Thermodynamics Test

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Thermodynamics Test - 79

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Question 1
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Directions For Questions

For the reaction at $$25^{o}C, X_{2}C_{4}O (I) \rightarrow 2XO_{2} (g), \triangle E^{o} = 2.1 \ kcal$$ and $$\triangle S^{o}= 20\ cal/K$$.

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The reaction is ?

A
spontaneous and exergonic

B
non-spontaneous and exergonic

C
spontaneous and endergonic

D
non-spontaneous and endergonic

Solution
Question 2
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When we take acetone in a test tube it feels cold. Which reaction occurs in the process?

A
endothermic reaction

B
exothermic reaction

C
reversible process

D
adiabatic process

Solution

Acetone is a very volatile solvent, it evaporates quickly.

The heat is absorbed from the surface. This process is called a endothermic reaction.

Option A is correct.
Question 3
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Which of the following salts shall cause more cooling when one mole of the salt is dissolved in the same amount of water ? (Integral heat of solution at $$298\ K$$ is given for each solute.)

A
$$KNO_{3} ; \triangle H = 35.4\ kJ/mol$$

B
$$NaCI; \triangle H = 5.35\ kJ/mol$$

C
$$KOH ; \triangle H= -55.6\ kJ/mol$$

D
$$HBr ; \triangle H=-83.3\ kJ/mol$$

Solution
Question 4
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In an ice calorimeter, a chemical reaction is allowed to occur in thermal contact with an ice-water mixture at $$0^{o}C$$. Any heat liberated by the reaction is used to melt some ice; the volume change of the ice-water mixture indicates the amount of melting. When solutions containing $$1.0$$ millimole each of $$AgNO_{3}$$ and $$NaCl$$ were mixed in such a calorimeter, both solution having been pre-cooled to $$0^{o}C$$, $$0.20\ g$$ of ice-melted. Assuming complete reaction in this experiment, what is $$\Delta H$$ for the reactions: $$Ag^{+}(aq)+Cl^{-}(aq)\rightarrow AgCl(s)$$ ? Latent heat of fusion of ice at $$0^{o}C$$ is $$80\ cal/g$$.

A
$$-16\ kcal$$

B
$$+16\ kcal$$

C
$$-16\ cal$$

D
$$+16\ cal$$
Question 5
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For an ideal solution containing two liquid components A and B, the Gibbs free energy of mixing is minimum, when the molar ratio of the liquids is

A
1 : 1

B
1 : 2

C
1 :10

D
1 : 1000
Question 6
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Ethyl chlorine is prepared by reaction of ethylene with hydrogen chloride as:

$$C_{2}H_{4}(g)+HCl(g)\rightarrow C_{2}H_{5}Cl(g); \Delta H=-72.3\ kJ$$

What is the value of $$\Delta U$$(in $$kJ$$) if $$70\ g$$ of ethylene and $$73\ g$$ of $$HCl$$ are allowed to react?

A
$$-69.8$$

B
$$-180.75$$

C
$$-174.5$$

D
$$-139.6$$

Solution
Question 7
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The factor of $$\triangle G$$ values is important in metallurgy. The $$\triangle G$$ values for the following reactions at $$800^{o}C$$ are given as :
$$S_{2} (s)+ 2O_{2} (g) \rightarrow 2SO_{2} (g) ; \triangle G=-544\ kJ$$
$$2Zn(s)+ S_{2} (s) \rightarrow 2Zn S(s); \triangle G= -293\ k J$$
$$2Zn(s) + O_{2} (g) \rightarrow 2ZnO(s) ; \triangle G= -480\ kJ$$
The $$\triangle G$$ for the reaction : $$2ZnS(s)+ 3O_{2} (g) \rightarrow 2 ZnO (s) + 2SO_{2} $$ will be

A
$$-357\ kJ$$

B
$$-731\ kJ$$

C
$$-773\ kJ$$

D
$$-229\ kJ$$

Solution
Question 8
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The strain energy (in $$kJ/mol$$) of cyclopropane from the following data:

$$\Delta_{f}H[C_{3}H_{6}(g)]=53.0\ kJ/mol; \Delta_{f}H[C(g)]=715.0\ kJ/mol; \Delta_{f}H[H(g)]=218.0\ kJ/mol$$

$$BE(C-C)=356.0\ kJ/mol; BE(C-H)=408.0\ kJ/mol$$

A
$$770\ kJ$$

B
$$116\ kJ$$

C
$$240\ kJ$$

D
$$346\ kJ$$

Solution
Question 9
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What is the thermodynamic condition for the feasibility of a process?

A
$$(\Delta S)_{sys} > 0$$

B
$$(\Delta G)_{sys} > 0$$

C
$$(\Delta S)_{sys} + (\Delta S)_{surr} > 0$$

D
$$(\Delta G)_{sys} + (\Delta G)_{surr} < 0$$

Solution

For the reaction to be feasible, total entropy change should be greater than zero. Hence, sum of entropy change of system and surrounding should be greater than zero.
Also, total Gibb's free energy should be less than zero for the reaction to be feasible.
Hence, the correct option is (C).
Question 10
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The standard state Gibbs energies of formation of C(graphite) and C (diamond) at T=298 K are
$$\Delta_f G^{\circ}[C(graphite)]= 0 KJ mol^{-1}$$
$$\Delta_f G^{\circ}[C(diamond)]=2.9 KJ mol^{-1}$$
The standard state means that the pressure should be 1 bar and substance should be pure at a given temperature. The conversion of graphite to diamond reduce its volume by $$2\times 10^{-6} m^3 mol^{-1}$$ If C(graphite) is converted C isothermally at T=298 K, the pressure at which C(graphite) is in equilibrium with C(diamond) is $$( 1J =1 kJ m^2 s^{-2}, 1 Pa=1 kJ m^{-1} s^{-2}, 1bar= 10^5Pa)$$

A
58001 bar

B
1450 bar

C
14501 bar

D
29001 bar

Solution