mol/L
2. Gas (P) = 1 bar
3. Activity for pure liquid/solid = 1

Question 12

Why is the activity of a pure liquid or solid 1 and unites

Answer 12

Because pure liquid and solids do not impact equilibria so they have a constant reactivity of 1

Question 13

K

Answer 13

Expresses relationship between reactants and products

Question 14

Direction of K

Answer 14

1. When K>1: Forward reaction (products) are favored
2. When K<2: Reverse reaction (reactants) are favored
3. When K = 2: Neither reaction is favored

Question 15

Rules for manipulating K

Answer 15

• If reaction is reversed, equilibrium constant is inverted
• If equation is multiplied, factor k is raised by the power of that factor
• If 2 individual equilibrium equations are adde, the product of K is the equilibrium constant of the equation

Question 16

ICE table

Answer 16

Change = equilibrium - initial, in I row, either reactants or products should have a concentration and the other is 0, in C row, use coefficient of equation +/-x, E is everything added

Question 17

Quadratic formula

Answer 17

x = -b +/ sqrt b^2-4ac/2a or use calculator lol

Question 18

Small x approximation

Answer 18

• Use when there is small k but large initial concentration by 1000x difference. You are just ignoring/omitting added or subtracted x in an equation
• eg. x^2/0.250-x –> x^2/0.250. Check if equilibrium constant is less than 5% of initial concentration by x/initial change

Question 19

Reaction quotient

Answer 19

Measures how far reaction is from equilibrium (same equation format is k with products/reactants

Question 20

Q and K relation (3)

Answer 20

1. Q<K: Reaction proceed to products to reach equilibrium
2. Q = K: Reaction at equilibrium
3. Q>K: Reaction proceed to reactants to reach equilibrium

Question 21

Le Chatelier’s principle

Answer 21

Tells us that if equilibrium is disturbed, it will shift to minimize or counteract change

Question 22

Affect of concentration in gaseous phase reaction

Answer 22

Adding or removing gas thats not an inert gas causes equilibrium to shift to side with fewer gas molecules

Question 23

Affect of pressure in gaseous phase reaction

Answer 23

If total pressure is increased, equilibrium will shift to side with fewer gas molecules unless its an inert gas (noble gas)

Question 24

If volume of container increases

Answer 24

• Pressure decreases
• Equilibrium shifts to side with more gas

Question 25

If volume of container decreases

Answer 25

• Pressure increases
• Equilibrium shifts to side with fewer gas

Question 26

When temperature increases

Answer 26

Heat is added to system

Question 27

When temperature decreases

Answer 27

Heat removed from system

Question 28

+∆H (H>0)

Answer 28

Endothermic (absorb heat)

Question 29

-∆H (H<0)

Answer 29

Exothermic (release heat)

Question 30

If container of exothermic reaction cooled

Answer 30

Moves to right

Question 31

If container of exothermic reaction heated

Answer 31

Moves to left

Question 32

If container of endothermic reaction cooled

Answer 32

Moves to left

Question 33

If container of endothermic reaction heated

Answer 33

Moves to right

Question 34

Affect of catalyst in equilibrium

Answer 34

No effect since it increases rate both forward and reverse reactions at the same time