CHM201 General Chemistry and Laboratory I

CHM201 General Chemistry and Laboratory I

 

Laboratory 7 – Thermochemistry and Hess’s Law

 

November 17, 2021

 

Name

Group

PLEASE ENABLE EDITING BEFORE FILLING OUT THIS REPORT!

 

Report Due by December 5, 2021.

 

No report will be accepted for credit after December 12, 2021

 

Grade:

 

Lab average to date:

 

Overall average to date:

 

 

Results: (60 pts)

 

Room Temperature

 

Reactant

 

Mg

 

Mg

 

MgO

 

MgO

 

Trial Number

 

1

 

2

 

3

 

4

 

Mass of reactant (from data)

 

Moles of reactant (calculate)

 

Initial time (ti) (from graph)

 

Initial Temperature (Ti)

 

(from the graph)

 

Linear Curve fit slope (m)

 

(from the graph)

 

Linear Curve fit intercept (b)

 

(from the graph)

 

Final Temperature (Tf)

 

(calculate from linear fit data)

 

∆T = Tf – Ti

 

qwater

 

qcalorimeter

 

qrxn

 

∆Hrxn

 

Use the following to determine the enthalpy of formation of magnesium oxide:

 

Mg (s) + 2HCl (aq) → MgCl2 (aq) + H2 (g)

 

ΔH = (calculated in the experiment)

 

MgO (s) + 2HCl (aq) → MgCl2 (aq)+ H2O (l)

 

ΔH = (calculated in the experiment)

 

H2 (g) + ½O2 (g) → H2O (l)

 

ΔH = – 285.8 kJ/mol

 

Mg (s) + ½ O2 (g) MgO (s)

 

ΔH = (determine using Hess’s Law)

 

Calculations: (40 pts)

 

1. Using the enthalpies of reaction computed in the lab and the value given for the enthalpy of formation of liquid water, show the Hess’s Law determination of the enthalpy of formation of solid magnesium oxide. Show your work. If you are including a scan of your handwritten work, it must be legible. (30 pts)

 

2. Compare the value you calculated with the actual value (-601.8 kJ/mol). Show your determination of percent error. Use the standard equation for this: (10 pts)

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