Chemical Engineering Thermodynamics MCQ Questions & Answers | Chemical Engineering

Sublimation means the conversion of solid phase directly in to vapor phase (without involvement of phase liquid). Actually for every substance this direct phase conversion occurs when the substance is below its triple point pressure and corresponding temperature.
Actually one of the point where the dry ice sublimates is 1 atm pressure and corresponding temperature is $$ - {78^ \circ }C.$$

The given equation is a thermodynamic equation of state which is true for every substance since it is relating point variables.

Henrys law is closely obeyed by a gas when its solubility is very low in an solution.

For an ideal solution both the volume of mixing and enthalpy of mixing is zero since an ideal solution behaves like a pure solvent.

Given $$\Delta H = - 22.4\,kcal$$     so it represents an exothermic reaction as heat is released out during the process.

As, we know the relation $$\Delta G = \Delta {G^ \circ } + RTlnQ$$      where $$Q =$$  reaction quotient, higher the value of gibbs free energy change $$ \Rightarrow $$ higher is the value of $$Q \Rightarrow $$ faster is the rate of the reaction.

For a given refrigeration effect, the system with the minimum value of Coefficient of Performance (COP) is the least efficient in terms of energy usage.

Option A: Reverse Carnot cycle. The Carnot cycle represents the maximum possible efficiency for a given temperature difference. Therefore, the reverse Carnot cycle would have the highest COP among the options.

Option B: Ordinary vapour-compression cycle. While not as efficient as the Carnot cycle, the vapour-compression cycle is commonly used in refrigeration systems and typically has a higher COP compared to other cycles.

Option C: Vapour-compression process with a reversible expansion engine. This would have a higher COP than the air refrigeration cycle because it involves a vapor-compression process.

Option D: Air refrigeration cycle. Air refrigeration cycles typically have the lowest COP among the options due to the lower efficiency of air as a refrigerant compared to vapor-compression cycles.

Therefore, the correct answer is Option D: Air refrigeration cycle.

Here work means expansion work since the expansion work ($$W$$) and we know expansion work $$W = \int {} {P_{ext}}dV$$   and since for isochoric process there will be no volume change i..e.., volume remains constant and hence $$dV = 0.$$
So, work done $$= 0$$

Since, the area under $$P-V$$   plot for isothermal is less than the area under $$p-v$$   plot for adiabatic process during compression. We can say adiabatic work done is more than isothermal work done.