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when do we use W=p dV and W= nRT ln Vi/Vf? i want to know because i got 2 different answer when i use them in the same question
curiosity colour said:when do we use W=p dV and W= nRT ln Vi/Vf? i want to know because i got 2 different answer when i use them in the same question
hmm, my question does involve isothermal process, it ask me to find the work done on gas.lychette said:What was the question you had to solve? Your second equation is a special case of the application of your first equation! It relates to isothermal change in P and V
curiosity colour said:hmm, my question does involve isothermal process, it ask me to find the work done on gas.
so for isothermal process we have to use the second equation? but why?
... then you should not be getting different answers unless there is not just an isothermal process.curiosity colour said:hmm, my question does involve isothermal process,
i'm sorry for the late reply, was busying on my assignment. thanks for your answer, it have sort thing out for me :)lychette said:For an isothermal change PxV =constant x T P x V = nRT and the graph of P against V is the Boyles law graph and P = nRT/V
The work involved going from V1 to V2 is given by ∫P dV
so for isothermal change W = ∫nRT/V dV
W= nRT∫dV/V
W= nRT ln(V1/V2)
If in doubt about the mathemeatics you can always draw the curve of P against V and calculate the area between V1 and V2 by 'counting squares' ! (another way to integrate)
i'm sorry for the late reply, was busying on my assignment. i will check on it, thanks for answering me :DSimon Bridge said:... then you should not be getting different answers unless there is not just an isothermal process.
Perhaps you have misapplied the first equation.
The equation for work done on gas is W = PΔV, where W represents work, P represents pressure, and ΔV represents the change in volume.
The equation for work done on gas is derived from the first law of thermodynamics, which states that the change in internal energy of a system is equal to the heat added to the system minus the work done by the system. In the case of a gas, work is done when the gas expands or contracts, causing a change in volume.
No, the equation for work done on gas is specifically for gases. Liquids have a different equation for work, which takes into account their incompressibility.
No, the sign of work done on gas depends on the direction of the gas expansion or compression. If the gas expands (ΔV is positive), then work is done on the gas and the value will be positive. If the gas is compressed (ΔV is negative), then work is done by the gas and the value will be negative.
The units for work done on gas are joules (J) in the SI system. However, other units such as calories (cal) or ergs (erg) may also be used, depending on the context. It is important to make sure that all units are consistent when using the equation for work done on gas.