Recent content by ricof

Sorry, 'Oh' as in the figure of speech. So I use ideal gas law with the same P but different V each time to find the temperatures? What does degree of freedom mean? I haven't heard of that before.

Homework Statement A closed system comprising a cylinder and frictionless piston contains 1kg of a perfect gas of which molecular mass is 26. The piston is loaded so that the pressure is constant at 200kPa. Heat is supplied causing the gas to expand from 0.5m^3 to 1m^3. Calculate heat...

I used T2/T1 = (P2/P2)^(n-1/n) and n = Cp/Cv

Homework Statement 1m^3 of air is heated reversibly at constant pressure from 288K to 573K. Then it is cooled reversibly at constant volume back to the initial T. Initial P is 103kPa Calculate overall change in entropy. Cp=1.02 Cv=0.702 Homework Equations dS=Cp x ln(T2/T1)-R x...

Thanks, have now got the answer

The atomic weight of nitrogen is 7 but as it is diatomic, the molecular weight is 7x2 = 14. So 1.2kgs represents 1200/14= 85.7 moles = n?

In your previous post you mentioned the ideal gas law which is PV=nRT no? n is the number of moles so I think you use the mass of the nitrogen (1.2kg) in there somewhere?

Oh right ok so 120kPa x V = 1.2 x R x 300K As the gas is Nitrogen do I still use R=8.314?

anyone?

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. Please help me I've been staring at this one for hours!

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) =...

Ok, so as dE = 0, Q = -W and as PV = nRT, -W=PV ln (v1/v2) which is Q Thanks guys, my answer is correct. Thanks for helping!

Because T is constant, there is no change in internal energy right? And also, in the above equation for isothermal expansion, how is n calculated?

Homework Statement Calculate the entropy change when 0.011m3 of a perfect gas at a constant temperature of 273K is compressed from an initial pressure 1x10^5 N/m/m to a pressure of 1x10^6 N/m/m. I know the equation but cannot work out Q! Please help! Homework Equations dS=Q/T The...