how far?

• dynamic equilibrium is the fact that the forward reaction is equal to the rate of the reverse reaction so the concentrations of reactants and products are static
• a closed system is a place where no particles can enter or escape, a chemical equilibrium can only exist in a closed system
• position of equilibrium describes the relative concentrations of reactants and products in a chemical reaction
• an equilibrium constant is a calculated value that expresses the relationship between products and reactants at equilibrium, it is unaffected by changes in concentration, pressure or catalyst
• partial pressures is the amount of pressure caused by a particular gas in a mixture of gases
• partial pressure is calculated by multiplying the total pressure due to all the gases in the mixture
• a mole fraction is equal to the number of moles of a particular gas divided by the total number of moles of gas in the mixture
• pH is a measure of the concentration of hydrogen ions in aqueous solution
• the concentration of hydrogen ions is often small so $pH=$$-\log_{10}H+$is used to calculate the value for concentration of hydrogen ions in a solution
• a conjugate acid is a protonated base
• a conjugate base is the species remaining after an acid has donated a proton
• a strong acid is an acid that is virtually completely ionside in aueous solution
• with a strong acid it can be assume that the concentration of the acid is equal to the concentration of hydrogen ions in the aqueous solution, the resulting Ka is very large
• a weak acid is an acid which is weakly ionised in aqueous solution
• with a weak acid it can be assumed that the concentration of the acid is equal to the concentration of undissociated acid molecules, therefore the Ka is very small
• a monobasic acid is an acid that has one hydrogen ion to donate to a base in an acid-base reaction
• the acid dissociation constant (Ka) is a special type of equilibrium constant which is the ratio of concentrations of the dissociated ions in the acid to the concentration of the un-dissociated acid molecules
• a buffer is a solution usually made of a 50:50 mixture of weak acid and the sodium salt of the weak acid, and it can resist changes to pH when small amounts of acid or alkali are added to it
• the ionic product of water (Kw) is the equilibrium constant for water when it dissociates into hydrogen ions and hydroxide ions, the expression for the equilibrium constant does not have a denominator because the concentration of water is effectively constant
• equation for Kw:

  $Kw=$$\left(H+\right)\left(OH-\right)$
• the equivalence point is the point in an acid-base reaction when all acid (or base) has been exactly neutralised
• the end point is the point at which the indicator being used in a titration changes colour
• if the equilibrium position lies to the right then there must be more products than reactants
• if the equilibrium position lies to the left then there must be more reactants than products
• if the position of equilibrium lies mainly towards the products then Kc will be large
• if the position of equilibrium lies mainly towards the reactants then Kc will be small
• every reversible reaction will have its own unique equilibrium so will have its own unique equilibrium constant provided the temperature is kept constant
• for the reaction aA +bB $\rightarrow$ cC +dD Kc equals:

  $Kc=$$\frac{\left|C\right|^c\left|D\right|^d}{\left|A\right|^a\left|B\right|^b}$
• Kc is only constant at a particular temperature so the convention is to always quote temperature along side the value of Kc
• the concentrations in the Kc expression are the concentrations at equilibrium
• catalysts have no effect on the equilibrium only temperature does
• the equilibrium constant changes with temperature as it alters the proportion of particles that exceed the activation energy in the forward and reverse reactions
• how to calculate the partial pressure of gases at a given temperature and pressure:

  1. calculate the total number of moles from the equation
  2. find the mole fractions of each gas (moles of gas$\div$total number of moles
  3. multiply each mole fraction by the given pressure
  4. substitute values into Kp equation
  5. work out the units for Kp from the Kp expression
• Kp is used to measure the pressure of gases
• the pressure of a gas is directly proportional to its concentration
• an acid is a proton donor
• a base is a proton acceptor
• members of a conjugate pair differ from each other by the presence or absence of a transferable hydrogen ion
• if HA is the acid then A- is the conjugate base
• if A- is a base then HA is its conjugate acid