What are Characteristics of a GAS?

Gases have no mass. Gases have no volume. Gases do not interact – elastic collisions. Gases have mass. Gases have volume. Gases exert forces on each other.

What does PRESSURE mean? P A F = In Life: Pressure = a stoichiometry quiz every day In Science: Pressure = force per unit area

How else can we measure Pressure?

Standard Temperature & Pressure 273 K 1 atmosphere (atm)

How is pressure measured? A barometer is a device used to measure atmospheric pressure. The first type of barometer introduced by Torricelli in the early 1600s.

How can we change Gases? ActionVariable Heat it up/Cool it downTemperature Compress or Decompress Pressure Change container sizeVolume

How are Temperature and Volume Related? InitialFinal Temperature Volume T1T1 T2T2 V1V1 V2V2

Temperature Volume x x x x x x x How are Temperature and Volume Related? x x x x x x “At constant pressure… temperature and volume are directly proportional.”

Charles’ Law “At constant pressure… temperature and volume are directly proportional.” V1V1 T1T1 V2V2 T2T2 = Temperature is always measured in Kelvin! 0ºC = 273 K

How can we change Gases? ActionVariable Heat it up/Cool it downTemperature Compress or Decompress Pressure Change container sizeVolume

How are Volume and Pressure Related? InitialFinal Volume Pressure V1V1 V2V2 P1P1 P2P2

How are Volume and Pressure Related? Pressure Volume x x x x x x x x x x x x x “At constant temperature… volume and pressure are inversely proportional.”

Boyle’s Law “At constant temperature… volume and pressure are inversely proportional.” V1V1 P1P1 V2V2 P2P2 = xx

How are Temperature and Pressure Related? InitialFinal Temperature Pressure T1T1 T2T2 P1P1 P2P2

Temperature Pressure x x x x x x x How are Temperature and Pressure Related? x x x x x x “At a constant volume… temperature and pressure are directly proportional.”

Gay-Lussac’s Law “At a constant volume… temperature and pressure are directly proportional.” P1P1 T1T1 P2P2 T2T2 = Temperature is always measured in Kelvin! 0ºC = 273 K

To Recap… Charles’ Law: Relates Temperature and Volume. V1V1 P1P1 V2V2 P2P2 = xx V1V1 T1T1 V2V2 T2T2 = Boyle’s Law: Relates Pressure and Volume

Gay-Lussac’s Law: Relates Temperature and Pressure. P1P1 T1T1 P2P2 T2T2 =

…THEREFORE: Temperature, Volume, and Pressure are all related! = V1V1 T1T1 P1P1 V2V2 T2T2 P2P2

A Reminder… We that we live in an world where: Gas particles have no mass Gas particles have no volume Gas particles have elastic collisions These assumptions are used when trying to calculate the AMOUNT of a gas we have!

Why are these assumptions important? PV = nRT

P RESSURE V OLUME n MOLES OF GAS R GAS CONSTANT T EMPERATURE

The MysteRious R R is a constant (doesn’t change). Number value of R depends on other units. Units of R are a combination of many units atm · L mol · K 8.31 kPa · L mol · K 62.4 mmHg · L mol · K

What? PV = nRT Solve for R: R = P V n T R = Plug in units: (mm Hg) (L) (mol) (K) (kPa) (atm)

Gas Laws, Gas Laws Everywhere! V1V1 T1T1 = V2V2 T2T2 P 1 x V 1 = P 2 x V 2 P 1 V 1 P 2 V 2 = T1T1 T2T2 Used with CHANGING CONDITIONS P V = n R T Used with only ONE SET OF CONDITIONS

When to Use PV = nRT Calculating amount of gas in moles Calculating P, V, or T if moles of gas are known. –IMPORTANT! We must have 3 out of 4 pieces of information: P V n T

How do the gas laws apply to gas mixtures, like air? In a mixture of nonreacting gases, each gas contributes to the total pressure in proportion to the fraction (by volume) in which it is present. This contribution is called the partial pressure of the gas. Total Pressure = Pressure of gas 1 + Pressure of gas 2 + Pressure of gas 3 + Pressure of gas 4 … P total = P 1 + P 2 + P 3 + … “The sum of the individual pressures is equal to the total pressure.”

Molar Volume of a Gas Do you remember the value of one mole? 6.02 x 10 23

One mole of oxygen, O 2, contains x oxygen molecules and has a mass of g. One mole of helium gas has a mass of g. Does helium have the same number of molecules? Yes! Equal volumes of gases at the same temperature and pressure contain equal numbers of molecules.

Will 1 mole of O 2 gas and 1 mole of He gas occupy the same volume (at the same temperature and pressure) despite different masses? Remember, according to Avogadro’s law, one mole of any gas will occupy the same volume as one mole of any other gas at the same temperature and pressure, despite mass differences. The volume occupied by one mole of gas at STP. It has been found to be L.