General approach to calculating K
Calculations involving equilibrium systems use
In the first problems in this set of questions Kp is calculated from
- the fact that, for a system at equilibrium at a particular temperature, the reaction quotient Q is equal to the equilibrium constant K .
The Q given is for reaction aA + bB
cC + dD, where A, B, C and D are all gases. Q where amounts are expressed in partial pressures is given the symbol Qp.
Each partial pressure substituted into Q when calculating K must be divided by the standard state pressure (100 kPa).
- the stoichiometry of the reaction occurring to reach equilibrium if the system is not initially at equilibrium.
| Qp = | p(C)cp(D)d |
| p(A)ap(B)b |
In the first problems in this set of questions Kp is calculated from
- known initial pressures of all gases appearing in Q expression and the known equilibrium pressure of one of them
- known initial pressures of all gases and the total pressure at equilibrium.
Use of Dalton's Law (The total pressure is the sum of the partial pressures of the individual gases.) is also required in addition to the above in this case.