Thermochemistry: Hess\' Law Name Lab Section: Date: Pre lab: Hess\' Law 1. (a) W

Question

Thermochemistry: Hess' Law Name Lab Section: Date: Pre lab: Hess' Law 1. (a) What is the overall net reaction for the system below? A,+ B C + 2D AH-54 kJ/mol H = 85 kJ/mol Overall reaction: (b) what is H for the overall reaction? AHrxn = 2. If a reaction that was placed in the sample dish of the picture shown in Figure 2 is exothermic a. How will the water that surrounds the reaction change temperature wise? So the sign for ATsoln will be r? b. Therefore the sign of ATnn will be? c. The sign for qson will be? d. The sign of qnn will be? ignition hemometer Sterer Stirrer Water Figure 3: Bomb Calorimeter 127 Insulated- Sample dish outside container Steel bomb

Explanation / Answer

1. a)

A + B ---> C + 2D   DH = -54

A + 2C ----> E        DH = 85

B ----> D + E        DH = 12

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2A + 2B + 2C ---> 2E + 2D + C (overall reaction)
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b) DHrxn = (-54+85+12)= -43 kj/mol

2) exothermic means temperature incteases.

a. so that DTsol = +ve

b. DTrxn = -ve

c. qrxn = -ve

3) q = msDT

      = (1.145+50)*4.18*5.9

     = 1261.34 joule

4) q rxn = -525 j

DHrxn = -525*2/0.0025 = -420 kj/mol

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