Question

The salt magnesium chloride is soluble in water. When 0.620 g MgCl2 is dissolved in 112.00 g water, the temperature of the solution increases from 25.00 °C to 27.33 °C. Based on this observation, calculate the dissolution enthalpy, ΔdissH, of MgCl2. Assume that the specific heat capacity of the solution is 4.184 J g-1 °C-1 and that the energy transfer to the calorimeter is negligible. ΔdissH = kJ/mol

Answer 1

The enthalpy of the dissociation of the magnesium chloride is -168.2 kJ/mol.

Step-by-step explanation:

Mass of magnesium chloride = 0.620 g

Moles of magnesium chloride =
`(0.620 g)/(95 g/mol)=0.006526 mol`

Mass of water = 112.00 g

Mass of solution, m = 0.62 g + 112 g =112.62 g

Heat capacity of the solution = c =
`4.184J/g^oC`

Initial temperature of the solution =
`T_1=25.00^oC`

Final temperature of the solution =
`T_2=27.33^oC`

Heat gained by solution = Q

`Q=m* c* (T_2-T_1)`

`Q=112.620 g* 4.184J/g^oC* (27.33^oC-25.00^oC)`

Q = 1,097.90 J =1.09790 kJ ≈ 1.098 kJ

Enthalpy of the dissociation magnesium chloride :

`\Delta H_(diss)=-(Q)/(n)=(-1.098 kJ)/(0.006526 mol)=-168.2 kJ/mol`

The enthalpy of the dissociation of the magnesium chloride is -168.2 kJ/mol.