A 3.505 g sample of quinone (C 6 H 4 O 2 ) is burned in a bomb calorimeter whose

Question

A 3.505 g sample of quinone (C6H4O2) is burned in a bomb calorimeter whose heat capacity is 7.854 kJ/oC.  The temperature of the calorimeter increases from 23.44 oC to 34.59 oC.  

______ kJ

b) What is the molar energy change for the process?

______ kJ/mol

c) What is the molar enthalpy change for the process?  Assume that quinone is a solid and all other reactants and products are in their standard states at 25.00 oC.

______ kJ/mol

A 3.505 g sample of quinone (C6H4O2) is burned in a bomb calorimeter whose heat capacity is 7.854 kJ/ Degree C. The temperature of the calorimeter increases from 23.44 Degree C to 34.59 Degree C. What is Delta E for the process? What is the molar energy change for the process? What is the molar enthalpy change for the process? Assume that quinone is a solid and all other reactants and products are in their standard states at 25.00 degree C.

Explanation / Answer

(a) ?E = -heat capacity x temperature change = -7.854 x (34.59 - 23.44) = -87.57 kJ

(b) Moles of quinone = mass/molar mass = 3.505/108.1 = 0.032423 mol

Molar internal energy change ?U = ?E/moles of quinone = -87.57/0.032423 = -2700 kJ/mol

(c) C6H4O2(s) + 6 O2(g) => 6 CO2(g) + 2 H2O(l)

Change in moles of gas ?n(gas) = 6 - 6 = 0

Molar enthalpy change ?H = ?U + RT?n(gas) = ?U = -2700 kJ/mol

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