When a 13.0 g sample of NaOH(s) dissolves in 400.0 mL of water to produce 413.0 g of solution in a constant pressure calorimeter,
the temperature of the water and reaction vessel changes from 22.6°C to 30.6°C. Assume that the specific heat capacity of the solution is 4.20 J/(g · °C), and that the heat capacity of the reaction vessel is 1.00 J/°C. What is the molar enthalpy of solution of sodium hydroxide (40.00 g/mol)?
When a 13.0 g sample of NaOH(s) dissolves in 400.0 mL of water to produce 413.0 g of solution in a constant pressure calorimeter,?
2016-10-24 4:17 am
回答 (1)
2016-10-24 4:34 am
(Please check the question. The heat capacity of the reaction vessel is unusually small.)
Heat released from the formation of NaOH solution
= Heat absorbed by the solution + Heat absorbed by the reaction vessel
= (413.0 g) × [4.20 J/g°C] × [(30.6 - 22.6)°C] + (1.00 J/°C) × [(30.6 - 22.6)°C]
= 13900 J
Enthalpy change of the process
= -13900 J
No. of moles of NaOH used
= (13.0 g) / (40.00 g/mol)
= 0.325 mol
Molar enthalpy of solution of NaOH
= (-13900 J) / (0.325 mol)
= -42800 J/mol
= -42.8 kJ/mol
Heat released from the formation of NaOH solution
= Heat absorbed by the solution + Heat absorbed by the reaction vessel
= (413.0 g) × [4.20 J/g°C] × [(30.6 - 22.6)°C] + (1.00 J/°C) × [(30.6 - 22.6)°C]
= 13900 J
Enthalpy change of the process
= -13900 J
No. of moles of NaOH used
= (13.0 g) / (40.00 g/mol)
= 0.325 mol
Molar enthalpy of solution of NaOH
= (-13900 J) / (0.325 mol)
= -42800 J/mol
= -42.8 kJ/mol
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