﻿ 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 ) | Thermodynamics

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# Thermodynamics

#### Multiple Choice Questions

11.

(∆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

229 Views

# 12.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

566 Views

13.

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.

14.

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

15.

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

590 Views

16.

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

213 Views

17.

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

511 Views

18.

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.

180 Views

19.

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

197 Views

20.

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

259 Views