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
993
13
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
993
13
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
993
13
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
993
13
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
993
13
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
993
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.
 
  • #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
993
13
What physical constants are given numerical values in this problem?
 
  • #15
m= 2g
t1=27 celsius=300 Kelvin
k=3
 
  • #16
993
13
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
993
13
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
993
13
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
993
13
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
993
13
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
 

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