Chapter 9: Gases

States of Matter StateShape and Volume Compressibilty Ability to flow Forces between Molecules Solid-Fixed shape -Fixed volume NO VERY STRONG Liquid-Takes shape of container -Fixed volume NOYESSTRONG Gas-Takes shape of container -Volume is not fixed Yes it is compressible YESVirtually 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 = o C, Kelvin (K) b) Pressure – force/unit area - Unit = N/m 2 = Pa kPa * old units: psi, mm Hg, torr, atm *Standard temp and Pressure (STP) = 0 o C & kPa

Kinetic Molecular Theory Assumptions 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 collide 4.In the gas phase, there are no attractive forces between particles 5.At any given temperature, the average kinetic energy of the particles in gases is the same.

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 ctfolder/flashfiles/gaslaw/boyles_law_graph.html