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Published byMelinda Norman Modified over 9 years ago
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CHANGES OF STATE & HEAT OF SOLUTION Chemistry
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Changes in States
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Sketch Time… You place an ice cube in a pot on the stove. You heat the ice cube at a constant rate until it melts, heats up, and eventually boils. Sketch the temperature of the water in the ice versus time. Have your sketch include the process of melting, heating, and then boiling.
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Temperature Changes The graph shows temperature the correct drawing of your sketch. Why does the graph level off at two places?
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Heat of Fusion Heat of Fusion – The heat it takes to melt a substance H Fus Amount of heat needed to melt = Amount of heat removed to freeze For water: To Melt: H Fus = 6.01 kJ/mol To Freeze (solidification): H Fus = -6.01 kJ/mol
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Heat of Vaporization Heat of Vaporization- the heat needed to vaporize a substance H Vap Amount of heat needed to vaporize = Amount of heat removed to condense For water: To Vaporize: H Vap = 40.7 kJ/mol To Condense: H Vap = -40.7 kJ/mol
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Heat of Solution Heat of Solution- the heat absorbed or released by dissolving a salt in water H Soln H Soln = Exothermic H Soln = Endothermic CaCl 2(s) Ca 2+ (aq) + 2 Cl - (aq) H Soln = -82.8 kJ/mol NH 4 NO 3(s) NH 4 + (aq) + NO 3 - (aq) H Soln = 25.7 kJ/mol
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Problems 1. How much heat is required to melt 8 g of ice? ( H Fus = -6.01 kJ/mol) 2. How much heat must be removed to condense 8 g of steam? ( H Vap = 40.7 kJ/mol) 3. If you dissolve 30 g of NaOH in water, how much heat will be released? ( H Soln = -44.5 kJ/mol) 4. How much heat is required to melt, heat up, and evaporate 100. g of ice originally at 0 °C?
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