Equilibrium

Question 1

What are the three types of dynamic equilibrium?

Answer 1

1. Phase equilibrium
2. Solubility equilibrium
3. Chemical reaction equilibrium

Question 2

Define: dynamic equilibrium

Answer 2

The balance of two opposite processes

Question 3

What is a phase equilibrium?

Answer 3

When a single chemical substance existing in more than one phase in a chemical system

Examples: liquid water and water vapour in a sealed container

Question 4

What is solubility equilibrium?

Answer 4

Single chemical compound dissolved in solvent, where excess solute is in contact with a saturated solution

Examples: CuSO_4(s) ⇌ Cu²⁺_(aq) + SO₄^2-_(aq)

Question 5

What is a chemical equilibrium?

Answer 5

Apparent static state between reactants and products of a reaction; forward and reverse reactions occur at the same rate (does NOT imply equal amounts of P and R)

Question 6

A system at equilibrium must be __________, will have ____________ ___________, and be at a __________ ____________.

Answer 6

A system at equilibrium must be closed, will have constant amounts (moles or concentration), and be at a constant temperature.

Question 7

What does Le Châtelier’s Principle state?

Answer 7

When a chemical system at equilibrium is disturbed by a change in the system, the system reacts to oppose/counteract that change, and a new equilibrium is reached

Question 8

What are the three most common types of stresses/changes to a chemical system?

Answer 8

1. Concentration changes
2. Temperature changes
3. Volume/pressure changes

Question 9

If a species is added to a chemical system at equilibrium, the system will shift ________ from the addition
If a species is removed from a chemical system, the system will shift ________ from the removal

Answer 9

If a species is added to a chemical system at equilibrium, the system will shift away from the addition
If a species is removed from a chemical system, the system will shift towards from the removal

Question 10

Which way will a chemical system shift when temperature is changed?

Answer 10

Increase in temperature = shift away from the side with energy
Decrease in temperature = shift towards the side with energy

Question 11

Changes in pressure/volume cause the system to…

Answer 11

If volume is decreased, there is an increase in pressure, and the system shifts to the side with the least moles of gas

If volume is increased, there is a decrease in pressure, and the system shifts to the side with the most moles of gas

Question 12

When no gas is present, or there is an equal amount of gas, volume/pressure changes have ____ _______ on the system’s equilibrium

Answer 12

When no gas is present, or there is an equal amount of gas, volume/pressure changes have no effect on the system’s equilibrium

Question 13

How does a catalyst shift a chemical system’s equilibrium?

Answer 13

Catalysts will not shift a system. They speed up reactions, but both the forwards and reverse reactions are sped up

Question 14

Adding a small amount of an inert gas _____ ____ shift a system

Answer 14

Adding a small amount of an inert gas will not shift a system

Question 15

If a chemical is added which causes other side reactions (ex. causing a precipitate to form), the system ____ ______

Answer 15

If a chemical is added which causes other side reactions (ex. causing a precipitate to form), the system may shift

Question 16

When graphing changes in an equilibrium system, the x-axis represents _______, and the y-axis ____________

Answer 16

When graphing changes in an equilibrium system, the x-axis represents time and the y-axis concentration (mol/L)

Question 17

Changes in what compounds will cause no change to the equilibrium and are therefore not included when graphing changes to an equilibrium?

Answer 17

Pure liquids and solids (unless this change affects the concentration of an aqueous or gas in the reaction)

Question 18

Decreasing the volume of a container by half will ________ the concentration (moles) of the gas inside

Answer 18

Decreasing the volume of a container by half will double the concentration (moles) of the gas inside

Question 19

Define: equilibrium constant (K_c)

Answer 19

The mathematical relationship for each closed equilibrium system at a constant temperature.

Question 20

How are coefficients included in the equilibrium expression?

Answer 20

The concentration of the given compound is put to the power of it’s coefficient

Question 21

In general…

If the K_c value is _______ than 1, the system will produce more products.
If the K_c value is _______ than 1, the system will produce more reactants

Answer 21

In general…

If the K_c value is greater than 1, the system will produce more products.
If the K_c value is less than 1, the system will produce more reactants

Question 22

Are spectator ions included in equilibrium expressions?

Answer 22

No, equilibrium expressions only show the species in the form that they exist, that are a part of the solution

Question 23

What is the water ionization constant (K_w)?

Answer 23

• Even highly purified water shows light conductivity due to the ionization of water (H₂O_(l) + H₂O_(l) ⇌ H₃O⁺_(aq) + OH^-_(aq)), therefore K_w = [H₃O⁺_(aq)] [OH^-_(aq)] = 1.00x10^-7mol/L

Question 24

How do you calculate [H₃O⁺_(aq)] from pH?

Answer 24

[H₃O⁺_(aq)] = 10^-pH

Question 25

How can you calculate pH from [H₃O⁺_(aq)]?

Answer 25

pH = -log[H₃O⁺_(aq)]

Question 26

How can you calculate the pOH of a substance from it’s pH, and vice versa?

Answer 26

pH + pOH = 14

Question 27

How can you calculate the pOH from the [OH^-_(aq)]?

Answer 27

pOH = -log[OH^-_(aq)]

Question 28

How can you calculate the [OH^-_(aq)] from the pOH?

Answer 28

[OH^-_(aq)] = 10^-pOH

Question 29

How can you calculate the [OH^-_(aq)] from the [H₃O⁺_(aq)], and vice versa?

Answer 29

[OH^-_(aq)] [H₃O⁺_(aq)] = 10^-14

Question 30

All strong acids react _________________/________________ in water

Answer 30

All strong acids react quantitatively/stoichiometrically in water (react completely; >99.9%)

Question 31

Define: acid ionization constant (K_a)

Answer 31

The equilibrium constant for a weak acid

Question 32

A ________ K_a means its a “stronger” weak acid; a ________ K_a means its a “weaker” weak acid

Answer 32

A higher K_a means its a “stronger” weak acid; a lower K_a means its a “weaker” weak acid

Question 33

Does the K_a value remain constant despite changes in concentration of the acid and conjuagte base?

Answer 33

Yes, however the value becomes less accuate as the concentration increases

Question 34

What is the base ionization constant (K_b)

Answer 34

The equilibrium constant for a weak base; the higher the value, the stronger the base, and vice versa

Question 35

What is K_w?

Answer 35

K_w is the ionization constant of water (1.00x10^-14)

Question 36

Define: Amphoteric

Answer 36

A substance with they ability to react as either an acid or base

Question 37

Define: Amphiprotic

Answer 37

Entity that can donate or accept a proton

Question 38

What is the proton transfer concept?

Answer 38

This concept does not define a substance as an acid or base, but identifies it acting as an acid or base.

Acid: proton donor
Base: proton acceptor

Question 39

Define: Bronsted-Lowry neutralization

Answer 39

The prton transfer from the strongest acid to the strongest base

Question 40

Define: conjuagte acid-base pair

Answer 40

A pair of substances that differ only by a proton (H⁺)