Gases

Nature of Gases1 – gases have mass (low density)2 – particles glide past one another (flow) - fluid3 – easily compressed4 – fill containers completely5 – diffuse easily*6 – gases exert pressure7 – pressure depends on temperature

*diffusion – spontaneous mixing of the particles of two substances-movement of one substance through another

Kinetic TheoryExplains properties of gases (ideal

gas)1. Gas particles are relatively far apart2. Collisions are elastic3. Gas particles are in constant, fast,

random motion (Brownian motion)4. Gas particles do not stick, like billiard

balls5. Kinetic energy depends on

temperature

Pressureforce per unit areapressure = force/areaSI unit of force – newton (N)STP – standard temperature and

pressure◦1 atm and 0°C

Units of PressureUnit of Pressure Standard

atmosphere 1 atm

millimeters of mercury 760 mm Hg

torr 760 torr

inches mercury 29.9 in

pounds per square inch 14.7 psi

bar 1 bar = 100 kPa

kilopascals 101.3 kPa

Conversions:How many atmospheres are equal to 10 psi?If a pressure is equal to 101.3 kPa, what is the pressure in mm Hg?

Types of Pressureatmospheric pressure

◦pressure exerted by the air pressing down on earths surface

◦measured by barometer and manometer

gas pressure◦gas particles colliding with the sides

of the container it is in

Barometeran instrument that measures

atmospheric pressure

Manometer an instrument that measures

pressure of a gas in a container vacuum

THE GAS LAWS

Avogadro’s Lawequal volumes of gases at the

same temperature and pressure have equal numbers of particles

1 mole of any gas = 22.4 L

Dalton’s Law of Partial Pressure

the sum of the partial pressures of each gas in a mixture equals the total pressure of the mixture

Pt = P1 + P2 + P3 ….

Classwork/HomeworkIn your books (Modern

Chemistry)◦pg 312

Section Review 1-4 pg 327 16-19 Pg 329 39

Skim Chapter 10 Section 3 for tomorrow

Boyle’s Law

P1V1 = P2V2

temperature remains constantpressure and volume are

inversely related

◦P – pressure◦V – volume◦T - temperature

Practice ProblemsAt a constant temperature, the

volume of a gas is 30.2 L and the pressure is 356 torr. If the pressure has increased to 700. torr, what is the new volume of the gas?

At STP, carbon dioxide fills a 6.5 L container. If the container is compressed to a volume of 3.2 L, what pressure (in kPa) will the gas exert?

Charles’ Law

V1 = V2

T1 T2

pressure remains constantvolume is directly related to

temperaturetemperature must be in K

K-273 = C

Practice ProblemsA balloon filled with helium at STP has

a volume of 4.7 L. If pressure is held constant and the temperature is raised 10 degrees Celsius, what is the new volume of the balloon?

A 500. mL container houses argon at 373 K. If the container is compressed to a new volume of 0.300 L, what will the temperature of the gas be (assuming pressure remains the same)

Gay-Lussac’s Law

P1 = P2

T1 T2

volume remains constantpressure is directly related to

temperature

Practice ProblemsA container of gas with a

temperature of 290 K has a pressure of 1.9 atm. This container is pressurized so the new temperature is 397 K. What is the new pressure?

The volume of a fixed container is 4.03 L. It is filled with neon gas at 46 degrees Celsius and the gas exerts a pressure of 800 torr. This container is heated to 84 degrees celcius. What pressure does the gas exert?

Combined Gas Law

P1V1 = P2V2

T1 T2

No variable remains constant

Practice ProblemsThe volume of a gas at 30 degrees

celcius is 8.54 L. The pressure is increased from 760 mm Hg to 943 mm Hg. If the temperature increases 8 degrees celcius, what is the new volume?

A 2.7 L container filled with carbon monoxide at 400 K has a pressure of 5.7 atm. If the container is compressed to a volume of 1.0 L and a pressure of 6.0 atm, how will the temperature change? What is the new temperature?

Classwork/HomeworkPlease work in your books on the

practice sections of pg 315, 319, 320, 322

If you do not finish this in class, please finish it for homework

Ideal Gas LawPV = nRT “piv nurt”

n - number of molesR - gas constant

◦Values of R: 0.0821 atm 62.4 mmHg 8.31 kPa

V in LT in Kn in mol

Practice ProblemsExactly 1 mole of carbon dioxide is in

a 4.0 L container at 283 K, what is the pressure the gas exerts?

2.4 moles of gas is exerting 760 torr on a 30.0 L container, what is the temperature of the gas in Celsius?

A gas is contained in 2.87 L container at 300 K. The pressure exerted is 220. kPa. If the gas is CO2, what mass of the gas is in the container?

Ideal Gas LawMolar Mass

◦MM = gRT/PV

Gas Density◦D= m/v d = PMM/RT◦As temperature increases, volume

increases◦As volume increases and mass

remains the same, density decreases

Practice Problems6.00 g of He is contained in a box

at STP, what is the volume of the box?

Calculate the density of a gas with a molar mass of 132 g/mol at STP.

Neon gas is contained in a 55 L container at 297 K; if the neon exerts a pressure of 1000. torr, what is the mass of the gas?

HWPg 357

◦16-19 letter c only◦20◦21

Graham’s Law of Diffusion

v1 = d2 v1 = m2 v2 d1 v2 m1

v – rate of diffusiond – densitym – molar mass

Practice ProblemsCalculate the relative rates of

diffusion of O2 and H2

H subscript 1, O subscript 2

Answer: molecule 1 is 4 times molecule 2◦H2 is 4 times faster than O2/diffuses

4x faster

Practice ProblemsIf equal amounts of helium and argon

are placed in a porous container and allowed to escape, which gas will escape faster and how much faster?

What is the molecular weight of a gas which diffuses 1/50 as fast as hydrogen?

How much faster does hydrogen escape through a porous container than sulfur dioxide?

Collecting a gas over water

Patm = Pgas + PH20

PH20 depends on temperature

Practice ProblemsIf we collected 310.0 mL of gas over

water at a pressure of 738 mmHg and a temperature of 20.0°C, what is the partial pressure in atm of H2(g) in the test tube?

193 mL of O2 was collected over water on a day when the atmospheric pressure was 762 mmHg. The temperature of the water was 23.0 o C. How many grams of oxygen were collected?