Thermodynamics Test

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Thermodynamics Test - 33

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Weekly Quiz Competition

Question 1
1 / -0

The specific heat of a gas is found to be $$0.075$$ calories at constant volume and its formula weight is $$40$$. The atomicity of the gas would be:

A
one

B
two

C
three

D
four

Solution

Total Heat$$=40\times 0.075=3$$cal$$=Cv$$
$$Cp-Cv=R$$
$$Cp=Cv+R$$
$$=3+2$$
$$=5$$cal
$$\dfrac{Cp}{Cv}=\dfrac{5}{3}$$
$$=$$monoatomic.
Question 2
1 / -0

A piston cylinder device initially contains $$0.2m^3$$ neon (assume ideal) at 200 kPa inside at $$T_1 ^0C$$. A value is now opened and neon is allowed to escape until the volume reduces to half the initial volume. At the same time heat transfer with outside at $$T_2 ^0C$$ ensures a constant temperature inside. Select the statement(s) for given process :

A
$$\Delta U$$ must be zero

B
$$\Delta U$$ may not be zero

C
q may be +ve

D
q may not be -ve

Solution

The process is Isothermal as temperature constant inside.
for Isothermal $$DU=0$$ when gas expands work done by the system is
$$-ve$$ and q is positive.
Option A is correct.
Question 3
1 / -0

Consider the reaction at $$300\ K$$, $$H_{2}(g) + Cl_{2}(g)\rightarrow 2HCl(g), \ \ \ \Delta H^{\circ} = -185\ kJ$$
If $$3$$ mole of $$H_{2}$$ completely reacts with $$3$$ mole of $$Cl_{2}$$ to form $$HCl$$, What is $$\Delta U^{\circ}$$ for this reaction?

A
$$0$$

B
$$-185\ kJ$$

C
$$555\ kJ$$

D
None of these

Solution

$$\begin{array}{l} H_{ 3 }^{ + }\, \, \, C{ l_{ 2 } }\, \, \, \to 2HCL,\, \, \, \, \Delta { H^{ \circ } }=-18kJ \\ 1mol\, \, \, \, \, 1\, mol\, \, \, \, \, \, \, \, \, \, \, \, 2mol \\ 3mol\, \, \, \, \, 3mol\, \, \, \, \, \, \, \, \, \, \, \, 6mol \\ \Delta ng=0 \\ \Delta { H^{ \circ } }=\Delta { U^{ 6 } } \\ \Rightarrow \Delta { U^{ 6 } }=\Delta { H^{ \circ } }=-185KJ. \\ Hence,\, the\, option\, B\, is\, the\, correct\, answer. \end{array}$$
Question 4
1 / -0

Given the bond energies $$N \equiv N$$, $$H - H$$ and $$N - H$$ bonds are 945, 436 and 391 KJ $$mole^{-1}$$ respectively, the enthalpy of the following reaction $$N_{2(g)} + 3H_{2(g)} \rightarrow 2NH_{3(g)}$$ is:

A
-93 KJ

B
102 KJ

C
90 KJ

D
105 KJ

Solution

It takes 945 kJ of energy to break $$N\equiv N$$.

It takes 436$$\times$$3=1308 kJ to break $$3H_{2}$$ molecules.

It releases 2$$\times$$3$$\times$$391=2346 kJ to form $$2NH_{3}$$ molecules.

