Gases And you

Gas demonstrations with LN2 (liquid nitrogen) Liquid Nitrogen boiling temp. ~ - 196oC (= - 320o F) Compare that to dry ice (solid CO2) Δ to gas at: ~ - 79OC ( - 109OF) 1) Balloon full of air at room temp.  into LN2 Observation: As air cools off in balloon it takes up less volume Conclusion: as T goes down, V goes down. (and phase Δ to liquid/solid – that take up much less volume than gas)

LN2 Demonstrations continued 2) Remove balloon from the LN2 and worm up in the air – Observations: The balloon apparently re-inflates Conclusion: As the air (mainly N2, O2, and CO2) warm up (from -320OF to 24O F) the liquids change phases to form gases that expand. This demonstrates that the atoms that make up liquids take up far less space than the same atoms in a gaseous phase. Also, as the gasses warm up (T goes up) – they also take up more volume (V goes up).

LN2 Demonstrations continued 3) LN2 into balloon  tie off and increase temp. to room temp. Observation: as temp. of the LN2 increases, the balloon appears to “blow up”. Conclusion: As T goes up, V goes up (and LN2 phase changes to gas N2) 4) Flask at room temp. with air covered with balloon  into LN2 Observation: As flask cools off, balloon is pushed into flask Conclusion: As the gasses in the flask cool down (T goes down), they take up less volume (V goes down) .

LN2 Demonstrations continued 5) Add a larger amount of LN2 to another balloon, tie off and let warm up. Observations: The balloon with more LN2 inflates to a larger volume than the first balloon with less LN2 Conclusion: More LN2 (more moles) at the same temperature results in more volume

Additional LN2 Demonstrations 6) LN2 into capped pop bottle (outside into warm water) Observations: As LN2 phase changes into a gas – and that gas heats up the pressure in the bottle increases (because the volume is held constant) until the bottle blows up. Conclusions: The pressure builds up until the structural integrity of the plastic is compromised and the bottle pops – allowing the volume to go up and consequently, the pressure to go down

Additional LN2 Demonstrations (that do not necessary involve gases – but are fun) LN2 poured onto the table LN2 poured onto the carpet Nilla wafers into LN2  into mouth ? Finger into LN2? Flower into LN2  shatter Discussion summary

When you discuss gases in chemistry or physics you need to consider several variables 1) Temperature of the gas 2) Volume of the gas 3) Pressure of the gas 4) Number of moles of the gas (based on the mass – do you recall how to do this from your chemistry class???)

Demonstrations with heated water 1) Cover cold flask (that has a small amount of water in it) with a balloon and heat up the flask on a hot plate Observations: Balloon expands when the gas is heated Conclusion: increase in T  increase in volume 2) Heat large flask, cover with balloon, cool off flask in cold water bath Observations: Balloon is pushed into flask when the gases cool Conclusion: decrease in T  Decrease in volume

Demonstrations with heated water continued 3) Heat a smaller flask with water in it until the water is boiling, cap with a cork, cool off in a ice bath. Observations: Water stops boiling for a time – then starts to boil again even though it is in the cold water Conclusion: Decrease in T  Decrease in P  water boils at low T

Demonstrations with heated water continued 4) Students heat up (on hot plate) small flask w/water that is corked w/ glass tube. Then using a hot pad the students invert the flask into a cold water bath. Observations: The water from the flask is violently pushed into the flask in a vortex of energy and excitement. Conclusion: decrease in T  decrease in Volume

The mathematical relationship that summarizes it all for gases (the Ideal gas law)…. PV = nRT P = pressure (in atmospheres) V = volume (in Liters) n = number of moles of the gas R = a gas constant T = temperature (in Kelvin)

Let’s talk Pressure The pressure units we will use in this class are atmospheres (atm.) Other units are used in studies of gasses - such as: 760 mmHg (= 1 atm) 760 Torr (= 1 atm) 101.32 Kilo Pascals (Kpa = 1 atm) 14.7 Pounds/square inch ( = 1 atm) The pressure units you use will influence the constant value you use in your calculations

Now let’s talk Volume Volume units that need to be used are Liters The volume is a measure of the space that the gas occupies (based on the size of the container that it is in).

Let’s talk about the number of moles (n) The number of moles is based on the molar mass of the sample that you are using (recall that from your chemistry class?) If I have 4.04 g of hydrogen gas, then I have: 4.04 g ( 1 mole hydrogen gas) = 2 moles of hydrogen gas 2.02 g But I will give you the number of moles rather than having you do that calculation on your own…

Let’s talk the constant (R) Pressure units R value to use atm. Use: 0.08206 mmHg Use : 62.4 Torr Use : 62.4 Kpa Use : 8.31

Let’s talk temperature In our calculations we will need to use Kelvin as the temperature unit But our thermometers have units of Celsius – so we need to do a conversion. # degrees Celsius + 273 = the temp. in Kelvin Example 1: 0OC = ? Kelvin 0 + 273 = 273 Kelvin! Example 2: 26OC = ? Kelvin 26 + 273 = 299 Kelvin!

Other relationships will be used in other classes (chemistry or physics) that focus on gas laws But all of those relationships can be derived from the ideal gas law PV = nRT so: P1 /T1 = nR/V = P2 /T2 For example: the relationship for pressure and temperature(when holding all other variables constant: P1 = P2 T1 T2 So if: The initial P and T in a container of gas is. 3 atm and 290K, and the temp. is increased to 320K, what is the new pressure?

Other relationships will be used in other classes (chemistry or physics) that focus on gas laws PV = nRT so: P1V1 = nRT = P2V2 For example: the relationship for pressure and volume (when holding all other variables constant: P1 = V2 P2 V1 SO if: The initial pressure and volume are 4 atm and 2L and the volume is decreased to 1.5 L, then what is the new pressure?

Other relationships will be used in other classes (chemistry or physics) that focus on gas laws PV = nRT so: V1 / T1 = nR/P = V2 / T2 For example: the relationship for volume and temperature (when holding all other variables constant: V1 = V2 T1 T2 So if: The initial volume and temperature are 4L and 302K, and the temperature is increased to 367 K, what will be the new volume?

Ping pong ball cannon demo

Implosion of tanker car https://www.youtube.com/watch?v=T9bpUfWy8Wg

Now some fun applied math problems for you