Chapter 18

The Combined Gas Law

&

Graham’s Law

Combined Gas Law

• 10.0 cm3 volume of a gas is collected at 75.6 kPa and 60.0C. What would its volume be at STP?

6.12 cm3

Combined Gas Law Problem

A sample of helium gas has a volume of 0.180 L, a pressure of 0.800 atm and a temperature of 29°C. What is the new temperature(°C) of the gas at a volume of 90.0 mL and a pressure of 3.20 atm?

Combined Gas Law Problem

A sample of helium gas has a volume of 0.180 L, a pressure of 0.800 atm and a temperature of 29°C. What is the new temperature(°C) of the gas at a volume of 90.0 mL and a pressure of 3.20 atm?

x 3.20 atm x 90.0 mL 0.800 atm 180.0 mL

604 K - 273 = 331 °C

302 K = 604 K

Weather Balloons

Weather Balloons• A weather balloon is an instrument which measures

temperature, humidity, and atmospheric pressure. The weather balloon is generally a balloon mounted with weather measuring equipment and a radio transmitter. Some weather balloons are equipped with GPS or global positioning systems for the weather station to track it more accurately.

• In North America prior to release the balloon is usually filled with hydrogen gas due to lower cost, though helium can be used as a substitute. Weather balloons may reach altitudes of 40 km (25 miles) or more where the diminishing pressure eventually causes the balloon to expand to such a degree that it pops.

• Weather balloons are sometimes cited as the cause for unidentified flying object sightings.

A weather balloon with a volume of 305L at STP is released and rises until it expands and explodes at a pressure of

7.00 torr and a temperature of –21°C. What was the volume of the balloon when it burst?

≈ 30,600 L

A weather balloon with a volume of 305L at STP is released and rises until it expands and

explodes at a pressure of 7.00 torr and a temperature of –21°C. How many times larger

is the balloon than when it was released?

About 100 times larger

Diffusion

• The spreading of a gas from an area of higher concentration to an area of lower concentration.

Which gas would diffuse throughout a room faster?

NH3(g) or HCl(g)

Gas Diffusion and Effusion

• Graham's Law:

• Allows for the calculation of the rate of diffusion of gas molecules.

Gas Diffusion and Effusion

Graham's Law: governs the rate of diffusion of gas molecules.

A of massmolar B of massmolar

B of RateA of Rate

Calculate the rate of diffusion of NH3(g) compared to HCl(g)

A of massmolar B of massmolar

B of RateA of Rate

NH3 diffuses 1.47 times faster than HCl

Use measurement to confirm the rate of diffusion of NH3(g) compared to HCl(g)

HCl NH3

Calculate the rate of diffusion of helium compared to argon.

A of massmolar B of massmolar

B of RateA of Rate

Helium diffuses 3.2 times faster than argon

Calculate the rate of diffusion of hydrogen compared to neon.

A of massmolar B of massmolar

B of RateA of Rate

hydrogen diffuses 3.2 times faster than neon

Homework

• Worksheet: Combined Gas Law & Graham’s Law

• Summarize the (I) Purpose and (II) Procedure of the “Gas Laws” Lab.