Enthalpy of the reaction $$=$$ Enthalpy of reactants $$-$$ Enthalpy of products $$=945+1308-2346=-93$$ kJ

$$\therefore$$ Enthalpy of reaction is $$-93$$ kJ.
Question 5
1 / -0

$${ H }_{ 2 }\left( g \right) +\dfrac { 1 }{ 2 } { O }_{ 2 }\left( g \right) \longrightarrow { H }_{ 2 }O\left( l \right)$$
$${ H }_{ 2 }O\left( l \right) \longrightarrow { H }_{ 2 }O\left( g \right); \Delta H={ x }_{ 4 }$$
Given,
$${ E }_{ H-H }={ x }_{ 1 }$$
$${ E }_{ O-O }={ x }_{ 2 }$$
$${ E }_{ O-H }={ x }_{ 3 }$$
$$\Delta { H }_{ F }$$ of $${ H }_{ 2 }O$$ vapour is:

A
$${ x }_{ 1 }+\dfrac { { x }_{ 2 } }{ 2 } -{ x }_{ 3 }+{ x }_{ 4 }$$

B
$$2{ x }_{ 3 }-{ x }_{ 1 }-\dfrac { { x }_{ 2 } }{ 2 } -{ x }_{ 4 }$$

C
$${ x }_{ 1 }+\dfrac { { x }_{ 2 } }{ 2 } -2{ x }_{ 3 }-{ x }_{ 4 }$$

D
$${ x }_{ 1 }+\dfrac { { x }_{ 2 } }{ 2 } -2{ x }_{ 3 }+{ x }_{ 4 }$$

Solution

$${ H }_{ 2 }+\dfrac { 1 }{ 2 } { O }_{ 2 }\left( g \right) \longrightarrow { H }_{ 2 }O\left( l \right) \quad ;\quad \Delta H$$
$$\Rightarrow \Delta H=2\left( 0-H \right) -\left( H-H \right) -\dfrac { 1 }{ 2 } \left( 0-0 \right) $$
$$=2{ x }_{ 3 }-{ x }_{ 1 }-\dfrac { { x }_{ 2 } }{ 2 } $$
for $${ H }_{ 2 }O\left( l \right) \longrightarrow { H }_{ 2 }O\left( g \right) \quad \Delta H={ x }_{ 4 }$$
$${ \Delta H }_{ f }={ x }_{ 4 }-\left[ { 2x }_{ 3 }-{ x }_{ 1 }-\dfrac { { x }_{ 2 } }{ 2 } \right] $$
$$={ x }_{ 1 }+\dfrac { { x }_{ 2 } }{ 2 } -2{ x }_{ 3 }+{ x }_{ 4 }$$
Ans :- D
Question 6
1 / -0

$$Al^{3+} (aq) + 3e^{-}\rightarrow Al(s); E^{\circ} = -1.66\ V$$
$$Cu^{2+} (aq) + 2e^{-}\rightarrow Cu(s); E^{\circ} = + 0.34\ V$$
What voltage is produced under standard conditions to give a spontaneous reactions by combination of these two-half cells?

A
$$1.32\ V$$

B
$$-1.32\ v$$

C
$$2.00\ V$$

D
$$-2.00\ V$$

Solution

$${ Al }^{ 3+ }+3{ e }^{ - }\rightarrow Al\quad { E }^{ 0 }=-1.66$$
$${ Cu }^{ 2+ }+{ 2e }^{ - }\rightarrow Cu\left( s \right) \quad ;\quad { E }^{ 0 }=+0.34V$$
$$\Rightarrow$$ When $${ 1 }^{ st }$$ reaction is reversed $$\Rightarrow$$ $$Al\longrightarrow { Al }^{ 3+ }+3{ e }^{ - }\Rightarrow { E }^{ 0 }=1.66V$$
$$\Rightarrow$$ $$Al$$ gets reduced and $${ Cu }^{ 2+ }$$ gets oxidized.
So, $${ E }_{ 1 }-{ E }_{ 2 }=1.66V-0.34V=1.32V$$
Question 7
1 / -0

What is the heat produced when 4 g of anhydrous solid is added to 50 g of water?

