2 Ideal Gases Ideal gases are imaginary gases that perfectly fit all of the assumptions of the kinetic moleculartheory.Gases consist of tiny particles that are far apartrelative to their size.Collisions between gas particles and betweenparticles and the walls of the container areelastic collisionsNo kinetic energy is lost in elastic collisions
3 Ideal Gases (continued) Gas particles are in constant, rapid motion. Theytherefore possess kinetic energy, the energy ofmotionThere are no forces of attraction between gasparticlesThe average kinetic energy of gas particlesdepends on temperature, not on the identityof the particle.
4 The Nature of Gases Gases expand to fill their containers Gases are fluid – they flowGases have low density1/1000 the density of the equivalent liquid or solidGases are compressibleGases effuse and diffuse
5 PressureIs caused by the collisions of molecules with the walls of a containeris equal to force/unit areaSI units = Newton/meter2 = 1 Pascal (Pa)1 atmosphere = 101,325 Pa1 atmosphere = 1 atm = 760 mm Hg = 760 torr
6 Measuring Pressure The first device for measuring atmospheric pressure was developed by Evangelista Torricelliduring the 17th century.The device was called a “barometer”Baro = weightMeter = measure
7 An Early BarometerThe normal pressure due to the atmosphere at sea level can support a column of mercury that is 760 mm high.
8 Standard Temperature and Pressure “STP” P = 1 atmosphere, 760 torrT = 0°C, 273 KelvinsThe molar volume of an ideal gas is liters at STP
9 Converting Celsius to Kelvin Gas law problems involving temperature requirethat the temperature be in KELVINS!Kelvins = C + 273°C = Kelvins - 273
10 The Combined Gas LawThe combined gas law expresses the relationship between pressure, volume and temperature of a fixed amount of gas.Boyle’s law, Gay-Lussac’s law, and Charles’ law are all derived from this by holding a variable constant.
11 Boyle’s Law Pressure is inversely proportional to volume when temperature is held constant.
12 Charles’s LawThe volume of a gas is directly proportional to temperature, and extrapolates to zero at zero Kelvin.(P = constant)
13 Gay Lussac’s Law The pressure and temperature of a gas are directly related, provided that the volumeremains constant.
14 Avogadro’s LawFor a gas at constant temperature and pressure, the volume is directly proportional to the number of moles of gas (at low pressures).V = ana = proportionality constantV = volume of the gasn = number of moles of gas
15 PV = nRT Ideal Gas Law P = pressure in atm V = volume in liters n = molesR = proportionality constant= L atm/ mol·KT = temperature in KelvinsHolds closely at P < 1 atm
16 Standard Molar VolumeEqual volumes of all gases at the same temperature and pressure contain the same number of molecules.- Amedeo Avogadro
18 Density and the Ideal Gas Law Combining the formula for density with the IdealGas law, substituting and rearranging algebraically:M = Molar MassP = PressureR = Gas ConstantT = Temperature in Kelvins
19 Gas Stoichiometry #1If reactants and products are at the same conditions of temperature and pressure, then mole ratios of gases are also volume ratios.3 H2(g) N2(g) NH3(g)3 moles H mole N moles NH33 liters H liter N liters NH3
20 Gas Stoichiometry #2How many liters of ammonia can be produced when 12 liters of hydrogen react with an excess of nitrogen?3 H2(g) N2(g) NH3(g)12 L H22L NH3= L NH38.03L H2
21 Gas Stoichiometry #3How many liters of oxygen gas, at STP, can be collected from the complete decomposition of 50.0 grams of potassium chlorate?2 KClO3(s) 2 KCl(s) + 3 O2(g)50.0 g KClO31 mol KClO33 mol O222.4 L O2g KClO32 mol KClO31 mol O2= L O213.7
22 Gas Stoichiometry #4How many liters of oxygen gas, at 37.0C and atmospheres, can be collected from the complete decomposition of 50.0 grams of potassium chlorate?2 KClO3(s) 2 KCl(s) + 3 O2(g)50.0 g KClO31 mol KClO33 mol O2= “n” mol O20.612mol O2g KClO32 mol KClO3= 16.7 L
23 Dalton’s Law of Partial Pressures For a mixture of gases in a container,PTotal = P1 + P2 + PThis is particularly useful in calculating the pressure of gases collected over water.
24 Kinetic Energy of Gas Particles At the same conditions of temperature, all gaseshave the same average kinetic energy.
25 The Meaning of Temperature Kelvin temperature is an index of the random motions of gas particles (higher T means greater motion.)
26 Kinetic Molecular Theory Particles of matter are ALWAYS in motionVolume of individual particles is zero.Collisions of particles with container walls cause pressure exerted by gas.Particles exert no forces on each other.Average kinetic energy µ Kelvin temperature of a gas.
27 DiffusionDiffusion: describes the mixing of gases. The rate of diffusion is the rate of gas mixing.
28 EffusionEffusion: describes the passage of gas into an evacuated chamber.
30 Real Gases corrected pressure corrected volume Videal Pideal Must correct ideal gas behavior when at high pressure (smaller volume) and low temperature (attractive forces become important).corrected pressurecorrected volumeVidealPideal