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Chapter 14

Chapter 14. Properties of Gases. Chapter Objectives:. Use Charles’ Law to determine thermal expansion Apply Boyle’s law to calculate volume changes of gases Relate gas density to pressure & temperature. Ideal Gas.

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Chapter 14

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  1. Chapter 14 Properties of Gases

  2. Chapter Objectives: • Use Charles’ Law to determine thermal expansion • Apply Boyle’s law to calculate volume changes of gases • Relate gas density to pressure & temperature

  3. Ideal Gas • Density of gas is sufficiently low – pressure, volume, & temperature of the gas are related in a simple way • Fairly accurate over broad range of temperatures and pressures • Applicable to many different gases • Charles’ & Boyle’s Laws mathematically describe relationships

  4. Charles’ Law If the pressure on a gas is constant, the volume is directly proportional to its absolute temperature (Kelvin/Rankine) V = V’ V = original volume; V’ = final volume T T’ T = original temp; T’ = final temp

  5. Boyle’s Law • If the temperature of a gas is constant, the volume is inversely proportional to the absolute pressure V = original volume V’ = final volume P = original pressure (abs) P’ = final pressure (abs) V = P’ V’ P or VP = V’P’

  6. Density & Pressure • Density is directly proportional to pressure as long as there is no change in state D = original density D’ = final density P = original pressure P’ = final pressure D = P D’ P’

  7. Charles’ & Boyle’s Laws Combined V = original volume P = original pressure T = original temperature V’ = final volume P’ = final pressure T’ = final temperature VP = V’P’ T T’ Or VPT’ = V’P’T

  8. Standard Temperature & Pressure • aka STP • Standard temperature = 0°C/32°F • Standard pressure = 101.32 kPa/14.7 psi • Gas laws are reasonably accurate except at very low temperatures and under extreme pressures

  9. Vapor Pressure & Humidity • Vapor Pressure: increase in pressure caused by the increase in the number of molecules in the air above an evaporating liquid • Can raise boiling points by increasing pressure • Lower bp by decreasing pressure (high altitudes) • Condensation occurs at dew point • Example: condensation occurs on side of cold can when temperature of can reaches dew point • Steam condensation is very dangerous because a large amount of heat is given off when steam changes to liquid • Absolute humidity: maximum amount of water vapor air will hold at given temperature • Relative Humidity: ratio of amount of water vapor air holds to amount it can hold at saturation

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