Question

A 6.67 g sample of an unknown salt (mm = 116.82 g/mol) is dissolved in 150.00 g water in a coffee cup calorimeter. Before placing the sample in the water, the temperature of the salt and water is 23.72 °C. After the salt has completely dissolved, the temperature of the solution is 28.54 °C. If -3.16 × 10³ J of heat was lost during the dissolution reaction of 0.0571 moles of the unknown salt, what is the enthalpy change (in kJ/mol of salt) for the dissolution reaction?

Answer 1

To calculate the enthalpy change for the dissolution reaction, use the formula q = mCΔT, where q is the heat lost or gained, m is the mass of the solution, C is the specific heat of the solution, and ΔT is the change in temperature. Divide the heat lost by the number of moles to find the enthalpy change per mole of the salt.

Step-by-step explanation:

To calculate the enthalpy change for the dissolution reaction, we can use the formula:

q = mCΔT

Where q is the heat lost or gained, m is the mass of the solution, C is the specific heat of the solution, and ΔT is the change in temperature.

In this case, we are given that -3.16 × 10³ J of heat was lost during the dissolution of 0.0571 moles of the unknown salt. To find the enthalpy change per mole of the salt, we divide the heat lost by the number of moles.

The enthalpy change is therefore -3.16 × 10³ J / 0.0571 mol = -55.3 kJ/mol.