An ideal gas is a hypothetical gas whose molecules exhibit no interaction and undergo elastic collision with each other and with the walls of the container.
Standard Temperature & Pressure (STP)
A temperature of 273.15 K (or 0° C) at 1 atm (or 101.325 kPa) pressure is known as STP.
Real Gases
A real gas molecules possess mass, volume and attractive forces.
Difference Between Ideal and Real Gases
1. Volume: An ideal gas assumes that the volume of gas molecules is negligible compared to the volume of the container. This assumption is not true in case of real gases.
2. Pressure: An ideal gas assumes that there are no intermolecular forces between the molecules. This assumption is not true in case of real gases.
The difference between ideal gases and real gases can be viewed clearly at high pressure and low temperature.
The real gas which behaves closest to an ideal gas is Helium, followed by Hydrogen.
2. Pressure: An ideal gas assumes that there are no intermolecular forces between the molecules. This assumption is not true in case of real gases.
The difference between ideal gases and real gases can be viewed clearly at high pressure and low temperature.
The real gas which behaves closest to an ideal gas is Helium, followed by Hydrogen.
PV = nRT
| P | : Pressure |
| V | : Volume |
| n | : Number of moles of gas in a closed system |
| R | : Universal Gas Constant = 8.3145 J/mol·K OR 0.08205 L·atm/mol·K |
| T | : Temperature |
Volume of 1 mole of an Ideal Gas at STP
(1 mol) × (8.3145 L·kPa/mol·K) × (273.15 K) 101.325 kPa
= 22.4 LPV = nRT = constant (if n, T = constant)
Compressibility Factor (z)
z =
PV nRT
V T
=nR P
= constant (if n, P = constant)Hence,
V1 T1
=V2 T2
V n
=RT P
= constant (if T, P = constant)Hence,
V1 n1
=V2 n2
Real Gas (van der Waals) Equation
Ideal gas equation cannot be applied to real gases, the ideal gas equation needs some correction in it's pressure and volume.
(P +
n2a V2
) (V - nb) = nRTWhere, a and b are experimentally determined contants, known as van der Waals constants, which are different for different gases.
| a | : Determined from the inter-molecular attraction of a gas. |
| b | : Determined from the volume of one gas mole. |
| Gas | a ((L2·atm)/mol2) | b (L/mol) |
|---|---|---|
| He | 0.03410 | 0.0238 |
| Ne | 0.205 | 0.0167 |
| Ar | 1.337 | 0.032 |
| H2 | 0.2420 | 0.0265 |
| N2 | 1.352 | 0.0387 |
| O2 | 1.364 | 0.0319 |
| Cl2 | 6.260 | 0.0542 |
| NH3 | 4.170 | 0.0371 |
| CH4 | 2.273 | 0.0430 |
| CO2 | 3.610 | 0.0429 |
| H2O | 5.46 | 0.0305 |