CRHS Academic Chemistry. 14 Thermochemistry. Homework. Notes, Homework, Exam Reviews and Their KEYS located on CRHS Academic Chemistry

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1 Unit 14 HW Page 1 of 12 Name Period CRHS Academic Chemistry Unit 14 Thermochemistry Homework Due Date Assignment On-Time (100) Late (70) Warm-Up C Notes, Homework, xam Reviews and Their KYS located on CRHS Academic Chemistry Website: corn

2 Page 2 of 12 Unit 14 HW

3 Unit 14 HW Page 3 of WHAT IS THRMOCHMISTRY 2 What is the!aw of conservation of energy? ÿ,,ÿ,,ÿ::ÿ,ÿ ÿ k4, [ 3 xplain from where the heart in an eÿ(othermic reaction comes ÿ-jÿpÿqjÿuv'ÿ ÿ9 4, Describe the direction of heat flow "ÿi:'ÿ 'ÿ' ÿ,i Classify these processes as exothermic or endothermic (Think about whether the "object" is gaining or releasing heat) A, Burning rubbing alcohol (ÿ!ÿpxothermieo] endothermic ) B Cooking an egg ( exothermic / ejqdothermic')ilÿ C Combustion of gasoline ;(exothermicl) endothermic) a, :, 6 Indicate whether AH is positive (+) or negative (-) for the following: A the reactants have > enthalpythan the products AH = B the products have >enthalpythanthe reactants AH = -ÿ C the surroundings lose heat as a reaction occurs AH = "ÿ D the temperature increases as a reaction occurs AH =, Label the graphs as endothermic or exothermic a P (k J) O 100 PF 60 (k J) C+D

4 Page 4 of 12 Unit 14 HW 142 NTHALPI5 OF RACTION, Why is Calorimetry important to the study of Thermochemistry? /k:cÿjÿ) What is the key principle of Calorimetry? ÿjÿc ÿ ÿ%, /1:ÿ ÿ ÿ V,ÿ'%ÿ :ÿ ÿyÿ : / Determine the AH for the following reactions and indicate with X if xothermic or ndothermic 3 N2Ig) + 021g) + 43,3 kj --) 2 &H= NO(g) ÿ ÿ ÿ ÿ ÿ'4 xothermic or ndothermic:iÿ? f 2 C2H6 (g) + 02 Ig) --) 4 C02 (g) + 6 H20 (I) kj ÿ or ndothermic 5 C3Hs(g) --> C3H8(I) + 41,8 Id &H =, xothermic or ndothermic? Rewrite the following equations by expressing the energy change as a term in the equation: 6 H20 (g) --) H20 (I) AH = kj AI '-) 2AI203 AH = -8038kJ ach of the following equations (with the ZIH provided) has been rewritten Find the ZlH for the new equation 6, CuO(ÿ) --) Cu(ÿ) + 1/2 021ÿ) AH = 371 kj 2Cu(s)+ O2(g) "-) 2CuOis) AH= 4 Fe Is) (g) ---) 2 Fe203 (s) 2 Fe Is) + 3/20ÿ (g) --) Fe203 Is) AH = kj AH= % < C2H2 + 5/2 02 -) 2 C02 + H20/I) kj 2 C2H2 (g) + 5 O2(g) "--ÿ 4 CO2 (g) + 2 H20 (I) H2(g)+ Br2(g) ---) 2 HBr(g) Id AH= t ÿ,,: HBr(g) -> 1/2 H2(g) + 1/2 Br2ig)

5 Unit 14 HW Page 5 of 12 Using each o/ the methods described on page 8 and 9 o/ Unit 14 Notes, apply Hess's Law and calculate the nthalpy of Reaction (AH ) /or problems 10-11, Method A - Combination o/ thermochemical equations Method B - AH = sum of [(AHf of products) x (tool of products)] - sum of [(AHf of reactants) x (mol of reactants)] i0 2 H202(I) ÿ 2 H20 (I) + O2(g) H2(g) + O2(g) --) H202(I) AHf = kj J-O q- 20(/A, ---28s8,J Method A,,, :ÿ:i / 'i '!Tt ÿ:v Method B/- // % 11 CaCO3 (s) "-) CaO (s) + CO2(G) Ca (s) + C(s) + 3/2 02 (g) --) CaCO3 (s) AHf = kj Ca (s) + O2 (g) --) CaO (s) AHf = -636 Id C (s) + ½ 02 (g) "-) CO2 (g) AHf = kj Method A Method B \,ÿ ( \

6 Page 6 of 12 Unit 14 HW 143 DRIVING FORCS FOF CHMCIAL RACTIONS 1 In nature, reactions tend to proceed in a direction that leads to, xplain why some endothermic reactions do occur!ÿ:ÿ'ÿ energy state,ÿ,ÿ}dÿd ÿ,ÿ d,,ÿ fÿ) 77fi+,o X! L 4 In nature there is tendency to proceed in direction thit IICRAIIÿy DCRASS the randomness of a system 5 Chemical reactions tend to go in direction(of IOIIASIII311NCRASING order,/ Predict whether the value of AS for each of the following reactions will greater than, less than, or equal to zero C3CO2(s) + 502(g) ÿ 3 CO2(g) + 4 H20(g) ÿ {ÿ}ÿ 302 (g) + P2 (g) --} 2 PO3 (g) NaCl (s) -) Na+l(aq) + Cl-l(aq) s ÿ4## 2Ca (s) + Clÿ (g) -> 2 CaCIÿ (s) d!:,>, 7 Decide if AG can ever be negative and therefore the reaction is spontaneous and fill in 3ÿ column with conclusions AH - value (exothermic) AS + value (more random) AG - value (exothermic) + value (endothermic) + value (endothermic - value (less random) + value (more random) -value (less ransom) Predict whether the reactions will be spontaneous at 298K by calculating AG from the given enthalpies and entropies, AH = Id/mol and AS = kj/(mol*k), AS = kjl(mol*k)

7 Unit 14 HW Page 7 of 12 xtra Credit- THRMOCHMISTRY ' III I-1 L,IN FI I---ll---II-]l-ll-l f fn LII IN N F IIIIIIiNIN NNNNFT]NNNF] Across 3 in an endothermic reaction heat is 61 calorie = heat flows from a obiect to a cooler object 9 accurate and precise measurement of heat change in a reaction 11, type of energy stored in chemical or nuclear bonds 12 heat flows out of system - system warms - negative change in enthalpy 15 type of energy - a type of potential energy stored in bonds between atoms in a substance 17, heat of a system at constant pressure 19 type of energy - total of all energy of position and movement of the particles in a system 21 type of energy - due to motion Down 1 substance on right side of reaction 2 a equation must be balanced 4 capacity for doing work or supplying heat 5 heat capacity is an property of matter 7 change in enthalpy of a reaction is the same with one step or many steps (answer is HSS'S LAW) loheat enters the system - system cools - positive change in enthalpy 13water has a specific heat capacity (c) 14water can hold a amount of heat 16substance on left side of reaction 18energy that transfers from one object to another because of temperature difference 20In an exothermic reaction heat is

8 Page 8 of 12 Unit 14 HW ofÿ 5 o,ÿ o Lÿ g NO ::Z: >, r-,,i o! [: oÿ'ÿ' gÿ o o,i,ÿ Z 0 g i11 g ÿ 0 o I (D <,,ÿ,-- ÿ,ÿ ÿ tÿ ÿ i:: ÿ:q +" O r o < 0,,I 0") 'qÿ IX) LD I"-ÿ --J