Chemical Thermodynamics MCQ Questions & Answers in Physical Chemistry | Chemistry
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141.
According to the first law of thermodynamics, $$\Delta U = q + w.$$ In special cases the statement can be expressed in different ways. Which of the following is not a correct expression ?
A
At constant temperature : $$q = - w$$
B
When no work is done : $$\Delta U = q$$
C
In gaseous system : $$\Delta U = q + P\Delta V$$
D
When work is done by the system : $$\Delta U = q + w$$
Answer :
When work is done by the system : $$\Delta U = q + w$$
When work is done by the system, $$\Delta U = q - w.$$
142.
In an irreversible process taking place at constant $$T$$ and $$P$$ and in which only pressure-volume work is being done, the change in Gibbs free energy $$(dG)$$ and change in entropy $$(dS),$$ satisfy the criteria
For spontaneous reaction, $$dS > 0$$ and $${\Delta G}$$ and $${\Delta G}$$ should be negative i.e. $$ < 0.$$
143.
The entropy change can be calculated by using the expression, $$\Delta S = \frac{{{q_{rev}}}}{T}.$$ When water freezes in a glass beaker, choose the correct statement amongst the following :
A
$$\Delta {S_{{\text{system}}}}$$ decreases but $$\Delta {S_{{\text{surroundings}}}}$$ remains the same.
B
$$\Delta {S_{{\text{system}}}}$$ increases but $$\Delta {S_{{\text{surroundings}}}}$$ decreases.
C
$$\Delta {S_{{\text{system}}}}$$ decreases but $$\Delta {S_{{\text{surroundings}}}}$$ increases.
D
$$\Delta {S_{{\text{system}}}}$$ decreases and $$\Delta {S_{{\text{surroundings}}}}$$ also decreases.
Answer :
$$\Delta {S_{{\text{system}}}}$$ decreases but $$\Delta {S_{{\text{surroundings}}}}$$ increases.
As water freezes from liquid to solid, randomness decreases, i.e., $$\Delta {S_{{\text{system}}}}$$ decreases. Heat released during the process, is absorbed by the surroundings hence, $$\Delta {S_{{\text{surroundings}}}}$$ increases.
144.
Which of the following value of $${\Delta _f}{H^ \circ }$$ represent that the product is least stable ?
A
$$ - 94.0\,kcal\,mo{l^{ - 1}}$$
B
$$ - 231.6\,kcal\,mo{l^{ - 1}}$$
C
$$ + 21.4\,kcal\,mo{l^{ - 1}}$$
D
$$ + 64.8\,kcal\,mo{l^{ - 1}}$$
Answer :
$$ + 64.8\,kcal\,mo{l^{ - 1}}$$
As $${\Delta _f}H$$ increases stability decreases.
145.
The value of $${\log _{10}}K$$ for a reaction $$A\, \rightleftharpoons \,B$$ is
$${\text{(Given}}\,:\,{\Delta _r}H_{298K}^ \circ = - 54.07\,kJ\,mo{l^{ - 1}},$$ $${\Delta _r}S_{298K}^ \circ = 10\,J{K^{ - 1}}\,mo{l^{ - 1}}\,{\text{and}}$$ $$R = 8.314\,J{K^{ - 1}}\,mo{l^{ - 1}};$$ $$2.303 \times 8.314 \times 298 = 5705)$$
146.
Which of the following is not a correct statement about enthalpy of solution ?
A
For most ionic compounds, $$\Delta H_{{\text{soln}}{\text{.}}}^ \circ $$ is positive and the dissociation process is endothermic.
B
Solubility of most salts increases with increase in temperature.
C
If the lattice enthalpy is very high, the dissolution of compound becomes very easy.
D
Enthalpy of solution is determined by the selective values of the lattice enthalpy and hydration enthalpy.
Answer :
If the lattice enthalpy is very high, the dissolution of compound becomes very easy.
Dissolution of compound may not take place if lattice enthalpy is very high.
147.
An ideal gas expands in volume from $$1 \times {10^{ - 3}}$$ to $$1 \times {10^{ - 2}}{m^3}$$ at $$300K$$ against a constant pressure of $$1 \times {10^5}N{m^{ - 2}}.$$ The work done is
148.
What is the entropy change $$\left( {{\text{in}}\,J\,{K^{ - 1}}\,mo{l^{ - 1}}} \right)$$ when one mole of ice is converted into water at $${0^ \circ }C?$$ ( The enthalpy change for the conversion of ice to liquid water is $$6.0\,kJ\,mo{l^{ - 1}}$$ at $${0^ \circ }C$$ )
149.
One mole of a non-ideal gas undergoes a change of state $$\left( {2.0\,atm,3.0\,L,95\,K} \right) \to \left( {4.0\,atm,5.0\,L,245\,K} \right)$$ with a change in internal energy, $$\Delta U = 30.0\,L\,atm.$$ The change in enthalpy $$\Delta H$$ of the process in $$L\,atm$$ is.
150.
Which of the following statements is correct ?
A
The presence of reacting species in a covered beaker is an example of open system.
B
There is an exchange of energy as well as matter between the system and the surroundings in a closed system.
C
The presence of reactants in a dosed vessel made up of copper is an example of a dosed system.
D
The presence of reactants in a thermos flask or any other dosed insulated vessel is an example of a dosed system.
Answer :
The presence of reactants in a dosed vessel made up of copper is an example of a dosed system.
In a closed system ( e.g., the presence of reactants in a closed vessel made of conducting material i.e. copper ) there is no exchange of matter, but exchange of energy is possible between system and the surroundings.