Not so long ago, in a chemistry lab far far away…May the FORCE/area be with you

Gas Laws: Avogadro’s and Ideal

At the conclusion of our time together, you should be able

to:1. Describe Avogadro’s Law with a formula.2. Use Avogadro’s Law to determine either

moles or volume3. Describe the Ideal Gas Law with a formula.4. Use the Ideal Gas Law to determine either

moles, pressure, temperature or volume5. Explain the Kinetic Molecular Theory

Kid’s Letters to

God:

Avogadro’s LawEqual volumes of gases at the same T

and P have the same number of molecules.

V = anV and n are directly related.

twice as many molecules

Avogadro’s Law Summary

For a gas at constant temperature and pressure, the volume is directly proportional to the number of moles of gas (at low pressures).

V = an a = proportionality constant V = volume of the gas n = number of moles of gas

Standard Molar Volume

Equal volumes of all gases at the same temperature and pressure contain the same number of molecules.

- Amedeo Avogadro

Avogadro’s Law Practice, Page 31:1

V1

n1

V2

n2

4.00 L

0.21 mol

7.12 L

n2

0.37 mol total0.16 mol added

Hittite Innovations:

IDEAL GAS LAW

Brings together gas properties.

Can be derived from experiment and theory.

BE SURE YOU KNOW THIS EQUATION!

P V = n R T

Ideal Gas Law

PV = nRT P = pressure in atm V = volume in liters n = moles R = proportionality constant

= 0.08206 L atm/ mol·K T = temperature in Kelvins

Holds closely at P < 1 atm

No Comment Needed…

Review of Kinetic Molecular

TheoryParticles of matter are ALWAYS in

motion Volume of individual particles is

zero. Collisions of particles with container

walls cause pressure exerted by gas.

Particles exert no forces on each other.

Average kinetic energy µ Kelvin temperature of a gas.

Deviations from Ideal Gas Law Real molecules have volume.The ideal gas consumes the

entire amount of available volume. It does not account for the volume of the molecules themselves.

There are intermolecular forces.

An ideal gas assumes there are no attractions between molecules. Attractions slow down the molecules and reduce the amount of collisions.› Otherwise a gas could not

condense to become a liquid.

R is a constant, called the Ideal Gas Constant

Instead of learning a different value for R for all the possible unit combinations, we can just memorize one value and convert the units to match R.

R = 0.08206

L • atm mol • K

Using PV = nRT

How much N2 is required to fill a small room with a volume of 960 cubic feet (27,000 L) to 745 mm Hg at 25 oC?

Solution1. Get all data into proper units V = 27,000 L T = 25 oC + 273 = 298 K P = 745 mm Hg (1 atm/760 mm Hg)

= 0.98 atmAnd we always know R, 0.08206 L atm / mol K

RT RT

Using PV = nRTHow much N2 is required to fill a small

room with a volume of 960 cubic feet (27,000 L) to P = 745 mm Hg at

25 oC? Solution2. Now plug in those values and solve for

the unknown. PV = nRT

n = (0.98 atm)(2.7 x 10 4 L)(0.0821 L • atm/K • mol)(298 K)

n = 1.1 x 103 mol (or about 30 kg of gas)

Is It REALLY Worth Fighting Over???

University of WashingtonChemistry

Midterm Exam QuestionIs Hell exothermic or endothermic? Support your

answer using the Ideal Gas Law.

PV=nRT(P)ressure x (V)olume = number of particles of the

gas (n) x the gas constant (R) x the (T)emperature of the gas

One enterprising student wrote the following:

First we need to know how the number of particles (souls) are changing over time. Are the number of souls increasing or decreasing? What is the rate of souls entering Hell as compared to souls leaving Hell?

Most religions teach that once in Hell, always in Hell, so lets assume that no soul is leaving Hell.

Most religions also teach that if you do not abide by their religious teachings, you will go to Hell. So let’s assume that most souls are going to Hell.

Given the current birth and death rates, we can assume that the number of particles (souls) in Hell is increasing exponentially.

According to the Ideal Gas Law, if n, the number of particles (souls) is increasing exponentially, for the temperature and pressure to stay the same, the volume must increase.

There are therefore two possibilities:

1. If the volume of Hell is not expanding or expanding slower than the increase in particles (souls), then the temperature and pressure in Hell will increase until all Hell breaks loose. (Exothermic)

2. If the volume of Hell is expanding faster than the increase of particles (souls), then the temperature and pressure will drop until Hell freezes over. (Endothermic)

If we accept the postulate given to me by Ms. Krissy Jones during my freshman year that “it will be a cold day in Hell before I sleep with you,” and taking into account that I still have not succeeded in having sexual relations with her, than the second (2) possibility cannot be true.

Therefore, I am sure that Hell is exothermic!

University of WashingtonChemistry

Midterm Exam QuestionIs Hell exothermic or endothermic? Support your

answer using the Ideal Gas Law.

PV=nRT

The kid got an “A”!!!!!!!!!!!!!!!!!

Ideal Gas Law Problems, Page 32:1

Using PV = nRT

(5.6 atm) (12 L) (0.08206 atm*L/mol*K) (T)

2.0 x 102 K

(4.0 mol)

Gas Laws: Avogadro’s and Ideal

Let’s see if you can:

1. Describe Avogadro’s Law with a formula.2. Use Avogadro’s Law to determine either

moles or volume3. Describe the Ideal Gas Law with a formula.4. Use the Ideal Gas Law to determine either

moles, pressure, temperature or volume5. Explain the Kinetic Molecular Theory

Review of Kinetic Molecular

TheoryParticles of matter are ALWAYS in

motion Volume of individual particles is

zero. Collisions of particles with container

walls cause pressure exerted by gas.

Particles exert no forces on each other.

Average kinetic energy µ Celcius temperature of a gas.

Try this One!!

A sample of argon gas is at a pressure of 148 kPa and temperature of 27.0oC in a rigid 42.0 L tank. How many moles of argon does this tank contain? (1 atm = 101.325 kPa)

1. 252 mol2. 2.49 mol3. 27.7 mol4. 2.80 x 103 mol5. Not listed