We NEED Air to Breathe!!! Gases form homogeneous mixtures with each other regardless of the identities or relative proportions of the component gases Air is a complex mixture of several substances both atomic & molecular in nature: N2 = 78%; O2 = 21%; Ar = 0.9%; H2; F2; Cl2; Ne; Kr; Xe Gases Diffuse (the spread of a substance throughout space) to form homogeneous mixtures

Properties of Gases – (remember Kinetic Molecular Theory!) a gas expands spontaneously to fill its container gases are highly compressible (when pressure is applied to a gas, its volume readily decreases) SO… the volume of a gas equals the volume of the container in which it is held. What about the nature of gases particles (remember KMT from Ch2) explains this characteristic??? LINKED

Pressure - the result of a force distributed over an area Popping Balloon Link Bed of Nails Link

“Standard” Conditions 1 atmosphere (atm) and 0C Barometer invented by Evangelista Torricelli 760 torr = 1 atm = 29.0in Hg LINKED

Boyle’s Law When the pressure on a balloon is decreased … what happens to the volume of the balloon??? This is how weather balloons work…

Boyle’s Law: Pressure-Volume Relationship If you keep a fixed amount of gas at constant temperature: What happens to the volume of gas if you increase the pressure on it? The volume of a fixed quantity of gas maintained at constant temperature is inversely proportional to the pressure

Boyle’s Law LINKED

Boyle’s Law: for changing conditions PRACTICE: A sample of air at 0.750atm is expanded from 250.0ml to 655.0ml. If the temperature remains constant, what is the final pressure in atm?

? Jacques Charles Why do hot air balloons go Warm air inside is less dense than the air outside at the same pressure ?

Charles’s Law: Temperature-Volume Relationship If you keep a fixed amount of gas at constant pressure: What happens to the volume of gas if you increase the temperature? The volume of a fixed quantity of gas maintained at constant pressure is directly proportional to its absolute temperature LINKED

Charles’s Law LINKED Linked

Charles’s Law - for changing conditions PRACTICE: A krypton balloon has a volume of 555mL at 21°C. If the balloon is cooled and the volume decreases to 475mL, what is the final temperature of the gas. (Assume the pressure remains constant)

Gay-Lussac’s Law: Pressure – Temp Relationship If you keep a fixed amount of gas at constant volume: What happens to the pressure of gas if you increase the temperature? The pressure of a fixed quantity of gas maintained at constant volume is directly proportional to its absolute temperature. LINKED

Gay-Lussac’s Law

Gay-Lussac’s Practice A copper sphere has a volume of 555mL and is filled with air @ 25°C. The sphere is immersed in dry ice and the pressure of the gas drops from 761 torr to 495torr. What is the final temperature of the air in the copper sphere?

Combined Gas Law Experimentally, all three variables (P; V; T) usually change simultaneously SO…looking at all the formulas…how are they alike? So…we bring all three together into a single formula… Practice: A nitrogen gas sample occupies 50.5mL at -80C and 1250torr. What is the volume at 20C and 560 torr?

Dalton’s Law - total pressure of a mixture of gases equals the sum the pressures that each gas would exert if it were present alone Partial pressure – the pressure exerted by one gas in a mixture of gases Ptotal = P1 + P2 + P3 + … Collecting gas over H2O Ptotal = P1 + ???

Practice An atmospheric sample contains nitrogen, oxygen, argon and traces of other gases. If the partial pressure of nitrogen is 587mmHg, oxygen is 158mmHg, and argon is 7mmHg, what is the observed pressure as read on the barometer?

Ideal Gas –a hypothetical gas whose pressure, volume, and temperature behavior is completely described by the ideal-gas equation P is inversely proportional to the V; directly proportional to number of molecules (n); and directly proportional to T (Kelvin). SO… PV = nRT R – is the ideal gas constant and can be expressed as 0.0821 (atmxL)/(molxK) write this as an equation However, real gases experimentally do not behave ideally at low temperatures and high pressures

Ideal Gas Law Practice How many moles of H2 gas occupy a volume of 0.500L at 273K and 1atm? An unknown gas having a mass of 2.041 g occupies a volume of 1.15L at 0.974atm and 20C. Calculate the molar mass (MM) of the unknown gas. (remember MM = g/mole)

It has been experimentally determined that: Avogadro’s hypothesis Equal volumes of gases at the same temp & pressure (Standard Temp = 0°C & Pressure = 1 atm) contain equal numbers of molecules. It has been experimentally determined that: 1mole of any gas @stp = 22.4L

Gas Stoichiometry REMEMBER THAT: coefficients of a balanced equation give ratios of molecules and/or moles. Since 1 mole of any gas @ STP = 22.4L coefficients also give volumes of gases in a reaction. H2 (g) + Cl2 (g)  HCl (g) 2 1 : 1 : 2 molecule molecule molecule Mole Mole Mole Volume (gas) Volume (gas) Volume (gas)

Practice What is the mass of 3.36L of ozone gas (O3 ) at Standard Pressure and Temperature (1 atm; 0°C)? SO2 (g) + O2 (g)  SO3 (g) How many liters of oxygen (O2) are needed to produce 17.95L of SO3 react? 2 2

Practice C2H6 (g) + O2 (g)  CO2 (g) + H2O (g) How many liter of CO2 are produced when 13.5 moles of oxygen react? NaN3 (s) Na (s) + N2(g) How many liters of nitrogen (N2) will be produced if 17.95g of NaN3 react? 2 7 4 6 2 2 3