Solve Air Heated @Constant Vol: Find 1Q2

[akhmed966]

Homework Statement

Air is heated from 300 to 350K at constant volume, Find ₁Q₂.

Homework Equations

₁Q₂ = m(u₂-u₁)+₁W₂
u₂-u₁ = cv(t2-t1)

The Attempt at a Solution

The PV diagram of the process is straight up, so the area under the curve is 0, so the work done is zero.
Cv is .717 from the back of the book

1Q2 = m*.717(350-300)+0

How do I find the mass? I don't think I'm doing it right.

 

[darkdream]

Its a isochoric process.

you are right about no work done.
using Q = n Cv delta T,

what is left is finding how much moles of air is heat.
if not given, just treat it as a variable. more information required. the mass of gas will tell you how many moles there are.

 

[akhmed966]

That's what I left it as,

1Q2 = 50*.717*m

Would that be right?

 

[darkdream]

moles = mass / (molecular weight x avogadro's constant)
avogadro constant = 6.02 x 10^23

molecular weight is something that you can find on the data booklet.

you can't leave the mass just like tt.
the m you wrote is moles not mass.

may i ask you wad you actually mean by 1Q2. delta heat energy input or delta internal energy.
delta means change in.

 

[akhmed966]

moles = mass / (molecular weight x avogadro's constant)
avogadro constant = 6.02 x 10^23

molecular weight is something that you can find on the data booklet.

you can't leave the mass just like tt.
the m you wrote is moles not mass.

may i ask you wad you actually mean by 1Q2. delta heat energy input or delta internal energy.
delta means change in.

Final heat, and in our thermodynamics class, we don't use moles (n), we use m for mass.