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PS8KEYF07 - Chemistry 391 PS8 KEY Fall 2007 1 a What...

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1 Chemistry 391 Fall 2007 PS8 KEY 1. a) What pressure is required to lower the melting temperature by 5.0ºC? 2 2 -1 -1 -3 -1 -3 -1 -3 -3 , , 7 -1 -1 22.0 J mol K 18.02 10 kg mol 18.02 10 kg mol 998 kg m 920 kg m 1.44 10 Pa K 144 bar K fusion fusion m m fusion fusion m H O l H O s S S dP M M dT V ρ ρ Δ Δ = = × × Δ = − × = − The pressure must be increased by 720 bar to lower the melting point by 5.0ºC. b) Assume that the width of the skate in contact with the ice is 25 x 10 –3 cm, and that the length of the contact area is 15 cm. If a skater of mass 85 kg is balanced on one skate, what pressure is exerted at the interface of the skate and the ice? -2 7 2 -2 -5 85 kg 9.81 ms = 2.2 10 Pa = 2.2 10 bar 15 10 m 25 10 m F P A × = = × × × × × c) What is the melting point of ice under this pressure? 2 1 C 2.20 10 bar 1.5 C 144 bar fusion dT T P dP Δ = Δ = × × = D D ; T m = – 1.5ºC d) If the temperature of the ice is –5.0ºC, do you expect melting of the ice at the ice-skate interface to occur?
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