Chapter 9: Gases

States of MatterState Shape and

VolumeCompressibilty Ability to

flowForces

betweenMolecules

Solid - Fixed shape- Fixed volume

NO NO VERY STRONG

Liquid - Takes shape of container

- Fixed volume

NO YES STRONG

Gas - Takes shape of container

- Volume is not fixed

Yes it is compressible

YES Virtually NON-EXISTANT

Kinetic Molecular Theory (Review)

solid liquid gas (vibrational) (vibrational, (translational) rotational, translational)

What is unique about “gas” state?- There is space between molecules so size of

molecules DOES NOT affect the VOLUME a gas occupies.

- The volume is affected when the space between the molecule changes by

a) Temperature - Unit = oC, Kelvin (K)b) Pressure – force/unit area - Unit = N/m2 = Pa kPa * old units: psi, mm Hg, torr, atm *Standard temp and Pressure (STP) = 0oC & 101.325 kPa

Kinetic Molecular TheoryAssumptions for Gases

1. Each gas molecule is separate, surrounded by empty space

2. Particles move rapidly in straight lines, often colliding with each other and the container walls.

3. There is no loss of energy when 2 particles collide4. In the gas phase, there are no attractive forces

between particles5. At any given temperature, the average kinetic

energy of the particles in gases is the same.http://www.chm.davidson.edu/vce/kineticmoleculartheory/basicconcepts.html

• In a container filled with gas there will be collisions between the particles and particles and also collisions between particles and the container walls.

• The collisions between the particles and the walls is known as GAS PRESSURE.

• The greater the amount of collisions with the wall in a given amount of time, will give a greater pressure.

• As the volume decreases, the particles collide more frequently with the containers walls. Therefore, the particles will exert greater force on the walls.

• Therefore, PRESSURE INCREASES.* Pressure = force/area = force per surface area

Boyle’s Law Simulation & Graph

http://www.chem.iastate.edu/group/Greenbowe/sections/projectfolder/flashfiles/gaslaw/boyles_law_graph.html