Comparison of Solids, Liquids, and Gasescircle5The density of gases is much less than that of solids or liquids.Densities (g/mL)SolidLiquidGasH2O0.9170.9980.000588CCl41.701.590.00503Gas molecules must be very far apart compared to liquids and solids.

An Overview of the Physical States of MatterThe Distinction of Gases from Liquids and Solids1. Gas volume changes greatly with pressure.2. Gas volume changes greatly with temperature.3. Gases have relatively low viscosity.4. Gases are miscible.

Pressurecircle5Pressure is force per unit area.circle5lb/in2circle5N/m2triangle45rightAtmospheric pressure is measured using a barometer.triangle45rightDefinitions of standard pressure◦76 cmHg◦760 mmHg◦760 torr◦1 atmosphere◦101.3 kPaHg density = 13.6 g/mL

or

2

Charles’ Law: The Volume-Temperature RelationshipEnd of data here since vapor liquefies

Charles’ Law: Volume-Temperature Relationshipcircle5Mathematical form of Charles’ law.circle5Standard temperature and pressure -STP.circle5It is a reference point for some gas calculations. circle5Standard P ≡1.00000 atmor 101.3 kPacircle5Standard T ≡273.15 K or 0.00oCTemperature conversion:

circle5A sample of hydrogen, H2, occupies 1.00 x 102mLat 25.0oC and 1.00 atm. What volume would it occupy at 50.0oC under the same pressure?

The Combined Gas Law Equationcircle5Boyle’s and Charles’ Laws combined into one statement is called the combined gas law equation.circle5Useful when the V, T, and P of a gas are changing.

circle5At 25oC a sample of He has a volume of 4.00 x 102mL under a pressure of 7.60 x 102torr. What volume would it occupy under a pressure of 2.00 atmat 300C?

Avogadro’s Law and the Standard Molar Volumecircle5V ∝n (moles of gas)circle51 mole of gas at STP has a volume called the standard molar volume.circle5The standard molar volume is 22.4 L at STP. circle511.2 L of a gas at STP = 0.500 molecircle544.8 L = ? moles

Avogadro’s Law and theStandard Molar Volumecircle5One mole of a gas occupies 36.5 L and its density is 1.36 g/L at a given temperature and pressure. (a) What is its molar mass? (b) What is its density at STP?