GasesKMS 8th Grade ScienceMs. Bormann

The Nature of Gases

The first gas to be studied was air & it was a long time before it was discovered that air was actually a mixture of particles rather than a single gas.

Although air is a mixture of several different gases, it behaves much the same as any single gas.

Regardless of their chemical identity, gases tend to exhibit similar physical behaviors

Characteristics of Gases

The Kinetic Molecular Theory

Kinetic =

Molecular =

The theory states

Motion

Molecules

the tiny particles in all forms of matter are in constant motion.

Boyle’s Law

Robert Boyle was among the first to note the relationship between of a gas.

During his experiments and were NOT allowed to change.

Boyle’s Law states

For example: If the volume is halved, the pressure would be

pressure and volume

temperaturethe amount of gas

The pressure exerted by a gas held at constant temperature variesinversely with the volume of the gas.

doubled

Pressure

Pressure – amount of force exerted per unit of area.

• Pa = Pascal. SI unit for pressure. One Pascal of pressure is 1 Newton per square meter – therefore a Pascal is

a very small unit.

• kPa = kilopascal. A kilopascal is 1,000 Pa. Example: At sea level atmospheric pressure is 101.3 kPa. This means that at Earth’s surface, the atmosphere exerts a force of 101,300 Newton’s on every square meter (this is about the weight of a large truck)

• Atm = standard atmosphere. 101.3 kPa or 101,300 Pa

Boyle’s Mathematical Law

A gas has a volume of 3.0 L at 2 atm. What is its volume at 4 atm?

P1V1 = P2V2

Boyle’s Law

1. Determine which variables you have

2. Determine which law is being represented

3. Rearrange the equation for the unknown variable.

4. Plug in the variables and solve.

P1 = 2 atm V1 = 3.0 L P2 = 4 atm V2 = ?

P and V = Boyle’s Law

Charles’s Law

Jacques Charles was among the first to note the relationship between of a gas.

During his experiments and are NOT allowed to change.

Charles’s Law states

For example: If the temperature is increased, the pressure will

temperature and volume

pressurethe amount of gas

At constant pressure, the volume of a fixed number of particles of gas is directly proportional to the absolute (Kelvin) temperature

increase

Temperature

Charles' Law must be used with the Kelvin temperature scale. This scale is an absolute temperature scale. At 0 K, there is no kinetic energy (Absolute Zero). According to Charles' Law, there would also be no volume at that temperature. This condition cannot be fulfilled because all known gases will liquefy or solidify before reaching 0 K.

oC 273 Kelvin

Charles’s Mathematical Law

Eg: A gas has a volume of 3.0 L at 127°C. What is its volume at 227 °C?

Charles’s Law

1. Determine which variables you have

2. Determine which law is being represented.

3. Plug in variables

4. Cross multiply and solve

T1 = 127°C + 273 = 400K

V1 = 3.0 L T2 = 227°C + 273 =

5ooK V2 = ?