PHYSICAL CHARACTERISTICS OF GASES

Or

GAS LAWS

KINETIC MOLECULAR THEORY

• 1. Ideal gases vs. Real gases• 2. Perfect elasticity• 3. Average kinetic energy• KE= ½ mv2

Properties of gases

• 1. Expansion• 2. Fluidity• 3. Low density• 4. Compressibility• 5. Diffusion• 6. Effusion

PressureWhat is it???

• Barometer/Manometer• Millimeters/Torrs• Atmospheres• kiloPascals• 1 atm. = 101.3 kPa = 760 mm• 7.5 mm = 1 kPa

Conversions

• Change 800 mm to atm. and to kPa.

• Change 108 kPa’s to mm and atm.

Practice:

• Convert 699 mm to kPa and atm.

• Convert 1.05 atm to kPa and mm.

• Convert 101.9 kPa to mm and atm

Gases and Temperature

• Kelvin scale 0o Celsius = 273K• Conversion:• Add 273 to Celsius temperature• Change 25oC to Kelvin• Change 287K to Celsius• Convert 45oC to Kelvin• Convert 30 K to Celsius

Boyle’s Law

• Robert Boyle theorized that the pressure and volume of a gas were indirectly proportional. What does this mean??

• PV = k

Problems

• A gas is collected at a constant temperature of 25o with a pressure of 689 mm and volume of 32 mL. Find the pressure if the volume goes to 55 mL?

• V1 P1 = V2 P2

One more:

• 45 mL of a gas is collected at 102.7 kPa. Find the volume if the pressure goes to 705 mm.

Charles’ Law

• Charles worked with temperature and volume of gases.

• Temperature and volume are directly proportional.

• V/T = k

Problems:V1/ T1 = V2/ T2

• If 28 mL of H2 are collected at 28oC. What is the volume at 36oC at constant pressure?

• Kelvin!!!

• If 35 mL of N2 are collected at 31oC,what is the temperature in oC if the volume rises to 45mL?

Gay –Lussac’s Law

• Gay- Lussac worked with pressure and temperature of gases.

• He said that pressure and temperature were directly proportional.

• P/T =k

Problems:

• A gas is collected at 43oC and a pressure of 1.2 atm. Find the new pressure if the temperature drops to 21oC. Kelvin!!!

• P1/T1 =P2 /T2

Another problem:

• At constant volume,CO2 is collected at 768mm with a temperature of 23oC. Find the new temperature in oC of 99.1 kPa’s of pressure.

COMBINED GAS LAW

• PUT THE THREE EQUATINS TOGETHER AND MAKE INTO ONE.

• WRITE THIS EQUATION.

• V1P1/T1 = V2P2/T2

PROBLEMS

• 25 CM3 OF HYDROGEN IS COLLECTED AT 260C WITH A PRESSURE OF 1.2 ATM. FIND THE NEW VOLUME IF THE PRESSURE DROPS TO .98 ATM AND THE TEMPERATURE DROPS TO 220C.

ANOTHER PROBLEM

• 78 cm3 OF OXYGEN IS COLLECTED AT 42OC WITH A PRESSURE OF 767mm. FIND THE NEW VOLUME AT STP.

Combined:

• 35 cm3 of N2 is collected at .98 atm of pressure with a temperature of 210C. What is the new temperature in 0C if the volume rises to 45 cm3 and pressure rises to 788 mm?

Over water problems

• 15 liters of Chlorine is collected over water at 718 mm of pressure at a temperature of 60oC. Find the new volume at 766 mm.

This is Dalton’s Law of partial pressure.

The total pressure of a container with many gases is the sum of the partial pressures.

ANOTHER PROBLEM:

• 25 mL of Fluorine gas is collected over water at 25 oC with a pressure of 102 kPa’s. Find the new pressure of 32 mL.

REVIEW

• 33 mL of O2 is collected over water at 40oC at a pressure of 697 mm. Find the new volume at 300C with a new pressure of 1.01 atm.

Another one:

• 65 mL of F2 are collected over water at 280C with a pressure of 101.8 kPa. Find the new temperature of the gas at standard pressure.

For the quiz:

• 50.0 mL of a gas is collected over water at STP. Find the new volume if the new pressure is .97 atm and new temperature is

• 180C.

Ideal gas law

• This is the last gas law and it involves all variables PLUS the mass of the gas.

• Variables:• P= atmospheres• R=.0821 L. Atm / K. mole• V=liters

n= moles• T = Kelvin

THE FORMULA

• PV = n RT• YOU MUST HAVE THE RIGHT UNITS

TO USE THE CONSTANT!!

EXAMPLES

• What is the volume of H2 gas if 15 grams is collected at 25oC with a pressure of .89 atm.?

PROBLEM #2

• What is the pressure of 3.5 grams of CO2 that is collected at 24oC with a volume of 550 mL?

PROBLEM #3

• What is the mass of chlorine gas,Cl2, if 4.8 liters are collected over water at 102.7 kPa’s with a temperature of 28oC?

Problem #4

•Find the volume of O2 that is collected over water at 25oC with a pressure of 736 mm and mass of 16 grams.

Molar mass problems

• What is the molar mass of 5.7 grams of a gas at 230C with a volume of 4.1 liters at 1.1 atm of pressure?

• Formula:

•M = mRT/PV•M = molar mass•m= mass

A problem:

• What is the molar mass of 4 grams of a gas with a pressure of 791 mm at 42oC with a volume of 450 mL?

Molar mass:

• What is the molar mass of a sample of Ar with .0045 moles that has a pressure of 725 mm at 210C and a volume of 55 mL.

Molar mass

• What is the molar mass of CO if 6.5 grams occupies 2.5 liters at 21oC with a pressure of 737 mm?

MOLAR VOLUMEPROBLEMS

• To calculate molar volume and molar mass, you need to know that:

• 1 mole of any gas occupies 22.4 liters of volume at STP.

PRACTICE:

• What is the molar volume of 35 grams of CO2 at STP?

More molar volume

• What is the number of moles of H2 at STP if you collect 350 mL?

Molar volume with a twist:

• How many grams of SO2 gas at STP occupies 450 millilters of volume?

Graham’s Law

• The rate of the movement of a gas is dependent on its mass.

• Which gas will diffuse or effuse faster?

• N2 or F2 ??

Ideal gas law review

• What is the mass of 68 mL of Ne with a pressure of 99.7 kPa’s that is collect OVER WATER at 26oC?

Molar volume review

• How many liters does 18 grams of Cl2 occupy at STP?