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eng-spring07-q206s

eng-spring07-q206s - CHEM 151 Quiz 6 NAME_KEY ID Show your...

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CHEM 151: Quiz 6 NAME ____________ KEY ________ ID #_______________ Show your work for full credit Eng Q206 You are allowed to use books/notes/etc, but you Due by the START of Thursday’s (3/8/07) lecture. are not allowed to receive help from others. Late quizzes will receive at least a 10 point deduction. 1. (2 pts) In an endothermic reaction, the system (or reaction) will ____ INCREASE _________ in temperature and the surroundings will ____ DECREASE ______ in temperature. (Place the words increase and decrease in the correct blanks.) 2. (6 pts) If 46.1 g Zn at 18.0 °C is placed in 80.0 g H 2 O at 75.0 °C, what is the final temperature of the mixture? The specific heat capacities of zinc and water are 0.388 J/g·K and 4.184 J/g·K, respectively. 0 = q Zn + q H2O 2 pts 0 = C Zn ·m Zn · Δ T Zn + C H2O ·m H2O · Δ T H2O 2 pts 0 = (0.388 J/g·°C)(46.1g)(T f – 18.0 °C) + (4.184 J/g·°C)(80.0g)(T f – 75.0 °C) 0 = 17.89 T f – 322.0 + 334.7 T f – 25100 1 pt work 0 = 352.6 T f – 25420 T f = 72.1 °C 1 pt answer (½ units) 3. (6 pts) When 0.560 g of solid sodium reacts with 0.560 g of fluorine gas to form solid sodium fluoride, 13.8 kJ of heat is evolved at standard-state conditions. What is the standard enthalpy of formation ( Δ H f °) of solid sodium fluoride? Hint: write the balanced reaction for sodium with fluorine gas to produce sodium fluoride and determine the number of moles of sodium fluoride that will form from the limiting reagent.
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