A
400 kJ

B
1672 J

C
200 kJ

D
836 kJ

Solution

As it is mention in the that either the temperature is rising or not we will take it as constant then the heat produced will be
$$Heat\ produced=50\times4=200kJ$$
Hence 200kJ heat is produced when 4g of anhydrous solid is added to 50g of water.
Question 8
1 / -0

The standard Gibbs energy change for a gaseous reaction at 27 is X Kcal. If equilibrium constant a reaction is 100 and R is 2 cal $${ K }^{ -1 }\ { mol }^{ -1 }$$. Then X is:

A
-2.7636

B
+2.7636

C
+ 807

D
- 807

Solution

$$\Delta G^o=-RTlnK$$
$$\therefore X= -2 \times 300\times ln 100$$
$$\therefore X= -2.7636 Kcal$$
Question 9
1 / -0

Which of the following statement(s) is/are true?
"Internal energy of an ideal gas ............"

A
Decreases in an isobaric process

B
Remains constant in an isothermal process

C
Increases in an isobaric process

D
Decreases in an isobaric expansion

Solution

In isothermal process $$\Delta U=0$$
In isobaric expansion $$V\propto T$$ so $$\Delta$$U increases.
Question 10
1 / -0

The heat released in the neutralisation of HCI and NaOH is 13.7 kcal/mol, the heat
released on neutralisation of NaOH with $$ { CH }_{ 3 }COOH$$ is 3.7 kcal/mol.
The $${ \Delta H }^{ }$$ of ionisation of $${ CH }_{ 3 }COOH$$ is:

A
10.2 kcal

B
10 kcal

C
3.7 kcal

D
9.5 kcal

Solution

1) In the neutralization process ions come to each other and form salt and water.

2) HCL is strong acid means $$H^+ + CL^-$$ and $$NaOH$$ is strong base means $$Na^+ + OH^-$$ So there is not any energy loss to break HCL or NaOH. total energy will come as neutralisation.

3) In Case of $$NaOH + CH_3COOH$$ $$ NaOH$$ is strong base means $$Na^+ + OH^-$$ But $$CH_3COOH$$ is a weak acid so have to give some energy to form $$CHCOO^- + H^+$$ So total released energy= total energy in case of (strong acid + strong base) - energy require to form ions. $$3.7 = 13.7$$ - energy require to form ions energy require to form ions$$= 10.00 kcal$$. only $$CH_3COOH$$ is weak nature So this enegy is ionisation energy of $$CH_3COOH.$$

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Thermodynamics Test - 33

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Thermodynamics Test - 33

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Question 1

one

two

three

four

Solution

Question 2

$$\Delta U$$ must be zero

$$\Delta U$$ may not be zero

q may be +ve

q may not be -ve

Solution

Question 3

$$0$$

$$-185\ kJ$$

$$555\ kJ$$

None of these

Solution

Question 4

-93 KJ

102 KJ

90 KJ

105 KJ

Solution

Question 5

$${ x }_{ 1 }+\dfrac { { x }_{ 2 } }{ 2 } -{ x }_{ 3 }+{ x }_{ 4 }$$

$$2{ x }_{ 3 }-{ x }_{ 1 }-\dfrac { { x }_{ 2 } }{ 2 } -{ x }_{ 4 }$$

$${ x }_{ 1 }+\dfrac { { x }_{ 2 } }{ 2 } -2{ x }_{ 3 }-{ x }_{ 4 }$$

$${ x }_{ 1 }+\dfrac { { x }_{ 2 } }{ 2 } -2{ x }_{ 3 }+{ x }_{ 4 }$$

Solution

Question 6

$$1.32\ V$$

$$-1.32\ v$$

$$2.00\ V$$

$$-2.00\ V$$

Solution

Question 7

400 kJ

1672 J

200 kJ

836 kJ

Solution

Question 8

-2.7636

+2.7636

+ 807

- 807

Solution

Question 9

Decreases in an isobaric process

Remains constant in an isothermal process

Increases in an isobaric process

Decreases in an isobaric expansion

Solution

Question 10

10.2 kcal

10 kcal

3.7 kcal

9.5 kcal

Solution

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