In corrected ideal gas equation?

Question

we take acual volumes occupied by the molecules but actual pressure exerted by the gas is less, then why dowe add some constant to make it ideal pressure, when this corrected equation is meant for real gases.

Answer 1

You are quite correct in saying that real gasses exert less pressure on their containers than ideal gases would (As long as they are not so compressed that the gas particles begin to be smashed together in which case real gasses exert more pressure than ideal gasses). I believe the problem you are having is a simple misinterpretation of the equation (I assume you are referring to the van der Waals equation).

The van der Waals equation is usually written as follows:

(P + an^2/V^2)(V - nb) = nRT

The ideal gas equation is usually written as:

PV = nRT

If we rearrange both of these equations to solve for pressure we obtain the following:

--from van der Waals:

Preal = nRT/(V - nb) - an^2/V^2

--from the ideal gas law:

Pideal = nRT/V

When the gas is not being extremely compressed the volume of the actual gas particles are negligible when compared to the volume of the container so that (V - nb) is practically the same as V. Therefore, substituting V in place of (V - nb) in the van der Waals expression for the pressure gives us:

Preal = nRT/V - an^2/V^2

But the first term on the right hand side of this equation is just the pressure from the ideal gas law. Therefore we may again rewrite the van der Waals expression for the pressure as:

Preal = Pideal - an^2/V^2

So we see in actuality (since a is always a positive number), that to find the pressure exerted by a real gas we subtract something from the ideal pressure rather than adding to it. Just as you said we should be doing!

Answer 2

Actually the ideal gas equation is PV = nRT.
This equation was derived from the assumption (postulates) that the volume of a gas molecule is negligible when compared to the total volume. But volume of a molecule have to be considered. ie what as volume was a little bit higher. so in corrected ideal gas equation we have to deduct the extra bit (volume of a molecule) of the volume.
In case of pressure we considered that the collision b/w the molecules was perfectly elastic (no energy transfer). In reality molecules experience a force of attraction b/w them. hence they do not collid as fast as that we assumed earlier. ie molecules collid with the walls of the container with a lesser force(low pressure). So we have to add a quantity to make ideal pressure

Answer 3

Ideal gas has no correction, since it is ideal there is no need to apply correction. The equation is good at NTP.

The equation is Pi*Vi/Ti = Pf*Vf/Tf

On left side "i" is the suffix to denote initial condition of gas.
On Right side "f" is the suffix to denote final condition of gas.
P is the pressure.
V is the volume.
T is the absolute temperature.

PS:

1. In most books 1 is used for i, and 2 is use for f.
2. Ideal gas has no impurities ie no partial pressures.

Answer 4

in wander waal's equation:
[P + n^2a/V^2 ] [V-nb]=nRT
a and b are wander vaals constant

an^2/V^2 is the internal pressure correction and is a measure of the force of attarction between the gas molecles.Gases that liquify easily have a larger value of 'a'

nb is called the Volume correction due to the finate size of the molecules.b is called covolume or excluded volume due to bonding at an atomic level..

'a' and 'b' are constants thta vary from gas to gas