F10Q7W9 - CHEM 0110 QUIZ 7 WEEK 9 MONDAY, 1:00 PM October...

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CHEM 0110 QUIZ 7 WEEK 9 MONDAY, 1:00 PM October 25, 2010 NAME_______________________________________________________________________ 1. Characterize each of the following processes as EXOthermic or ENDOthermic. Give your reasoning. (a) Dissolving NH 4 Cl in water: We know that when NH 4 Cl solid dissolves in water, the temperature of the water decreases. (b) The reaction: NH 3 (g) + HCl(g) → NH 4 Cl(s). We know that the enthalpy of NH 4 Cl(s) is smaller than the enthalpy of [NH 3 (g) + HCl(g)]. 2. An electrical heater was used to heat water from a temperature of 19.0 ° C to 100.0 ° C. The heater used a voltage of 110. V, a current of 3.75 A and was run for 8.00 minutes (480. seconds). Electrical energy (J) = Voltage (V) x current (A) x time (sec) a) How many joules of energy were produced by the heater? b) What mass of water could be heated from 19 ° C to 100 ° C? The specific heat of water is 4.18 J/g o C. ANSWERS 1. (a) Heat is absorbed in this process, which indicates an endothermic process. (b) From the given information, ΔH of this reaction is negative, which indicates an exothermic process. 2. a) Energy = 3.75 A x 110. V x 480. sec = 1.98 x 10 5 J. b) q = m.s. T m = 19)C - (100 x C J/g 18 . 4 J 10 x 98 . 1 5 = 585 g For Make-up Only Regular recitation Day: Time: instructor: Quiz Score: Group score: Scores recorded by:
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CHEM 0110 QUIZ 7 WEEK 9 MONDAY, 6:00 PM October 25, 2010 NAME_______________________________________________________________________ 1. The thermochemical equation for the decomposition of sodium azide (used in air bags) is: 2 NaN 3 (s) 2 Na(s) + 3 N 2 (g), H o = -43.3 kJ a) Is the reaction exothermic or endothermic? b) From the given information, determine the enthalpy change in kJ when 38.5g of sodium azide decomposes. c) From the given information, determine the molar enthalpy of formation , H o f , in kJ/mol, of sodium azide. ANSWERS 1. a) Exothermic, as H o < 0. b) H o = 38.5g x 3 NaN mol 2 43.3kJ - x 65.0g mol 1 = -12.8kJ c) The formation reaction is: Na(s) + 3/2 N 2 (g) NaN 3 (s) Hence H o f = +43.3kJ / 2 mol = +21.6kJ/mol For Make-up Only Regular recitation Day: Time: instructor: Quiz Score: Group score: Scores recorded by:
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CHEM 0110 QUIZ 7 WEEK 9 TUESDAY, 8:00 AM October 26, 2010 NAME_______________________________________________________________________ 1. Consider the reaction: 2 C 2 H 6 + 7 O 2 4 CO 2 + 6 H 2 O , H = ? The heat released when 17.8g of C 2 H 6 reacts with excess O 2 is 884 kJ. Determine the enthalpy change, H, in kJ for the above equation as written. 2. Which one of the following is the formation reaction of C 2 H 6 (g)? That is, for which reaction is the enthalpy change equal to the enthalpy of formation of C 2 H 6 ? Give your reasoning. a) C
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This note was uploaded on 02/20/2011 for the course CHEM 110 taught by Professor Dr.huston during the Spring '06 term at Pittsburgh.

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F10Q7W9 - CHEM 0110 QUIZ 7 WEEK 9 MONDAY, 1:00 PM October...

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