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Discussion 12 - key

# Discussion 12 - key - Key for Discussion Worksheet 12 Hfus...

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Key for Discussion Worksheet 12 ΔH fus = 6.02 kJ/mol c ice = 2.09 J/g·ºC ΔH vap = 40.7 kJ/mol c water = 4.18 J/g·ºC c steam = 2.01 J/g·ºC 1. Identify the phases for all four points. A - _Gas _______ C - _Liquid ______ B - _Solid ______ D - _Triple Point __ 2. How much energy, in J, is released when 47.5 g of water freezes? q = nΔH fus = 47.5 g (1mole/18.0g)(6.02 kJ/mole)(1000 J/ 1 kJ) q = 15900 J 3. An 8.5 g ice cube, at 0 ºC, is placed into 255 g of water, at 80 ºC. Calculate the temperature change in the water upon the complete melting of the ice. Assume that all of the energy required to melt the ice comes from the water. n ice ΔH fus + m ice C water ΔT = -[m water C waterΔT ] n ice ΔH fus + m ice C water (T f – T i ) = -[m water C water (T f – T i )] (0.472mol)(6020J.mol)+(8.5g)(4.18)(T f – 0) = -[(255g)(4.18)(T f – 80)] 2843 J + 35.53 T f = -1066 T f + 85272 J 1102 T f = 82429 J T f = 74.8 ºC

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4. How much ice, in grams at -5 ºC, would you need to melt to condense 5.00g of
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Discussion 12 - key - Key for Discussion Worksheet 12 Hfus...

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