Exam04answers pg2

# Exam04answers pg2 - tropy 1 2 kg of liquid H 2 O 2 1 kg of...

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2. +29 . 5 kJ · mol - 1 correct 3. - 50 . 7 kJ · mol - 1 4. +14 . 8 kJ · mol - 1 5. - 29 . 5 kJ · mol - 1 Explanation: 005 (part 1 of 1) 12 points Calculate the standard reaction enthalpy for the reaction NO 2 (g) NO(g) + O(g) given +142.7 kJ/mol for the standard en- thalpy of formation of ozone and O 2 (g) 2O(g) Δ H = +498 . 4 kJ / mol NO(g) + O 3 (g) NO 2 (g) + O 2 (g) Δ H = - 200 kJ / mol Remember the definition of the standard en- thalpy of formation of a substance. 1. +592 kJ / mol 2. +355 kJ / mol 3. +306 kJ / mol correct 4. +192 kJ / mol 5. +555 kJ / mol Explanation: O 2 (g) 2O(g) Δ H = +498 . 4 kJ / mol NO(g) + O 3 (g) NO 2 (g) + O 2 (g) Δ H = - 200 kJ / mol The standard formation of ozone is 3 2 O 2 (g) O 3 (g) ΔH = +142 . 7 kJ / mol We calculate the ΔH rxn using Hess’ Law: To combine the reactions and get the de- sired reaction, reverse the second and third equations and add half of the first one: NO 2 (g) + O 2 (g) NO(g) + O 3 (g) ΔH = +200 kJ / mol O 3 (g) 3 2 O 2 (g) ΔH = - 142 . 7 kJ / mol 1 2 O 2 (g) O(g) ΔH = 1 2 (498 . 4 kJ / mol) NO 2 (g) NO(g) + O(g) ΔH rxn = 306 . 5 kJ / mol 006 (part 1 of 1) 10 points Which of the following has the greatest en-
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Unformatted text preview: tropy? 1. 2 kg of liquid H 2 O 2. 1 kg of solid H 2 O 3. 2 kg of gaseous H 2 O correct 4. 1 kg of liquid H 2 O 5. 1 kg of gaseous H 2 O Explanation: 007 (part 1 of 1) 12 points 257 g of ice at-10 . ◦ C is put in 418 g of water at 85.0 ◦ C. All of the ice melts. What is the Fnal temperature of the water? Correct answer: 20 . 3 ◦ C. Explanation: m ice = 257 g T ice =-10 . ◦ C m water = 418 g T water = 85 . ◦ C Take the ice and the water to zero degrees. Then see how much heat is left over (the Joules of heat from the hot water heats and melts all of the ice AND there will be heat left over). All the ice melts with 91209 . 3 J. All the hot water will cool to zero with 148658 J. The di±erence is 57448 . 2 J. Now use the excess joules to heat the 675 g of water and get 20 . 3 ◦ C....
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