Multiple Choice QuestionsWhen 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.
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
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
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
A 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
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.
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
(∆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
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
Switch
