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Heats of Vaporization and Fusion

Heats of Vaporization and Fusion. Mr. Chapman Chemistry 30. Main Idea:. Energy is required to move particles between phases. Heat Calculations to This Point:.

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Heats of Vaporization and Fusion

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  1. Heats of Vaporization and Fusion Mr. Chapman Chemistry 30

  2. Main Idea: Energy is required to move particles between phases.

  3. Heat Calculations to This Point: In the past we have been using the equation q = mcΔt to calculate energy changes based on temperature change. All of the calculations have something in common, and that is the fact that previously none of them involved a change in state.

  4. Heat Calculations Generally, we have noted that whenever energy is added to a system, the temperature of that system increases (due to an increase in kinetic energy). When a substance changes from a solid to a liquid or a liquid to a gas, energy is required.

  5. Phase & Energy Changes This is why the graph that you drew from page 531 has two portions in it that level out. When the temperature of the water reaches 0 degrees, energy must be added to separate the particles from a solid to a liquid. This is known as the heat of fusion. Once this occurs, the addition of energy once again begins to increase the temperature of the water.

  6. Phase & Energy Changes When the temperature of the water reaches 100 degrees Celsius, the graph levels out again. This is because energy is required to separate the molecules in the liquid further to form a gas. This required energy is known as the heat of vaporization.

  7. This Guy Does A Great Job Explaining What’s Going On... http://www.youtube.com/watch?v=zz4KbvF_X-0

  8. Some Useful Enthalpies of Water... Molar heat of fusion = 6.01 kJ / mol • For every mole of water that changes state from solid to liquid, 6.01 kJ of energy are required. Molar heat of vaporization = 40.7 kJ / mol • For every mole of water that changes state from liquid to gas, 40.7 kJ of energy are required. Also note that the specific heat of water CHANGESdepending on what state it is in.

  9. Specific Heats of Water... Water ice = 2.05 J / g°C Water liquid = 4.19 J / g°C Water gas = 2.08 J / g°C

  10. Practice Calculation: A 36.04 g mass of water is heated from an initial temperature of – 30 °C to a final temperature of 150 °C. How much heat energy is required in order to bring about this temperature change?

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