Thermodynamics MCQs

171. It is desired to bring about a certain change in the state of a system by performing work on the system under adiabatic conditions.

by
A. The amount of work needed is path dependent
B. Work alone can not bring out such a change of state
C. The amount of work needed is independent of path
D. More information is needed to conclude anything about the path dependence or otherwise of the work needed
✅ The correct answer is option A.

172. At 60° C, vapour pressure of methanol and water are 84.562 kPa and 19.953 kPa respectively. An aqueous solution of methanol at 60° C exerts a pressure of 39.223 kPa; the liquid phase and vapour phase mole fractions of methanol are 0.1686 and 0.5714 respectively. Activity co-efficient of methanol is

by
A. 1.572
B. 1.9398
C. 3.389
D. 4.238
✅ The correct answer is option A.

175. The reaction A (l) R(g) is allowed to reach equilibrium conditions in an autoclave. At equilibrium, there are two phases, one a pure liquid phase of A and the other a vapor phase of A, R and S. Initially A alone is present. The number of degrees of freedom are

by
A. 1
B. 2
C. 3
D. 0
✅ The correct answer is option B.

177. On a P-V diagram of an ideal gas, suppose a reversible adiabatic line intersects a reversible isothermal line at point A. Then at a point A, the slope of the reversible adiabatic line (∂P/∂V)S and the slope of the reversible isothermal line (∂P/∂V)T are related as (where, y = Cp/Cv) )

by
A. (∂P/∂V)S = (∂P/∂V)T
B. (∂P/∂V)S = [(∂P/∂V)T]Y
C. (∂P/∂V)S = y(∂P/∂V)T
D. (∂P/∂V)S = 1/y(∂P/∂V)T
✅ The correct answer is option C.