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Question 17 Not yet answered Calculate the increase of entropy (in J/K) when 73 g of ice melts at 0 °C and 1 atm. (The heat of fusion for ice is 6,000 J/mol.) Marked out of 1.00 Answer: P Flag question Calculate the change in entropy (in J/K) when 98.2 g of water is heated from 28.7 °C to 76.7 °C at 1 atm. (The specific heat is 4.184 J/(g-K).) Question 18 Not yet answered Marked out of 1.00 Notice that entropy and heat capacity have the same units. P Flag question Answer: Question 19 Not yet answered Calculate the change in entropy (in J/K) when 91.9 g of nitrogen gas is heated at a constant pressure of 1.50 atm from 29.2°C to 77.7 °C. (The molar specific heats are C, is 20.8 J/mol-K) and Cp is 29.1 J/mol-K).) Marked out of 1.00 Answer: P Flag question

Answer 1

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Q. Calculate the increase of entropy (J/K) when 73 g of ice melts at 0°C and 1 atm. (the heat of fusion of ice is 6,000 J/mol) Answer: Pressure = 1 atm, T = 0°C = 273 K moles of ice = (73/18) = 4,04 q=n AHjus = (4.05 X 6000) J = 24,300 J [: n=4.04 mole and AHjus = 6000 J/mol] Entropy change AS = qice / Tico = (24300 J)/(273 K)= 89.01 J/K Q. Calculate the change in entropy (J/K) when 98.2 g of water is heated from 28.7°C to 76.7 °C at 1 atm. (the specific heat is 4.184 J/g-K) Notice that entropy and heat capacity have same units Answer: Pressure = 1 atm, T1 = 28.7°C = 301.7K, T2 = 76.7°C = 349.7K Mass of water = 98.2 g specific heat (Cp) = 4.184 J/g-K Entropy change AS = mCp In(T//T1)= 98.2 x 4.184 x In (349.7/301.7) = 60.66 J/K Q. Calculate the change in entropy (J/K) when 91.9 g of nitrogen gas is heated at a constant pressure of 1.50 atm from 29.2°C to 77.7 °C. (the molar specific heats are C, is 20.8 J/g-K and Cp is 29.1 J/g-K) Notice that entropy and heat capacity have same units Answer: Pressure = 1.50 atm, T, = 29.2°C = 302.2K, T2 = 77.7°C = 350.7K Mass of N2 gas = 91.9 g specific heat (C) = 20.8 J/g-K Cp = 29.1 J/g-K Entropy change AS = mCp In(T//T1) = 91.9 x 29.1 x In (350.7/302.2) = 398.04 J/K