Question

Coffee Cup Calorimetry: Solution Enthalpy

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. Thermometer In the laboratory a general chemistry student finds that when 1.46 g CaCl(s) is dissolved in 113.70 g water, the temperature of the solution increases from 22.49 to 24.83 °C. Cardboard or Styrofoam lid The heat capacity of the calorimeter (sometimes referred to as the calorimeter constant) was determined in a separate experiment to be 1.78 J/°C. Nested Styrofoam cups Based on the student's observation, calculate the dissolution enthalpy of CaCl(s) in kJ/mol. Reaction occurs in solution. Assume the specific heat capacity of the solution is equal to the specific heat capacity of water. Adis H = kJ/mol Submit Answer Retry Entire Group 4 more group attempts remaining

Answer 1

Calculating heat: Temperature difference AT = 24.83 22.49 = 2.34 CaCl2 1.46 mass of =m g 113.7 g mass of water =m total mass of solution 115.16 g 1.46 113.7 + m 4.184 J/gK Specific heat of water heat capacity calorimeter = Cp 1.78 J/°C Heat = s AT Cp AT + q m 115.16 x x 2.34) (1.78 x 2.34) Heat 4.184 q Heat 1127.48 + 4.1652 1131.65 J Heat q Calculating number of moles: number of moles Mass /Molar mass 1.46 110.98 number of moles of 0.013 mol CaCl2 n Calculating Molar Enthalpy of dissolution AH (Heat /Moles) 1131.65 /0.013 -86020.6 J/mol kJ/mol AH = -86.02 II II