# What is Air? It’s a GAS! Mostly Nitrogen= 78% Oxygen = 21%

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What is Air? It’s a GAS! Mostly Nitrogen= 78% Oxygen = 21%
Argon = about 1% Trace amounts of other gases Since air is a gas, it is matter – which means it has mass and occupies space. In the picture, you see the composition of Earth’s atmosphere ( 78% N2, 21% O2, 1% Ar, with trace amounts of elements in lower chart) Photo: Composition of Earth’s Atmosphere

Volume Define system Molar Volume of any gas at STP = 22.4 L
Contest - blow up balloon in bottle to show that air occupies space- one bottle has holes and one doesn’t “Wilbur’s Space Machine” book Put bead cases on viewer Just because you learned that gases expand to fill their container, doesn’t mean that every bit of that space is occupied with a gas at any one time, lots of empty space When determining the amount of a gas (blow up balloon), you have to define your system. Are you looking at the entire atmosphere as a whole (As a whole, the atmosphere extends to at least 800 miles above the earth's surface.) or just small areas of the atmosphere (microclimate) or a closed system such as this balloon? When comparing gaseous systems, we use a measurement called molar volume. The molar volume of any gas at Standard Temp and Pressure is 22.4 L Pic - Earth pic-http://www.chemistryland.com/CHM107/AirWeBreathe/AirMisconceptions.html

Amount of Gas 1 Molar Volume (22.4 L) =
6.02 x 1023 particles (Avogadro’s number) 1 Mole Add beads to cases, we can count these particles. How many particles are in this balloon? Since we can’t see them, counting would be difficult. An easier method would be to use the volume that we just discussed. A molar volume of any gas at STP is 22.4 L and this volume contains Avogadro’s number of particles. So, to determine the number of particles in this balloon, we could use water displacement to determine its volume and calculate the number of particles. In 5th grade, you wouldn’t have to do anything like that. The amounts of gas that you discuss will just be relative (more air or less air - release air from balloon). However, since kids ask all sorts of questions, I just want you to be prepared.

Pressure The force exerted by the weight of air molecules
Atmospheric pressure = 14.7 lbs/in2 Pressure – Demo – can crush, newspaper and shims, Egg in bottle, air bag Pic-http://kids.earth.nasa.gov/archive/air_pressure/index.html

Behavior of Gases Parameters Definition Amount of gas
Number of particles, mass Volume Amount of space occupied Temperature Average kinetic energy of the particles Pressure Force exerted To understand our atmosphere with its weather and climate changes, you have to first understand how gases behave. In this portion of our workshop, we will develop some basic principles of Meteorology as we investigate the behavior of gases. I’m also going to demo a model of gases that can be used in an inquiry fashion for student investigations. There are 4 parameters that determine the behavior of gases: - Amount of the gas – number of beads - Volume – size of container - Temperature - shaking Pressure – collisions

Principles of Meteorology
Foldable Envelope fold Add information at each of 4 stations Show how to do envelope fold with foldable Pic-

Station 1 Temp vs. Volume Charles’ Law (closed system, constant P)
As temperature decreases, volume decreases As the air cools it condenses. Temp is a measure of avg KE. If temp decreases, less KE so particles are slowing down. If they move around less, the take up less space. Think of a hot crowded gym with kids sitting on bleachers, when its hot the kids are moving around more, don’t want anyone touching them sit farther apart. Think of the same gym in the winter time, everyone is huddled together for warmth, not moving as much. Charles’ law – if ideal gas in a closed container Thermal expansion

Station 2 Temp Vs. Density
When temperature decreases, density increases As cooler air condenses it becomes more dense and sinks forcing warmer air upwards. In station 2 – how does temp relate to density? If you change volume, then density has to change since D = mass/volume. In balloon from station 1, fixed amount of gas. As temp inc, volume inc, and as temp dec, volume dec. Look at math and model density with beads and cases Let’s say, when heated, we have 10 g in 100 mL of space D= 10/100 = 0.1g/ml When cool, we have the same mass in less volume - 10 g in 50 mL of space D= 10/50 = 0.2 g/ml So density increases Model density 2 bead cases – different volumes but same number of beads

