13-4: The Ideal 13-4: The Ideal Gas LawGas Law

What If I Told You That You What If I Told You That You Could Combine All Four Gas Could Combine All Four Gas

Laws Into One?Laws Into One?• By combining all of the laws into one

equation we can arrive atP = R nT/V

Again, P = Pressure, T=Temperature (Kelvins), n=number of moles, V=volume.

This can also be stated as:PV = nRT

The Ideal Gas EquationThe Ideal Gas Equation• PV=nRT is the ideal gas equation. It

describes the physical behavior of a of an ideal gas relating to pressure, volume, temperature and number of moles.

Types of GasesTypes of Gases• An ideal gas, is a gas that follows the

postulates of the kinetic-molecular theory.• A real gas: all gases are real gases,

behave like ideal gases under all conditions EXCEPT

1) low temperature (as molecules slow down, attractive forces

between them increase)

2) high pressure (molecules do take up space)

But what was the “R” in the But what was the “R” in the equation?equation?

• The constant R in the ideal gas equation is known as the gas constant.

• R = 0.0821 L·atm/mol·K• R has other values for other units…you

can find this in a chart in your book.

Why is it important?Why is it important?• But why does it matter that the Ideal

Gas Law and Kinetic-Molecular Theory are in agreement?

• Due to the fact that the Ideal Gas Law was obtained through experimentation, it needs to hold true when tested with a theory…

which it does.

Is The Ideal Gas Law Is The Ideal Gas Law ALWAYS Right?ALWAYS Right?

• The Ideal Gas Law doesn’t always hold up though.

• The first being when gases are at VERY high pressure.

• It fails because the ideal gas law assumes the actual volume of gas particles to be zero, when in reality they have now become a large portion of the total gas.

Second Failure Second Failure • The second situation in which the Ideal

Gas Law fails is when gases are at low temperatures. When temp. decreases the gas particles slow down, the attractive forces between gas particles become very significant.

• But the Ideal Gas Law assumes those attractive forces to be non existent!

All Things Considered…All Things Considered…• In the end, The Kinetic-Molecular

Theory makes two assumptions that don’t apply to real life situations.