Chapter 11 Behavior of Gases 11.1 Gas Pressure Relates volume, temperature, and the number of particles. Pressure of a gas is directly proportional to mass. (Increase the mass of a gas increase the pressure). Pressure will increase if temperature increases, ( when the volume and mass are held constant). example: (car tires). Evangelista Torricelli ( ) - Italian Scientist He invented the Barometer. An instrument that measures air pressure. Air pressure is often called ‘barometric pressure’

A unit used to describe air pressure is called the standard atmosphere (atm) – Standard ‘atm’ = pressure that supports a column of mercury at 760 mm high or 76 cm tall. Conversion 1.00 atm = 760 mm Hg Torricelli’s barometer

The SI unit for measuring Pressure = pascal (Pa) Named after the French scientist Blaise Pascal. Conversions: All equivalent units 1.00 atm = 760 Torr = 760 mm Hg = 14.7 psi = kPa = in Hg

Sphygmomanometer – (pronounced: sfig-mo-mah-nah-muh-ter Device that measures blood pressure. Other Devices that Measure Pressure

Pressure in the Eye (Intraocular Pressure) Tire gauge measure pressure inside a tire

Pressure Conversions Factor Label Method : Mathematical relationship that converts one quantity to another. multiplying the value by a factor that equals one. Sample Problem p. 379– In weather reports, barometric pressure is often expressed in inches of mercury. (in Hg) What is one standard atmosphere (1 atm) expressed in inches of mercury? Convert atm to inches of Hg 1 atm= 760 mm Hg – How many inches of Hg in 760 mm Hg? Conversion factor: 1 in = 2.54 cm = 25.4 mm 1 atm 760 mm 1.00 in = 29.9 inches Hg 1atm 25.4 mm Multiply across then divide.

Sample Problem # 2 p The reading of a tire-pressure gauge is 35 pounds per square inch (psi). What is the equivalent pressure in kilopascals? Given: 35 pounds per square inch (psi) Conversion factor: 14.7 psi = kPa Hint: always write the unit you want to end up with in the numerator. In the factor Label Method terms are arranged so that units will cancel out. Write what is given, then multiply by the conversion factor. 35 psi kPa = 35 x kPa = 241 kPa 14.7 psi 14.7

11.2 The Gas Laws Robert Boyle – experimented with gases at Constant Temp. Boyles’ Law: The pressure and volume of a gas at constant temperature are inversely proportional. Increase one – decrease the other. Formula: P 1 ● V 1 = P 2 ● V 2 What do the subscripts mean? 1 = initial 2 = final

gas laws Animation of Boyle's Law

Boyles’ Law: A graph of an inverse relationship Question: If the Pressure initially is 50 atm and the volume is 100 L and then the pressure doubles (P 2 ) what happens to the volume (V 2 )? Answer: it is cut in half – half as much – or 50 L

V 1 = T 1 V 2 T 2 Jacques Charles – French scientist (1746 – 1823) studied hot-air balloons. Charles’s Law: at constant pressure, the volume of a gas is directly proportional to its Kelvin temperature. Increase one, increase the other. Formula: V 1 T 2 = V 2 T 1 OR

Animation of Charles's law

Graph: Charles’s Law - A direct relationship Always have to convert 0 C temp to Kelvin by adding 273 first before you do any calculations. Question: If the temperature of a gas is initially at 300K and has a volume of 25 L then is heated up to 600K what is the new volume? Answer: 50 L

Combined Gas Law –  Combining Boyle’s Law and Charles’s Law P 1 V 1 = P 2 V 2 - Boyle’s Law V 1 = V 2 Charles’s law T 1 T 2 Combined Gas Law: P 1 V 1 = P 2 V 2 Always convert to Kelvin Temp T 1 T 2 Or P 1 V 1 T 2 = P 2 V 2 T 1 Standard Temperature and Pressure S.T.P = 0 0 C and 1 atm

Gay-Lussac’s Law: Pressure and Temperature The pressure of a gas is directly proportional to the Kelvin temperature if the volume is held constant. If the temperature of a gas increases then the pressure increases. Formula: P 1 / T 1 = P 2 / T 2 Example: (car tires). Should not check pressure after a long drive

Law of Combining Gas Volumes: all the atoms present initially are accounted for in the product.  Where did the 3 rd volume disappear? Or if looking at a decomposition reaction (reverse) where did the mysterious third volume appear?  Amedeo Avogadro (1776 – 1856) Italian physicist was the first to interpret the law of combining gas volumes in terms of particles.

 Avogadro’s Principle = equal volumes of gases at the same temperature and pressure contain equal number of particles.