IDEAL GASES

WHAT VARIABLES DO WE USETO MEASURE GASES?

PRESSURE (P)

VOLUME (V)

TEMPERATURE (T)

MOLES OF GAS (n)

STPSTANDARD TEMPERATURE

and PRESSURE

T = 273 K = 0oC

P = 1 atm = 760 mmHg =101.3 kPa

Boyle’s Law: P1V1 = P2V2

Law Equations

Charles’ Law: V1 = V2

T1 T2

Gay-Lussac’s Law

P1 = P2

T1 T2

Combined Gas Law

P1V1 = P2V2

T1 T2

Volume: 155 cm3

Temp: 20.0 CPressure: 1.00 atm

What volume would the gas occupy at a temp of -20.0 C and a pressure of 690. mmHg?

The Fourth Variable

What do we use to describe the amount of different molecules in a sample?

MOLES: n

1 moleof gas@ STP

2 molesof gas@ STP

3 molesof gas@ STP

Twice as muchmoles meanstwice as much volume

1 Lof gas@ STP

2 Lof gas@ STP

3 Lof gas@ STP

This has TWICE as manymolecules as the firstballoon.

This has THREE TIMESas many molecules asthe first balloon.

As more gas (more moles) is added to the red balloon, the volume increases.

V1 = V2

n1 n2

P1 = P2

n1 n2

As more gas (more moles) is added to a metal can, the pressure increases.

Practice:

A sample of nitrogen gas has a volume of 478 mL and a pressure of 104.1 kPa. What volume would the gas occupy at 88.2 kPa if the temperature remains constant?

Practice:

8.98 L of hydrogen gas is collected at 38.8 °C. Find the volume the gas will occupy at -39.9 °C if the pressure remains constant. DO NOT FORGET TO CONVERT TO K

Practice:

A sample of gas has a volume of 215 mL at 23.5 °C and 84.6 kPa. What volume will the gas occupy at STP?

What is a constant (like R)? (this is not for your notes, just to be sure

you understand)• In an experiment following the scientific

method, a constant is a variable that cannot be changed or is purposely not changed during the experiment. Some constants are purposeful and selected by the scientist to control an experiment while others are more universal and beyond a researcher's controluniversal and beyond a researcher's control

Ideal Gas Constant

PV = ideal gas constant (R)nT

kPa R = 8.31 kPa x L mol x K

The number can change depending on what pressure units you use. i.e. kPa, atm, mmHg, psi

Other R values:

Torr R= 62.3637 L·Torr mol·K

8.3145 L kPa / mol·K

Atm R=0.0821 liter·atm mol·K

Mm Hg R= 62.3637 L·mm Hgmol·K

PV = nRT

IDEAL GAS LAW

P = nRT V

V = nRT P

T = PV nR

n = PV RT

Practice:

 R=0.0821 liter·atm

mol·K

R = 8.31 kPa x L mol x K

Torr R= 62.3637 L·Torr mol·K

Mm Hg R= 62.3637 L·mm Hg mol·K

Grahams Law of Diffusion/Effusion

• Lighter molecules (those with a lower mm) will move faster than heavier molecules at the same temperature

https://www.youtube.com/watch?v=I2klwb-V1HQ

Sample of DiffusionHCl & NH3

• Here, the gases travel where a chemical reaction occurs and a white ring appears.

• Note the distance traveled. The ammonia travels further than the hydrochloric acid because the ammonia has a lower

mm.

Diffusion• Moving of gas particles throughout a

container or area.• Mass determines speed

Effusion• Moving through a porous barrier.

Separated by size as well as speed.

•

Graham’s Law

• Example: What is the rate of hydrogen gas to oxygen gas effusion/diffusion in a system at STP.

Equation:

**Assume that you will compare the heavier particles with a rate of 1 to the increased rate of the faster particles.

Dalton’s law of partial pressure

• The total pressure in a system is the sum of the pressures of all gasses in the system

• Example: If I have a balloon with samples of oxygen gas of pressure 5.6 kPa, hydrogen gas of pressure 4.5 kPa, and nitrogen gas of pressure 3.2 kPa, what is the total pressure in the balloon?

Example:

• What is the partial pressure of oxygen gas in a mixture of nitrogen gas and oxygen gas with a total pressure of 0.48 atm if the partial pressure of nitrogen gas is 0.24 atm?

Example: What is the partial pressure (dry) of a gas if it was trapped using water displacement at 75oC with a total pressure (wet) of 109.5 kPa?