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Understanding Phase Changes and Boiling Points

Learn about phase changes, boiling points, and the energy involved in melting, condensation, and vaporization. Discover the meaning of volatile substances and the processes of sublimation and deposition.

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Understanding Phase Changes and Boiling Points

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  1. Ch 13 Game Review

  2. The boiling temperature of water at normal (standard) atmospheric pressure is 100oC. When the atmospheric pressure is increased, the boiling temperature of water is • A Equal to 100oC • B Less than 100oC • C Greater than 100oC • D Impossible to predict • Ans: C

  3. For a substance that is ordinarily a liquid at room temperature, the gas phase is called a • vapor

  4. What does volatile mean? Give an example of a substance that is volatile. • Substance with high vapor pressure. Alcohol, perfume, acetone (nail polish remover).

  5. Calculate the energy required to melt 4.05 moles of H2O. • Q= m x ▲Hfus • 24.4 kJ or 24,400 J • 4.05 mol x 6.02 kJ/mol = 24.4 kJ

  6. During condensation, the particles of a substance undergo a • A) Loss of potential energy • B) Loss of kinetic energy • C) Gain of potential energy • D) Gain of kinetic energy • Ans: A

  7. What is the pressure when CCl4 boils at 76°C? • 101.325kPa (or something close to it) • What is the pressure when water boils at 50°C? • 20°C (or something close to it) • What is the boiling point of CHCl3 if the pressure on the surface of the liquid is 65 kPa. • 53°C or something close to it

  8. Which letter on the graph corresponds to each of the following: The melting point A Steam begins heating AB Melting begins C Condensation begins AB Water begins cooling E Boiling begins E

  9. Calculate the energy released (Q) when 54.2 grams of steam at 100oC is condensed to liquid water. • Q= m x ▲Hvap • 54.2 g x 2260 J/g • 123 kJ or 123,000 J

  10. The process by which a gas or a vapor becomes a liquid is called • condensation

  11. Calculate the energy released when 8.5 grams of water drops from 85.7oC to 40.2oC. • Q= m x ▲T x s • 8.5 g x 45.5oC x 4.184 J/goC • 1600 J or 1.6 kJ

  12. The energy required to change one gram of a solid to a liquid at its normal melting point is the • Enthalpy of fusion • ∆Hfus • latent heat of fusion • heat of fusion

  13. Dynamic equilibrium between a liquid and vapor is reached when the rates of ________ and _________ are equal. • Condensation and evaporation (or vaporization)

  14. The temperature at which the vapor pressure of a liquid is equal to standard atmospheric pressure is the liquid’s • Normal boiling point

  15. The pressure exerted by a vapor over a liquid is called • Vapor pressure

  16. The process by which a solid changes directly to a gas without first becoming a liquid • Sublimation

  17. The process by which a substances changes from a gas or vapor to a solid without first becoming a liquid • deposition

  18. When a substance is cooling, the particles of the substance undergo a (gain/loss) of (potential/kinetic) energy • Loss of kinetic energy

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