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Published byTrevon Lemmer Modified about 1 year ago

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State Changes Heat of Fusion Heat energy required to convert a solid at its melting point to a liquid Value for water: 333 J/g Heat of Vaporization Heat energy required to convert a liquid at its boiling point to a solid Value for water: 2260 J/g

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Vaporization endothermic process ( H positive) Melting endothermic process ( H positive) Freezing exothermic process ( H negative) Condensation exothermic process ( H negative)

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Finding the Energy to Change the State of a Given Mass of a Substance - Pause the video and solve the problems below. J = (mass)(heat of vaporization or heat of fusion) Find the heat energy needed to change 50.0 g of water from liquid to gas. How much heat energy will be released when 50.0 g of water freeze (change from liquid to solid)?

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Finding the Energy to Change the State of a Given Mass of a Substance - Pause the video and solve the problems below. J = (mass)(heat of vaporization or heat of fusion) Find the heat energy needed to change 50.0 g of water from liquid to gas. (2260J/g)(50.0g) = 1.13 x 10 6 J How much heat energy will be released when 50.0 g of water freeze (change from liquid to solid)? (-333J/g)(50.0g) = x 10 5 J

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Graphing Temperature v. Time During a State Change Time (min) Temperature ( C)

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Why do the plateaus occur in this graph even though heat was steadily added over time?

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Specific heat of ice = 2.06 J/gK Specific heat of water = 4.184J/gK C pgas = 1.86 J/gK heat of fusion = 333 J/g Heat of vaporization = 2260J/g

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Find the energy needed to convert 500.g of ice at C to steam at 200. C. Pause the video while you solve the problem. Solve this in 5 steps by finding energy needed to: 1.Heat ice from to 0 using specific heat of ice 2.Melt ice using heat of fusion of ice 3.Heat water from 0 to 100 using specific heat of water 4.Boil water using heat of vaporization of water 5.Heat steam from 100 to 200. using specific heat of steam Then add all of these q values together to find the total amount of energy needed.

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Find the energy needed to convert 500.g of ice at C to steam at 200. C. Pause the video while you solve the problem. Solve this in 5 steps by finding energy needed to: 1.Heat ice from to 0 using specific heat of ice q = (2.06J/gK)(50.0g)(0 C C) = 5.15 x 10 4 J 1.Melt ice using heat of fusion of ice q = (333J/g)(50.0g) = 1.67 x 10 5 J 1.Heat water from 0 to 100 using specific heat of water q = (4.184J/gK)(50.0g)(100 C - 0 C) = 2.09 x 10 5 J 1.Boil water using heat of vaporization of water q = (2260J/g)(50.0g)= 1.13 x 10 6 J 1.Heat steam from 100 to 200. using specific heat of steam q = (1.86J/gK)(50.0g)(200. C – C) = 9.30 x 10 4 J Then add all of these q values together to find the total amount of energy needed. 1650kJ

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Let’s try something harder!!! Pause the video while you solve the problem. Suppose you pour 250. mL of tea (density 1g/mL) at 18.2 C into a glass with 5 ice cubes (each weighing 15g). What quantity of ice will melt and what mass will remain? (Hint: the tea will cool until it is at thermal equilibrium with the ice at 0 C.) Assume the specific heat of tea is 4.2J/gK.

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