CHANGES OF STATE & HEAT OF SOLUTION Chemistry. Changes in States.

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Presentation transcript:

CHANGES OF STATE & HEAT OF SOLUTION Chemistry

Changes in States

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.

Temperature Changes  The graph shows temperature the correct drawing of your sketch.  Why does the graph level off at two places?

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 = kJ/mol

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 = kJ/mol

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 = kJ/mol  NH 4 NO 3(s)  NH 4 + (aq) + NO 3 - (aq)   H Soln = 25.7 kJ/mol

Problems 1. How much heat is required to melt 8 g of ice? (  H Fus = 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 = kJ/mol) 4. How much heat is required to melt, heat up, and evaporate 100. g of ice originally at 0 °C?