Question

HELP!!! please :)
Steam at 400 ⁰C and 4 MPa expands in a heavily-insulated cylinder to 158.85 ⁰C and 600
kPa through an unknown quasi-equilibrium process. Calculate the work in kJ if the water initial
volume was 8000 cm3.

Answer 1

oh i know a looooong way of working it out

Answer 2

are you familiar with these formulas?
PV= nRT
q= mc Delta T

Answer 3

I am familiar with these formulas!
I thought I may not have enough information to answer this question because, I do not know the state of state 2! All i know is that it is saturated. I don't know how to tell if it's a saturated, mixture, liquid or vapour with the information given!

Answer 4

well its not a problem

Answer 5

look you have initial volume, pressure and temperature
so u can find mole
after that use that mole to find final volume, since u r given final temperature and final pressure

Answer 6

can u do that?

Answer 7

i'll go to next step once you do this one

Answer 8

r u there??

Answer 9

anyway i need to leave so i'll just tell what to do
PV=nRT
Steam at 400 ⁰C and 4 MPa and 8000 cm3 given
change ⁰C to Kelvin (by adding 273 to ⁰C)
MPa to Pa (by multiplying MPa by 10^6)
cm3 to dm3 (by dividing cm3 by 1000)

then put the values and get the mole

now u have mole and 158.85 ⁰C and 600kPa
again change ⁰C to Kelvin
kPa to Pa (by multiplying kPa by 10^3)
so find Volume this time


next you have 2 volumes =>convert both to cm3
here volume can be taken as mass in g

so subtract initial volume from final
then subtract initial temperature in ⁰C from final

that means you have change in mass and change in temperature
so use q=mcDeltaT
q= change in mass * specific heat capacity * change in temperature
specific heat capacity is 4.18

Answer 10

i took change i volume because some of it is lost and its due to that work done
so by taking change in volume we find work done to cause this change
this is what the question is asking for

Answer 11

hope that helps :)

Answer 12

wait wait sorry the volume in PV= nRT should be changed to m3 not dm3
so divide by 1000000
im talking about first part

Answer 13

then when you get the answer for the second volume, unit will be m3 so multiply it by 1000000 so that it becomes cm3

Answer 14

thank you very much that helps!

Answer 15

you are welcome :D

Answer 16

I just had a question even thought I am using steam i can use the ideal gas equations? My professor told me to treat steam as water and that I can't use those equations.

Answer 17

dk to be honest
btw i just remembered that shortcut way
its using this formula
P1V1/ T1 = P2V2/ T2
this way u won't even need to find moles and straight get final volume

Answer 18

hmmm i didn't know this but apparently yeah we can't use gas laws

Answer 19

i think i found something
http://www.expertsmind.com/questions/specific-volume-of-the-superheated-steam-thermodynamics-30118036.aspx

Answer 20

http://en.wikipedia.org/wiki/Superheated_steam

Answer 21

in this question Steam is superheated because temperature is more than water's boiling point
i think your professor was talking about saturated steam

Answer 22

well do ask him, since i just finished my AS level, im not uni student or anything so im not really sure about this