Gas Behavior, part 1

January 12, 20166th grade Chapter 4.3

Scientist of the Day

Joseph Louis Gay-Lussac

• Father arrested in the French Revolution so he was raised by an abbot

• Used hot air balloons to find gas laws, gave credit to Charles

• Found 2 new elements• Figured out formula for water• Married an unimportant shop

girl because he saw her reading a chemistry book

How does a hot air balloon work?

Gas Molecules• What will happen if we

increase the temperature of a gas?

Temperature: the energy of molecules moving

Increasing Temperature

• If the temperature goes up, the gas molecules move faster

• If the molecules are moving faster, they’ll hit the sides more often

• This increases pressure• If you want to keep

pressure the same, you have to increase volume instead

Charles’ Law• Temperature goes up, volume goes up• Temperature and volume are directly

proportional

T ∝ V

Graphing Charles’ Law

Temperature (K)

Temperature (°C)

Volume (mL)

0 5020 5440 5860 6280 66

100 70120 74

Graphing Charles’ Law

• Charles’ law is a case where we have to use K• If we graphed with °C instead of K, we wouldn’t

be directly proportional• Sometimes we’d have a negative temperature

with a positive volume – that’s not directly proportional

• Kelvin can never be negative, so it fixes the problem!

Pressure• Since gas molecules fill the entire container and

are constantly moving, they are constantly banging into the sides of their container

• This is called pressure• Pressure can be used for liquids & solids, but then

you have to worry about gravity too

Increasing Pressure

Boyle’s Law• Boyle’s Law looks at volume and pressure

• Volume and pressure are inversely proportional

Inversely proportional: when one goes up, the other goes down

Graphing Boyle’s LawVolume (mL) Pressure

(kPa)300 20250 24200 30150 40100 6050 120

Graphing Boyle’s Law• Shows up as a curve• Any time we multiply volume x pressure for the

same amount of gas, we’ll get the same number

VaporizationVaporization: liquid gas• Can be caused by evaporation or boiling• Add thermal energy

Evaporation: liquid gas, below the boiling point• Only some liquid molecules have enough energy

to escape their bonds to other liquid molecules• No boiling

Boiling: liquid gas, getting hotter• Happens at the boiling point• Bubbles of gas form at & below the surface

Graphing Changes of State