| 1. | Safety |
| 2. |
Objectives/Overview |
| 3. |
Procedures |
| 4. | Observations |
|
5. |
Equipment |
| 6. | View
Techniques |
| 7. | |
| 8. | Calculations/Set-ups |
| 9. | Conclusions |
| 10. | Grading Scale |
|
11. |
Review Prelab Questions |
|
12. |
Review Postlab Questions |
Experiment
8
Enthalpy
of Combustion
CALCULATIONS/SET-UPS
ENTHALPY OF REACTION: MgO(s) + 2 HCl(aq) ---> MgCl2(aq) + H2O(l)
| Mass
of MgO |
mMgO
= mass of MgO and weigh boat - mass of weigh boat |
|
| Temperature change Note: Tf and Ti are both determined from the graph of temperature versus time for this reaction |
DT = Tf - Ti | |
| Mass
of HCl solution |
mHCl = (DHCl)(VHCl) = (1.00 g/mL)(VHCl) | |
| Heat
gained by solution |
qsoln = (mHCl)(sHCl)(DT) = (mHCl)(4.184 J/g°C)(DT) | |
| Heat
gained by calorimeter
Note: for Ccal use value determined in experiment 6 |
qcal = (Ccal)DT | |
| Total
heat produced by the reaction |
qrxn = (- qsoln ) + (- qcal ) | |
|
Moles of
MgO used |
MMMgO = molar mass of MgO | |
| n = mMgO / (MMMgO) | ||
| Enthalpy
of reaction |
DH(MgO) = qrxn / n | |
ENTHALPY OF REACTION: Mg(s) + 2 HCl(aq) ---> MgCl2(aq) + H2(g)
| Mass
of Mg |
mMg
= mass of Mg and weigh boat - mass of weigh boat |
|
| Temperature change Note: Tf and Ti are both determined from the graph of temperature versus time for this reaction |
DT = Tf - Ti | |
| Mass
of HCl solution |
mHCl = (DHCl)(VHCl) = (1.00 g/mL)(VHCl) | |
| Heat
gained by solution |
qsoln = (mHCl)(sHCl)(DT) = (mHCl)(4.184 J/g°C)(DT) | |
| Heat
gained by calorimeter
Note: for Ccal use value determined in experiment 6 |
qcal = (Ccal) DT | |
| Total
heat produced by the reaction |
qrxn = (- qsoln ) + (- qcal ) | |
|
Moles of
Mg used |
AMMg = atomic mass of Mg | |
| n = mMg / (AMMg) | ||
| Enthalpy
of reaction |
DH(Mg) = qrxn / n | |
COMBUSTION OF Mg: DHcombustion Mg(s) + 1/2 O2(g) ---> MgO(s)
| Note: for the reactions and DH values
Note: The values of each of the factors a, b, and c in the below equation are determined from the Hess' Law rules for combining the three reactions that correspond to the three DH values to produced the desired net reaction (Mg(s) + ½ O2(g) ---> MgO(s) ). An equation that is combined with no changes has a factor of +1. An equation that is reversed before being combined has a factor of -1. If all the coefficients of the reaction equation are multiplied by a number, the factor is the same as that number. |
|
| Experimental
DHcombustion of Mg (J/mol)
|
DHcombustion = (a)DH(Mg) + (b)DH(MgO) + (c)DHf°(H2O) |
| Theoretical
DHcombustion of Mg (J/mol) |
DHcombustion = S(nprod x DHf(products)) - S(nreact x DHf(reactants)) |
| %
error in experimental DHcombustion
of Mg |
% error = ((Theoretical DHcombustion - Experimental DHcombustion) / Theoretical DHcombustion) x 100 |
