Problem Set 12 Solutions

Problem Set 12 Solutions - Problem Set 12 Solutions 1 What...

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Unformatted text preview: Problem Set 12 Solutions 1. What is the increase in entropy of one gram of ice at O o C is melted and heated to 50 C ? The change in entropy is given by dS = dQ T . In this case, the dQ must be calculated in two pieces. First there is the heat needed to melt the ice, and then there is the heat needed to raise the temperature of the system. Therefore, Δ Q = mL f + mc w Δ T where m = 1 g is the total mass of the system, L f = 80 cal/g is the heat of fusion, and c w = 1 cal/ ( g · K ) is the specific heat of water. Thus, the total change in entropy is Δ S = mL f T i + Z T f T i mc w dT T where T i = 0 o C = 273 K and T f = 50 o C = 323 K . Plugging in numbers, and remembering that we always use temperatures in Kelvin, Δ S = (1 g )(80 cal/g ) 273 K + Z 323 273 (1 cal/g )(1 g ) dT T = 80 273 cal/K + ln 323 273 cal/K Δ S = 0 . 461 cal/K 2. Find the change in entropy if 500 g of water at 80 o C is added to 300 g of water at 20 o C ....
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Problem Set 12 Solutions - Problem Set 12 Solutions 1 What...

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