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 8.01 g of CsBr(s) are dissolved in 111.10 g of water, the temperature of the solution drops from 24.31 to 21.97 °C.
The heat capacity of the calorimeter (sometimes referred to as the calorimeter constant) was determined in a separate experiment to be 1.64 J/°C.
Based on the student's observation, calculate the enthalpy of dissolution of CsBr(s) in kJ/mol.
Assume the specific heat of the solution is equal to the specific heat of water.
ΔHdissolution = ??
kJ/mol
When a solid dissolves in water, heat may be evolved or absorbed. ?
2020-07-28 10:44 pm
回答 (2)
2020-07-28 11:04 pm
Heat absorbed by the reaction
= Heat loss of the solution + Heat loss of the colorimeter
= m c ΔT + 1.64 ΔT
= [(111.10 + 8.01) × 4.184 × (24.31 - 21.97)] + [1.64 × (24.31 - 21.97)] J
= 1170 J
= 1.17 kJ
Molar mass of CsBr
= (132.9 + 79.9) g/mol
= 212.8 g/mol
Moles of CsBr dissolved
= (8.01 g) / (212.8 g/mol)
= 0.03764 mol
As temperature drops, energy is absorbed by the reaction. The reaction is endothermic and thus heat of dissolution is positive.
Heat of dissolution
= +(1.17 kJ) / (0.03764 mol)
= +31.1 kJ/mol
= Heat loss of the solution + Heat loss of the colorimeter
= m c ΔT + 1.64 ΔT
= [(111.10 + 8.01) × 4.184 × (24.31 - 21.97)] + [1.64 × (24.31 - 21.97)] J
= 1170 J
= 1.17 kJ
Molar mass of CsBr
= (132.9 + 79.9) g/mol
= 212.8 g/mol
Moles of CsBr dissolved
= (8.01 g) / (212.8 g/mol)
= 0.03764 mol
As temperature drops, energy is absorbed by the reaction. The reaction is endothermic and thus heat of dissolution is positive.
Heat of dissolution
= +(1.17 kJ) / (0.03764 mol)
= +31.1 kJ/mol
2020-07-28 11:03 pm
Total heat lost = heat lost by calorimeter + heat lost by solution
Total heat lost=(1.64 J/°C)(21.97 -24.31°C)+119.11g (4.184 J/g°C)(21.97-24.31°C) = -1170.J
So, the dissolving absorbed +1170. J of heat
ΔHdissolution = +1170 J/8.01 g X 212.84 g/mol = 3.11X10^4 J/mol = 31.1 kJ/mol
Total heat lost=(1.64 J/°C)(21.97 -24.31°C)+119.11g (4.184 J/g°C)(21.97-24.31°C) = -1170.J
So, the dissolving absorbed +1170. J of heat
ΔHdissolution = +1170 J/8.01 g X 212.84 g/mol = 3.11X10^4 J/mol = 31.1 kJ/mol
收錄日期: 2021-04-24 07:56:55
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