Help Termodynamic problem getting grade tommorow

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Homework Help Overview

The discussion revolves around a thermodynamic problem involving the isobaric expansion of hydrogen gas. The original poster seeks assistance in determining the work done (L), the heat absorbed (Q), and the change in internal energy (ΔU) given specific parameters such as mass, initial temperature, and the factor by which the volume increases.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning, Assumption checking

Approaches and Questions Raised

  • Participants discuss the meaning of work (L) and its relation to mechanical force, with some suggesting that L is equivalent to work done. There are attempts to relate pressure, volume, and temperature using the ideal gas law. Questions arise about how to find pressure and the initial volume, as well as the implications of the isobaric process on the calculations.

Discussion Status

The discussion is active, with participants exploring various equations and relationships between pressure, volume, and temperature. Some guidance has been offered regarding the equations for work and the ideal gas law, but there is still uncertainty about specific values needed for calculations and how to proceed with the problem.

Contextual Notes

Participants note the absence of a numerical value for the initial volume, which is crucial for solving the problem. There is also mention of the parameters provided, including mass and initial temperature, but clarity on how these relate to the calculations remains a point of discussion.

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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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What is the meaning of L?
 
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
 
Fxd is called WORK.

Work is defined as the ...
 
yes i found on wiki english its Work :) but we note it whit L
so how i do the problem?
 
W= p x V??
can you tell me what to do?
 
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
 
hence your equation for W is correct since the pressure is constant.
 
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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