A+ Solution UOP CHM/150 Week 4 Lab Hess’ Law

Hess’ Law

Peter Jeschofnig, Ph.D. Version 42-0158-00-01

Lab Report Assistant                                                                                              

This document is not meant to be a substitute for a formal laboratory report. The Lab Report Assistant is simply a summary of the experiment’s questions, diagrams if needed, and data tables that should be addressed in a formal lab report. The intent is to facilitate students’ writing of lab reports by providing this information in an editable file which can be sent to an instructor.

Part 1: Reaction: HCl & NaOH → NaCl + H2O

Data Table 1: Sample data

Initial Temperature of HCl - oC

Initial Temperature NaOH - oC

Average Initial Temperature - oC

Final Temperature of mixture

(extrapolated)

Change in Temperature of mixture, ΔT

Data Table 2: Sample data

Time after mixing- secondsTemperature - °C

20

40

60

80

100

120

140

160

180

200

220

240

260

280

300

Part 2: Reaction 2: NH4Cl + NaOH → NH3 + NaCl + H2O

Data Table 3:

Initial Temperature of NaOH - oC

Initial Temperature NH Cl - oC

4

Average Initial Temperature - oC

Final Temperature of mixture (extrapolated)

Change in Temperature of mixture, ΔT

Data Table 4:

Time after mixing- secondsTemperature - oC

20

40

60

80

100

120

140

160

180

200

220

240

260

280

300

Part 3: Reaction : NH3 + HCl → NH4Cl

Data Table 5:

Initial Temperature of HCl - oC

Initial Temperature NH  - oC

3

Average Initial Temperature - oC

Final Temperature of mixture (extrapolated)

Change in Temperature of mixture, ΔT

Data Table 6:

Time after mixing- secondsTemperature - oC

20

40

60

80

100

120

140

160

180

200

220

240

260

280

300

Questions

For A. through E. See the calculations for the Data Tables above.

A.  Using the data from your data tables calculate ΔT for all three reactions: B.   Calculate the heat loss or gain of the three solution mixtures:

C.   Use Hess’ Law and ΔH for the first two reactions: NaOH (aq) + HCl (aq) → H2O (l) + NaCl (aq)

NaOH (aq) + NH4Cl (aq) → NH3 + NaCl + H2O (l)

to determine ΔH for this reaction: NH3 + HCl → NH4Cl

D.  Compare the results of step 3 above with the experimental results of the

NH3 + HCl → NH4Cl

E.   Use  the  thermodynamic quantities given below to calculate the theoretical ΔH for this reaction: NH3 + HCl → NH4Cl

●ΔH°f for NH3 (aq) = - 80.29 kJ/mol

●ΔH°f for HCl (aq) = - 167.2 kJ/mol

●ΔH°f for NH4 (aq) = - 132.5 kJ/mol

●ΔH°f for Cl- (aq) = - 167.2 kJ/mol

F.What was the ΔH value obtained for NH3 + HCl à NH4Cl from Hess’ Law method? G.  What was the ΔH value obtained for NH3 + HCl à NH4Cl experimentally?

H.  What  was  the  calculated  ΔH  value  obtained  for  NH3   +  HCl  à NH4Cl  using  published thermodynamic data?

I.What was the % error of the various methods used? (i.e. comparing the results of the results of Hess’ Law method and the experimental results to the calculated value?

J.Name three examples of the practical application for the use of ΔH values.