Chapter 5: Gases- Gases o Gases are composed of particles that are flying around very fasto Gas molecules are constantly in motiono As they move and strike a surface, they push on that surface Push = Forceo The pressure of a gas depends on several factors Number of gas particles in a given volume Volume of the container Average speed of the gas particles- How to measure Air Pressure o Atmospheric pressure is measured with a barometero Column of mercury supported by air pressureo Force of the air on the surface of the mercury counterbalances the force of gravity on the column of mercury- Pressure Units o 1 atm = 760 mmHgo 1 torr = 760mmHg 1 atm = 1 torro The SI unit is Pascal (Pa) 1 Pa = 1 N/m2 1 atm = 101,325 Pao 1 atm = 29.92 inHgo 1 atm = 14.7 psi- Manometer o The pressure of a gas trapped in acontainer can be measured with aninstrument called a manometer In this sample, the gas has a larger pressure than the atmosphere - Boyle’s Lawo Robert Boyle, 1627-1691o “Pressure of a gas is inversely proportional to its volume” Constant T and amount of gas Graph P vs V is curve Graph P vs 1/V is straight lineo As P increase, V decreases by the same factoro P x V = constanto P1V1 = P2V2o When you decrease the volume of the container with the same number of molecules in the container, more molecules will hit the wall at the same rate- Charles’s Law o Jacques Charles, 1746-1823o “Volume is directly proportional to temperature” Constant P and amount of gas Graph V vs T is straight lineo As T increases, V also increaseso Kelvin T = Celsius T + 273o V = constant x T If T measured in Kelvin- Charles’s Law – A Molecular View o The pressureof gas insideand outsidethe balloonare the sameo At hightemperatures, the gas moleculesare moving faster, so they hit thesides of the balloon harder –causing the volume to becomelarger- Avogadro’s Law o Amedeo Avogadro, 1776-1856o “Volume is directly proportional to the number of gasmolecules” V = constant x n Constant P and T More gas molecules = larger volumeo Count number of gas molecules by moles o Equal volumes of gases contain equal numbers of molecules The gas doesn’t matter- Ideal Gas Law o By combining the gas laws we can write a general equationo R is called the gas constanto The value of R depends on the units of P and V We will lose .08206 (atm L/mol K) and convert P to atm and V to Lo The other gas laws are found in the ideal gas law if two variables are kept constanto Allows us to find one of the variables if we know theother three- Standard Conditions o STP (Standard Temperature and Pressure)o Standard Pressure = 1 atmo Standard Temperature = 273.15 K 0 C- Molar Volume o Solving the ideal gas equation for the volume of 1 mol of gas at STP gives 22.4 L 6.022 x 1023 molecules of gas Notices: the gas is immaterialo We call the volume of 1 mole of gas at STP the molar Volume It is important to recognize that one mole measures of different gases have different masses, even though they have the same volume- Density at Standard Conditions o Density is the ratio of mass to volumeo Density of a gas is general given in g/Lo The mass of 1 mole = molar masso The volume of 1 mole at STP = 22.4 Lo Density = (Molar Mass,g/22.4L)-- Molar Mass of a Gas o One of the methods Chemists use to determine the molar mass of an unknown substance is to heat a weighed sample until it becomes a gas, measure the temperature, pressure, and volume, and use the ideal gas lawo Molar Mass = Mass in grams / moles- Mixture of Gases o When gases are mixed together, their molecules behave independent of each other All the gases in the mixture must have the same volume- All completely fill the container, each gas’s volume = the volume of the container All gases in the mixture are at the same temperature- Therefore they have the same average kinetic energyo Therefore, in certain applications, the mixture can be thought of as one gas- Composition of Dry Air o Nitrogen (N2) 78% by Volumeo Oxygen (O2) 21% by Volumeo Argon (Ar)o .9% by Volumeo Carbon Dioxide (CO2) .04% by Volume- Partial Pressure o The pressure of a single gas in a mixture ofgases is called its partial pressureo The sum of the partial pressures of all thegases in the mixture equals the total pressure if gases behave independently (Do not react to each other)o Dalton’s Law of Partial Pressureso PTotal = PA + PB + PC + …- Mole Fraction o The fraction of the total pressure that a single gas contributes is equal tothe fraction of the total number of moles that a single gas contributeso The ratio of the moles of a single component to the total number ofmoles in the mixture is called the mole fraction, c  Gases = Volume % /100%o The partial pressure of a gas is equal to the mole fraction of that gastimes the total pressure- Collecting Gas by Water Displacement - Reactions Involving Gases o The principle of reaction stoichiometry from Chapter 4 can be combined with thegas laws for reactions involving gaseso In reactions of gases, the amount of a gas is often given as a volume  Instead of moles As we’ve seen, you must state pressure and temperatureo The ideal gas law allows us to convert from the volume of the gas to moles; then we can use the coefficients in the equation as a mole ratioo When gases are at STP, use 1 mol = 22.4 Lo P, V, T of Gas A Mole AMole BP,V,T, of Gas B- Kinetic Molecular Theory o The particles of the gas (either atoms or molecules) are constantly movingo The attraction between particles is negligibleo When the moving gas particles hit another gas particle or the container, they do not stick and continue moving in another direction, hence collision is elastico There is a lot of empty space between the gas particleso The average kinetic energy of the gas particles is directly proportional to the Kelvin temperature 1. Because the gas particles are constantly moving, they strike the sides of the container with a force 2. Because the gas keeps moving around and spreading out until they fill the container they take the shape and the volume of the container they are in 3. Because there is a lot of unoccupied space in the structure of a gas, thegas molecules can be squeezed closer together.  4. The more molecules added, the higher the pressure and density becomes 5. Decreasing the volume will increase the pressure 6.