energy - gas pressure

[Rocket Man]

how would i go about determining the energy stored in a volume of gas under pressure?

[swansont]

http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/thepot.html#c1

[Rocket Man]

i cant see an equation in there that describes energy pressure and volume, that site mostly deals with heat

[swansont]

i cant see an equation in there that describes energy pressure and volume, that site mostly deals with heat

 

 

Heat is a form of energy (transfer) and temperature is one way that the enegy of compression or expansion will manifest itself. There are a number of places energy can be stored. You have to specify the conditions, e.g. isothermal, adiabatic and go from there.

 

The basic idea is that PV is an energy term. The rest tells you, though, that doubling the pressure may require more than twice the energy to get there. And if you want to do work with the PV term, you will be able to use differing amounts of it, depending on how the expansion takes place.

 

(Also, in Bernoulli's equation you get [math]P + \rho gh + \frac1 2 \rho v^2[/math], which has a volume term divided out, so there's a PV term there, too. But that equation assumes certain things, like incompressible fluids and (IIRC) isothermal conditions)

[Rocket Man]

right, i forgot that the temperature drops during expansion.

i was thinking about the mechanical work that could be done by a volume of gas under pressure, so assuming the pressure is relative to STP, and and the temperature is initialy at 0 celcius (to match ambient conditions)