ricof said:Homework Statement
A piston cylinder device contains 1.2kg of nitrogen at 120kPa and 300K. Gas is compressed slowly in a polytropic process during which PV^1.3 = constant. The proces ends when the volume is reduced by one half. What is the entropy change?
Homework Equations
(P2/P1) = (V1/V2)^n
The Attempt at a Solution
Assuming V1 = 1 and therefore V2 = 0.5, I have worked out P2 as 295.5kPa but I am stuck on what to do next.
ricof said:I should add that I have absolutely no idea where or how the 1.2kg of nitrogen comes into the equation, nor if V1 is in fact 1.
This looks wrong. Where does this equation come from, and what does the 1.2 represent here? Include units with all quantities, and ask yourself if the units are what the should be.ricof said:Oh right ok so
120kPa x V = 1.2 x R x 300K
No, use R = 8.314 Pa*m^3 / (mole*K). "8.314" is not the same thing.As the gas is Nitrogen do I still use R=8.314?
Entropy is a measure of the disorder or randomness in a system. It is a thermodynamic quantity that describes the distribution of energy within a system.
In a polytropic process, the entropy of a system remains constant as the system undergoes a specific type of expansion or compression. This means that the disorder or randomness within the system remains unchanged.
The change in entropy in a polytropic process is affected by the heat transfer into or out of the system, the work done on or by the system, and the specific heat ratio of the gas involved.
The equation for calculating change in entropy in a polytropic process is ΔS = Cpln(T2/T1) - Rln(P2/P1), where Cp is the specific heat at constant pressure, T1 and T2 are the initial and final temperatures, P1 and P2 are the initial and final pressures, and R is the universal gas constant.
A change in entropy can affect the efficiency of a polytropic process by influencing the amount of work that can be extracted from the system. Generally, a higher change in entropy results in a decrease in efficiency due to the decrease in available work. However, this relationship can vary depending on the specific conditions and processes involved.