How Much Energy is Needed to Heat Air in a Movable Piston Cylinder to 755 K?

So, in summary, to find the energy input required to raise the temperature of the air in the vertical cylinder with a heavy piston from 315 K to 755 K, you need to use the equation Q = n * Cp * ΔT and also factor in the work done.
  • #1
lackos
38
0

Homework Statement



A vertical cylinder with a heavy piston contains air at 315 K. The initial pressure is 2.85 105 Pa, and the initial volume is 0.250 m3. Take the molar mass of air as 28.9 g/mol and assume CV = 5/2R.

(d) Assume again the conditions of the initial state and assume the heavy piston is free to move. Find the energy input required to raise the temperature to 755 K.
4 kJ


Homework Equations


Q=nCp(delta)T;
and possibly;
(delta)E=Q+W


The Attempt at a Solution


im confused as to whether all i need to use is the first equation or if in need to factor in the work done.
i already have to number of moles and Cp=7/2R
Thanks!
 
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  • #2
I would say that you also need to calculate the work done. Because the piston is "free to move". If the piston has moved, there has been a change in the volume. If there is a change in the volume, there is work done.
 

FAQ: How Much Energy is Needed to Heat Air in a Movable Piston Cylinder to 755 K?

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