Calculate molar enthalpy

Question

React 50.0 mL of 0.250 M sulfuric acid with 50.0 mL of 0.250 M potassium hydroxide in a bomb calorimeter. If the initial temperature of both reactants were 22.10oC and the final temperature of the solution was 25.26oC. If the calorimeter’s heat capacity was 5.17kJ/oC and assuming the density of the solution is 1.00g/mL. Calculate the molar enthalpy of this reaction.

Answer 1

The balanced equation is H2SO4 + 2KOH ---> K2SO4 + 2H2O.

The number of moles present in the actual reaction are 0.0125 moles for H2SO4 and 0.0125 for KOH.

Since there are the same number of moles of each reactant present, only ½ of 0.0125 moles of H2SO4 can react or 0.00625 moles. H2SO4 is the limiting reactant, so we will base of molar enthalpy on this reactant.

The total heat evolved from the reaction is the sum of the heat change for the solution and the heat change of the calorimeter.

4.18 J/gC x 100 g x 3.16 C + 5.17 x  10^3 J x 3.16 C = 1.77 x 10 ^4 J where Δt = 3.16 C and heat is in joules.

The heat evolved from one mole of H2SO4 is then given by 1.77 x 10^4 J / 0.00625 moles = 2.83 x 10^6  Joules/ mole.

Check math.