17. Calculate heat of reaction, q rnx 18. Convert heat of reaction, q rnx to kil
ID: 880637 • Letter: 1
Question
17. Calculate heat of reaction, qrnx
18. Convert heat of reaction, qrnx to kilojoules, kJ.
19. Calculate the moles of Mg reacted (MW=24.305 g/mole)
20. Calculate the molar heat of reaction, (hint: qrnx /mol Mg)
21. Is this reaction an exothermic or endothermic reaction? How do you know?
22. How would someone know whether the reaction is exothermic or endothermic if the only thing they would have available is the molar heat of reaction value such as that you calculated above?
23. Considering your answer to questions 11 and 12 write the molar heat of rection (enthalpy) with the proper algebraic sign, (+ or -).
Can someone please help me answer all these questions, I am so stuck!!!!
Explanation / Answer
1. Volume of water = 50 ml
3. mass of water = 50 g
3. temp of water = 40.2 oC
6. qwater = 50 x 4.184 x 18.7 = 3912.04 J
7. temperature of water belofre mixing = 21.5 oC
8. Mass of cold water = 50 g
9. temperature of water after mixing = 40.2 oC
10. change in temerature of water = 40.2 - 21.5 = 18.7 oC
11. qwater = 50 x 4.184 x 18.7 = 3912.04 J
12. qcal = (qmetal + qwater) = -(-34.83 + 3912.04) = 3946.87 J
13. volume of HCl = 50 mL, conc. of HCl = 0.0082 x 2/0.05 = 0.328 M
14. Initial temp of HCl = 21.5 oC
15. mass of Mg = 0.2 g
16. temperature change in calorimeter = 40.2 - 21.5 = 18.7 oC
17. Heat of reaction
delta H = q = 50 x 4.184 x 19.8 = 4142.16 J
18. Heat of reaction = 4.14 kJ
19. moles of Mg = g/molar mass = 0.2/24.305 = 0.0082 mols
20. molar heat of reaction
qmg = 0.2 x 1.020 x -1.4/0.0082 = -34.83 J/mol
21. This reaction is exothermic
22. The -ve sign of the molar heat of reaction tells it is exothermic [similarly a +ve sign would mean endothermic reaction]
23. molar heat of reaction = 3946.87 J
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