Gas Laws: Gay-Lussac’s Law and

Dalton’s Law

Gay-Lussac’s Law Pressure and temperature relationship

Pressure results from molecular collisions Pressure of gas is DIRECTLY proportional to

temperature. P , T P , T

P1 = P2 SOOO T1 = T2

P1T2 = P2T1

Remember to keep units the same. Temperature MUST be in Kelvin

Example 1:

A coke can has 5.00atm of gas at 21°C. Calculate the pressure inside the can when it is found in a warehouse during the summer at 38°C.

Example 2:

The pressure of my tires before a road trip to Wyoming was 1.5atm at 25°C. After returning to North Carolina, my tire pressure is 1.7atm. What is the temperature (in °C) outside?

Example 3:

A gas sample in a closed container with a temperature of 100°C and a pressure of 3.00atm is heated to 300°C. What is the pressure of the gas at this elevated temperature?

Avogadro’s Law

Volume of a gas is DIRECTLY proportional to # of gas particles (moles of gas) Temperature and Pressure are held constant

V1 = V2 n1 = n2 # gas particles, volume # gas particles, volume

Ex. Blowing up a balloon

Dalton’s Law of Partial Pressures

Pressure of each gas DIRECTLY proportional to amount of moles of a gas Increase gas particles, increase pressure Decrease gas particles, decrease pressure

Partial pressure— Pressure of one gas that contributes to the total

pressure in a mixture of gases Total mixture pressure----

The sum of the individual gas pressures in a mixture

Dalton’s Law of Partial Pressures

Total Pressure (PT) of gas mixture = Sum of partial pressures of each gas in the

mixture

PT = P1 + P2 + P3

Example 1:

Calculate the partial pressure (in mmHg) exerted by the 4 main gases in air at 760 mmHg: nitrogen, oxygen, argon, and carbon dioxide. Their abundance by volume is 78.08%, 20.95%, 0.934%, and 0.035% respectively.

Water Displacement with Dalton’s Law

How do we collect and measure gases? Water displacement

Gas displaces water but the gas is mixed with water vapor

Application of Dalton’s Law allows the adjustment for the amount of water vapor to be made so just the amount of gas collected can be measured.

Water Displacement with Dalton’s Law

(cont.) Water vapor is mixed in with gas of interest

so need to separate.

PT = Pgas + Pwater

look up vapor pressure of water at different temperatures

Example 2:

A sample of nitrogen gas is collected over water at a temperature of 23.0°C. What is the pressure of the nitrogen gas if atmospheric pressure is 785 mmHg?

Example 3:

A student has stored 100.0 ml of neon gas over water on a day when the temperature was 27.0°C. If the barometer in the room reads 743.3 mmHg, what is the pressure of the neon gas in the container?

Homework

Read over lab procedure