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Published on: 31/07/2019
Thermodynamics
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Questions + Answers key
Take MCQ Chemistry Test
1.
When 20.0 g of ammonium nitrate (NH4NO3) is dissolved in 125 g of water in a coffee cup calorimeter. (Treat heat capacity of water as the heat capacity of the calorimeter and its contents).
2.
If the same gas expands isothermally in a reversible manner, then what will be the value of work done?
3.
How are internal energy change, free energy change and entropy change are related to one another?
4.
Define extensive properties.
5.
Which one of the following is not extensive state function?
6.
Calculate the number of kJ of heat necessary to raise the temperature of 60.0 g of aluminium from 35°C to 55°C. Molar heat capacity of Al is 24 J mol–1 K–1.
7.
Given, \({ N }_{ 2 }(g)+{ 3H }_{ 2 }(g)\longrightarrow 2{ NH }_{ 3 }(g); \Delta ,{ H }^{ o }=-92.4 \ kJ \ { mol }^{ -1 }\)
What is the standard enthalpy of formation of NH3 gas?
8.
If enthalpy of fusion and enthalpy of vaporisation of sodium metals are 2.6 and 98.2KJ mol-1 respectively, what is the enthalpy of sublimation of sodium.
9.
Why in some reactions heat is evolved while some reactions take place only on absorption of heat?
10.
Heat has randomising influence on a system and temperature is the measure of average chaotic motion of particles in the system. Write the mathematical relation which relates these three parameters.
11.
What is bond energy? Why is it called enthalpy of atomisation?
12.
The enthalpy of vaporization of liquid diethyl ether (C2H5)20 is 26.0 KJ mol-1 at its boiling point (35.0oC). Calculate \(\triangle \)So for the conversion of Liquid to vapour and
13.
Which one is the correct unit for entropy?
KJ mol
JK-1 mol
JK-1 mol -1
KJ mol-1
14.
The process depicted by the equation.
H2O (s) \(\rightarrow\) H2O (l)
\(\Delta\)H = +1.43 kcal represents
fusion
melting
evaporation
boiling
15.
For an endothermic reaction ______.
\(\Delta\)H is-ve
\(\Delta\)H is+ve
\(\Delta\)H is zero
none of these
16.
The bond energy depends upon ______.
size of the atom
electronegativity
bond length
all of the above
17.
Which of the following relation is true?
Cp > cu
cu > Cp
Cp = Cu
Cp = C;u= 0
18.
An isochoric process takes place at constant ______.
temperature
pressure
volume
concentration
19.
Thermodynamics is applicable to ______.
macroscopic system only
microsopic system only
homogeneous system only
heterogeneous system only
20.
As per the available data: ______.
CH4(g) + 2O2(g) \(\rightarrow \) CO2(g) + 2H2O(l); \(\triangle \)C \(H^{ \ominus }\) = -890.3 KJ mol-1
C(s) + O2(g) \(\rightarrow \) CO2(g) \(\triangle \)C \(H^{ \ominus }\)=-393.5 KJ mol-1
H2(g) + 1/2O2(g) \(\rightarrow \) H2O (l); \(\triangle \)C\(H^{ \ominus }\)= -285.8 KJ mol-1
21.
A reaction, A + B → C + D + q is found to have a positive entropy change. The reaction will be _______.
possible at high temperature
possible only at low temperature
not possible at any temperature
possible at any temperature
22.
Choose the correct answer. A thermodynamic state function is a quantity _______.
used to determine heat changes
whose value is independent of path
used to determine pressure volume work
whose value depends on temperature only.
1.
A heat capacity of water = heat capacity of calorimeter, the heat gained by water = heat lost by calorimeter
\(=125\times (296.5-286.4)\times 4.184 \ J=5282J=5.282kJ\)
2.
\(For \ isothermal \ reversible \ expansion \ of \ ideal \ gas\)
\({ W }_{ rev }=-2.303nRT \ log\frac { { V }_{ 2 } }{ { V }_{ 1 } }\)
\( =-2.303\times 5.2\times 8.314\times 298 \ log \ \left( \frac { 127.05 }{ 42.35 } \right)\)
\( =14156.38J\)
3.
△G = △H - T△S (At constant pressure)
4.
Properties which depend upon the amount of the substance are called as extensive properties.
5.
Enthalpy change, internal energy change and pressure
6.
Given, mass of Al = 60.0g
Molar mass of Al = 27g mol\(^{ -1 }\)
Molar heat capacity, C = 24Jmol\(^{ -1 }\) K\(^{ -1 }\)
\(\triangle T=55^{ \circ }C-35^{ \circ }C=20^{ \circ }C \ or \ 20K\)
\(Heat, q=n.C.\triangle T\)
\( q=\frac { 60 }{ 27 } \times 24Jmol^{ -1 }K^{ -1 }\times 20K\left( n=\frac { 60 }{ 27 } mol \right)\)
\( =1066.66J=1.067kJ\)
7.
Given, \({ N }_{ 2 }(g)+{ 3H }_{ 2 }(g)\longrightarrow 2{ NH }_{ 3 }(g); \ { \Delta }_{ r }{ H }^{ o }\)
= -92.4 kJ mol-1
Chemical reaction for the enthalpy of formation of NH3 (g) is as follows.
\(\frac { 1 }{ 2 } { N }_{ 2 }(g)+\frac { 3 }{ 2 } { H }_{ 2 }(g)\longrightarrow { NH }_{ 3 }(g)\)
Therefore, \({ \Delta }_{ f }{ H }^{ o }=\frac { -92.4 }{ 2 } =-46.2 \ kJ\ { mol }^{ -1 }\)
8.
△subH∘=△fusH∘+△vapH∘ = 2.6+98.2
= 100.8KH mol-1
9.
Every substance has energy stored in it in the form of heat content. If heat content of reactants (HR) is greater than that of products (HP), heat is evolved. If HR < HP, heat is absorbed.
10.
Heat has randomising influence on a system and temperature is the measure of average chaotic motion of particles in the system. The mathematical relation which relates these three parameters is ΔS=qrev/T
Here, ΔS = change in entropy
qrev= heat of reversible reaction
T = temperature
11.
Bond energy is the amount of energy required to dissociate one mole of bonds present between the atoms in the gaseous phase. As the molecules dissociate completely into atoms in the gaseous phase therefore bond energy of a diatomic molecule is called enthalpy of atomisation.
12.
For vaporization of diethyl ether
\(\therefore \ \triangle _{ vap }{ S }^{ o }=\frac { \triangle _{ vap }{ H }^{ o } }{ T }\)
\( \triangle _{ vap }{ H }^{ o }=26.0kJ \ mo{ l }^{ -1 }, \ T=273+35=308K\)
\(\triangle _{ vap }{ S }^{ o }=\frac { 26.0\times{ 10 }^{ 3 }J{ mol }^{ -1 } }{ 308K } =84.4J{ K }^{ -1 }{ mol }^{ -1 }\)
13.
(c)
JK-1 mol -1
14.
(a)
fusion
15.
(b)
\(\Delta\)H is+ve
16.
(d)
all of the above
17.
(a)
Cp > cu
18.
(c)
volume
19.
(a)
macroscopic system only
20.
(a)
CH4(g) + 2O2(g) \(\rightarrow \) CO2(g) + 2H2O(l); \(\triangle \)C \(H^{ \ominus }\) = -890.3 KJ mol-1
21.
(d)
possible at any temperature
22.
(b)
whose value is independent of path
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