Enthalpy of a solution

Question

The enthalpy of solution (🔼H) of KOH is -57.6 kJ/ mol. If 2.26 g KOH is dissolved in enough water to make a 150.0 mL solution, what is the change in temperature (°C) of the solution? (The specific heat capacity of the solution is 4.184 J/g•

°C and the density of the solution is 1.02 g/mL).

Answer 1

First, find the heat generated by dissolving 2.26 g KOH in 150.0 ml of water:

2.26 g KOH x 1 mol KOH / 56.1 g = 0.0403 mols

0.0403 mols x 57.6 kJ /mol = 2.32 kJ of heat generated

Use q = mC∆T to find the change in temperature of the water:

q = heat = 2.32 kJ

m = mass of water = 150 ml x 1.02 g / ml = 153 g

C = specific heat = 4.184 J/gº

∆T = change in temperature = ?

Solving for ∆T...

∆T = q / (m)(C) = 2.32 kJ / (153 g)(0.004184 kJ/gº) ... note to change units of C to agree with q

∆T = 3.62º