 # Aim: How to measure energy absorbed during a phase change

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Aim: How to measure energy absorbed during a phase change
DO NOW: What are the states as of matter for H2O? State the processes to go from one state to another. Is energy absorbed or released from solid to liquid? Liquid to gas? Explain.

Energy is absorbed Energy is released

Vocab Potential Energy- stored energy
Kinetic Energy- energy having to do with motion Heat of Fusion- the amount of heat needed to change solid to liquid at constant temperature Heat of Vaporization- the amount of heat needed to change liquid to gas at constant temperature

Heat of Fusion amount of heat needed to be asborbed to convert a unit of mass of a substance from a solid to a liquid at its melting point q= mHf Look at Table B: heat of fusion for water is 334 joules per gram. Example: How many joules are required to melt 255 g of ice at 0 C?

Heat of Vaporization amount of heat needed to be absorbed to convert a unit mass of a substance from its liquid phase to gas phase. q = Hvm Look at Table B: heat of vaporization for water is joules per gram. Example: How many joules of energy are required to vaporize 423 g of water at 100 C and 1 atm?

Practice What is the heat of solidification for 3.4 g of water?
2. How much energy is released to the environment by grams of condensing water vapor? 3. Is melting endothermic or exothermic? Explain.

Practice 4. Calculate the amount of heat needed to melt 35.0 g of ice at 0 ºC. Express your answer in kilojoules. 5. How many joules must be added to 10.0g of water to raise its temperature from 10 C to 15 C.

5 4 3 2 1

Heating Curve Temperature of the ice (solid) is increasing; increase in temperature means an increase in kinetic energy. At 0oC the ice begins to melt. During melting, the temperature stays the same; there is no change in kinetic energy. There is a change in potential energy; potential energy is increasing. The temperature of the water now rises from 0oC to 100oC.

Heating Curve 4. At 100oC, the water boils (changes to gas). When the water boils, the temperature stays the same; no change in kinetic energy. There is a change in potential energy; potential energy increases. 5. After all the water boils, the temperature of the gas rises.

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