Help Termodynamic problem getting grade tommorow

  • Thread starter Termodinamica
  • Start date
In summary: We know that the temperature at T3 is 300K.So the temperature of the gas at T3 is 300*(4*99+17)/(4*300) = 1440K.
  • #1

Homework Statement


The volume of a m (mass) hydrogen quantity,which wear initially at the temperature t1, increases k times by isobar dilatation.Find: a) L= ? b) the heath Q absorbed. c)Δ U =?

Homework Equations


How to solve it?




The Attempt at a Solution



pv/t=p2v2/t2 ?
L= p * Δ V ?
I don't know... and I am getting grade tomorrow on it...
 
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  • #2
What is the meaning of L?
 
  • #3
L- mecanic force
idk how the say it in english

its the mecanic stuff that in Mecanic phisics is L=f*d and the values are in joules
 
  • #4
Fxd is called WORK.

Work is defined as the ...
 
  • #5
yes i found on wiki english its Work :) but we note it whit L
so how i do the problem?
 
  • #6
W= p x V??
can you tell me what to do?
 
  • #7
W = force x distance moved

But Pressure P = Force / Area

therefore F = P x A

Hence W = F x d

= P x A x d

= P x change in Volume
 
  • #8
hence your equation for W is correct since the pressure is constant.
 
  • #9
what A means
and =P x delta Volume is the equation to fiend W right?
also how do i fiend the pressure? whit p1/t1=p2/t2?
 
  • #10
A means Area.

Use pV = nRT which becomes p1V1/T1 = p2V2/T2 since we assume the number of moles in gas, n, is constant.

But since the process is isobaric the pressure is constant so that the last equation becomes

V1/T1= V2/T2.
 
  • #11
you said earlier that W= P x change in Volume Right?
so what i do whit v1/t1=v2/t2? as i see nothing that can help in the above
 
  • #12
W = P x change in volume
= P x kV1

Other equation can be used to find final temperature required to find the heat given.
 
  • #13
grzz said:
W = P x change in volume
= P x kV1

Other equation can be used to find final temperature required to find the heat given.

and how do i find the p?
 
  • #14
What physical constants are given numerical values in this problem?
 
  • #15
m= 2g
t1=27 celsius=300 Kelvin
k=3
 
  • #16
Is initial volume given a numerical value?
 
  • #17
It say :The volume of a quantity of Hydrogen of mass m , found initial at the temperature t1, rises of K times in izobare dilatation.Fiend the W ,Q absorbed and the Delta u (Intern energy)
m=2g t1=27 Celsius and k=2

For b i think is W=Delta U + Q i think
 
  • #18
Since k is positive there is an expansion, so work is done BY the system and so heat must enter the system.

Hence

change in U = heat in - work by system.
 
  • #19
grzz said:
Since k is positive there is an expansion, so work is done BY the system and so heat must enter the system.

Hence

change in U = heat in - work by system.

yes bur for W what i do? how i fiend the pressure?
 
  • #20
I think that some other physical quantity must be given a numerical value.
 
  • #21
we got to exprime V2=V1 x K i think as it say that the second volume is rising by K times
 
  • #22
PV = nRT

So p = nRT/V
= 1 x R x 300/V

So we have to know R and V to find P.
 
  • #23
grzz said:
PV = nRT

So p = nRT/V
= 1 x R x 300/V

So we have to know R and V to find P.

R has the value 8.314 J·K−1·mol−1.
 
  • #24
And numerical value for initial volume V?
 
  • #25
grzz said:
And numerical value for initial volume V?

i don't know, doesn't mention but here are the answers W= 4,99 kJ Q = 17 Kj Δ U= 12,47Kj
 
  • #26
but in izobaric process the Pressure is constant so we don't use it in equations :)
this helps?
 
  • #27
To find W one NEEDS pressure.
 
  • #28
Try this problem:In a box closed by a piston is a quantity of ideal gas characterized whit the parameters p1,V1,T1.The gass is put to this processes:
1. izocore heating up to p1= 1,5p1
2.izobar uncompression up to V3= 2 V1
3. izocore cooling up to p4=p1
4. izobare comprimation up to initial state.
a) Represent graphic in the coordinates (p1,V)(p,T) and (V,T) the processes suffered.
b)Calculate the temperature of the gass in the state 3,T3, knowing that T1=300K
c)Calculate the randament of a Carnot cicle who would function bettwhen the extreme temperatures touched in this succesion of termodynamic processes
 
  • #29
re 2nd problem:

We are going to use PV = nRT with n and R being constant.

So PV/T is constant.

So P1V1/T1 = P3V3/T3.
 

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