Problems for EXA X Downloads/Practice%20Problems%20for%20EXAM-3.pdf Practice Exa

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Problems for EXA X Downloads/Practice%20Problems%20for%20EXAM-3.pdf Practice Exam-3 Name MULTIPLE CHOICE. Choose the one altemative that best completes the statement or answers the question. 1) Use the rf and AHmn information provided to alculate AHf for IF: AHY (kJ/mol) [Fy(g)+12(g) IF5(g) + 2 IF(g) IF7ig) IF5(g) -941 -840 A) 101 kJ/mol B) -95 kJ/mol C) -190. kJ/mol D)-146 kJ/mol E) 24 kJ/mol 2) Use the standard reaction enthalpies given below to determine AH pn for the following reaction: nan for the folwving reaction: 25(s) +3O2(g) 2503(g) AHrxn® ? Given: SO2 (g) S(s) + O2 (g) 2502(g) + O2(g) 2503(g) AHrxn® +296.8 kJ AHrxn®-1978 kJ A)-293.0k B)-494.6 kJ C)-791.4J D)-6924 k] E) 1583 kJ 3) A piece of iron (mass 25.0 g) at 398 K is placed in a styrofoam coffee cup containing 25.0 mL of water at 298 K. Assuming that no heat is lost to the cup or the surroundings, what will the final SONY

Explanation / Answer

delta H rxn = delta Hf (product ) - delta H f (reactant)

Given delta H rxn = -89kJ

delta H rxn =[(Hf (IF5) + 2 Hf (IF)] - delta Hf (IF7)

-89kJ = [-840 + 2 Hf (IF) ] - (-941kJ)

-89-941 = -840 + 2Hf (IF)

Hf (IF) = -190/2 = - 95kJ

2. First of all multiply ex 1 i.e SO2 ----> S + O2 by 2 which gives 2SO2 -----> 2S + 2O2 Delta Hrxn = 296.8kJ X 2 = 593.6kJ

Now subtract equation 1 from 2

2SO2 + O2 ------> 2SO3 - 2SO2 -----> 2S + 2O2 [ delta Hrxn eq 2 - delta H rxn eq1]

which given 2S + 3O2 -----> 2SO3   [-197.8 kJ - (593.6kJ)] = -791.4kJ

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