GAS LAWS!

A “model” is an approximation that attempts to explain observable behavior, allows for future predictions in experimentation.

Based on behavior of individual gas particles: (atoms: Ne,He ; molecules H2,Cl2,CO2)

4 Postulates1. The volume of individual particles is assumed to be negligible (zero).

2. The Particles are at great distances from each other – between them, empty space.

3. The particles are assumed to exert no forces on each other, nor do they attract or repel each other.

4. The average KE of a “collection” of gas particles is assumed to be directly proportional to Kelvin.

***This model works only for ideal gases***

Real Gases do have volume, they take up space, and they do exert forces on each other b/t them (melting/boiling)

We use Ideal gases + their behaviors in Chem. 1

1. The Kelvin Scale:- An index of gas motion- NOT a measurement of heat

2. T, temperature is directly proportional to KE, kinetic energy, energy in motion.

- heat a gas sample T ^, KE ^, motion ^

- “absolute zero” – 0K – all motion stops

- a gas sample at 100K has half the KE of a gas sample at 200K

- K = Degrees Celsius + 273 - 273K is standard temperature

1. Individual gas particles exert a force on the side of their containers (balloon).

2. Atmospheric Pressure: Gravity pulling particles

3. Atmospheric pressure can change with altitude, greater elevation, less pressure, less gas molecules

Kinetic Theory works for IDEAL gas behavior – theoretical for almost all situations of T + P

Remember! T – in Kelvin, measure of KE of gas particles

Remember… Kinetic theory asserts 2 assumptions about gas particles.1. Gases have no volume, REAL gases do, they are matter therefore they take up some space, though very little.2. No attractive forces exist b/t gas molecules, but REAL gases do have them, otherwise how could they take condense back to the liquid state.

1 ATM = 760 mmHg = 760 torr = 101.3 KPa

ATM= atmospheres mmHg= millimeters of mercury Torr= Torricelli's KPa= kilo Pascal's

Ex: convert 9.23 atmospheres of pressure to KPa9.23 atm x 101.3 KPa = 9.35 x 102 KPa 1 atm

Ex: 99.2 KPa to mmHg99.2 KPa x 760 mmHg = 744 mmHg 101.3 KPa

Dalton’s Law of Partial Pressures - PTotal = P1 + P2 + P3 + …. + P8

at a constant T and VThe total pressure exerted by a mixture of gases is the sum of the partial pressure of each gas.

Air is a mix of gas. The partial pressures are: PN2= 593.4mmHg, PCO2= 0.3mmHg, Pothers= 7.1mmHg, oxygen is also a component. Calculate partial pressure of oxygen at a barometric pressure of 1 atm.

Boyle’s Law for Pressure – P1V1=P2V2

Constant Temperature, an inverse relationship b/t P + V, as P increases V decreases and vice versa.

P1V1 = P2V2

Example) A 153 cm3 sample of N2 gas originally at a P of 82.34 KPa will occupy what volume at standard pressure?

Charles Law for Temperature – Volume ChangesV1 = V2

T1 T2

Constant P, a direct relationship b/t V + T, as V increases, T must also increase and vice versa. T in Kelvin (can’t have a negative volume or motion)

V1 = V 2

T1 T2

Example) A balloon has a volume of 98 cm3 on a 32 C day. If the temperature the following day is 48C, what is the volume?

Guy-Lussac’s Law for Pressure – Temperature ChangesP1 = P2

T1 T2

Constant V, a direct relationship b/t P + T , as one increases/decreases so does the other

Combined Gas Law: P1V1 = P2V2

T1 T2

Ideal Gas Law• Ideal Gas Law: PV=nRT or gRT/FM

P1V1 = P2V2

T1 T2

Ex) A sample of diborane gas, B2H6, a substance that bursts into flame when exposed to air, has a P of 345 torr at a T of -15C and a V of 3.48 L. If conditions are change such that the T is 36C and the P is 0.616 atm, what will be the V?

PV=nRT n=# of moles

How many moles of Argon gas can be found in a cylindrical light tube with a volume of 3.7 L and a under a pressure of 162 KPa. The T in the tube is 350 K.

PV= g (R)(T)FM

Ex) How many grams of carbon dioxide are in your lungs at a T of 37C and under a pressure of 768 mmHg. Your lung capacity is 4.8 L.

PFM = g = dRT V

Ex) Calculate the density of NO2 at 300K if its under a P of 6 atm in a 5.0 L container.