Further chemical equilibria

Question 1

How do you work out the activity of species A?

Answer 1

{A} = [A] / C ⦵
[A] = concentration of A
C ⦵= standard concentration (1 mol kg -1)

Question 2

What is the equation for the Gibbs energy of reaction at standard state?

Answer 2

ΔG⦵ = -RT ln K

Question 3

What is the van’t Hoff equation?

Answer 3

(𝛿lnK/𝛿1/T)pni = - ∆H⦵ / R

Question 4

What is the van’t Hoff equation when ΔH⦵ doesn’t change with temperature?

Answer 4

ln K2 - ln K1 = - ∆H⦵ / R (1/T2 - 1/T1)

Question 5

What is the ionic product of water equation?

Answer 5

Kw = Ka x Kb

Question 6

What is the equation of the pKw?

Answer 6

pKw = pKa + pKb

Question 7

How do you work out the pH using the acid dissociation equation?

Answer 7

pH = pKa + log10 {A-}/{HA}

Question 8

What is {A-} equal to when half the endpoint volume has been added?

Answer 8

{HA}

Question 9

What is pH equal to when half the endpoint volume has been added?

Answer 9

pKa

Question 10

What is the buffer region on the titration curve?

Answer 10

For a weak acid, the curve is flat near the pKa

Question 11

What are there substantial concentrations of in the buffer region?

Answer 11

Both HA and the conjugate base A-

Question 12

What happens to the buffer when you add more acid?

Answer 12

Drives the equilibrium to the left and the extra protons are removed by reaction with the conjugate base

Question 13

What happens to the buffer when you add more hydroxide?

Answer 13

Dissociation of the weak acid to replace H+

Question 14

What does a buffer work to do?

Answer 14

Maintain the pH

Question 15

What is the pH range a buffer works in?

Answer 15

Range of pKa +/- 1

Question 16

How do you work out the solubility from the Ksp?

Answer 16

S = C ⦵√Ksp

Question 17

How do you work out Ksp?

Answer 17

1) Write the general equation equation for Ksp expressing the stoichiometry for each
2) Convert the amount of reactant dissolved into moles per litres
3) Create an ice table to work out the change in concentration for the two products
4) Using the calculated concentrations and the stoichiometry, calculate the Ksp using the eq,

Question 18

What is a coupled reaction?

Answer 18

A chemical reaction which has a common intermediate

Question 19

For the coupled reactions:
AB ; ∆GAB >0
CD ; ∆GCD < 0
What is the overall reaction?

Answer 19

A+C B+D; ∆G=∆GAB+∆GCD

Question 20

What is vapour pressure?

Answer 20

The pressure of a vapour in contact with its liquid at equilibrium

Question 21

For the coupled reactions:
AB ; ∆GAB >0
CD ; ∆GCD < 0
What is the overall reaction?

Answer 21

A+C B+D; ∆G=∆GAB+∆GCD

Question 22

What is {A(liq)} equal to for a pure liquid?

Answer 22

1

Question 23

What is P⦵?

Answer 23

1 bar

Question 24

What does precision relate to?

Answer 24

Random errors

Question 25

What does accuracy relate to?

Answer 25

Systematic error

Question 26

What is the boiling point?

Answer 26

The temperature when the vapour pressure becomes equal to the atmospheric pressure
Vapour pushes back against atmosphere and liquid boils away