Presentation on theme: "During this unit you will be able to answer the following questions:"— Presentation transcript:
1During this unit you will be able to answer the following questions: The Gas LawsDuring this unit you will be able to answer the following questions:Why does pumping a tire become difficult as it becomes more inflated?Why does a hot air balloon lift off the ground and the air inside is heated?Why does soda eventually go flat, and what could you do to slow that process down?Why do your car ties seem like they have lost air, or go flat in the cold winter months, but then as spring/summer approaches, they seem to have re-inflated on their own?
2What do you know?What is the name of the gas, mostly responsible for the greenhouse effect?Carbon Dioxide
3The Atmosphere Made of a sea of gases The air is made of 78% nitrogen, 21% oxygen, 0.9% argon, and 0.033% carbon dioxide.The trapping of heat energy in the atmosphere is called the greenhouse effect.Increasing the greenhouse gases could be increasing the worlds average temperature.
4Warmer temps. mean the ice caps would melt and cause coastal flooding CO2 in the atmosphere is increasing due to the combustion of fossil fuels and loss of forests
5The ozone is another main component of our atmosphere. Ozone is the molecule O3Shields us from UV rays given off by the sun. These UV rays cause cancer, and are called a mutagen.The ozone is approximately 3 mm thick
11Kinetic Molecular Theory Predicts the behavior of gases and assumes that gases are ideal gasesIdeal gases are gases that travel in a straight line and only change direction when they collide another gas molecule.There is no attractive forces between ideal gases.
12The average kinetic energy of gas particles is directly proportional to temperature in Kelvin. –THIS IS WHY WE USE KELVIN FOR ALL GAS LAW PROBLEMSMeaning: if gas molecules move faster,and hit each other more often, then thetemperature will increase. If the moleculesmove slowly and hit each other less often, thetemperature will decrease. Temperature depends onhow often and how hard molecules hit each other.
13Different gases at the same temperature move at different speeds. Why? They have different masses.Lighter molecules/compounds, such as H2, move faster than heavier molecules/compounds such as N2 or CO2
14Temperatures for gases are always given in Kelvin Temperatures for gases are always given in Kelvin. Remember that if the temperature is given in Celsius use the equation K = ºC
15Fluidity Gases are in constant motions and flow like liquids Gases are in constant motion and collide with each other and their container.The kinetic molecular theory assumes that the collisions are elasticThis means energy is not lost after a collision happens.
16DensityGases have a density that is less than solids and liquids because there’s more space between atoms.The kinetic molecular theory says that the volumes of the individual molecules can be ignored when compared to the total volume of the gas
17Volume and Compressibility Remember, volume is the amount of space something takes up.If you apply a pressure to a gas, the gas molecules come closer together.This decreases the volume of the gas.
18Volume = length * width * height Common units of volume include: liters (L), milliliters (mL), cubic meters (m3), or cubic centimeters (cm3)
19Avogadro’s principle states that equal volumes of gases under the same conditions have equal numbers of molecules. The volume of 1 mole of any gas at STP is 22.4 liters.This is called molar volume
20PressureWhen a gas fills a container it puts a pressure on the container in all directions.Think of blowing air in a balloon.Pressure is caused by the collision of gases running into each otherThe more collisions occurring, the more the pressure increasesPressure is defined as force exerted over a specific area
21Pressure = force/unit area The metric unit of force is the pascal (Pa) 1 pascal = 1 Newton/meter2
22All the air above your exerts (gives) a pressure. This is called atmospheric pressure1 atmosphere of pressure causes the a column of mercury 760 mm high.1 atmosphere = 760 mmHg
23PressureAbbreviationEquivalantPascelPaBarbar1 bar = 100,025 PaMillimeter of mercurymmHg1 mmHg = PaPound per square inchpsi1 psi = PaTorrtorr1 torr = PaAtmosphereatm1 atm = 101,325 Pa
24STP = standard temperature and pressure Values include 0ºC and 1 atm OR 273 K and kPa.
