To calculate the enthalpy change, use the enthalpy values given:

$ext{Enthalpy change} = ext{Enthalpy of solution of MgCl₂·4H₂O} - ext{Enthalpy of solution of MgCl₂}$ $= (-39) - (-155) = 116 ext{ kJ mol}^{-1}$

Stage 1: Method

1. Measure a known volume of distilled water (e.g., 100 ml) into a calorimeter.
2. Weigh about 0.8 g of anhydrous magnesium chloride.
3. Record the initial temperature of the water in the calorimeter.

Stage 2: Mixing

4. Add the weighed magnesium chloride to the water and stir to ensure complete dissolution.
5. Record the highest temperature reached after the salt has dissolved.

Stage 3: Results

6. Calculate the temperature change (ΔT) by subtracting the initial temperature from the final temperature.
7. Use the formula to calculate the enthalpy of solution: ext{Enthalpy of solution} = -rac{q}{n} where q is the heat absorbed, and n is the number of moles of MgCl₂ used.

The results from the experiment provide the enthalpy of solution for anhydrous magnesium chloride. This value could then be compared to literature values or used in further calculations to find related thermodynamic data for processes involving MgCl₂.

To calculate the gradient of the graph of ΔG against temperature (T):

o Use two points from the graph. For example, using (298 K, -592.5 kJ mol⁻¹) and (240 K, -602.2 kJ mol⁻¹):

ext{Gradient} = rac{ ext{Change in } ext{ΔG}}{ ext{Change in T}} = rac{-592.5 - (-602.2)}{298 - 240}

Calculate to get: ext{Gradient} = rac{9.7}{58} ext{ kJ K}^{-1} ext{ mol}^{-1}

Then, using the relationship with entropy, calculate ΔS as: $ext{ΔS} = - ext{Gradient} imes 1000 = -167 ext{ J K}^{-1} ext{ mol}^{-1}$