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Unformatted text preview: goins (jmg3964) – Post-lab 5 – lyon – (51215) 1 This print-out should have 20 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0 points An endothermic reaction corresponds to one in which 1. Δ H is positive; heat is evolved 2. Δ H is positive; heat is absorbed correct 3. Δ H is negative; heat is evolved 4. Δ H is negative; heat is absorbed Explanation: In endothermic reactions, heat flows into a system, or heat is absorbed. Since the amount of energy in the system increases, Δ H is positive. 002 10.0 points Which of the reactions below is a formation reaction? 1. 2H 2 (g) + 2C graphite (s) + O 2 (g) → 2CH 2 O( ℓ ) 2. 2Fe(s) + 3 2 O 2 (g) → Fe 2 O 3 (s) correct 3. N 2 ( ℓ ) + 2H 2 (g) → N 2 H 4 ( ℓ ) 4. H 2 (g) + C graphite (s) + 3 2 O 2 (g) → CO 2 (g) + H 2 O(g) Explanation: A formation reaction produces exactly one mole of one product from elements in their standard states. 003 10.0 points In calculating the heat given off by a reaction in a calorimeter, you must account for heat absorbed by 1. water and the calorimeter. correct 2. water only. 3. air only. 4. the calorimeter only. Explanation: 004 10.0 points The heat of combustion of octane (C 8 H 18 ) is 47 . 8 kJ / g and one gallon of C 8 H 18 has a mass of 2620 g. If a car using octane is driven 10,000 miles in one year and gets 25 miles per gallon of octane, what is the total energy consumption? 1.- 13 × 10 3 kJ 2. 5 . 01 × 10 7 kJ correct 3. 34 × 10 7 kJ 4. 7 . 80 × 10 3 kJ 5. 8 . 45 × 10 2 kJ Explanation: 005 10.0 points Consider the following specific heats: cop- per, 0.384 J/g · ◦ C; lead, 0.159 J/g · ◦ C; water, 4.18 J/g · ◦ C; glass, 0.502 J/g · ◦ C. If the same amount of heat is added to identical masses of each of these substances, which substance at- tains the highest temperature? (Assume that they all have the same initial temperature.) 1. water 2. copper 3. lead correct 4. glass Explanation: 006 10.0 points Consider the reaction 2 Al 2 O 3 (s) → 4 Al(s) + 3 O 2 (g) . Δ H = +3339 . 6 kJ/mol goins (jmg3964) – Post-lab 5 – lyon – (51215) 2 What is Δ H for the formation of one mole of Al 2 O 3 (s) from the elements? 1.- 1669.8 kJ correct 2. +3339.6 kJ 3.- 3339.6 kJ 4. +1669.8 kJ 5.- 6679.2 kJ Explanation: The reverse of this reaction, 4 Al(s) + 3 O 2 (g) → 2 Al 2 O 3 (s) has a Δ H of- 3339.6 kJ/mol. You might no- tice that both Al and O 2 are elements in their standard states, hence their Δ H f values are both 0. Dividing the equation by two pro- vides us with the equation for the formation of only one mol of Al 2 O 3 (s) and leads us to the Δ H f for Al 2 O 3 (s)....
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This note was uploaded on 10/25/2010 for the course CH 204 taught by Professor Leytner during the Fall '08 term at University of Texas.

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solution4_pdf - goins (jmg3964) – Post-lab 5 – lyon –...

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