25What do you know?The average kinetic energy (temperature) of a gas molecule depends on _____________________.Pressure is caused by the ___________________ of gas molecules against each other and the container.HOW FAST THE MOLECULES MOVECollisions
26Properties of Gases They don’t always behave ideally At high pressures gas molecules get close and attractive forces are significant.Same thing occurs at low temperaturesTwo assumptions that the kinetic molecular theory doesn’t always follow:The volume of gas molecules is negligibleThere are no attractive forces between gas molecules.
27Low temperatures & high pressure cause gases to misbehave. If the temperature is low enough, and the pressure is high enough, then molecules can condense.
28Depending on the temperature and the amount of water in the air, water can be in a gas form and a liquid form at almost the same time. Water changes from liquid to gas and back to liquid. This is called fog. H2O(l) H2O(g)
29The two opposing arrows tells us that the system is in equilibrium. In a closed container the pressure caused from water evaporating reaches a maximum valueEx: butane lighter. Gas evaporates until it can’t
30Equilibrium vapor pressure is just called vapor pressure. As temperature increases, vapor pressure increases
31Liquids boil when its vapor pressure equals the atmospheric pressure. The higher you are, the smaller the atmospheric pressure, so it takes less heat to boil water on top of a mountain than sea level.Water boils at 94ºC in the mountains of Denver.Water boils instantly in outer space.Which substance from the graph has the highest boiling point? Which ahs the lowest?
32Evaporation Vs. Boiling point Evaporation happens at temperatures lower than boiling pointEvaporation happens at the surface of the liquid.Random molecules gain enough energy to break free of intermolecular forces
33Boiling happens when bubbles of vapor form inside the liquid. The pressure inside the liquid has to be greater than the pressure outside the liquid.
34Shows the temperatures and pressures a substance exists in different phases. X-axis is temperature and Y-axis is pressurePhases are in equilibrium with one another at each lineEquilibrium means that the phases are changing back and forth at equal times.Phase Diagram
35In each region the substance exists in one phase If you increase the temperature, vapor increases.At the same time the density of liquid decreases.Over time, the liquid and vapor will have the same density, so vapor won’t existThis is called the critical point
36At one point of the diagram, solid liquid and gas all exist at the same point (point A) This is called the triple point
37The normal boiling point is where the liquid-gas line crosses 1 atm of pressure.
38Phase Diagrams Practice Label the diagram:a. triple pointb. solid-vapor equilibriumc. solid-liquid equilibriumd. critical pointe. normal boiling pointf. normal freezing point
39Phase Diagrams Practice What’s Happening?:77. A?78. D?79. E?80. F?Triple point- all three phases exist in equilibriumCritical point- no longer tell diff btween L and G, vapor not exist…Normal boiling point- liquid-gas line crosses 1atmNormal freezing/melting point- solid/liquid line crosses 1atm
40Phase Diagrams Practice s, l or g ?:220.127.116.11.86.gasliquidsolidliquidgasliquid
41Simple Gas Laws You MUST know what these variables represent P = Pressure ( what are units for pressure? )V = Volume ( what are units for volume? )n = molesT = Temperature in KelvinCalculations with temperature must be made in Kelvin
42Charles’ Law Relates temperature and volume If the temperature increases, then the volume must increaseThe opposite is also true. If the volume decreases, the temperature must also decreaseThis is called a direct relationship
44Charles’ Law Heating a gas will make it expand. Gas molecules move faster when heat is added, striking the container walls with more force.More frequent and forceful collisions make the volume of a flexible container like a balloon increase.
45If heating a gas makes it expand, what will cooling it do?
47T1 and T2 must have the same units V1 and V2 must also have the same unitsBeware: some problems will give you extra information that you don’t need, such as how many moles are in the container or what the pressure is
48Charles Law Example 1: 7. Basic Charles Law example: A chamber has an initial temperature of 298 K and is 2.5 L. The chamber volume changes to 1.75 L. What is the new temperature?
