When a solid dissolves in water, heat may be evolved or absorbed. The heat of di

Question

When a solid dissolves in water, heat may be evolved or absorbed. The heat of dissolution (dissolving) can be determined using a coffee cup calorimeter.

In the laboratory a general chemistry student finds that when 7.35 g of K2SO4(s) are dissolved in 108.40 g of water, the temperature of the solution drops from 25.18 to 22.73 °C.

The heat capacity of the calorimeter (sometimes referred to as the calorimeter constant) was determined in a separate experiment to be1.54 J/°C.

Based on the student's observation, calculate the enthalpy of dissolution of K2SO4(s) in kJ/mol.

Assume the specific heat of the solution is equal to the specific heat of water.

Hdissolution = ______________kJ/mol

Explanation / Answer

ANSWER

The enthalpy chenge in the experiment is given as

H = m X Cp X T

m = mass of water (solvent),  Cp = specic heat of calorimeter = 1.54J/oC

T = temeprature difference = 25.18 - 22.73 = 2.45oC

H = 108.4 X 1.54 X 2.45 = 408.99J

This is the heat change when 7.35g of K2SO4.

Enthalpy chane for 1g of K2SO4 = 408.99 / 7.35 = 55.64J

For one mole or 174.23g of K2SO4 heat change will be given as

H = 55.64 X 174.23 = 9695.01J/mol = 9.695KJ/mol

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