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 28th Sep 2012, 17:56 #1 (permalink) Join Date: Jun 2010 Location: Belfast Age: 23 Posts: 98 Understanding The Gas Equation P=Pressure V=Volume T=Temperature p=Density Combining Boyle's and Charles laws, the gas equation becomes (where R is the gas constant): PV=RT Does this above mean; pressure times volume = the gas constant times temperature? What does the 'gas constant' part mean'? Density can also be a part of the equation. In ideal gas, as volume increases, density decreases. This is due to the mass of air being contained in a larger volume. So: p 1 - V What does the 1 mean are represent in this equation? Substituting this into the ideal gas equation: P - = RT p How come the density becomes the volume and why it is now a divided equation which was a times equation at the start? Re-arranging to make density the subject of the equation: p = P - RT So, maintaining a constant temperature: if pressure goes up, density goes up. Providing the pressure is constant, an increasing temperature results in decreasing density. Cheers
28th Sep 2012, 21:38   #2 (permalink)

Join Date: Feb 2001
Location: Planet Earth (sometimes)
Posts: 2,038
I think there might be some typos in the latter half of your post but you might want to have a look at this:

The Ideal Gas Equation

Quote:
 What does the 'gas constant' part mean'?
It doesn't really "mean" anything - FWIW the very simple answer is it's a number that you plug into an equation to make the sums/units work and if push comes to shove that really is all you need to know .... If you insist then in more detail it what's known as a "constant of proportionality", simply speaking a number that allows you to stop using the phrase/symbol "is proportional to" in the algebra and instead actually use an equals sign (and hence do arithmetic calculations).

One simple example of this is good old "pi" (3.14159............ etc).

We know that as a circle's diameter gets larger then so does it's circumference, or in other words

circumference c is proportional to diameter, d.

That doesn't allow us to do any numeric calculations.

However once we know that the constant of proportionality is 3.14159..., or pi, we can change the "is proportional to " to "pi" and rewrite the equation as

c= pi X d

and actually do some meaningful sums.

Last edited by wiggy; 28th Sep 2012 at 22:03.

 28th Sep 2012, 22:27 #3 (permalink) Join Date: Jun 2010 Location: Belfast Age: 23 Posts: 98 Thanks wiggly actually found a good vid on it too for anyone that comes stubbing upon this again Ideal Gas Equation: PV=nRT | Ideal gas laws | Khan Academy cheers

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