Chemical Engineering - Chemical Engineering Thermodynamics - Discussion

Understand this problem is to see the P-V graph of Carnot cycle. Work done in any process will follow.

dW = p.dV.

It means if we plot a graph between pressure and volume of the gas then area covered under the curve followed by a process will show the work done.

Now, see the Carnot cycle and slopes of adiabatic and isothermal processes. There you can see that isothermal process will be covering more area than adiabatic process. And hence work done will be more in an isothermal process.

In the first law of thermodynamics:

1. v is inversely proportional to pressure.
2. Expansion means increasing volume which means a decrease in pressure.
3. Pressure decreasing indicates that there is no change in temperature.
4. Increasing volume means Max work (w=Pv).

Hope this will be cleared. Thank you.

Consider a system possessing a piston-cylinder arrangement. Now are asked that; which process requires maximum heat (Q) to raise the piston.

So it is clear that if the piston-cylinder arrangement is considered as isothermal; then I have to provide maximum heat (Q) to the system. So the answer is (A).

Here, 1 point. Expanding of gas means volume is not const. The pressure is given, so we have a relation P inversely proportional to V. Pressure decreases therefore in this case temp didn't came into the picture because it is considered as constant variable. So the process is ISOTHERMAL.

The graph under the PV diagram for closed system gives the work. In the expansion region the graph of isotherm is above the graph of adiabatic curve, as the slope of adiabatic curve (gamma) is greater than that of isotherm curve. So the area under the isotherm is larger.

Boyle's law proves the answer is (A) ISOTHERMAL. For pressure to increase significantly and bringing about maximum work then absolute temperature must be held constant.

Under this Isothermal process we have Maximum Work Reversible,

i.e Wr = P1V1*ln (P2/P1).

Adiabatic lines on a PV diagram are always steeper than isothermal lines. This means that if we change the pressure by a specific amount the change is volume is always going to be more for an isothermal process then an adiabatic process.

The PV graph of isothermal process cover max area as compare to adaibatic and isentropic process in expansion of gas that's why max work secured in isothermal process.

Hence option A is right.

Answer should be A.

As we know that, the here expansion process is occurring. And also it is a closed process. So from graph of P-V you can see the maximum area covered is by ISOTHERMAL LINE.

An isentropic process implies an adiabatic and reversible process. Reversible work will produce your highest yield of available work so the answer is C.