The Properties The Properties of Gasesof Gases

Properties of GasesProperties of Gases1.1. Gases expand to fill the container.Gases expand to fill the container.

2.2. Gases take on the shape of the Gases take on the shape of the container.container.

3.3. Gases are highly compressible. Gases are highly compressible. (Can be liquefied at high pressures).(Can be liquefied at high pressures).

4.4. Gases have low densities.Gases have low densities.

5.5. Gases mix uniformly.Gases mix uniformly.

The Kinetic Molecular The Kinetic Molecular TheoryTheory

The kinetic molecular theory The kinetic molecular theory describes the behavior of describes the behavior of ideal gases.ideal gases.

An ideal gas is one that An ideal gas is one that conforms to the KMT.conforms to the KMT.

1. Molecules are in constant 1. Molecules are in constant random motionrandom motion

Temperature is proportional to the Temperature is proportional to the average kinetic energy of the average kinetic energy of the molecules. molecules. KE = ½ mvKE = ½ mv22

KE = ½ mass times speed squaredKE = ½ mass times speed squared

The speed is proportional to the The speed is proportional to the absolute temperature (Kelvin).absolute temperature (Kelvin).

2. A gas is mostly empty space2. A gas is mostly empty space

Molecules are far apart from each Molecules are far apart from each other. This accounts for the low other. This accounts for the low density and high compressibility.density and high compressibility.

The volume of the individual The volume of the individual molecules is negligible compared molecules is negligible compared to the volume of the gas.to the volume of the gas.

3. No intermolecular forces3. No intermolecular forces

There are no attractive or repulsive There are no attractive or repulsive forces between gas molecules.forces between gas molecules.

Adjacent molecules do not attract Adjacent molecules do not attract or repel each other.or repel each other.

4. Collisions are elastic4. Collisions are elastic

When gas molecules collide with When gas molecules collide with each other they may speed up or each other they may speed up or slow down, slow down, BUT …BUT …

The net (total) energy of the gas The net (total) energy of the gas molecules does not change.molecules does not change.

Kinetic Molecular TheoryKinetic Molecular Theory1.1. Gases in constant motion, speed Gases in constant motion, speed

depends on temperature.depends on temperature.

2.2. Molecules have negligible Molecules have negligible volume.volume.

3.3. No intermolecular forces.No intermolecular forces.

4.4. Elastic collisions. No change in Elastic collisions. No change in energy.energy.

Temperature reminderTemperature reminder

When doing calculations, When doing calculations, temperature must always be in temperature must always be in an absolute temperature scale …an absolute temperature scale …

… … where the lowest possible where the lowest possible temperature is zero degrees.temperature is zero degrees.

Use Kelvin degrees!Use Kelvin degrees!

Temperature conversionTemperature conversion

K =K = C +C + 273273

1. 1. PressurePressure is the force per unit is the force per unit area exerted by the gas molecules.area exerted by the gas molecules.

2. 2. PressurePressure is proportional to is proportional to the number of collisions the number of collisions between the gas molecules and between the gas molecules and the walls of the container.the walls of the container.

PressurePressure

PressurePressure1. 1. PressurePressure is a measure of the is a measure of the

force per unit area.force per unit area.P = P =

forceforceareaareaPressure can be in Pressure can be in

pounds per square pounds per square inch (PSI), or …inch (PSI), or …

… … newtons per square meter (N/mnewtons per square meter (N/m22))

pascal (Pa) = N/mpascal (Pa) = N/m22

PressurePressure1. 1. PressurePressure is a measure of the is a measure of the

force per unit area.force per unit area.P = P =

forceforceareaareaGlass Glass

tube tube with with

HgHg

Bowl of HgBowl of Hg

At sea level, air pressure At sea level, air pressure holds up a column of holds up a column of mercury 760 mm high.mercury 760 mm high.

TorricelliTorricelli

Pressure MeasurementsPressure Measurements

Standard sea level pressure is…Standard sea level pressure is…

1.00 atmospheres (atm)1.00 atmospheres (atm)760 mm Hg760 mm Hg760 torr (from Torricelli)760 torr (from Torricelli)101.3 kilopascals (kPa) 101.3 kilopascals (kPa) 14.7 lb/in14.7 lb/in22

Pressure MeasurementsPressure Measurements

Standard sea level pressure is…Standard sea level pressure is…

1.00 atmospheres (atm)1.00 atmospheres (atm)760 mm Hg760 mm Hg760 torr (from Torricelli)760 torr (from Torricelli)101.3 kilopascals (kPa) 101.3 kilopascals (kPa) 14.7 lb/in14.7 lb/in22

ExactExact

PressurePressure2. 2. PressurePressure is proportional to the is proportional to the

number of collisions between the number of collisions between the gas molecules and the walls of gas molecules and the walls of the container.the container.

If you change the If you change the number of number of

collisions, you collisions, you change the pressure.change the pressure.

Do the following conversions:Do the following conversions:

1.1. Express 20.0 C in K.Express 20.0 C in K.

2.2. What is 200. K in Celsius?What is 200. K in Celsius?

3.3. Convert 695 torr to atm.Convert 695 torr to atm.

4.4. Convert 0.952 atm to kPa.Convert 0.952 atm to kPa.

5.5. Convert 500. kPa to atm.Convert 500. kPa to atm.

Now do these conversions:Now do these conversions:

1.1. Express -30.0 C in K.Express -30.0 C in K.

2.2. What is 576 K in Celsius?What is 576 K in Celsius?

3.3. Convert 705 mm Hg to kPa.Convert 705 mm Hg to kPa.

4.4. Convert 3.50 atm to torr.Convert 3.50 atm to torr.

5.5. Convert 84.3 kPa to atm.Convert 84.3 kPa to atm.