PRESENTATION PROPERTIES OF GASES II

Properties of Gases 1. Gases have mass – find mass of empty balloon and filled balloon 2. It is easy to compress gases – squeezed gas reduces its volume; car air bags 3. Gases fill their containers completely – 4. Different gases can move through each other quite rapidly – diffusion (body spray, body gas, etc) 5. Gases exert pressure – ear drums “popping”, filled balloon 6. The pressure of a gas depends on its temperature ↑ temp = ↑ pressure; ↓ temp = ↓ pressure

Properties of Gases and the Air we Breathe Main Ideas (in no order):  Atmospheric Pressure  Volume  Temperature  Kinetic Molecular Theory  Composition of Air How will we do it:  Notes  Labs and Activities  Worksheets  Practice Problems and Questions

MEASURING GASES Four Variables:  Amount of gas  Volume  Temperature  Pressure

AMOUNT OF GAS (n) Quantity of gas in a given sample is expressed in terms of moles of gas n =mass = m (g)____ molar mass M (g/mol) One mole of NaCl, = mass of g. One mole of the liquid, = mass of 18.0 g and occupies a volume of 18.0 mL. One mole of the gas, = mass of 32.0 g and occupies a balloon whose diameter is 35 cm

VOLUME (V) Gas uniformly fills any container in which it is placed Volume of gas = volume of its container Metric unit = L  1 L = 1000 cm 3

TEMPERATURE (T) Measured with thermometer in degree Celsius (˚C) Must be converted to Kelvin temp scale  No negative temps  T (K) = T ( ˚C) + 273

PRESSURE (P) Outward force of gas spread over the area of the container is called pressure P = Force Area Pressure = Pascal (Pa)

ATMOSPHERIC PRESSURE Gases of atmosphere also exert pressure on everything come into contact with (gas) density = Mass (of gas) Volume P = m V Atmospheric Pressure decreases with height

Pressure of Atmosphere Can Crushing 55 Gallon Drum

Pressure Measuring Devices Weather Prediction  Barometer  QeAp3CuGjk8 QeAp3CuGjk8 Regulation of gas flow 

Units of Pressure 1 atmosphere (atm) = 101,325 Pa 1 atm = 760 mm Hg = 760 torr 1 atm = lb/in 2 1 bar = 100,000 Pa = atm

Sample Problems Mercury (Hg) column in barometer is 745 mm above the mercury reservoir at the bottom. What is the atmospheric pressure in pascals? 745 mm Hg x 101,325 Pa = 99,300 Pa 760 mm Hg

Practice Problem The air pressure inside the cabin of an airplane is 8.3 lb/in 2 What is this pressure in atmosphere units?

Practice Problem 2 Pressure is considered the most accurate measure of storm strength, with lower pressure indicating a stronger storm. One of the lowest recorded pressures in the Western Hemispheres is kPa. How high a column of mercury would be balanced by this atmospheric pressure?

Pressure Conversions STP means standard temperature and pressure 1 standard atmosphere = atm = mm Hg = torr =101,325 Pa = psi ***all of these equal each other!*** Temperature: 0 ˚C or 273 K