Equilibrium

Question 1

Law of Chemical Equilibrium

Answer 1

At equilibrium, there is a constant ratio between the concentrations of the products and reactants in any change.

Question 2

Equilibrium constant (Keq)

Answer 2

(kr) divided by (kf) also represented by Kc

Question 3

K > 1

Answer 3

Products are favoured. The equilibrium lies far to the right

Question 4

K < 1

Answer 4

Reactants are favoured. The equilibrium lies far to the left.

Question 5

When can you ignore x?

Answer 5

If the concentration divided by Kc is greater than 500

Question 6

when can’t you ignore x?

Answer 6

If the answer is less than 100, it is not justified. The equilibrium expression must
be solved in full.

Question 7

Reaction quotient (Qc)

Answer 7

Identical to the equilibrium constant expression, but its value is calculated using concentrations that are not necessarily those
at equilibrium.

Question 8

Qc < Kc

Answer 8

The system attains equilibrium by moving right, favouring products.

Question 9

Qc > Kc

Answer 9

The system attains equilibrium by moving to the left, favouring reactants.

Question 10

Le Châtelier’s principle

Answer 10

A dynamic equilibrium tends to respond so as to relieve the effect of any change in the conditions thataffect the equilibrium.

Question 11

What does Le Châtelier’s principle predict?

Answer 11

Qualitatively predicts what you can show quantitatively by evaluating the reaction quotient.

Question 12

Common ion effect

Answer 12

When an ion is added to a solution in which the ion is already present the equilibrium shifts away from the added ion

Question 13

What does Le Châtelier’s principle predict in terms of volume and pressure?

Answer 13

When volume decreases, pressure increases, thus Le Châtelier’s principle predicts a shift to reduce the pressure of the gases. Equilibrium shifts in the direction of fewer gas molecules.

Question 14

Value of Kw

Answer 14

1.0 x 10^14

Question 15

Weak acids Ka values

Answer 15

Between 1 and about 1×10^−16.

Question 16

Very weak acids have Ka
values that are less than

Answer 16

1×10^−16

Question 17

Percent dissociation

Answer 17

The fraction of acid molecules that dissociate compared with the initial concentration of the weak acid, expressed as a percentage.

Question 18

Polyprotic Acids

Answer 18

More than one hydrogen atom that dissociates. All polyprotic acids, except sulfuric acid, are weak.

Question 19

Calculating polyprotic acids

Answer 19

When calculating [H3O+] and pH of a polyprotic acid, only the first dissociation needs to be considered.

Question 20

The conjugate of a strong acid is always

Answer 20

a weak base

Question 21

The conjugate of a strong
base is always

Answer 21

a weak acid

Question 22

What can Kw = KaKb be used for?

Answer 22

to calculate [H3O+] or [OH-]

Question 23

Buffer solution

Answer 23

a weak acid/conjugate base mixture or a weak base/conjugate acid mixture that resists changes in pH when acid or a base is added to it.

Question 24

Why does adding an acid or a base has little effect?

Answer 24

The added H3O+ or OH−
ions are removed by one of the components in the buffer solution.

Question 25

Buffer Capacity

Answer 25

the amount of acid or base that can be added before considerable change occurs to the pH.

Question 26

What is the role of salt in buffer solutions?

Answer 26

When an acid/base is added to a buffer solution, the salt present neutralizes the additional H+ or OH- ions by absorbing excess hydrogen or hydroxide ions without drastically altering the overall pH of the solution.

Question 27

Adding an acid to a buffer causes equilibrium…..

Answer 27

Equilibrium shifts to the right to counteract the increase in H+ ions, favoring the production of the conjugate base

Question 28

Adding a base to a buffer

Answer 28

Equilibrium shifts to the right because the system counteracts the increase in OH- ions by favoring the formation of the weak acid to neutralize the added base.

Question 29

Dynamic Equilibrium

Answer 29

Macroscopic properties (concentrations of reactants and products) appear constant, but there’s still molecular activity at the microscopic level (molecules of reactants and products are constantly reacting).

Question 30

Equilibrium examples

Answer 30

Heating a Pot of Water: water reaches a dynamic equilibrium between its liquid phase and its gaseous phase. The rate of water vaporization equals the rate of condensation.

Chemical Equilibrium in caramelizing sugar: As sugar heats, it undergoes a chemical reaction, reaching an equilibrium between the sugar molecules breaking down and forming caramelized products.