According to the third law of thermodynamics which one of the following quantities for a perfectly crystalline solid is zero at absolute zero ?
Free energy
Entropy
Enthalpy
Internal energy
Considering entropy (S) as a thermodynamic parameter, the criterion for the spontaneity of any process is
Ssystem + Ssurrounding > 0
Ssystem - Ssurrounding > 0
Ssystem > 0 only
Ssurrounding > 0 only
Identify the correct statement for change of Gibb's energy for a system (ΔGsystem ) at constant temperature and pressure.
If ΔGsystem > 0, the process is spontaneous
If ΔGsystem = 0, the system has attained equilibrium
If ΔGsystem = 0, the system is still moving in a particular direction
If ΔGsystem< 0, the process is not spontaneous
From the following bond energies :
H—H bond energy : 431.37 kJ mol-1
C==C bond energy : 606.10 kJ mol-1
C—C bond energy : 336.49 kJ mol-1
C—H bond energy : 410.50 kJ mol-1
Enthalpy for the reaction,
will be
1523.6 kJ mol-1
-243.6 kJ mol-1
-120.0 kJ mol-1
553.0 kJ mol-1
If the bond energies of H—H, Br -Br and H—Br are 433, 192 and 364 kJ mol-1 respectively, then Ho for the reaction H2(g) + Br2(g) → 2HBr(g) is
-261 kJ
+ 103 kJ
+ 261 kJ
- 103 kJ
The enthalpy of combustion of H2, cyclohexene (C6H10) and cyclohexane (C6H12) are - 241, -3800 and -3920 kJ per mol respectively. Heat of hydrogenation of cyclohexene is
- 121 kJ per mol
+ 121 kJ per mol
+ 242 kJ per mol
- 242 kJ per mol
A reaction occurs spontaneously if
TS < H and both H and S are + ve
TS > H and both H and S are + ve
TS = H and both H and S are + ve
TS > H and H and is +ve and S is -ve
For the gas phase reaction,
PCI5 (g) PCI3(g) + CI2(g)
Which of the following conditions are correct ?
ΔH = 0 and ΔS < 0
ΔH > 0 and ΔS > 0
ΔH < 0 and ΔS < 0
ΔH > 0 and ΔS < 0
Unit of entropy is
JK-1 mol-1
J mol-1
J-1 K-1 mol-1
JK mol-1
Given the following entropy values (in JK-1 mol-1) at 298 K and 1 atm : H2(g) : 130.6, CI2(g) : 223.0, HCI(g) : 186.7. The entropy change (in Jk-1 mol-1) for the reaction
H2(g) + CI2(g) → 2HCI(g), is
+ 540.3
+ 727.0
- 166.9
+ 19.8
