G ASES Chapter 12

H 2 N 2 O 2 F 2 Cl 2 He Ne Ar Kr Xe Rn W HAT ELEMENTS EXIST AS A GAS AT ROOM TEMPERATURE ?

1. Gases have very low densities. Solids and liquids have much higher density. Gas particles are spread out.

2. Gases have mass. A filled balloon is heavier than an empty balloon. 3. Gases are the most compressible state of matter. Gas particles can be squished closer together.

4. Gases take the shape and volume of their containers. Gases fill the entire space they are in. 5. Different gases will mix evenly and completely called diffusion. You can smell brownies baking in the oven when in a different room.

6. Gases exert pressure. You can feel the wind hit your face. 7. The pressure of a gas depends on its temperature. Temperature is a measure of kinetic energy. The more energy, the more force the gases hit a surface, the higher the pressure.

G AS M EASUREMENTS

M EASURING G ASES MeasurementSymbolUnitAbbrev. AmountnMolesMol VolumeVLitersL TemperatureTKelvinK PressurePatmosphereatm

R EMEMBER : 1 mol = 6.02 x particles 1 mL = 1 cm 3 K = o C + 273

K = 0 C K = 0 0 C 373 K = C Convert the following temp into Kelvin: 25 0 C232 0 C

Units of Pressure

Measuring Gas Pressure Atmospheric pressure is measured by a barometer. The pressure is then read on the column. Barometer 760 mm

Measuring Gas Pressure At sea level, the atmosphere keeps the mercury in a barometer at an average height of 760 mm (equals 1 atmosphere, atm.) One millimeter of mercury is also equal to a torr, after Evangelista Torricelli, the Italian physicist who invented the barometer.

Sea level1 atm 4 miles0.5 atm 10 miles0.2 atm Measuring Gases

Scientists have specified a set of standard conditions called standard temperature and pressure STP = 0°C and 1 atm.

T HE G AS L AWS

As P (h) increases V decreases P RESSURE AND V OLUME R ELATIONSHIP

P i x V i = P f x V f Constant temperature Constant amount of gas pressure and volume are inversely related T HIS IS CALLED : BOYLE’S LAW

A sample of chlorine gas occupies a volume of 946 mL at a pressure of 726 mmHg. What is the pressure of the gas (in mmHg) if the volume is reduced at constant temperature to 154 mL? P i x V i = P f x V f P i = 726 mmHg V i = 946 mL P f = ?V f = 154 mL P f = P i x V i VfVf 726 mmHg x 946 mL 154 mL = = 4460 mmHg

As T increasesV increases T EMPERATURE AND V OLUME R ELATIONSHIP

T (K) = ( 0 C) Temperature must be in Kelvin Constant pressure Constant amount of gas V i = V f T i T f temperature and volume are directly related T HIS IS CALLED : CHARLES’ LAW

A sample of carbon monoxide gas occupies 3.20 L at C. At what temperature will the gas occupy a volume of 1.54 L if the pressure remains constant? V i = 3.20 L T i = 398 K V f = 1.54 L T f = ? T f = V f x T i ViVi 1.54 L x 398 K 3.20 L = = 192 K V i = V f T i T f