GAS LAWS * (Heath. Ch.7 pp.187-)

 

1.  Avogadro’s Hypothesis: Equal volumes of gases at the same temp.and pressure contain equal number of particles.

 

2.  Ideal Gas law: 1 mol of all gases at STP

(standard temp. 0° C, 273 K and Pressure 101.325 kPa) occupies 22.4 L

 

3.  Boyles Law: Pressure and Volume are inversely proportional (temp. constant).  P1V1 = P2V2 = k

example – If you increase the pressure on a gas the volume decrease (compression).   If you increase the volume of a sample of air, say by spinning the mass of air like in a hurricane, the air pressure at the centre gets very, very low.

 

4.  Charles Law:  Temperature and Volume are directly proportional (pressure constant)

                                V1 = V2

                                T1    T2

example: if you heat up a gas, keeping pressure constant, the volume increase (expansion).   Also if you cool a gas, the volume decreases (contraction).

Note.  if you increase the volume the temperature has to go up so the molecules are forced to absorb heat from the surroundings (refridgeration).

 

 

 

 

 

 

 

 

 

5.  Buoyancy Law: The upward force on an object placed in a liquid or gas is equal to the mass of the medium displaced.

 

 

 

 

 

 

 

 

 

GAS DEMONSTRATIONS

 

1.  Noble gas examples

– He, Ne, Ar, (fire extinguishers)

2.  CO2  

- bubbled through basic solution using indicator causes change in pH due to H2CO3

- denser than air will flow and put out flame

 

3.  H2 demos

– balloon filled will ignite with oxygen in air

- bottle with higher concentration of oxygen will explode

 

4.  O2

-will cause iron wool to combust quickly

 

5. N2

- BP = -196 °C

- gas pressure will explode a 750 mL plastic bottle when dampered by a garbage pale containing water

 

6.  Gas-powered Rockets

- Water rockets

- Solid rocket fuel

- Methane in can

- Methanol in bottle fires cork

- Methanol in film canister sparked by BarBQ starter

 

 

GAS & BUBBLES

1.  Read “So What’s a Bubble?”

Define nucleation

 

Pop Demos

- CO2 dissolves in water, better in cold than in hot

-  Bubbles in glass form on side, also small bubbles nucleate more bubbles, shaking, but prevented from releasing when capped

- Bubbles formed over sharp crushed ice more than over smooth rounded ice

- Feeling at back of throat when drinking fizzy drinks is the gas bubbles formed when they are nucleated

- Bubbles form on chocolate chips causing them to rise and fall

- Ice cream crystals cause much more nucleation and cream has greater surface tension to make bubbles stay longer

- Milk added to drinks can make them frothy

- Mentos  (rough sugar crystals) placed in a fresh bottle of Coke will cause it to release much gas