Question

1. When 1.32 g of KClO3 was added to 149.57 g of water in a calorimeter, the temperature dropped by 0.669 °C. The heat capacity of H2O is 4.184 J/g°C. Assume the specific heat of the solution equals that of pure H2O and that the calorimeter neither absorbs nor leaks heat. What is the molar heat of solution of solid potassium chlorate?

Answer 1

mass of KClO₃ = 1.32 g

mass of water = 149.57 g

mass of solution = (mass of KClO₃) + (mass of water)

mass of solution = (1.32 g) + (149.57 g)

mass of solution = 150.89 g

heat change of solution = (mass of solution) * (specific heat of solution) * (temperature change)

heat change of solution = (150.89 g) * (4.184 J/g.^oC) * (-0.669 ^oC)

heat change of solution = -422.4 J

heat change for reaction = -(heat change of solution)

heat change for reaction = -(-422.4 J)

heat change for reaction = 422.4 J

moles of KClO₃ = (mass of KClO₃) / (molar mass of KClO₃)

moles of KClO₃ = (1.32 g) / (122.55 g/mol)

moles of KClO₃ = 0.01077 mol

molar heat of solution = (heat change for reaction) / (moles of KClO₃)

molar heat of solution = (422.4 J) / (0.01077 mol)

molar heat of solution = 39211.9 J/mol

molar heat of solution = 39.2 kJ/mol