Multiple Choice QuestionsA Carnot engine, having an efficiency of η = 1/10 as heat engine, is used as a refrigerator. If the work done on the system is 10 J, the amount of energy absorbed from the reservoir at lower temperature is
99 J
90 J
1 J
1 J
B.
90 J
When a solid melts reversibly :
H decreases
G increases
E decreases
S increases
D.
S increases
When a solid melts, its entropy (S) increases because on changes from solid to liquid disorder or randomness of molecules increases.
The work of 146 kJ is performed in order to compress one kilo mole of gas adiabatically and in this process the temperature of the gas increases by 7° C. The gas is
(R = 8.3 J mol−1 K−1 )
monoatomic
diatomic
triatomic
triatomic
B.
diatomic
146 = Cv∆T
⇒ Cv = 21 J/mol K
The standard molar heat of formation of ethane, CO2 and water (l) are -21.1, -94.1 and -68.3 kcal respectively. The standard molar heat of combustion of ethane will be
-372 kcal
162 kcal
-240 kcal
183.5 kcal
A.
-372 kcal
The enthalpy changes for the following processes are listed below:
Cl2(g) = 2Cl(g), 242.3 kJ mol–1
I2(g) = 2I(g), 151.0 kJ mol–1
ICl(g) = I(g) + Cl(g), 211.3 kJ mol–1
I2(s) = I2(g), 62.76 kJ mol–1
Given that the standard states for iodine and chlorine are I2(s) and Cl2(g), the standard enthalpy of formation for ICl(g) is
–14.6 kJ mol–1
–16.8 kJ mol–1
+16.8 kJ mol–1
+16.8 kJ mol–1
C.
+16.8 kJ mol–1
In the conversion of limestone to lime, CaCO3(s) → CaO(s) + CO2(g) the values of ∆Hº and ∆Sº are + 179.1 kJ mol–1 and 160.2 J/K respectively at 298K and 1 bar. Assuming that ∆Hº and ∆Sº do not change with temperature, temperature above which conversion of limestone to lime will be spontaneous is
1008 K
1200 K
845 K
845 K
D.
845 K
We know, ∆G = ∆H-T∆S
So, lets find the equilibrium temperature, i.e. at which
∆G = 0
∆H-T∆S
T= 179.1 x 1000/160.2
= 1118 K
So, at the temperature above this, the reaction becomes will spontaneous.
Identify the correct statement regarding a spontaneous process –
For a spontaneous process in an isolated system, the change in entropy is positive
Endothermic processes are never spontaneous
Exothermic processes are always spontaneous
Exothermic processes are always spontaneous
A.
For a spontaneous process in an isolated system, the change in entropy is positive
When a system is taken from state i to state f along the path iaf, it is found that Q = 50 cal and W = 20 cal. Along the path’ ibf Q = 36 cal. W along the path ibf is
6 cal
66 cal
16 cal
16 cal
A.
6 cal
In the reaction,
2Al(s) + 6HCl(aq) → 2Al3+ (aq) + 6Cl¯(aq) + 3H2(g)
6L HCl(aq) is consumed for every 3L H2(g) produced
33.6 L H2(g) is produced regardless of temperature and pressure for every mole Al that reacts
67.2 L H2(g) at STP is produced for every mole Al that reacts
67.2 L H2(g) at STP is produced for every mole Al that reacts
D.
67.2 L H2(g) at STP is produced for every mole Al that reacts
2Al(s) + 6HCl(aq) → 2Al3+ (aq) + 6Cl¯(aq) + 3H2(g)
For each mole of HCl reacted, 0.5 mole of H2 gas is formed at STP.
1 mole of an ideal gas occupies 22.4 lit at STP.
Volume of H2 gas formed at STP per mole of HCl reacted is 22.4 × 0.5 litre
(∆H −∆U) for the formation of carbon monoxide (CO) from its elements at 298 K is
(R = 8.314 J K–1 mol–1)
–1238.78 J mol–1
1238.78 J mol–1
–2477.57 J mol–1
–2477.57 J mol–1
A.
–1238.78 J mol–1
∆H −∆U =∆ngRT
= (-1 x 8.314 x 298)/2
= - 1238.78
