IdealGasesNotes
Boyle’sLaw:
V∝1/P
Volumeisindirectlyproportionaltopressure(asoneincreasestheotherdecreases)
Charles’sLaw:
V∝T
Volumeisdirectlyproportionaltotemperature(asoneincreasestheotherincreasesandvice
versa)
Gay-Lussac’sLaw:
P∝T
Pressureandtemperaturearedirectlyproportional(asoneincreasestheotherincreasesand
viceversa)
Avogadro’sLaw:
V∝n
Numberofmoles(n)andvolumearedirectlyproportional(asoneincreasestheotherincreases
andviceversa)
IdealGasesNotes
*IdealGasLaw:
PV=nRT
Pispressure
• Possibleunitswewillsee:
o mmHg(millimetersofmercury)
o atm(atmosphericpressure)-thesearetheunitswewantourpressuretobein
• 760mmHg=1atm
Visvolume
• possibleunitswewillsee:
o mL
o L-thesearetheunitswewantourvolumetobein
• 1000mL=1L
nisnumberofmoles
• possibleunitswewillsee
o mol-thesearetheunitswewanttobein
o grams
• Usethemolarmasstoconvertgramstomoles
Tistemperature
• Possibleunitswewillsee:
o ˚C
o K-thisiswhatwewantourtemperaturetobein
• ˚C+273=K
Ristheidealgasconstant
• itisalways0.08206L・atm/mol・K(yesIknowtheunitsarelong)
IdealGasesNotes
i.e.Ifthereis1moleofanidealgasatSTP,whatisthevolume?
*reminderSTPisstandardtemperatureandpressure(273Kand1atm)
usePV=nRT
solveforvolume:
Pluginnumbers:
V=22.4L
*fortheseproblemsmakesureyournumbersareinthecorrectunits!
IdealGaseswithchangingvariables:
i.e.Aballoonthathas2molesofgasis4L.Ifairisletoutuntilthereareonly0.5molesofgas,
whatisthenewvolume?
Forthefirstsetofvariables:
P1V1=n1RT1 Forthesecondsetofvariables:
P2V2=n2RT2
Risaconstantsoitisthesameinbothequations(thiswillalwaysbetrue).Iwillsolveboth
equationsforRbydividingbynT:
P1V1
P2V2
=R
=R
n1T1
n2T2
SincebothequationsareequaltoR,wecansaytheequationsareequaltoeachother:
P1V1
P2V2
=
n1T1
n2T2
*thisistheequationyouwillusewhenyouhavevariablesthatarechanging!
IdealGasesNotes
IfIdonotgiveyouavariable,assumeitremainsconstant.Inthatcaseitwouldbethesameon
bothsidesandthereforecancelout.
Inthiscasepressureandtemperatureareconstant(P1=P2andT1=T2)sotheywillcanceloutof
theequation:
P1V1
P2V2
=
n1T1
n2T2
Sonowwejusthave:
V1
V2
=
n1
n2
Nowwecanpluginournumbers:
V2
4L
=
2 mol 0.5 mol
Nowsolveforthenewvolumeandyoushouldget:
V2=1L
*makesurethatyouareconvertingyourunitswherenecessaryandyouarecorrectlylabeling
yournumberswithunits!