IDEAL GAS LAW & Avogadro’s Law

What is the IDEAL GAS LAW?What are the variables involved?

What is Avogadro’s Law and didn’t I already learn about him with the

mole?

Avogadro’s Law

Avogadro’s Law - used to compare number of particles of gases

States that at constant temperature and pressure, the volume is directly proportional to the number of moles of gas

Volume and amount of gas (# of moles, n) are directly proportional

V α n

Amedeo Avogadro

Avogadro’s Law

- Containers of equal volume have equal numbers of molecules, regardless of the Gas Type.

THE BIG FINALE!IDEAL GAS LAW

We will now combine all of the laws that we have learned thus far …. Boyle’s, Charle’s, Gay-Lussac’s, with Avogadro’s….

Use a Gas Constant (R) AND RESULT WITH ONE FINAL EQUATION THAT RELATES

T, P, V, n,

What is R ?

- R is called the Ideal Gas Constant or Universal Gas Constant

- Instead of learning a variety of values of R for all the possible unit combinations, we memorize one value and convert the units

R = 0.0821 L * atm Mol * K

- Derived from the fact that one mole of gas at STP occupies 22.4 L

Using PV=nRT

P = Pressure (atm)V= Volume (L)T = Temperature (K)n = number of molesR = gas constant 0.0821 L * atm

Mol * K

** ALL DATA MUST BE IN PROPER UNITS **

- Always check your units as you set up your equation!

Practice Problem PV=nRT

EX. How many moles of N2 are in a 750 mL vessel at 26 degrees Celsius and 625 mm Hg?

Step 1 : Convert knowns to correct units so we can use R. P = 625 mm Hg x 1 atm = 0.822 atm

760 mm HgV = 750 mL x 1 L = 0.750 L

1,000 mLT = 273 + 26 = 299 K

R= 0.0821 L * atm n = ? Mol * K

EX. How many moles of N2 are in a 750 mL vessel at 26 degrees Celsius and 625 mm Hg?

Step 2: Plug in values and solve for unknown.

PV = nRT --> rearrange values to solve for n PV = n RT

0.822 atm (0.750 L) = n 0.0821 L * atm (299 K)

Mol * K

0.025 mol = n

Deviations from IDEAL Gas Law

Remember- Real gases deviate from ideal behavior at:• LOW Temp and HIGH Pressure• REAL gas molecules have volume• REAL gas molecules have intermolecular forces

More Practice

Dinitrogen monoxide (N2O), laughing gas, is used by dentists. If 2.86 mol of gas occupies a 20.0 L tank at 23 degrees Celsius, what is the pressure ( mm Hg) in the tank at the dentists office?

How would we tackle this problem?

Don’t forget your concept map!

Homework: Finish handout on Ideal Gas Law. Be prepared to ask questions on Monday!