# Homework Help: Need help understanding this question

1. May 13, 2012

### naim

1. The problem statement, all variables and given/known data
Dry steam is compressed isothermally from a pressure of 1 bar to 4 bar. if the initial volume is 0.5 m^3, calculate the volume of the steam after compression

2. Relevant equations

Dont know

3. The attempt at a solution

2. May 13, 2012

### tiny-tim

it means with the temperature staying constant

(from the greek "iso-", meaning "same")

3. May 13, 2012

### naim

so how do i calculate it , does anyone know the equation of how to do it?

4. May 13, 2012

### pm35

Since this is dry (completely vapor state) you could model with the ideal gas law

PV=nRT

since it is isothermal T is does not change, therefore: n,R, and T are all constant and the right side of the equation is the same before and after compression, so
P1V1=P2V2

V2 = (P1V1)/P2 , plug and chug

5. May 13, 2012

### naim

do i convert the 1 bar ? or do i just keep it as
v2=(1x0.5)/4 ?

6. May 13, 2012

### Astronuc

Staff Emeritus
Is there anymore information, e.g., the temperature, or the amount of superheat? Using the ideal gas law, or Boyle's law would be appropriate for an approximation. If the temperature is at a saturation level between 1 bar and 4 bar, then at the intermediate pressure, there would be some condensation (vapor to liquid transformation).

7. May 13, 2012

### naim

no that was all the information that was given