Its a GasIts a Gas

Kinetic Molecular Theory

Kinetic Molecular Theory

The theory that modern day chemist’s use to explain the behaviors and characteristics of gases

• The word kinetic refers to motion.

• The word molecular refers to molecules

The theory that modern day chemist’s use to explain the behaviors and characteristics of gases

• The word kinetic refers to motion.

• The word molecular refers to molecules

ContinuedContinued

The theory states that the tiny particles in all forms of matter in all forms of matter are in constant motion.This theory is used to explain the behaviors common among gases

The theory states that the tiny particles in all forms of matter in all forms of matter are in constant motion.This theory is used to explain the behaviors common among gases

Gas AssumptionsGas Assumptions

The particles in a gas move in constant random motion.Particles move in straight paths and are completely independent of each of otherParticles path is only changed by colliding with another particle or the sides of its container.

The particles in a gas move in constant random motion.Particles move in straight paths and are completely independent of each of otherParticles path is only changed by colliding with another particle or the sides of its container.

Gases fill their containersGases fill their containers

Gases expand until they take up as much room as they possibly can.Gases spread out to fill containers until the concentration of gases is uniform throughout the entire space.This is why that nowhere around you is there an absence of air.

Gases expand until they take up as much room as they possibly can.Gases spread out to fill containers until the concentration of gases is uniform throughout the entire space.This is why that nowhere around you is there an absence of air.

Gases exert pressureGases exert pressure

The sum of all of the collisions makes up the pressure the gas exerts.

The sum of all of the collisions makes up the pressure the gas exerts.

Gas particles exert pressure by colliding with objects in their path.

Gas particles exert pressure by colliding with objects in their path.

Units for Pressure (P)Units for Pressure (P)

The pressure of a gas is the force exerted on the wall of the container a gas is trapped in.There are several units for pressure depending on the instrument used to measure it including:

The pressure of a gas is the force exerted on the wall of the container a gas is trapped in.There are several units for pressure depending on the instrument used to measure it including:• atmospheres

(atm)• atmospheres

(atm)• Millimeters of Mercury (mmHg)

• Millimeters of Mercury (mmHg)• Kilopascal (kPa)• Kilopascal (kPa)

Volume (V)Volume (V)

The volume of the gas is simply the volume of the container it is contained in.The metric unit of volume is the liter (L)

The volume of the gas is simply the volume of the container it is contained in.The metric unit of volume is the liter (L)

Boyle’s LawBoyle’s Law

Robert Boyle was among the first to note the relationship between pressure and volume of a gas.He measured the volume of air at different pressures, and observed a pattern of behavior which led to his mathematical law.During his experiments Temperature and amount of gas weren’t allowed to change

Robert Boyle was among the first to note the relationship between pressure and volume of a gas.He measured the volume of air at different pressures, and observed a pattern of behavior which led to his mathematical law.During his experiments Temperature and amount of gas weren’t allowed to change

As the pressure increases

As the pressure increases

VolumedecreasesVolume

decreases

Gas particles have a high velocity, relative to their masses.Space can be lowered by pressure allowing gas particles less room to move which lowers the volume.

Gas particles have a high velocity, relative to their masses.Space can be lowered by pressure allowing gas particles less room to move which lowers the volume.

Pressure and VolumePressure and Volume

How does Pressure and Volume of gases relate

graphically?

How does Pressure and Volume of gases relate

graphically?

Volu

me

Volu

me

PressurePressure

PV = kPV = k

Temperature, # of particlesremain constant

Temperature, # of particlesremain constant

Boyle’s Mathematical Law:Boyle’s Mathematical Law:

since PV = ksince PV = k

P1V1 = P2V2P1V1 = P2V2

Eg: A gas has a volume of 3.0 L at 2 atm. What is its volume

at 4 atm?

Eg: A gas has a volume of 3.0 L at 2 atm. What is its volume

at 4 atm?

What if we had a change in conditions?What if we had a change in conditions?

1)determine which variables you have:

1)determine which variables you have:

P1 = 2 atm V1 = 3.0 L P2 = 4

atm V2 = ?

P1 = 2 atm V1 = 3.0 L P2 = 4

atm V2 = ?

Eg: A gas has a volume of 3.0 L at 2 atm. What is its volume

at 4 atm?

Eg: A gas has a volume of 3.0 L at 2 atm. What is its volume

at 4 atm?

2) Rearrange the equation for the variable you don’t know

2) Rearrange the equation for the variable you don’t know

3) Plug in the variables and chug it on a calculator:

3) Plug in the variables and chug it on a calculator:

P1V1 = V2P1V1 = V2

P2P2

(2.0 atm)(3.0L) = V2(2.0 atm)(3.0L) = V2

(4atm)(4atm)V2 = 1.5LV2 = 1.5L