Chemical Engineering Thermodynamics(Chemical Engineering ) Questions and Answers

Question 1. Kopp's rule is used to calculate the heat capacity of
  1.    Solids
  2.    Liquids
  3.    Gases
  4.    All of the above
Explanation:-
Answer: Option A. -> Solids
Kopp's rule states that the heat capacities of a molecular compound are sum of the contributions for each element in the compound. And it generally used to find the heat capacities of solids or liquid at $${20^{\text{o}}}C$$   for example the heat capacity of calcium chloride $$\left( {CaC{l_2}} \right)$$   can be written as heat capacity of $$Ca + {2\,\,*}$$   heat capacity of $$Cl$$ .
Question 2. __________ decreases during adiabatic throttling of a perfect gas.
  1.    Entropy
  2.    Temperature
  3.    Enthalpy
  4.    Pressure
Explanation:-
Answer: Option D. -> Pressure
During Throttling under adiabatic conditions the pressure energy decreases because some of the pressure energy gets lost as frictional losses thereby increase in intermolecular energy. Hence always there will be loss in pressure energy there by reducing the pressure.
Question 3. Cv is given by
  1.    $${\left( {\frac{{\partial {\text{E}}}}{{\partial {\text{T}}}}} \right)_{\text{V}}}$$
  2.    $${\left( {\frac{{\partial {\text{E}}}}{{\partial {\text{V}}}}} \right)_{\text{T}}}$$
  3.    $${\left( {\frac{{\partial {\text{E}}}}{{\partial {\text{P}}}}} \right)_{\text{V}}}$$
  4.    $${\left( {\frac{{\partial {\text{V}}}}{{\partial {\text{T}}}}} \right)_{\text{P}}}$$
Explanation:-
Answer: Option A. -> $${\left( {\frac{{\partial {\text{E}}}}{{\partial {\text{T}}}}} \right)_{\text{V}}}$$
Definition of $${C_V}$$ : when we add the heat to a system which is undergoing only expansion work or $$PdV$$ work at constant volume than the amount of heat required to raise the temperature by an infinitesimal amount is called as $${C_V}$$.
$${C_V} = \mathop {\lim }\limits_{\delta T \to \,0} \frac{{\partial Q}}{{\partial T}}$$
By first law of thermodynamics: $$\delta Q = dU + \delta W\left( {PdV} \right)$$     Since here $$dV=0$$
$$\delta Q = dU$$
So, $${C_V} = {\left( {\frac{{dU}}{{dT}}} \right)_V}.$$   Where $$U=$$  internal energy.
Question 4. A system in which there is exchange of energy but not of mass, is called a/an __________ system.
  1.    Isolated
  2.    Open
  3.    Insulated
  4.    Closed
Explanation:-
Answer: Option D. -> Closed
A system which exchanges the energy but not mass is called as closed system or control mass system where the identity of mass also should remain same.
Question 5. The temperature at which a real gas obeys the ideal gas laws over a wide range of pressure is called __________ temperature.
  1.    Boyle
  2.    Inversion
  3.    Critical
  4.    Reduced
Explanation:-
Answer: Option A. -> Boyle
The temperature at which a real gas obeys the ideal gas laws over a wide range of pressure is called as Boyle temperature.
Question 6. A gas shows deviation from ideal behaviour at
  1.    Low pressure and high temperature
  2.    Low pressure and low temperature
  3.    Low temperature and high pressure
  4.    High temperature and high pressure
Explanation:-
Answer: Option C. -> Low temperature and high pressure
A gas is close to ideal gas behavior at low pressure and high temperatures since at these conditions the gas satisfies the required conditions to be an ideal gas like the attractive forces between the molecules of gas becomes zero.
Question 7. Fugacity and pressure are numerically not equal for the gases
  1.    At low temperature and high pressure
  2.    At standard state
  3.    Both A and B
  4.    In ideal state
Explanation:-
Answer: Option C. -> Both A and B
The fugacity is also called as effective pressure in case of real gas ,and for ideal gas it numerically becomes equal to pressure so, for an gas to behave ideally we know the required conditions should be high temperature and low pressure and an standard state is usually selected where we know the value of fugacity so, it may or may not be equal to pressure.
Question 8. Entropy change of mixing two liquid substances depends upon the
  1.    Molar concentration
  2.    Quantity (i.e. number of moles)
  3.    Both A and B
  4.    Neither A nor B
Explanation:-
Answer: Option C. -> Both A and B
Since entropy change of mixing is $${\left( {\Delta s} \right)_{mix}} = - nR\sum {} {x_i}\ln {x_i}$$
So, it is dependent on both number of moles and composition as we can see physically also that more and more number of moles we add to the system the system behavior changes and the properties changes.
Question 9. __________ equation predicts the activity co-efficient from experimental data.
  1.    Lewis-Randall
  2.    Margules
  3.    Van Laar
  4.    Both B & C
Explanation:-
Answer: Option D. -> Both B & C
Both van-laar and margules equations are models to find out the activity co-efficient.
Question 10. Pick out the correct statement.
  1.    If an insoluble gas is passed through a volatile liquid placed in a perfectly insulated container, the temperature of the liquid will increase
  2.    A process is irreversible as long as Δ S for the system is greater than zero
  3.    The mechanical work done by a system is always equal to ∫P.dV
  4.    The heat of formation of a compound is defined as the heat of reaction leading to the formation of the compound from its reactants
Explanation:-
Answer: Option D. -> The heat of formation of a compound is defined as the heat of reaction leading to the formation of the compound from its reactants
The heat of formation is defined as amount of heat absorbed or evolved when I mol of a compound is formed from its elements in their standard states.
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