Combined Gas Law

Agenda Demos & Notes on gas laws Homework: Gas Laws

Combined Gas Law

Date:

Kinetic Molecular Theory

The theory that a gas consists of molecules in constant

random motion.

Postulate 1 Gases are composed of molecules

whose size is negligible compared with the average distance between them.

Postulate 2 Molecules move randomly in

straight lines in all directions and at various speeds.

Pressure is the same in all directions

Changes directions when it collides

Postulate 3 The forces of attraction or

repulsion between two molecules in a gas are very weak or negligible, except when they collide.

Postulate 4 When molecules collide with one

another, the collisions are elastic.

Postulate 5 The average kinetic energy of a

molecule is proportional to the absolute temperature.

Variables P: pressure V: volume T: temperature – must be in Kelvin

Celsius, oC and Kelvin oC + 273 = K

Pressure Force exerted per unit of area Has multiple units: psi, kg/ms2 =

pascal, mmHg = torr, atm. Evagelista Torricelli created the

mercury barometer

Standard Pressure 1 atm = 760 torr = 760 mmHg =

101.3 kPa Convert between units using std

pressures as conversion factors.

Temperature Measure of the average kinetic

energy of the molecules.

Volume The space occupied by matter For which state of matter can the

volume be changed simply by changing the pressure or temperature?

What does a vacuum pump do?

Decreases the pressure by removing air molecules

Observe the balloon and marshmallow.

What is the relationship between pressure and

volume?

Modified Volcano Vinegar and baking soda make

CO2. As more MC of gas are created,

pressure increases and it needs more volume.

Stopper blows

Boyles Law P1V1 = P2V2

Pressure varies inversely with volume.

This little light of mine Flame burning = high T, MC moving

fast = high P and take up more space.

Cover with graduated cylinder, use up all O2 flame goes out instantly reducing T.

Less movement, less pressure. Atm forces liquid up!

Gay – Lussac Law P1T2 = P2T1

Pressure varies directly with temperature.

Temperature MUST be in Kelvin and is not used to determine SF.

Hand Warmer Cold jar, balloon deflated Warm jar, increase T, volume of

balloon increases.

Charles Law V1T2 = V2T1

Volume varies directly with temperature.

Temperature MUST be in Kelvin and is not used to determine SF.

Fountain Increase pressure in container, by

decreasing space between gas molecules.

Stop blowing, releases pressure and creates more space by spraying water!

Combined Gas Law P1V1T2 = P2V2T1

Shows the relations between variables and predicts results of adjustments made to system.

Use for changing conditions! If one variable is constant, enter the same value twice or remove that variable from the equation.

STP Conditions Standard temperature is 273 K Standard pressure can be

1 atm 101.3 kPa 760 torr 760 mmHg

A 50. L sample of a gas at a pressure of 1.0 atm

and a temperature of 25oC is moved to an area

where the pressure is 5.0 atm and the

temperature is 30oC. What is the new volume of

the gas? P1V1T2 = P2V2T1

(1.0atm)(50.L)(30+273K) = (5.0atm)(X)(25+273)

15150 = 1490X 10. L

V1 P1

T1

P2 T2

A 50.0 mL sample of a gas has a pressure of 2.00

atm when the temperature is 25oC. What volume

will the gas occupy at a pressure of 4.00 atm

when a constant T?

P1V1T2 = P2V2T1

(2.00atm)(50.0mL) = (4.00atm)(X) 100 = 4X 25.0 L

V1 P1

T1

P2

A 5.0 mL sample at 20oC has a pressure of 1.0

atm. What volume will the gas occupy when the

temperature is raised to 60oC at constant

pressure?

P1V1T2 = P2V2T1

(5.0mL)(60+273) = (X)(20+273) 1665 = 293X 5.7 mL

V1 T1 P1

T2

A 20.0 mL sample of a gas has a pressure of 2.0

atm at a temperature of 20oC. What will the

temperature be when the pressure is raised to 4.0

atm at a constant volume.

P1V1T2 = P2V2T1

(2.0atm)(X) = (4.0atm)(20+273) 2X = 1172 586K

V1P1

T1

P2