gases are easily compressed gases can expand large amount of space between particles

Properties of Gases and Gas Laws

Ch. 14.1 & 14.2

Properties of Gases

Gases are easily compressed

Gases can expand› Large amount of space between

particles

Properties of Gases

Compressing a gas causes pressure to increase

3 Factors Affect Gas Pressure› Volume of the container (V)

Measured in Liters› Amount of gas (n)

Measured in the number of moles› Temperature

Measured in Kelvins (T)

Properties of Gases

Amount of gas affects on pressure› Increase in number of particle› Increases in number of collisions› Increase in Pressure

As the amount of gas changes, the pressure changes directly› Ex. When the number of moles is doubled

the pressure double.› Also works when the moles decreases

Properties of Gases

Gases will flow to the area with lower pressure.› Ex:

Deflating balloon Gas will leave the balloon into the surroundings

Vacuum sealed container Gas will rush into the container

Properties of Gases

Volume’s effects on pressure› Decrease in volume of the container› Increase in the number of collisions› Increase in pressure

Volume inversely affects pressure A volume decrease causes a pressure

increase If the volume is halved, the pressure is

doubled. Squeezing a pack of Ketchup

Properties of Gases

Temperature’s affects on pressure› Increase in Temperature› Increase in the speed of the gas particles› Increase in the number of collisions› Increase in pressure

Temperature directly affects pressure› If the temperature double, so will the

pressure› Ex: Frozen balloon

The Gas Laws

Boyle’s Law› For a given mass of gas at constant

temperature, the volume of a gas varies inversely with pressure.

The Gas Laws

Boyle’s Law

›P ×V =P ×V₁ ₁ ₂ ₂

› Pressure in units of kilopascals (kPa)› Volume in units of liters (L)

The Gas Laws

Boyle’s Law Ex:› The volume of a raft has an initial volume

of 1.2 liters and an initial pressure of 87kPa. If the final volume was 2.9 liters what was the final pressure?

› P =87kPa V =1.2L P =? V =2.9₁ ₁ ₂ ₂› P ×V =P ×V (₁ ₁ ₂ ₂ P ×V )/ V =P₁ ₁ ₂ ₂› (87x1.2)/2.9= 36 kPa

The Gas Laws Charles Law: As the temperature of an

enclosed gas increases, the volume increases, if the pressure is constant.

The Gas Laws

Charles Law:

› V₁/T₁=V₂/T₂

› Volume in units of Liters (L)› Temperature in units of Kelvins (K)

The Gas Laws

Charles Law Ex:› The volume of an inflated balloon at 24˚C

has a volume of 4 liters. The balloon is then moved to a room with a temperature of 58˚C. What is the Volume? T = 24˚C+ 273 = 292 K T = 58˚C + 273 = 331 K₁ ₂ V₁/T₁=V₂/T₂ V = (V xT )/ T₂ ₁ ₂ ₁ (4.00L x 331 K)/ 297 K= 4.46L

The Gas Laws

Gay-Lussac’s Law› As the temperature of an enclosed gas

increases, the pressure increases, if the volume is constant.

› P /T =P /T₁ ₁ ₂ ₂

› Pressure: kPa› Temperature: K

The Gas Laws

Gay-Lussac’s Law Ex:› An aerosol can is stored at 25˚C and has a

pressure of 103 kPa. If the f=can is heated to 928˚C, what is the final pressure?

› T =25˚C + 273= 298 K₁› T = 928˚C + 273= 1201 K₂› P /T =P /T T (P /T )=P₁ ₁ ₂ ₂ ₂ ₁ ₁ ₂› 103kPa x (1201 K / 298 K)= 415 kPa› Or 4.15 x 10² kPa

The Gas Laws

The Combined Gas Law› Calculates for situations where the amount

of gas is constant.

› (P x V )/T = (P x V )/ T₁ ₁ ₁ ₂ ₂ ₂

› P: kPa› V: L› T: K

The Gas Laws

Combined Gas Law Ex:› The volume of a balloon is 30.0 L at 313 K

and 153 kPa pressure. What would the volume be at standard temperature and pressure (STP)

› STP: 273K and 101.3 kPa› (P x V )/T = (P x V )/ T₁ ₁ ₁ ₂ ₂ ₂› V = (V x P x T )/ (P x T )₂ ₁ ₁ ₂ ₂ ₁› (30L x 53kPa x 273K)/(101.3kPa x 313K)= 39.5 L

#1

Gas law

Ideal Gas Law14.3

Ideal Gas Law

Ideal Gas Law was created to calculate the number of moles of a contained gas.

Symbol for number of moles is “n” Number of moles is directly

proportional to volume

Ideal Gas Law

1mol of every gas is 22.4 L at STP

The Ideal Gas Constant R=(P x V)/(T x n)

At STP :› (101.3 x 22.4)/(273 x 1)=

8.31(L·kPa)/(K·mol)› R= 8.31

Ideal Gas Law

Common Equation

PV= nRT P: kPa V: L n: mol R: (L·kPa)/(K·mol) T: K

Review

Converting mass to moles. 12 grams of CO₂ how many moles?

› 12grams/(MMof C + 2 x the MMof O)› 12/(12+2·16)= .2727 mols

Ex.

What is the pressure of 113g of Xenon gas at 187˚C, held in a 1.2L container?

nRT/V=P 113g/131.3MM of Xe= .8606 mols T= 187˚C+ 273= 460k (.8606·8.31·460)/1.2= 2741.44 kPa

Gases, Part 3

Real Gases vs. Ideal Gases: Ideal gases follow the gas laws at all

pressures and temperatures.

Real gases can not be described by the gas laws at certain temps or pressures.

An ideal gas has particles with NO volume, and there are no attractions between the particles.

A real gas has particles that have volume, and there are interactions between particles.

Real gases differ most from ideal gases at high pressures and low temperatures.

Partial pressure: The pressure that one gas contributes to the total pressure.

Dalton’s Law: Ptotal = P1 + P2 + P3 + …

101.3 kPa

On top of Mt. Everest, air pressure is 33.73 kPa. Since oxygen is 21% of air, the pressure of oxygen is 7 kPa.

You need 10.67 kPa Oxygen to live, so mustHave compressed O2.

Diffusion: The tendency of molecules to spread out evenly.

Effusion: A gas escapes through a tiny hole.

Lower the molar mass of a gas = Faster Effusion and Diffusion.

Graham’s Law: RateA / Rate B = (Molar mass B / Molar mass A)^.5