Section 3.7Gas LawsHow can we calculate Pressure, Volume and Temperature of our airbag?

Pressure UnitsSeveral units are used when describing pressureUnitSymbol atmospheresatmPascals, kiloPascalsmillimeters of mercurypounds per square inchPa, kPamm Hgpsi1 atm = 101300 Pa = 101.3 kPa = 760 mm Hg = 14.7 psi

DefinitionKelvin (K) temperature scale with an absolute zeroTemperatures cannot fall below an absolute zeroA temperature scale with absolute zero is needed in Gas Law calculations because you cant have negative pressures or volumes

DefinitionStandard Temperature and Pressure (STP) 1 atm (or the equivalent in another unit) and 0C (273 K)Problems often use STP to indicate quantitiesdont forget this hidden information when making your list!

Gas Laws

KMT and Gas LawsThe Gas Laws are the experimental observations of the gas behavior that the Kinetic Molecular Theory explains.

Before and After in Gas LawsThis section has 4 gas laws which have before and after conditions.For example:Where P1 and n1 are pressure and # of moles beforeand P2 and n2 are pressure and # of moles afterBoth sides of the equation are talking about the same sample of gaswith the 1 variables before a change, and the 2 variables after the change

Avogadros LawAvogadros Law relates # of particles (moles) and volume.Where Temperature and Pressure are held constantV = Volumen = # of moles of gasExample:A sample with 0.15 moles of gas has a volume of 2.5 L. What is the volume if the sample is increased to 0.55 moles?The two volume units must match!

Avogadros LawAvogadros Law relates # of particles (moles) and volume.Where Temperature and Pressure are held constantV = Volumen = # of moles of gasExample:A sample with 0.15 moles of gas has a volume of 2.5 L. What is the volume if the sample is increased to 0.55 moles?The two volume units must match!n1 = 0.15 molesV1 = 2.5 Ln2 = 0.55 molesV2 = ? LV2 = 9.2 L

Boyles LawBoyles Law relates pressure and volumeWhere temperature and # of molecules are held constantP = pressureV = volumeThe two pressure units must match and the two volume units must match!Example:A gas sample is 1.05 atm when 2.5 L. What volume is it if the pressure is changed to 0.980 atm?

Boyles LawBoyles Law relates pressure and volumeWhere temperature and # of molecules are held constantP = pressureV = volumeThe two pressure units must match and the two volume units must match!Example:A gas sample is 1.05 atm when 2.5 L. What volume is it if the pressure is changed to 0.980 atm?P1 = 1.05 atmV1 = 2.5 LP2 = 0.980 atmV2 = ? LV2 = 2.7 L

Charles LawCharles Law relates temperature and pressureWhere pressure and # of molecules are held constantV = VolumeT = TemperatureThe two volume units must match and temperature must be in Kelvin!Example:What is the final volume if a 10.5 L sample of gas is changed from 25C to 50C?V1 = 10.5 LT1 = 25CV2 = ? LT2 = 50CTemperature needs to be in Kelvin!25C + 273 = 298 K50C + 273 = 323 K

Charles LawCharles Law relates temperature and pressureWhere pressure and # of molecules are held constantV = VolumeT = TemperatureThe two volume units must match and temperature must be in Kelvin!Example:What is the final volume if a 10.5 L sample of gas is changed from 25C to 50C?V1 = 10.5 LT1 = 25CV2 = ? LT2 = 50CV2 = 11.4 L= 298 K= 323 K

Combined Gas LawP = PressureV = Volumen = # of molesT = TemperatureEach pair of units must match and temperature must be in Kelvin!Example:What is the final pressure if a 0.125 mole sample of gas at 1.7 atm, 1.5 L and 298 K is changed to STP and particles are added to 0.225 mole?

Combined Gas LawP = PressureV = Volumen = # of molesT = TemperatureEach pair of units must match and temperature must be in Kelvin!Example:What is the final volume if a 0.125 mole sample of gas at 1.7 atm, 1.5 L and 298 K is changed to STP and particles are added to 0.225 mole?P1 = 1.7 atmV1 = 1.5 Ln1 = 0.125 moleT1 = 298 KP2 = 1.0 atmV2 = ? Ln2 = 0.225 moleT2 = 273 KV2 = 4.2 LSTP is standard temperature (273 K) and pressure (1 atm)

The combined gas law can be used for all before and after gas law problems!For example, if volume is held constant, thenand the combined gas law becomes:When two variables on opposites sides are the same, they cancel out and the rest of the equation can be used.Why you really only need 1 of these

Watch as variables are held constant and the combined gas law becomes the other 3 lawsHold pressure and temperature constantAvogadros LawHold moles and temperature constantBoyles LawHold pressure and moles constantCharles LawTransforming the Combined Law

The Ideal Gas LawThe Ideal Gas Law does not compare situationsit describes a gas in one situation.P = PressureV = Volume n = molesR = Gas Law ConstantT = TemperatureThere are two possibilities for R:Choose the one with units that match your pressure units!Volume must be in Liters when using R to allow the unit to cancel!

The Ideal Gas Law ExampleThe Ideal Gas Law does not compare situationsit describes a gas in one situation.P = PressureV = Volume (in L)n = molesR = Gas Law ConstantT = TemperatureExample:A sample with 0.55 moles of gas is at 105.7 kPa and 27C. What volume does it occupy?

The Ideal Gas Law ExampleExample:A sample with 0.55 moles of gas is at 105.7 kPa and 27C. What volume does it occupy?n = 0.55 molesP = 105.7 kPaT = 27C + 273 = 300 KV = ?R = 8.31 L kPa / mole KV2 = 13 LThe Ideal Gas Law does not compare situationsit describes a gas in one situation.P = PressureV = Volume (in L)n = molesR = Gas Law ConstantT = TemperatureChosen to match the kPa in the P above

Example:What is the final volume if a 15.5 L sample of gas at 755 mm Hg and 298 K is changed to STP?Lets Practice

Example:What is the final volume if a 15.5 L sample of gas at 755 mm Hg and 298 K is changed to STP?P1 = 755 mm HgV1 = 15.5 LT1 = 298 KP2 = 760 mm HgV2 = ? LT2 = 273 KV2 = 14.1 Lmoles is not mentioned in the problemtherefore it is being held constant.It is not needed in the combined law formula.STP is standard temperature (273 K) and pressure (1 atm or 760 mm Hg)Lets Practice

What did you learn about airbags?

AirbagsStates of MatterPropertiesChangesGas LawsDensityKinetic Molecular TheoryGas

****What are the gas laws?*****************