50Charles Law Example 2: Intermediate problem: A container has an initial volume of 17 L at a temperature of 313 K and a pressure of 1 atm. If the temperature changes to 350K and the pressure stays the same, what would the new volume have to be?Since the pressure didn’t change, we don’t have to worry about it. We use the same equation!
52Charles Law Example 3: Advanced problem: A chamber has 12 moles of a gas, a volume of 25 L, and a temperature of 300 K. Assuming the number of moles stays the same, what is the new volume if the temperature increases 25ºC?(K = ºC + 273)(ºC = K – 273)
53A. To solve this problem, you’ll need to convert ºC to K in order to make the units the same. Once the units are the same, you need to use your new T2 temperature in the equation. The number of moles is unnecessary information.
61Boyle’s Law Example 2: Intermediate problem: A container with an unknown pressure has a 12 moles of gas and a volume of 35 L. When the volume is decreased to 20 L, the pressure is 5 atm. What is the initial pressure?The number of moles is not important in this problem
63Boyle’s Law Example 3: Advanced problem: A container is 2.7 L and is under 2017 torr of pressure. If the volume changes to 1500 mL, what is the new pressure in units of atm? (760 torr = 1 atm)(1000 mL = 1 L)To solve, convert 2017 torr to atm, then convert 1500 mL to L. Once done, plug into the Boyle’s Law equation.
65Other Simple Gas Equations to Know Gay-LussacThere is a direct relationship between pressure and temperature, when other variables are constant.Avogadro’s LawThere is a direct relationship between moles and volume, when other variables are constant.
66The total pressure of the gas in a mixture can be found. The pressure of a single gas in a mixture is called its partial pressure.Adding up all the partial pressures gives the total pressure.Simply add up the pressures of the other gasses in the mixture.Ptotal=PA+PB+PC…Daltons Gas Law
67Combined Gas LawsAs long as the number of molecules in the gas doesn’t change (the moles stay constant) the combined gas law can be used to find a missing volume, temperature, or pressure.Combined Gas Law Equation:
68Combined Gas Law Example 1: Example problem:A weather balloon containing helium with a volume of L rises in the atmosphere and is cooled from 27°C to -27°C. The pressure on the gas is reduced from kPa to 25.0 kPa. What is the volume of the gas at the lower temperature and pressure?Remember to convert ºC to K
69P1= P2=V1= V2=T1= T2=110.0 kPa25.0 kPa410.0 L?300 K246 K
71Ideal Gas LawWhen you combine all the gas laws together you get the ideal gas lawPV = nRTn = molesR = gas constant
72Gas constant:Number was determined by using STP values and solving for RDue to the units of R, all variables must be in atm OR kPa, L, mol, and K
73Ideal Gas Law Example 1:A sample of carbon dioxide with a mass of grams is placed in a mL container at 400.0K. What is the pressure exerted by the gas?You need pressure, volume, moles, and temperature. Your missing variable is pressure. Find moles by converting your grams of CO2 to moles (use the molar mass of CO2) and then convert mL to L
76Volume ConversionsEqual volumes of gases contain equal volumes of molecules at the same temperature and pressure. The chemical equation gives a conversion factor or mole ratio to solve the problem. The mole ratio from the chemical equation is the same as the volume ratio.
771 N2 (g) + 3 H2 (g) 2 NH3 (g)3L of H2 will contain 3 times as many molecules as 1 L of N2.2L of NH3 will contain twice as many molecules as 1 L of N2.
78Volume Conversion Example 1: N2 (g) + 3 H2 (g) 2 NH3 (g)How many liters of H2 are needed to react completely with 22L of N2?66 L H2=
79Quick Review Volume vs. ________ or ________? Inverse or Direct? What Law/s does this represent?Charle’s Law – with TemperatureORAvogadro’s Law – with molesBoth are DIRECT
80Quick Review Volume vs. ______________? Inverse or Direct? What Law does this represent?Boyle’s Law- PressureInverse
81Quick Review Pressure vs. ______________? Inverse or Direct? What Law does this represent?Gay-Lussac’s Law- TemperatureDirect