To calculate the heat of hydration for magnesium ion, we first need to find the heat released when 0.5 moles of magnesium chloride is dissolved in water. We can use the enthalpy change of solution for magnesium chloride to find this.Enthalpy change of solution for magnesium chloride = -641 kJ/molMoles of magnesium chloride = 0.5 molesHeat released during dissolution = Enthalpy change of solution Moles of magnesium chlorideHeat released = -641 kJ/mol 0.5 moles = -320.5 kJNow, we need to find the heat absorbed by the water. We can use the specific heat capacity of water and the temperature change to find this.Specific heat capacity of water = 4.18 J/gCMass of water = 500 ml = 500 g assuming the density of water is 1 g/ml Initial temperature of water = 25CFinal temperature of water = THeat absorbed by water = Mass of water Specific heat capacity Final temperature - Initial temperature Heat absorbed = 500 g 4.18 J/gC T - 25C Since the heat released during dissolution is equal to the heat absorbed by the water, we can set up the following equation:-320.5 kJ = 500 g 4.18 J/gC T - 25C First, we need to convert kJ to J:-320.5 kJ 1000 J/1 kJ = -320500 JNow, we can solve for T:-320500 J = 500 g 4.18 J/gC T - 25C -320500 J = 2090 J/C T - 25C Divide both sides by 2090 J/C:-153.11 = T - 25CAdd 25 to both sides:T = -128.11CSince the final temperature is lower than the initial temperature, the heat of hydration for magnesium ion is exothermic. The heat of hydration for magnesium ion when 0.5 moles of magnesium chloride is dissolved in 500 ml of water at 25C is -320.5 kJ.