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ch 302 hw 5 pretest solution

# ch 302 hw 5 pretest solution - reyes(mr29667 H05 pre-exam2...

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reyes (mr29667) – H05: pre-exam2 – Mccord – (90540) 1 This print-out should have 21 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0 points Explain why equilibium constants are dimen- sionless. 1. The statement is not true. Equilibrium constants have units that involve some multi- ple of atmospheres or moles per liter. 2. Every concentration or pressure that en- ters into K c or K p is really divided by the cor- responding concentration or pressure of the substance in its standard state. correct 3. They are dimensionless because the pres- sures or concentrations we put in are all for the substances in their standard states. 4. They are not really dimensionless but we must treat them as such in order to be able to take ln K in the expression Δ G 0 = - RT ln K . 5. They are dimensionless because concen- trations and pressures have no units. Explanation: The amount of each component is in terms of activity, which is the measured amount (concentration, pressure) divided by the amount of that component in its standard state in that unit. The units in the numera- tor and denominator are identical and cancel out. 002 10.0 points Consider the reaction 2 HgO(s) 2 Hg( ) + O 2 (g) . What is the form of the equilibrium constant K c for the reaction? 1. K c = [O 2 ] correct 2. K c = [Hg] 2 [O 2 ] [HgO] 2 3. None of the other answers is correct. 4. K c = [O 2 ] [HgO] 2 5. K c = [Hg] 2 [O 2 ] Explanation: Solids and liquids are not included in the K expression. 003 10.0 points Consider the following reactions at 25 C: reaction K c 2 NO(g) N 2 (g) + O 2 (g) 1 × 10 30 2 H 2 O(g) 2 H 2 (g) + O 2 (g) 5 × 10 82 2 CO(g) + O 2 (g) 2 CO 2 (g) 3 × 10 91 Which compound is most likely to dissociate and give O 2 (g) at 25 C? 1. H 2 O 2. CO 2 3. NO correct 4. CO Explanation: Only two are dissociation reactions: disso- ciation of NO and dissociation of H 2 O. K c is greater for dissociation of NO. 004 10.0 points If K c = 1 . 57 × 10 5 for the reaction A(g) 2 B(g) , what is K c for the reaction written as 2 B(g) A(g) ? Correct answer: 6 . 36943 × 10 6 . Explanation: K c , ini = 1 . 57 × 10 5 A(g) 2 B(g) , K c = [B] 2 [A] = 1 . 57 × 10 5

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reyes (mr29667) – H05: pre-exam2 – Mccord – (90540) 2 2 B(g) A(g) K 1 c = [A] [B] 2 = 1 K c = 1 1 . 57 × 10 5 = 6 . 36943 × 10 6 005 10.0 points The reaction A + B C + 2 D has an equilibrium constant of 3 . 7 × 10 3 .
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ch 302 hw 5 pretest solution - reyes(mr29667 H05 pre-exam2...

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