Further chemical equilibria Flashcards
How do you work out the activity of species A?
{A} = [A] / C ⦵
[A] = concentration of A
C ⦵= standard concentration (1 mol kg -1)
What is the equation for the Gibbs energy of reaction at standard state?
ΔG⦵ = -RT ln K
What is the van’t Hoff equation?
(𝛿lnK/𝛿1/T)pni = - ∆H⦵ / R
What is the van’t Hoff equation when ΔH⦵ doesn’t change with temperature?
ln K2 - ln K1 = - ∆H⦵ / R (1/T2 - 1/T1)
What is the ionic product of water equation?
Kw = Ka x Kb
What is the equation of the pKw?
pKw = pKa + pKb
How do you work out the pH using the acid dissociation equation?
pH = pKa + log10 {A-}/{HA}
What is {A-} equal to when half the endpoint volume has been added?
{HA}
What is pH equal to when half the endpoint volume has been added?
pKa
What is the buffer region on the titration curve?
For a weak acid, the curve is flat near the pKa
What are there substantial concentrations of in the buffer region?
Both HA and the conjugate base A-
What happens to the buffer when you add more acid?
Drives the equilibrium to the left and the extra protons are removed by reaction with the conjugate base
What happens to the buffer when you add more hydroxide?
Dissociation of the weak acid to replace H+
What does a buffer work to do?
Maintain the pH
What is the pH range a buffer works in?
Range of pKa +/- 1
How do you work out the solubility from the Ksp?
S = C ⦵√Ksp
How do you work out Ksp?
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,
What is a coupled reaction?
A chemical reaction which has a common intermediate
For the coupled reactions:
AB ; ∆GAB >0
CD ; ∆GCD < 0
What is the overall reaction?
A+C B+D; ∆G=∆GAB+∆GCD
What is vapour pressure?
The pressure of a vapour in contact with its liquid at equilibrium
For the coupled reactions:
AB ; ∆GAB >0
CD ; ∆GCD < 0
What is the overall reaction?
A+C B+D; ∆G=∆GAB+∆GCD
What is {A(liq)} equal to for a pure liquid?
1
What is P⦵?
1 bar
What does precision relate to?
Random errors
