Properties of Gases

Properties of gases  ______shape and volume  can ______to a larger volume  can ______a smaller volume  low ______compared to solids and liquids  high ______; molecules can glide past one another  high ______; gas particles mix during random motion to reach an even distribution(equilibrium) spontaneously.  high ______; gas particles under pressure can pass through a tiny opening LOWER molar mass gases EFFUSE SLOWER than LARGER molar mass gases.

CO2 gas effuses slower than H2 gas (44.01g/mol) (2.02 g/mol)

Kinetic Molecular Theory

 states that all particles are in constant motion  helps explain the properties of solids, liquids, and GASES!  There are 5 assumptions. These assumptions apply to an ideal gas  An ideal gas is an imaginary gas that fit the assumptions seen below:

1. Gases are made of ______particles that are extremely far apart from one another. Gases are mostly empty space.  Gases have no volume! 2. Gas particles move in ______, rapid, random motion traveling in straight lines. They possess ______energy. 3. Collisions between gas particles are ______. This means there is no net loss of kinetic energy within the gas. The KE of 1 gas molecule ______to another. 4. There are no______nor repulsive forces between gas particles. 5. The average kinetic energy of a gas molecule is directly proportional to the ______of a gas in Kelvin.

 Most real gases behave like an ideal gas at low pressure and high temperatures. Real Gases Deviate from Ideal Gas Behavior

 When real gases are at high pressure, the gas molecules are compressed making the volume they take up more signifigant than if they were spread out.  When real gases are at low temperature, the lower KE causes the molecules to move slower and ATTRACTIVE FORCES that really exist will take effect.

 Polar gases ( HCl) deviate more than nonpolar gases ( He or H2 )

Example: Which gases will deviate the most from ideal gas behavior, NH3 or BF3 ?

Pressure

o Defined as the ______per unit area o Actually the forces created when the gas molecules ______with one another and their container o Atmospheric pressure is the pressure of air molecules that surround us colliding with each other o At ______altitudes, there is a______atmospheric pressure o Use a______to measure atmospheric pressure o At sea level, atmospheric pressure is ______mmHg. This is referred to as ______pressure. o STP = standard temperature and pressure (OC and 1atm)

Pressure Units of Importance

Atmosphere (atm) Millimeters of Mercury (mmHg) Torricelli(torr) Kilopascal (kPa)

*****An important conversion factor to transfer between pressure units is***** 1 atm = 760 mmHg = 101.3 kPa Examples: Convert 745.8 mmHg to atm

Convert 3.65 atm to kPa Gas Mixtures  Each gas exerts its own pressure in a mixture called its ______. The total pressure of a gas mixture is the sum of the partial pressures of all gases.

PT = P1 + P2 + P3… Example: Calculate the partial pressure of oxygen gas in a mixture that consists of oxygen, carbon dioxide and nitrogen gases. The total pressure of the mixture is 1atm. PCO2 = .285 torr PN2 =593.525 torr

Gas Laws  There are 4 factors that affect the behavior of a gas 1. pressure: see the pressure units above 2. volume: L, mL, cm3 , mm3 3. temperature: C and F BUT we use the Kelvin scale K = C + 273 4. amount of gas (mole)

Boyles Law

 Volume and pressure are ______proportional when temperature and moles are constant

VP = k V1P1 = V2P2 Tripling pressure reduces volume by one-third Example: Given the volume of gas as 200.0 ml at 800 mm Hg, what is the volume of the same gas at 765 mmg. Assume temperature and moles are constant.

Charles Law

 Volume and temperature are ______proportional when pressure and moles are constant. Temperature must be in Kelvin units! V/T = k V1/T1 = V2/T2 Doubling volume doubles the Kelvin temperature of gas Example: The volume of a gas at 20C is 500.0ml. Find the new volume at standard temperature if pressure and moles are held constant.  Standard temperature is 0 C

Gay-Lussac Law

 Pressure and temperature are ______proportional when volume and moles are constant. Temperature must be in Kelvin units! P/T = k P1/T1 = P2/T2 Halving Kelvin temperature will cut the pressure of the gas in half Example: A sample of hydrogen gas at 47 C exerts a pressure of .329atm. The gas is heated to 77 C at constant volume and moles. What will the new pressure be?

Combined Gas Law  Expresses the relationship between volume , pressure, and temperature when moles is held constant. Temperature must be in Kelvin units!

VP/T = k V1P1/T1 = V2P2/T2

Example: The volume of a gas at 780 mmHg and 30C is 500.0 ml. What volume would the gas occupy at STP? No additional gas is added to the container. Ideal Gas Law (an AT NOW equation)  The volume of a gas varies directly with the number of ______or molecules and its Kelvin temperature  R is the ideal gas law constant. Its value is dependent on its units. It can equal .0821 atm L/molK. It can also equal 62.4mmHg  L/molK.

PV=nRT

Example: A 2.07 L cylinder contains 2.98 moles of He gas at 22 C. What is the pressure in atm of the gas in the cylinder?

Example: What mass of hydrogen gas in grams is contained in a 10.0 L tank at 27C and 3.50 atm of pressure?