Do Now & Announcements Turn in SOL Review Packet Take out handout from Friday Unit 10 Test THURS 12/18 (open note) Bring in Baby Food/Small Mason Jars

Variables that Define a Gas Volume (V) - may be expressed in liters, milliliters, cm 3, dm 3. Temperature (T) – Always expressed in Kelvin!!!! ( o C = Kelvin) Note: Standard Temperature= 273 K Number of Moles (n) - how many particles are present in the sample of gas

Collisions Cause Pressure

The force per unit area on a surface Exerted by all gases on any surface they collide with Units of pressure: Pascal, Millimeter of mercury, Torr, Atmosphere STANDARD PRESSURE: 1atm = 760mmHg = 760 torr = kPa = 1.01x10 5 Pa STANDARD PRESSURE: 1atm = 760mmHg = 760 torr = kPa = 1.01x10 5 Pa Pressure-

Pressure Barometer- used to measure atmospheric pressure The higher the altitude the __________ the atmospheric pressure and the _________ the height of the mercury in the barometer lower Whatever the height is, that is your pressure

Measuring Pressure of a Gas Manometer- measures the pressure of an enclosed sample Can be open or closed Whatever the height difference is, that is your pressure in mmHg Closed Manometer

Pressure Gas pressure is less than atmospheric pressure when the height of the liquid in the manometer is higher on the _______________. Therefore you will ________________ the height and the atmospheric pressure. Open Manometer -h +h left side of the U subtract

Examples 1. If the atmospheric pressure is 757.8mmHg, what is the pressure of the gas in each of the following manometers?

Dalton’s Law 1) the total pressure exerted by a mixture of gases is the sum of the individual pressures of each gas and 2) each individual gas behaves as if it were independent of the others. P total = P 1 + P 2 + P 3 + …

Examples 1. Two gases such as oxygen and nitrogen are present in a flask at the following pressures. When combined, what is the pressure of the flask? P Nitrogen =250. mm Hg P Oxygen =300. mm Hg

Examples 2. Neon gas has a pressure of 1.49atm in its container. When added to a container holding helium gas the total pressure is 2.34atm. What is the pressure of the helium gas?

Dalton’s Law Water displacement of gas: Gases given off from the rxn travel through the tube and into the adjacent container for collection Gas is impure and contains some water vapor P atm = P gas + P H2O Value depends on temperature

Dalton’s Law Examples A 250 mL sample of oxygen is collected over water at 25°C and 760 torr pressure. What is the pressure of the dry gas alone? The vapor pressure of water at 25°C is 23.8 torr. Oxygen gas from the decomposition of potassium chlorate was collected by water displacement. The barometric pressure and the temperature during the experiment were 731.0torr and 20.0˚C respectively. What was the partial pressure of the oxygen collected? The vapor pressure of water at 20°C is 17.5 torr Some hydrogen gas was collected over water at 20.0 ˚C. The partial pressure of hydrogen is torr. What is the barometric pressure of the gas? The vapor pressure of water at 20°C is 17.5 torr

Graham’s Law of Diffusion Under ideal conditions, the rates at which different gases diffuse (spread out) are inversely proportional to their molar masses. The rate of effusion and diffusion depend upon the velocity (speed) of the gas molecules

Graham’s Law Speed is dependent upon molar mass In other words, larger gas molecules will move slower than smaller gas molecules.

Graham’s Law Examples i. Compare the rates of diffusion of H 2 and O 2 gases at the same temperature and pressure. ii. Rank the following gases from slowest to fastest rate of diffusion: H 2, CO 2, Ne, H 2 S.

Avogadro’s Law The volume of a gas under constant temperature and pressure conditions is directly proportional to the number of moles of gas. 1 mole of gas at STP = 22.4 Liters

Boyle’s Law P 1 V 1 = P 2 V 2 Inversely proportional As the pressure decreases, the volume increases (temp. constant)

Charles’s Law

Gay-Lussac’s Law

Combined Gas Law Relates pressure, temperature, and volume in one equation

Ideal Gas Law PV=nRT n= # moles R=universal gas constant To determine which R to use in your equation you have to look at the _____________. R is the universal gas constant. Will be GIVEN on tests/quizzes! Pressure units being used!!

Solving Gas Laws Questions Determine your known variables and convert temperature to Kelvin if necessary Identify the unknown (what are you trying to find?) Identify the appropriate gas laws formula to use Plug in your values and solve

Gas Laws Practice Final Answers 1) 3.27 atm 2) 8.2 L 3) K 4) 60.0 L 5) 17.7 L