Thermodynamics Test

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Thermodynamics Test - 46

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Question 1
1 / -0

Born-Haber cycle can be used to estimate :

A
Lattice energy of ionic crystals

B
Electron gain enthalpy

C
Electronegativity

D
Both (A) and (B)

Solution
Question 2
1 / -0

Which one of the following gases possesses the largest internal energy?

A
2 moles of helium occupying $$1m^{3}$$ at 300 K

B
56 kg of nitrogen at 107$$Nm^{-2}$$ and 300 K

C
8 grams of oxygen at 8 atm and 300 K

D
$$6\times 10^{26}$$ molecules of argon occupying $$4m^{3}$$ at 900 K

Solution
Question 3
1 / -0

Which of the following relationship is not correct for the relation between $$\Delta H$$ and $$\Delta U$$?

A
When $$\Delta n_{g} = 0$$ then $$\Delta H = \Delta U$$

B
When $$\Delta n_{g} > 0$$ then $$\Delta H > \Delta U$$

C
When $$\Delta n_{g} < 0$$ then $$\Delta H < \Delta U$$

D
When $$\Delta n_{g} = 0$$ then $$\Delta H > \Delta U$$

Solution

We know,

$$\Delta H=\Delta U+\Delta n_{g}RT$$

When $$\Delta n_{g} = 0$$ then $$\Delta H=\Delta U$$
Question 4
1 / -0

For the electrochemical cell, $$ \mathrm{M} | \mathrm{M}^{+} \| \mathrm{X}^{-} \mid \mathrm{X}, $$
$$ E_{M}^{o}+/ M=0 \cdot 44 V $$ and $$ E_{x / x^-}^{\circ}=0 \cdot 33 V $$From these data one can deduce that

A
$$ M+X \rightarrow M^{+}+X^{-} $$ is the spontaneous reaction

B
$$ M^{+}+X^{-} \rightarrow M+X $$ is the spontaneous reaction

C
$$ E_{c e l l}=0 \cdot 77 V $$

D
$$ \mathrm{E}_{\mathrm{cell}}=-0.77 \mathrm{V} $$

Solution

$$ \mathrm{M}^{+}+e^{-} \rightarrow \mathrm{M} ; \quad \mathrm{E}^{\circ}=+0 \cdot 44 \mathrm{V} \dots(i)$$
$$ X+e^{-} \rightarrow X^{-} ; \quad E^{\circ}=+0.33 \mathrm{V} \dots(ii)$$
Subtracing Equ. (ii) from Eqn. (i), we have
$$M^{+}-X \rightarrow M-X^{-} ; \quad E^{\circ}=+0 \cdot 11 V$$
or $$ \quad M^{+}+X^{-} \rightarrow M+X ; \quad E^{\circ}=+0 \cdot 11 V $$
i.e., $$ \quad M^{+}+X^{-} \rightarrow M+X $$ is the spontaneous reaction.
Question 5
1 / -0

Hess's law is applicable for the determination of heat of

A
transition

B
formation

C
reaction

D
all of these

Solution

According to this law, the total enthalpy change is independent of the intermediate steps involved in the change. It depends only on initial and final values of enthalpy change.
Question 6
1 / -0

The relationship between enthalpy and internal energy change is

A
$$\Delta E=\Delta H+P\Delta V$$

B
$$\Delta H=\Delta E+P\Delta V$$

C
$$\Delta H=-\Delta E-P\Delta V$$

D
$$P\Delta V=\Delta E+\Delta H$$
Solution
- The change in the enthalpy of the system during a chemical reaction is equal to the change in its internal energy plus the change in the product of the pressure times the volume of the system. i.e
$$\Delta H=\Delta E+P\Delta V$$
Hence option B is correct answer.
Question 7
1 / -0

Consider the following processes.
$$\Delta H (kJ/mol)$$
$$1/2A\rightarrow B$$ +150
$$3B\rightarrow 2C+D$$ -125
$$E+A\rightarrow 2D$$ +350
For $$B+D\rightarrow E+2C, \Delta H$$ will be:

A
325 kJ/mol

B
525 kJ/mol

C
-175 kJ.mol

D
-325 kJ/mol

Solution

$$2(i)-(iii)+(ii)$$
$$\Delta H=2(150)-350-125$$
$$=-175kJ/mol$$
Question 8
1 / -0

The data given below are for vapour phase reactions at constant pressure.
$$C_{2}H_{6}\rightarrow \overset{\bullet} C_{2}H_{5}+ \overset{\bullet}{H};\ \Delta H=420\ kJ\ mol^{-1}$$
$$\overset{\bullet}{C}_{2}H_{5}\rightarrow C_{2}H_{4}+\overset{\bullet}{H};\ \Delta H=168\ kJ\ mol^{-1}$$
The enthalpy change for the reaction for the given reaction is :
$$2\overset{\bullet}{C}_{2}H_{5}\rightarrow C_{2}H_{6}+C_{2}H_{4}$$

