Question

A 50 g sample of NaOH is dissolved in 1.00 L of water at 20 °C in a calorimeter. The final temperature of the solution is 33.2 °C. Calculate the molar heat of solution. Assume the heat capacity of the calorimeter is 16 J/K.

Answer 1

Given from the question,

m (mass of solution)= 50g(mass of NaOH)+1000g(mass of water)=1050g [consider density of water=1g/ml]

$\Delta$t (change in temperature)= 33.2^oC - 20^oC=13.2^oC

also, heat capacity of water is 4.18J/g/^oC

The heat of solution q can be given by the formula,

q=m x c x $\Delta$t

=[1050 x 4.18 x 13.2] J

=57934.8J = 57.9348kJ

But, we need molar heat of solution;

moles of NaOH= (50/40) mol [mol=given mass/ molar mass]

= 1.25mol

molar heat= (57.9348/1.25) kJ/mol

=46.3478kJ/mol

Therefore, the molar heat of solution is 46.3478kJ/mol.