The pressure-volume work for an ideal gas can be calculated by using the expression W=ViVfpexdV.

The work can also be calculated from the pV-plot by using the area under the curve within the specified limits.
An ideal gas is compressed (a) reversibly or (b) irreversibly from volume Vi to Vf.
The correct option is:

1.  W (reversible)=W (irreversible)

2.  W (reversible)<W(irreversible)

3.  W (reversible)>W (irreversible)

4.  W (reversible)=W (irreversible)+pex.V

Subtopic:  First Law of Thermodynamics |
 62%
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The entropy change can be calculated by using the expression S=qrevT. When water freezes in a glass beaker, the correct statement among the following is:

1. ∆ S  (system) decreases but  ∆ S  (surroundings) remains the same
2. ∆ S  (system) increases but  ∆ S  (surroundings) decreases
3. ∆ S  (system) decreases but  ∆ S  (surroundings) increases
4. ∆ S  (system) decreases but  ∆ S  (surroundings) also decreases

Subtopic:  Spontaneity & Entropy |
 59%
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On the basis of thermochemical equations (i), (ii), and (iii), find out which of the algebraic relationships given in options (a) to (d) is correct:

(i). C(graphite) + O2(g) → CO2 (g) ; ∆rH = x kJmol-1
(ii). C(graphite) + \(\frac{1}{2}\)O2(g) → CO(g) ; ∆rH = y kJ mol-1
(iii). CO(g) + \(\frac{1}{2}\)O2(g) → CO2(g); ∆rH = z kJ mol-1

1. z=x+y

2. x=y-z

3. x=y+z

4. y=2z-x

Subtopic:  Thermochemistry |
 76%
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Consider the reactions given below. On the basis of these reactions find out which of the

the algebraic relationships is correct?

(i) C(g) +4H (g) CH4(g); 
Hr =x kJ mol-1
(ii) C(graphite) + 2H2 (g)   CH4; 
Hr  = y kJ mol-1

1. x=y 2. x=2y
3. x>y 4. x<y
Subtopic:  Enthalpy & Internal energy |
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The enthalpies of elements in their standard states are taken as zero. The enthalpy of formation of a compound is-

1. Generally negative 2. Always positive
3. Zero 4. Never negative
Subtopic:  Thermochemistry |
 54%
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The enthalpy of sublimation of a substance is equal to-

1. Enthalpy of fusion + Enthalpy of vaporisation

2. Enthalpy of fusion

3. Enthalpy of vaporisation

4.  Twice the enthalpy of vaporisation

Subtopic:  Thermochemistry |
 86%
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Which of the following is not correct?

1. G is zero for a reversible reaction.

2. G is positive for a spontaneous reaction.

3. G is negative for a spontaneous reaction.

4. G is positive for a non-spontaneous reaction.

Subtopic:  Spontaneity & Entropy |
 82%
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In an adiabatic process, no transfer of heat takes place between the system and its surroundings. The correct option for free expansion of an ideal gas under adiabatic condition from the following is -

1. q=0, T0, W=0

2. q0, T=0, W=0

3. q=0, T=0, W=0

4. q=0, T=0, W0

Subtopic:  Thermodynamics' Properties and process |
 69%
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fU of formation of CH4(g) at certain temperature is -393 kJ mol-1. The value of fH is-

1. Zero

2. <fU

3. >fU

4. Equal to fU

Subtopic:  Enthalpy & Internal energy |
 61%
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During complete combustion of one mole of butane, 2658 kJ of heat is released. The thermochemical reaction for this change is -

1. 2C4H10(g)+13O2(g)8CO2(g)+10H2O(l); 
cH=-2658.0 kJ mol-1

2. C4H10(g)+132O2(g)4CO2(g)+5H2O(l); 
cH=-1329.0 kJ mol-1

3. C4H10(g)+132O2(g)4CO2(g)+5H2O(l); 
cH=-2658.0 kJ mol-1

4. C4H10(g)+132O2(g)4CO2(g)+5H2O(l); 
cH=+2658.0 kJ mol-1

Subtopic:  Enthalpy & Internal energy |
 80%
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