A
$$+ 250$$ kJ mol$$^{-1}$$

B
$$+ 588$$ kJ mol$$^{-1}$$

C
$$- 252$$ kJ mol$$^{-1}$$

D
$$- 588$$ kJ mol$$^{-1}$$

Solution

$$i) \ C_{2}H_{6}\rightarrow \overset{\bullet}C_{2}H_{5}+\overset{\bullet}H; \Delta H=420\ kJ/mol$$

$$ii)\ \overset{\bullet}C_{2}H_{5}\rightarrow C_{2}H_{4}+\overset{\bullet}H; \Delta H=168\ kJ/mol$$

$$iii)\ C_{2}H_{4}+\overset{\bullet}H\rightarrow \overset{\bullet}C_{2}H_{5}; \Delta H=-168\ kJ/mol$$

Adding (i) and (iii) we get
$$C_{2}H_{6}+C_{2}H_{4}\rightarrow 2\overset{\bullet}C_{2}H_{5}$$;
$$\Delta H=420-168=252\ kJmol^{-1}$$
So, $$\Delta H'=-252\ kJmol^{-1}$$
Question 9
1 / -0

Assertion (A): At equilibrium $$\Delta G$$ becomes zero.
Reason (R): At equilibrium the two tendencies $$\Delta H$$and $$T\Delta S$$ become equal.

A
Both Assertion and Reason are true and Reason is the correct explanation of Assertion.

B
Both Assertion and Reason are true but Reason is not the correct explanation of Assertion.

C
Assertion is true but Reason is false.

D
Assertion is false and Reason is true.

Solution

$$\Delta G=\Delta H-T\Delta S$$

at $$eq^{m}\Delta G=O$$

$$\therefore \Delta H=T\Delta S$$

Also at $$eq^{m}\Delta H=T\Delta S$$

$$\therefore \Delta G=O$$
Question 10
1 / -0

Match the list -I with list - II.
List-I List - II
A) Hess law is not applicable for 1) is not a state function
B) All combustion reactions are 2) Heat of dilution
C) Work 3) Exothermic
D) Difference between two integral 4) Nuclear reaction
heats of solutions

A
A-1, B-2, C-3, D-4

B
A-4, B-3, C-1, D-2

C
A-3, B-2, C-4, D-1

D
A-2, B-1, C-4, D-3

Solution

A) Hess law is not applicable for 4) Nuclear reaction
B) All combustion reactions are 3) Exothermic
C) Work 1) is a path function , not a state function
D) Difference between
two integral heats of solution 2) Heat of dilution

Option B is correct.

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	$$\Delta H (kJ/mol)$$
$$1/2A\rightarrow B$$	+150
$$3B\rightarrow 2C+D$$	-125
$$E+A\rightarrow 2D$$	+350

Thermodynamics Test - 46

Result

Thermodynamics Test - 46

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Question 1

Lattice energy of ionic crystals

Electron gain enthalpy

Electronegativity

Both (A) and (B)

Solution

Question 2

2 moles of helium occupying $$1m^{3}$$ at 300 K

56 kg of nitrogen at 107$$Nm^{-2}$$ and 300 K

8 grams of oxygen at 8 atm and 300 K

$$6\times 10^{26}$$ molecules of argon occupying $$4m^{3}$$ at 900 K

Solution

Question 3

When $$\Delta n_{g} = 0$$ then $$\Delta H = \Delta U$$

When $$\Delta n_{g} > 0$$ then $$\Delta H > \Delta U$$

When $$\Delta n_{g} < 0$$ then $$\Delta H < \Delta U$$

When $$\Delta n_{g} = 0$$ then $$\Delta H > \Delta U$$

Solution

Question 4

$$ M+X \rightarrow M^{+}+X^{-} $$ is the spontaneous reaction

$$ M^{+}+X^{-} \rightarrow M+X $$ is the spontaneous reaction

$$ E_{c e l l}=0 \cdot 77 V $$

$$ \mathrm{E}_{\mathrm{cell}}=-0.77 \mathrm{V} $$

Solution

Question 5

transition

formation

reaction

all of these

Solution

Question 6

$$\Delta E=\Delta H+P\Delta V$$

$$\Delta H=\Delta E+P\Delta V$$

$$\Delta H=-\Delta E-P\Delta V$$

$$P\Delta V=\Delta E+\Delta H$$

Solution

Question 7

325 kJ/mol

525 kJ/mol

-175 kJ.mol

-325 kJ/mol

Solution

Question 8

$$+ 250$$ kJ mol$$^{-1}$$

$$+ 588$$ kJ mol$$^{-1}$$

$$- 252$$ kJ mol$$^{-1}$$

$$- 588$$ kJ mol$$^{-1}$$

Solution

Question 9

Both Assertion and Reason are true and Reason is the correct explanation of Assertion.

Both Assertion and Reason are true but Reason is not the correct explanation of Assertion.

Assertion is true but Reason is false.

Assertion is false and Reason is true.

Solution

Question 10

A-1, B-2, C-3, D-4

A-4, B-3, C-1, D-2

A-3, B-2, C-4, D-1

A-2, B-1, C-4, D-3

Solution

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