Gases
Pressure Pressure = force/area Atmospheric pressure Because air molecules collide with objects More collisions greater pressure
Pressure is a measure of the number of collisions between atoms or molecules with the walls of the container
Pressure Units Atmosphere If Atm =1 Pounds per square inch (psi)=14.7 mm Hg =760 Torr = 760 Pascal (Pa) or kilopascal (kPa)=101.3
Temperature Temperature is a measure of average kinetic energy. Temperature measures how quickly the particles are moving. (Heat IS NOT the same as temperature!) If temperature increases, kinetic energy increases.
Kelvin-Celsius Conversions K = oC + 273.15 oC = K – 273.15 Mass to Moles is Hard to Find
Kelvin-Celsius Conversions K = oC + 273.15 oC = K – 273.15 Try to divide all the time
Kelvin-Celsius Conversions K = oC + 273.15 oC = K – 273.15 Mass to Moles is Hard to Find
Physical Characteristics of Gases Physical Characteristics Typical Units Volume, V liters (L) Pressure, P atmosphere (1 atm = 1.015x105 N/m2) Temperature, T Kelvin (K) Number of atoms or molecules, n mole (1 mol = 6.022x1023 atoms or molecules) Before the IA we had been looking at gases Here is a refresher of the units that we must use. To make the ideal gas equation work we must use volume in L Pressure in Atms Temp in K
“Father of Modern Chemistry” Chemist & Natural Philosopher Boyle’s Law Pressure and volume are inversely related at constant temperature. PV = K As one goes up, the other goes down. P1V1 = P2V2 “Father of Modern Chemistry” Robert Boyle Chemist & Natural Philosopher Listmore, Ireland January 25, 1627 – December 30, 1690
Boyle’s Law: P1V1 = P2V2
Boyle’s Law: P1V1 = P2V2 An inverse proportion graph is always an exponential decay curve. Notice as volume doubles pressure is halved Teacher will highlight this on the graph
Jacques-Alexandre Charles Mathematician, Physicist, Inventor Charles’ Law Volume of a gas varies directly with the absolute temperature at constant pressure. V = KT V1 / T1 = V2 / T2 PPP per Prince Charles keeps PPP Pressure constant. So he varied volume and temperature Jacques-Alexandre Charles Mathematician, Physicist, Inventor Beaugency, France November 12, 1746 – April 7, 1823
Charles’ Law: V1/T1 = V2/T2 This is a direct proportionality double the temp in K and the volume would double
Charles’ Law: V1/T1 = V2/T2 This give a straight line graph
Gay-Lussac Law At constant volume, pressure and absolute temperature are directly related. P = k T P1 / T1 = P2 / T2 Gay-Lussac kept volume constant and so varied pressure and temp this is another direct correlation Experimentalist Limoges, France December 6, 1778 – May 9, 1850
Avogadro’s Law At constant temperature and pressure, the volume of a gas is directly related to the number of moles. V = K n V1 / n1 = V2 / n2 Amedeo Avogadro Physicist Turin, Italy August 9, 1776 – July 9, 1856
Avogadro’s Law: V1/n1=V2/n2
KMT outline Particles in an ideal gas… have no volume. have elastic collisions. are in constant, random, straight-line motion. don’t attract or repel each other. have an avg. KE directly related to Kelvin temperature.
Only at very low P and high T Differences Between Ideal and Real Gases Ideal Gas Real Gas Obey PV=nRT Always Only at very low P and high T Molecular volume Zero Small but nonzero Molecular attractions Small Molecular repulsions
Real Gases Real molecules do take up space and do interact with each other (especially polar molecules). Need to add correction factors to the ideal gas law to account for these.
Ideally, the VOLUME of the molecules was neglected: at 1 Atmosphere Pressure at 10 Atmospheres Pressure at 30 Atmospheres Pressure Ar gas, ~to scale, in a box 3nm x 3nm x3nm
In other words the measured volume will always be slightly higher than expected but there is always a molecular volume which needs to be accounted for so the measured volume is higher than the theoretical