If the bond energies of H-H, Br-Br, and H-Br are 433, 192 and 364 kJ mol-1 respectively, 

the H° for the reaction

H2(g) + Br2(g) 2HBr(g) is

1.  -103 kJ               

2. -261 kJ

3. +103 kJ               

4. +261 kJ

Subtopic:  Enthalpy & Internal energy |
 57%
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One mole of methanol when burnt in O2 gives out 723 kJ mol-1 heat. If one mole of O2 is used, what will be the amount of heat evolved?

1.  482 kJ           
2.  241 kJ
3.  723 kJ               
4.  924 kJ

Subtopic:  Thermochemistry |
 59%
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For a given reaction, H =35.5 kJ mol-1 and S = 83.6JK-1 mol-1. The reaction is spontaneous at:
(Assume that H and S do not vary with temperature)

1. T < 425 K 2. T > 425 K
3. All temperatures 4. T > 298 K
Subtopic:  Gibbs Energy Change |
 73%
From NCERT
NEET - 2017
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A gas is allowed to expand in a well insulated container against a constant external pressure of 2.5 atm from an initial volume of 2.50 L to a final volume of 4.50 L. The change in internal energy U of the gas in joules will be

(1) 1136.25 J

(2) - 500 J

(3) - 505 J

(4) + 515 J

Subtopic:  First Law of Thermodynamics |
 64%
From NCERT
NEET - 2017
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For a sample of perfect gas when its pressure is changed isothermally from pi to pf, the entropy change is given by

(1) S = nRln(pf/pi)               

(2) S = nRln(pi/pf)

(3) S = nRTln(pf/pi)             

(4) S = RTln(pf/pi)

Subtopic:  Spontaneity & Entropy |
 73%
NEET - 2016
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The correct thermodynamic conditions for the spontaneous reaction at all temperatures is

(a) H>0 and S<0
(b) H<0 and S>0
(c) H<0 and S<0
(d) H<0 and S=0

Subtopic:  Gibbs Energy Change |
 79%
From NCERT
NEET - 2016
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The heat of combustion of carbon to CO2 is -393.5 kJ/mol. The heat released upon the

formation of 35.2 g of CO2 from carbon and oxygen gas is

1. -315 kJ               

2. +315 kJ             

3. -630 kJ                 

4. -3.15 kJ

Subtopic:  Thermochemistry |
 71%
From NCERT
NEET - 2015
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For the reaction, X2O4(l) 2XO2(g)

U = 2.1 kcal, S = 20 cal K-1 at 300 K. Hence, G is

1. 2.7 kcal

2. -2.7 kcal

3. 9.3 kcal

4. -9.3 kcal

Subtopic:  Gibbs Energy Change |
 73%
From NCERT
NEET - 2014
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The standard enthalpy of vaporisation vapH° for water at 100°C is 40.66 kJ mol-1. The

internal energy of vaporisation of water at 100°C (in kJ mol-1) is- 

(Assume water vapour to behave like an ideal gas)

1. +37.56                   

2. -43.76

3. +43.76                   

4. +40.66

Subtopic:  Enthalpy & Internal energy |
 57%
From NCERT
NEET - 2012
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If the enthalpy change for the transition of liquid water to steam is 30 kJ mol-1 at 27°C,

the entropy change for the process would be

1. 1.0 J mol-1 K-1

2. 0.1 J mol-1K-1

3. 100 J mol-1K-1

4. 10 J mol-1K-1

Subtopic:  Enthalpy & Internal energy |
 81%
From NCERT
NEET - 2011
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