Station 3 Volume and Pressure
Boyle’s Law (closed system, constant T) As volume increases, pressure decreases As warm air rises, it expands (volume inc). As volume increases, pressure it exerts decreases Warm fronts = low pressure Cold fronts = high pressure Boyle’s law - if ideal gas in a closed container P & V vary inversely, as volume inc, P dec Use model to explain: Same number of particles = beads Change volume – different size containers Same temp/KE – shake at same rate What happens to pressure (number of collisions) (also higher density as in cold front, more pressure)

Station 4 – Pressure and Temperature
Gay-Lussac’s Law As pressure decreases, temperature decreases As the pressure of the rising air decreases, the air cools. The moisture in the air condenses to form clouds. Gay-Lussac’s law – if ideal and in closed system As pressure dec, temp dec Model Same number of particles or beads Same volume – container size Easier to look at effects of temp on pressure Shake one gently and one hard – which exert more pressure? (high temp) less P? (low T)

When 3 factors change… Combined Gas law P1V1 = P2V2 T1 T2
VOLUME increases (rising air) PRESSURE decreases (Boyle’s Law) TEMPERATURE decreases (Gay-Lussac’s Law) Looks like charles’ law has been violated (volume inc and temp dec) not a closed system either

Fronts Carol – density flow model

Cold Front Forms cumulus clouds
Strong cold front forms cumulonimbus clouds, storms, tornado, snow squalls Low humidity Cold air mass advances toward warm air mass Cold air mass slides under warm air mass Forces warm air to rise and cool rapidly Can produce rapid temperature drops and severe weather Carol – density flow model (add info?)

Warm Front Warm air advances toward cold air mass
Warm air slides over cold air Front moves more slowly with a gentle rise in temperature Produces less severe weather, steady precipitation lasting for days Leading edge forms high cirrus clouds at first, then cirrostratus, altostratus, and nimbostratus later High humidity Carol – density flow model

Condensation Cool air causes water VAPOR to condense - contains less moisture than warm air Relative humidity - a measurement of the amount of water vapor in the atmosphere compared to the amount of moisture that can be in gas form at a given temperature. Dew point - the temperature to which air would have to be cooled to become “saturated”. Once the air is cooled enough, the water vapor condenses to form a liquid. ﾐ relative humidity lab ﾐ water cycle model – book bringing the rain to kapiti plain - Draw phase changes Warm air can hold more water vapor than cool air so the relative humidity is based on air temperature.

Rain and Clouds What are other examples of water cycle – on large or smaller scale? Lid with condensation on stove Steam up mirror in bathroom

There is a fine line Precipitation and cloud formation is all about states of matter When water evaporates at the surface, it is an invisible gas. As the water vapor (gas) rises, it cools and condenses to a liquid droplet. Clouds are liquid! (condensed water vapor) Rain is larger droplets of liquid that fall to the ground. States of matter depend on the energy of the molecules Rain droplets are also round, not teardrop shaped

Careful explanation Air does not “hold” water. So what can we say: Air is a mixture. Water vapor is commonly found in air. If the air is cold enough, water cannot remain in gas state and becomes liquid. The size of the drops and amount of water will determine if it can stay aloft or if the force of gravity is enough to pull the liquid to the ground. This can perpetuate a misconception that gases are like solid sponges or liquid solutions. Gas mixtures do not behave like either of these scenarios.

Atmosphere Exosphere Ionosphere Thermosphere Mesosphere Stratosphere
Troposphere Our atmosphere is composed of Troposphere - weather Stratosphere - Temperature increases with height - contains the ozone layer, the part of the Earth's atmosphere which contains relatively high concentrations of ozone. Mesosphere - temperature decreases with height Thermosphere - temperature increases with height. Ionosphere- ionized by solar radiation - Influences radio propagation to distant places on the Earth. It is located in the thermosphere and is responsible for auroras. Exosphere - particles are exchanged with magnetosphere or solar winds Photo:

Atmosphere

Atmosphere Misconceptions: The atmosphere traps radiation.
The atmosphere “re-radiates” the radiation back to Earth. The atmosphere works like a greenhouse, blanket or car.- NO! True Statement- Radiation is absorbed by the atmosphere and radiates back to the Earth. Two times more heat comes from our atmosphere than the Sun. The atmosphere promotes convection instead of preventing convection.

Misconception?

Weather Station Temperature Barometric pressure Relative humidity
Light Anemometer UVA/UVB

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