Help Termodynamic problem getting grade tommorow

  • #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 dont know... and im getting grade tomorrow on it...
 

Answers and Replies

  • #2
998
15
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
998
15
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
998
15
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
998
15
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
998
15
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
998
15
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
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
998
15
What physical constants are given numerical values in this problem?
 
  • #15
m= 2g
t1=27 celsius=300 Kelvin
k=3
 
  • #16
998
15
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
998
15
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
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
998
15
I think that some other physical quantity must be given a numerical value.
 
  • #21
we gotta exprime V2=V1 x K i think as it say that the second volume is rising by K times
 
  • #22
998
15
PV = nRT

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

So we have to know R and V to find P.
 
  • #23
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
998
15
And numerical value for initial volume V?
 
  • #25
And numerical value for initial volume V?

i dont know, doesnt 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
998
15
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
998
15
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.
 

Related Threads on Help Termodynamic problem getting grade tommorow

  • Last Post
Replies
5
Views
2K
  • Last Post
Replies
12
Views
2K
  • Last Post
Replies
2
Views
6K
Replies
10
Views
2K
Replies
4
Views
2K
  • Last Post
Replies
1
Views
2K
Replies
2
Views
1K
  • Last Post
Replies
3
Views
6K
Replies
11
Views
2K
Replies
4
Views
2K
Top