8/11/2019 Ch.5 Outline

1/2

Newsha Sajadi

CHEM 101

Firtha

6 Apr 2014

Chapter 5 Outline: Gases

1.

Water from Wells: Atmospheric Pressure at Work

a.

Pressure is the force exerted per area by gas molecules as they strike at surface

2.

Pressure: The result of Molecular Collisions

a.

Pressure can be measured using a barometer, an evacuated tube inverted in a pool of mercury. The

pressure from the atmosphere pushes the mercury up the tube until the weight of the mercury

column is equal and opposite to the force from the atmosphere.

b. Common units of pressure are mmHg, torr, atm, psi, and the SI unit of pressure, Pa.

c. A manometer is used to measure pressures of samples in a laboratory. It consists of a u-tube that

contains mercury an dis open to the atmosphere on one end and the sample vessel on the other.

The difference in mercury height between the two sides of the u-tube is equal to the differences

in pressure between the vessel and the atmosphere.3. The Simple Gas Laws: Boyles Law, Charless Law, and Avogadros Law

a. The properties of gases can be described completely using the temperature, pressure, volume, and

the sample size (moles). We can look at the relationships between any two of these variables by

holding the other two constant.

b.

Boyles law: volume and pressure are inversely related when the temperature and number of moles

are held constant.

c.

Charless law: volume and temperature are directly related when the number and pressure are held

constant

d.

In order for these relationships to hold, the temperature must be expressed in kelvins.

e.

Avogadros law: the number of moles and volume are directly related when the temperature and

pressure are held constant

4.

The Ideal Gas Law

a.

We can combine the simple gas laws into a single expression

5.

Applications of the Ideal Gas Law: Molar Volume, Density, and the Molar Mass of a Gas

a.

Molar volume of a gas at standard temperature and pressure (STP) is the volume that an ideal gas

occupies at 0 degrees Celsius and 1 atm

i.

Standard temperature and pressure is also known as standard conditions

ii. We can calculate the molar volume using the ideal gas law

iii. The density of one mole of a gas at standard conditions can be calculated by diving the

molar mass by the molar volume

1. Density can also be calculated using the ideal gas law and the relationship

between the number of moles, mass (m), and the molar mass (MM):

b.

The molar mass of a gas can be calculated using a rearranged form: MM = mRT/PV

6.

Mixtures of Gases and Partial Pressure

a.

The pressure exerted by a single component of a mixture of gases is the partial pressure of that

component

b.

The partial pressure of a gas, at a given temperature and volume, is determined by the number of

moles of that gas

c.

Daltons law of partial pressures states that the total pressure exerted by a mixture of gases is

equal to the sum of the partial pressures of each component of the mixture

d.

The partial pressure of a gas is related to the mole fraction of the gas

e.

The vapor pressure of a liquid is the pressure that the gaseous phase of the liquid exerts in a closed

container; the vapor pressure is temperature-dependent

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i.

When gases are collected over a liquid, the vapor pressure of the liquid must be taken

into account

7. Kinetic Molecular Theory

a. Kinetic molecular theory assumes that gases are in constant random motion and that

i. The size of the gas particles is negligible as compared to the empty space in a container

ii. The kinetic energy of the particles is proportional to the temperature in kelvins

iii.

The collisions between gas particles and the walls of a container are elastic1. An elastic collision is one in which no energy is lost, although energy can be

exchanged between colliding particles

b. Kinetic molecular theory can be used to understand simple gas laws

i.

Boyles law states that pressure and volume are indirectly proportional; when the

pressure increases, the number of collisions that occur with the walls of the container will

increase.

ii.

Charless law states that the volume and temperature are directly related; when the

volume increases, the number of collisions with the walls of the container can only

remain constant if the particles are moving faster.

iii.

Avogadros law states that the volume and number of moles are directly proportional;

when the volume increases the number of collisions with the walls of the container can

only remain constant if the number of moles of the gas increases.iv.

Daltons law states that the total pressure is the sum of the partial pressures of the

components of the gas. Kinetic molecular theory states the pressure is a result of

collisions between the gas particles and containers of the wall.

c. Ideal gas law can be derived directly using the postulates of kinetic molecular theory

i. Pressure of a sample gas is equal to the total force divided by the area

ii. The mass time velocity required is proportional to the temperature, the pressure is equal

to the total force over area, and the constants can be removed because it is a

proportionality

d. Since the temperature determines the average kinetic energy of a sample of gases, gases with a

lower mass will travel faster at a given temperature

e.

When the temperature of a gas increases, the distribution of molecular speeds gets broader and has

a higher average value

8.

Mean Free Path, Diffusion, and Effusion of Gases

a.

The mean free path of a gas is the average distance that a gas particle can travel before colliding

with another gas particle

b.

Diffusion is the process by which molecules spread out

c.

Effusion is the process of a gas escaping a container with a small hole in it.

i.

Grahams law of effusion relates the rate of molecular effusion to the molar ma ss of the

gas

9.

Real Gases: The Effects of Size and Intermolecular Forces

a.

Real gases behave ideally when the size of the gas particle is negligible compared to the distance

between the gas particles and when forces between particles are insignificant

i. Ideal behavior is best approximated at low pressures and high temperatures.

b. Intermolecular forces are attractions and repulsions that exist between atoms or molecules; at

lower pressures particles are too far away from each other to exert large forces and at hightemperatures particles are moving too fast to be affected by these forces.

c. Different molecules and atoms will have different deviations from ideal behavior.

10. Chemistry of the Atmosphere: Air Pollution and Ozone Depletion

a.

The troposphere is the region of the atmosphere that is closest to the earth and is most affected by

air pollution

i.

Pollutants in the troposphere include sulfur oxides, carbon monoxide, nitrogen oxides,

and ozone.