Equilibria

What is dynamic equilibrium?

The rate of the forward reaction equals the rate of the reverse reaction, hence the concentrations of the reactants and products remains constant.

What is Le Chatelier’s principle?

If a system in dynamic equilibrium is subjected to a change, then the position of equilibrium will shift to minimise this change.

What is Kp ?

The equilibrium constant for reactions in the gaseous phase.
Similar to K c but it uses partial pressures instead of concentrations.

What conditions are used for the Haber process?

450C
200 atm
iron catalyst

What conditions are used for the Contact process?

450C
2 atm
vanadium pentoxide catalyst

What is a Brønsted-Lowry acid?

a proton donor

What is a Brønsted-Lowry base?

a proton acceptor

What is a conjugate acid-base pair?

A conjugate acid-base pair is two species that differ from each other by a proton

What is a strong acid?

A strong acid is an acid that completely dissociates in solution

Write the general equation for Ka

(H+)(A-)/(HA)

Write a general equation for pKa

-logKa

What is pH?

A way to measure/ compare hydrogen ion concentration.

How do you calculate the pH of a strong acid?

HA → H+ + A
Concentration of acid = concentration of H + ions.
pH = -log(H+)

What is Kw ?

The ionic product of water.

How do you calculate the pH of a strong base?

XOH → X+ + OH
Concentration of base = concentration of OH- ions.

Write an equation that can be used to calculate the concentration of protons from pH

[H+ ] = 10^-pH

How would you use a pH curve to determine a suitable indicator for an acid-base titration?

Weak acid-weak base reactions have no suitable indicator because they have no vertical region.

Why must an indicator change colour within the vertical section of pH curve for an acid-base titration?

Within the vertical section, the volume of acid (or alkali) added changes very little. When the indicator changes colour, this is the end point of the titration which should show when the correct volumes of acid and alkali have been combined so that neither reactant is in excess. If the indicator changes colour outside the vertical sections, the volumes of acid and alkali won’t be close to the actual volumes required for the neutralisation reaction.

What is a buffer?

A system that minimises pH changes on addition of small amounts of an acid or base.

What is a weak acid buffer?

A mixture of a weak acid and its conjugate base (usually in the form of one of its salts.

How do buffers control the pH of blood?

It is important that blood remains within a specific pH range to prevent disastrous effects on enzymes and proteins in the blood that could put our life at risk.
One way that blood pH is maintained is with the carbonic acid-hydrogen carbonate buffer system.
If small amounts of acid or base are added, the position of equilibrium shifts to minimise this pH change.

What is the carbonic acid-hydrogen carbonate buffer system?

H2CO3(aq) <=> H+ (aq) + HCO3 - (aq)

What is solubility product?

The solubility product constant, Ksp , is an equilibrium constant for a solid dissolving in (aqueous) solution.
The higher its Ksp , the more soluble a substance is and hence the more solute that dissolves.

How does Ksp affect whether a precipitate will form?

A precipitate will only form if the ionic concentrations give a give a value that is greater than the solubility product. If not, the solution is not saturated.

What is the common ion effect?

The extent of which a solute dissolves in solution is affected by the presence of a common ion.
This prevents dissociation due to shifting the position of equilibrium towards the solid reactant.

What is meant by the partition coefficient?

A dynamic equilibrium is established between two immiscible layers in a separating funnel when a substance (X) is dissolved in the liquids
X(in more dense liquid)<=>X(in less dense liquid)

Write an equation for Kpc

X(in less dense liquid)/X(in more dense liquid)