PHYSICAL CHARACTERISTICS OF GASES Or GAS LAWS KINETIC MOLECULAR THEORY 1. Ideal gases vs. Real gases 2. Perfect elasticity 3. Average kinetic energy.

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?