U NIT 5: G AS AND A TMOSPHERIC C HEMISTRY 11.2 & 11.3 Gas Laws

C ONTEXT In a gas, the particles are very far apart This means that there is a lot of empty space between them This makes gases compressible

C ONSIDER THIS … What happens to the volume of a gas when you increase the pressure? Ex: press a syringe that is stoppered) Why? Gases are compressible

A NIMATION /projectfolder/flashfiles/gaslaw/boyles_law_graph. html

B OYLE ’ S L AW In the 17 th, Robert Boyle described this as “the spring in the air” As pressure on a gas increases, the volume of the gas decreases proportionally, if temperature and amount of gas (moles) remain constant. P α 1/V PV = k P 1 V 1 = P 2 V 2

E XAMPLE P ROBLEM A 550 L weather balloon at 98 kPa is released from the ground and rises into the atmosphere. It is caught a later height and instruments indicate the air pressure is 75 kPa. What is the volume of the captured balloon? P1=P1= V1=V1= P2=P2= V2=V2= 98 kPa 550 L 75kPa ? P 1 V 1 =P 2 V 2 (98 kPa)(550L) = (75 kPa)(V 2 ) V 2 = 719 L

R EAL L IFE A PPLICATIONS Scuba Diving As they dive down underwater, the pressure increases  volume? What happens to volume as you ascend in water? Ears popping!

C HARLES ’ L AW Temperature and Volume

A BSOLUTE Z ERO This temperature is absolute zero, the lowest possible temperature. A theoretical temperature at which matter has no kinetic energy (volume of 0) and therefore transmit no thermal energy ˚C

T EMPERATURE S CALES 1˚C = 1 K ˚C = K K = ˚C Kelvin devised a new scale that would have no negative values In this unit, we will ALWAYS use K

C HARLES ’ L AW A direct relationship V α T V = kT Vi = Vf Ti Tf As the temperature of a gas increases, the volume increases proportionally, when pressure and amount of gas (moles) remains constant. Temperature (in Kelvins) is directly proportional to volume

C HARLES ’ L AW Ex. A balloon with a volume of 1.0L at 25°C is cooled to -190°C. The new volume is… V 1 = V 2 V1= 1.0L T1 = = 298K T 1 T 2 T2 = = 83K V 2 = 1.0 L x 83 K 298K V 2 = 0.28L = 280mL V 1 = V 2 T 1 T 2

P RESSURE AND T EMPERATURE : G AY -L USSACS L AW Pressure increases proportionally as temperature increases, provided volume and amount remain constant. Pressure is directly proportional to temperature (in Kelvins) P  T A direct relationship P = kT P = k T P 1 = P 2 T 1 T 2

E XAMPLE Ex. A gas cylinder with a pressure of 1000kPa at 25°C is placed in a boiling water bath. What will the new pressure reading be? P1 = P2 P1 = 1000kPa T1 = = 298K T1 T2 P2 = ? T2 = = 373K P2 = 1000kPa x 373 K 298 K P2 = 1252 kPa

Video!

P RACTICE !! Popsicle stick analogy P. 435 # 2,5 P. 451 # 2-5 Worksheet – “Problems – Gas Laws”