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**

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