If water vapour is assumed to be a perfect gas, molar enthalpy change for vapourisation of 1 mol of water at 1 bar and 100°C is 41kJ mol–1. The internal energy change, when 1 mol of water is vapourised at 1 bar pressure and 100°C is-

1. 35.5 kJ mol–1

2. 37.9 kJ mol–1

3.  41 kJ mol–1

4. 44.2 kJ mol–1

 

Subtopic:  Enthalpy & Internal energy |
 58%
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1g of graphite is burnt in a bomb calorimeter in excess of oxygen at 298 K and 1 atmospheric pressure according to the equation

C (graphite) + O2(g) → CO2(g)

During the reaction, the temperature rises from 298 K to 299 K. If the heat capacity of the bomb calorimeter is 20.7kJ/K, the enthalpy change for the above reaction at 298 K and 1 atm is-

1. – 2.48 ×102 kJ mol–1

2. – 3.45 ×102 kJ mol–1

3. – 1.65 ×102 kJ mol–1

4. – 1.88 ×102 kJ mol–1

Subtopic:  Enthalpy & Internal energy |
 54%
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A swimmer coming out from a pool is covered with a film of water weighing about 18g. The internal energy of vaporization at 298K. is-

vap H for water at 298K= 44.01kJ mol–1

1. 38.63 kJ
2. 43.82 J
3. 41.53 kJ
4. 40.33 J

Subtopic:  Enthalpy & Internal energy |
 68%
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