The gas phase pressure of a liquid is called its vapour pressure p and increases with increasing temperature of the liquid

Where ΔH^{0}_{vap} is the enthalpy of vaporization, the amount of heat required to vaporize a mole of liquid in its standard state; R is the gas constant; and T_{1} and T_{2} are low and high temperatures having p_{1} and p_{2} vapour pressures. Rearrange the equation to get T_{2} as the subject of the equation.

**Solution**

This question is not as easy as it first appears. The method suggested is one of several but with this type of question it is easy to make a mistake and obtain an incorrect solution, a step by step method is best.

(1 )split the term in brackets into two terms; (2) cancel out top and bottom separately for each term inside the right hand bracket; (3) expand the bracket by multiplying it out;

then (4) rearrange the equation so that the term containing T_{2} becomes the subject;

(5) multiply by R/ ΔH^{0}_{vap} throughout and

(6) then cancelling out top and bottom within each term;

(7) before we can take the reciprocal on both sides we need to bring the right hand side to the common denominator T_{1} ΔH^{0}_{vap}, and finally

(8) we can now take reciprocals on both sides of the equation.