Question

When a solid dissolves in water, the solution may become hotter or colder. The dissolution enthalpy (dissolving) can be determined using a coffee cup calorimeter. In the laboratory a general chemistry student finds that when 10.13 g K2SO4(s) is dissolved in 114.80 g water, the temperature of the solution drops from 24.11 to 20.86 °C. The heat capacity of the calorimeter (sometimes referred to as the calorimeter constant) was determined in a separate experiment to be 1.77 J/°C. Based on the student's observation, calculate the dissolution enthalpy of K2SO4(s) in kJ/mol. Assume the specific heat capacity of the solution is equal to the specific heat capacity of water.

ΔdisH = _________kJ/mol

Answer 1

heat absorbed(q) = m*s*DT + C*DT

                  = (114.8+10.13)*4.184*(24.11-20.86)+ 1.77*(24.11-20.86)

                  = 1.704 kj

no of mol of K2SO4 dissolved = 10.13/174.26 = 0.058 mol

DHdissolution = +q/n

            = +1.704/0.058

            = +29.38 kj/mol