Unit 9 chem states of matter

Kinetic theory

theory that deals with the movement of particles (atoms, molecules)

3 main Ideas (related to gases)

1. Particles are small, have insignificant volume, are far apart, and are independent.

2. The motion of gas is rapid, chaotic, rando,m and constant for a given temp 

3. Collisions with another particle or object are perfectly elastic (no energy lost)

Gas pressure

•  is caused by the force exerted when gas particles collide with something

• One molecule - not much force

• Billions of molecules - measurable force

• No particles - no collisions = vacuum 

atmospheric pressure

• results from collisions of air molecules with objects

  • Measured with a barometer

  • Decreases as move up the mountain (higher elevation)

    • Ex-Mt. Everest

Units of pressure (SI)

Pascals (pa)

US

pounds per inch

Atmospheres

Atm

Millimeters of measure

mmHg or torr

Millibars

Mb—used in weather class (hurricanes) 

relationship 

1 atm = 101.3 kPa =14.7 psi=760 mmHg (torr) =1013 Mb

Ex: How many atm in 1169 mmHg

1160 x 1 atm/760 mmHg

Kinetic energy and temp 

• As energy is added to particles, some of it is absorbed (stored or potential)

• The rest of the energy is used to speed up the particles (kinetic)

• This results in an increase in temp

Average Kinetic energy

• Not all particles in a substance are moving at the same speed

• Some fast, some slow, most in the middle

• When the temp is taken, it is a measure of the average kinetic energy of that substance.

All substances at the same temperature have the same average no matter the state they are (solid, liquid, or gas)

Average Kinetic energy and temp 

If so cold all motion were to stop we would call that temp absolute zero 

O kelvin or 213 kelvin 

Direct relationship (in, K not C

If double the kelvin temp ( remember it is based on the n motion of particles) the motion would double)

liquids

• Similar to gases, but one big difference

  • Liquids have an attraction for each other; gases do not

  • This attraction holds the liquid particles close together

  • The greater the attraction, the more difficult it is to break the liquids apart into gases

  • are close together (more dense than gases)

Evaporation (a form of vaporization)

• Going from liquid to gas at the surface of the liquid

• Only liquid particles that can escape have enough energy to break free.

• More evaporation occurs at higher temp b/c liquid particles have more average kinetic energy.

• High-energy particles are  removed, so evaporation is a cooling process

  • Ex. sweat, shower, pool

• Evaporation will continue in an open container, but in a closed container will reach an equilibrium.

Vapor Pressure

• force exerted by a gas above a liquid

  • The easier something evaporates, the higher the vapor pressure 

    • Ex. gasoline, alcohol (not water or veg oil)

  • Increases with temp increase

    • More particles have enough KE to escape

  • Measured with a manometer

Boiling Point

• when the vapor pressure is equal to the external air pressure

  • It depends on temp of liquid and external pressure

  • Changes depending on external pressure

    • For water at sea = 100°C

    • On top of Mt. Everest = 70°C (external pressure lower)

    • chtr143.pdf

    • Effects of cooking at high altitudes 

      • Must boil things longer (water not as hot)

    • Increases water temp if opposite occurs (more pressure)

      • Use of “pressure cooker”

  • Normal B.P. is when at 1 atm pressure

Solids

• Solid particles, unlike liquids and gases, can’t move freely (but are still vibrating rapidly)

  • Particles held in a fixed position by strong forces

  • Tightly packed (more dense than liquid or gas) (wax demo)

• Usually have an orderly arrangement= crystalline

  • 7 different shapes

allotropes

• Some solids exist in more than one form

  • Ex. Carbon

    • Diamond, graphite, or buckminsterfullerene

amorphous

• Some solids have no ordered arrangement

  • Ex. rubber, plastic, glass

    • No definite melting point

• Going from one state to another

Melting point

•  temp which solid turns to liquid

  • Particles have enough KE to break attractive forces

S → L

melting ( ← freezing)

L → G

vaporization, boiling (← condensation)

S → G

sublimation ( ← deposition) .

ex - iodine, carbon dioxide (dry ice), water (freeze drying), air fresheners, mothballs

During a state change

• the temp remains constant!!!

  • Ice water melting stays at 0^oC, water boiling stays at 100^oC

 Factors Affecting Gases

• Pressure 

  • Kilopascals (kPa), atmospheres (atm), or millimeters of mercury (mmHg) aka torr

• Volume

  • Liters (L) or milliliters (mL)

• Temperature

  • Kelvins (K) for Gas Laws, not Celsius (^oC)! 

• Number of particles or amount 

  • Moles (may have to convert to/from grams)

Boyle’s Law

as pressure increases, volume decreases

• P₁xV₁=P₂xV₂

• A big concern for scuba divers!

• If pressure is 2.1atm and volume is 1.75L, what is the new volume (L) at 1.3atm?

Charles’s Law

• as temp increases, volume increases

  • V₁/T₁ = V₂/T₂

  • The basic concept in hot air balloons

If the volume at 30^oC is 1.5L, what is the new volume (L) at 100^oC?

Gay-Lussac’s Law

• as temp increases, pressure increases

  • P₁/T₁ = P₂/T₂

  • Must be concerned when burning canisters

    • Increasing temp may cause too great of pressure Kaboom!

  • Ex. If the temp at 1.5atm is 300K, what is temp (K) at 2.4atm?

Combined Gas Law

• P₁xV₁ = P₂ x V₂

      T₁           T₂

• Ex. If a 20.0L balloon at 273K and 1.0atm is now at 373K and 1.5atm, what is the new V (L)?

Ideal Gas Law

• The other gas laws don’t take into amount of gas (moles) which be symbolized with an “n”

  • Moles will affect pressure and volume directly, so goes in the bottom of the combined gas law

  • At STP, we know T=273K, P=1atm, n=1.0mol and V=22.4L, so we set this to a constant (R) which = .0821

    • P₁xV₁ = P₂ x V₂       1atm(22.4L) = .0821

   n₁xT₁      n₂xT₂           1mol(273K)

• So, PV= R 

        nT   

• as long as all values are in units related to R (atm, L, K and mol)

• Rearranging, we get PV=nRT (use this formula!)