Chapter 11 Gases
4 Variables that affect properties of gases Pressure (P) Volume (V) Temperature (T) Amount of gas (n) Imagine inflating bicycle tire Squeeze air into smaller volume Results in pressure increasing Increase # of collisions
Robert Boyle Determined how volume of fixed amt of gas varies with pressure Mercury added to J-shaped tube holding trapped gas at constant temp Result - increasing pressure caused volume of trapped gas to decrease
Boyle’s Law Boyle’s Law (PV Law) Volume of a given amt of gas held @ constant temperature varies inversely with applied pressure V 1/P V = 1/P x C PV = C C is constant of proportionality http://www.stmatthewsschool.com/deep/deep2001/06/bckgrnd.html
Graphing Boyle’s Law Graph pressure vs. volume Downward slope Graph pressure vs 1/volume Straight line
Boyle’s Law Experiment http://www.chem.iastate.edu/group/Greenbowe/sections/projectfolder/flashfiles/gaslaw/boyles_law.swf Take 10 measurements Use excel to graph these points V vs. P V vs. 1/P Give equation of this line Show R squared value
Problem.. And a solution! With precise measurements, Boyle’s law does not always work No gas obeys law exactly over all ranges of temperatures and pressures Law poorest when gas under high pressure (10 atm or more) or at low temperature (below 200 K) Solution: An ideal gas would obey gas law exactly over all temperature and pressures
Jacques Alexander Charles French Chemist and mathematician Interested in hot-air ballooning Study of volume of sample of gas when temperature varied, keeping pressure constant Graph Solid lines - where measurements made Dotted lines - extrapolation
Absolute Zero All plots of volume vs. temp extrapolated to zero, the temperature axis crosses at -273.15C Represents at temp where gases, if not condense, would have volume = 0 or less This is nature’s coldest temperature (absolute zero) TK=TC + 273.15 Cannot have negative volumes so this is lowest temperature!! http://chemistry.umeche.maine.edu/~amar/fall2004/Charles5.gif
Charle’s Law (TV law) Straight line suggest At constant pressure, volume of gas is proportional to temperature (in Kelvin) V T (pressure and amt of gas held constant V = C’T
Gay-Lussac’s Law (PT Law) French scientist Studied relation of pressure and temperature of fixed amt of gas at constant volume Exist for rigid walled container Pressure of a fixed amt of gas held at constant temp is directly proportional to Kelvin Temperature P T P = C”T