GASESChapter 12

H2 N2 O2 F2 Cl2 He Ne Ar Kr Xe Rn

WHAT 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.

GAS MEASUREMENTS

MEASURING GASES

Measurement Symbol Unit Abbrev.

Amount n moles mol

Volume V Liters L

Temperature

T Kelvin K

Pressure Patmospher

eatm

REMEMBER:

1 mol = 6.02 x 1023 particles

1 mL = 1 cm3

K = oC + 273

K = 0C + 273

273 K = 0 0C 373 K = 100 0C

Convert the following temp into Kelvin:

25 0C 232 0C

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 level 1 atm

4 miles 0.5 atm

10 miles 0.2 atm

Measuring Gases

• Scientists have specified a set of standard conditions called standard temperature and pressure

• STP = 0°C and 1 atm.

THE GAS LAWS

As P (h) increases V decreases

PRESSURE AND VOLUME RELATIONSHIP

Pi x Vi = Pf x Vf

Constant temperatureConstant amount of gas

pressure and volume are inversely related

THIS 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?

Pi x Vi = Pf x Vf

Pi = 726 mmHg Vi = 946 mL Pf = ? Vf = 154 mL

Pf = Pi x Vi

Vf

726 mmHg x 946 mL154 mL

= = 4460 mmHg

As T increases V increases

TEMPERATURE AND VOLUME RELATIONSHIP

T (K) = (0C) + 273

Temperature must be in Kelvin

Constant pressureConstant amount of gas

Vi = Vf

Ti Tf

temperature and volume are directly related

THIS IS CALLED: CHARLES’ LAW

A sample of carbon monoxide gas occupies 3.20 L at 125 0C. At what temperature will the gas occupy a volume of 1.54 L if the pressure remains constant?

Vi = 3.20 L

Ti = 125oC 398 K

Vf = 1.54 L

Tf = ?

Tf = Vf x Ti

Vi

1.54 L x 398 K3.20 L

= = 192 K

Vi = Vf

Ti Tf