Week 10

Question 1

ΔG: the Change in the Gibbs Free Energy

Answer 1

ΔG = ΔH -TΔSsystem = -TΔStotal

Question 2

Precipitation

Answer 2

a loss of entropy → ΔS < 0
a loss of enthalpy → ΔH < 0

Question 3

Shifting equilibrium with temperature

Answer 3

• The exo direction of a reaction will be favoured as we lower T
• The endo direction of a reaction will be favoured as we raise T

Question 4

If the concentration ____, the system acts to ____ some of it

Answer 4

• increases, consumes
• decreases, produces

Question 5

There are 3 ways in which the pressure of a system can be changed:

Answer 5

1. By adding (or removing) a gaseous reactant or product:
2. By adding a gas that is not involved in the reaction:
3. By changing the volume of the container.

Question 6

Change in volume

Answer 6

• If the volume decreases, the system acts to decrease the # of moles present
• If the volume increases, the system acts to increase the # of moles to fill it.

Question 7

We have two approaches to determining the direction of spontaneous change, what is the connection?

Answer 7

ΔGº = – RT lnKeq

Question 8

If ΔHº < 0 then increasing T

Answer 8

will make Keq smaller
* The equilibrium will shift to favour the reactants and so to reduce the heat released

Question 9

If ΔHº > 0 then increasing T

Answer 9

will make Keq larger
* The equilibrium will shift to favour the products and absorbing more heat

Question 10

increase reactant concentrations ⇒

Answer 10

more products produced

Question 11

Increase pressure / decrease volume ⇒

Answer 11

less gas produced

Question 12

Increase temperature ⇒

Answer 12

endothermic reaction favoured

Question 13

Brønsted - Lowry

Answer 13

(H+) + (A-) ⟺ HA
* ACID: proton (H+) donor.
* BASE: proton (H+) acceptor.

Question 14

Arrhenius

Answer 14

H+(aq) + OH-(aq) ⟺ H2O(l)
* ACID: H+ producer in aqueous solution.
* BASE: OH- producer in aqueous solution

Question 15

What is H+(aq)?

Answer 15

In water: an acid (e.g., HCl) ionises to produce H+ (aq)

Question 16

Acids & equilibrium

Answer 16

A STRONG acid has equilibrium to the right
* (HA completely ionised)

A WEAK acid has equilibrium to the left
* (HA partly/mostly intact)

Question 17

Conjugate acid-base pairs

Answer 17

conjugate base has one less proton than its conjugate acid

Question 18

H2SO4 is a dibasic or diprotic acid:

Answer 18

H2SO4(aq) + H2O(l) ⟺ H3O+(aq) + HSO4-(aq)

HSO4-(aq) + H2O(l) ⟺ H3O+(aq) + SO42-(aq)

Question 19

Autoionisation of Water

Answer 19

2H2O(l) ⟺ H3O+(aq) +OH-(aq)

Question 20

pH

Answer 20

pH = -log[H+]
* Acid : pH < 7
* Neutral: pH = 7
* Basic: pH > 7

Question 21

Strong acids and bases…

Answer 21

Completely ionise in water:
* e.g. HCl(aq) ⟺H+ (aq) + Cl- (aq)
* Equilibrium lies completely to the right, Ka ≈ ∞

Question 22

Weak acids

Answer 22

They do not completely ionise in water
* HA(aq) ⟺ H+(aq)+ A-(aq)

Acid dissociation constant:
* Ka= (H+)(A-)/(HA)

pKa = - log(Ka)

Question 23

The larger the value of Ka…

Answer 23

the stronger the acid and the lower the value of pKa

Question 24

Weak base

Answer 24

Ionisation of a weak base:
* NH3(aq) + H2O(l) ⟺ NH4+ (aq) + OH-(aq)

Equilibrium constant is called base ionisation constant:
* Kb=(NH4+)([OH-)/(NH3)