Chem 111 Lab: Thermochemistry—Report Form Page J-1
REPORT FORM
THERMOCHEMISTRY
Your name _______________________________________________ Grade =________/10
Your partner's name _____________________________________
PART 1. Reaction of Mg(s) with HCl(aq)
Molarity of HCl solution used (M) __________________
Masses of Magnesium Used
Run 1 Run 2 Run 3 (if needed)
Mass of paper + Mg (g)
Mass of paper (g)
Mass of Mg (g)
Volume of HCl (mL)
When you enter data for this experiment into the computer, enter data for only two runs. Choose the two runs thatyou believe are the most accurate.
Page J-2 Chem 111 Lab: Thermochemistry—Report Form
Temperature readings
Temperature (°C)Run 1
Temperature (°C)Run 2
Temperature (°C)Run 3 (in needed)
Initial temperature of HCl
solution
After 0.5 minutes
After 1.0 minutes
After 1.5 minutes
After 2.0 minutes
After 2.5 minutes
After 3.0 minutes
After 3.5 minutes
After 4.0 minutes
After 4.5 minutes
After 5.0 minutes
Maximum temperature (oC)
Observed temp. change, ∆T
(oC), (∆T = Tmax - initial T)
Chem 111 Lab: Thermochemistry—Report Form Page J-3
PART 2. Reaction of MgO(s) with HCl(aq)Molarity of HCl solution used (M) __________________
Masses of Magnesium Oxide Used
Run 1 Run 2 Run 3 (if needed)
Mass of paper + MgO (g)
Mass of paper (g)
Mass of MgO (g)
Volume of HCl (mL)
Temperature readingsTemperature (°C)Run 1
Temperature (°C)Run 2
Temperature (°C)Run 3 (if needed)
Initial temperature of HCl(aq)
After 0.5 minutes
After 1.0 minutes
After 1.5 minutes
After 2.0 minutes
After 2.5 minutes
After 3.0 minutes
After 3.5 minutes
After 4.0 minutes
After 4.5 minutes
After 5.0 minutes
Maximum temperature (oC)
Observed temp. change,
∆T(˚C)
(∆T = Tmax - initial T)
Page J-4 Chem 111 Lab: Thermochemistry—Report Form
PART 3. Calculations
(a) The Reaction of Magnesium with HCl
Prepare a graph of your data for change in temperature (∆T) versus the quantity of magnesium metal. (You may use
the paper provided in the laboratory and draw the best straight line through the origin of the plot and the points for
runs 1, 2, and 3. OR, use computer software such as MS Excel or the plotting software on the General Chemistry
CD-ROM to prepare the graph. (This is recommended because it gives you an accurate slope.) Plot the data as
illustrated here. (Turn in your graph with this report.)
y
x (Mass of Mg)
(∆T)
b = intercept y = mx + b
m = slope of line
From the computer plot, record the following information: (see pages viii-x of this manual)
Slope of the line = (∆T/g of Mg) = _________________
Intercept = _________________ (This should be about 0)
(Note: This same information can also be obtained readily from the graph done on paper.)
Use your plot, or the equation developed from the plot, to calculate the temperature change for
(a) 0.75 g ∆T = ___________
(b) 1.0 g ∆T = ___________
What is the relationship between the mass of magnesium in the reaction and the change in temperature? Comment
on this relationship.
Is this a general relationship? That is, if you did some other reaction, say the reaction of HCl and NaOH, would a
similar relationship be observed?
Chem 111 Lab: Thermochemistry—Report Form Page J-5
(b) Calculate ∆H2 , the Molar enthalpy forMg(s) + 2 H+(aq) ! Mg2 +(aq) + H2 (g)
This uses data from PART 1 of the experiment.
Run 1 Run 2
1. Mass of Mg reacting __________ __________
2. Moles of Mg reacting __________ __________
3. Mass of HCl used __________ __________(assume density = 1.0 g/mL)
4. Total mass of solution __________ __________(g Mg + g HCl)
5. Temperature change observedin Part I (∆T) __________ __________
6. Heat evolved by your mass of Mg (J) __________ __________
q = -(total mass)(sp. ht.)(∆T)
(sp. ht. = 4.18 J/g-deg)
(q is negative)
7. Molar enthalpy change, ∆H2 (kJ) __________ __________
∆H2 ( kJ / mol) = q from line 6 ( J )
( g Mg / 24. 3 g•mol− 1 ) ( 1000 J / kJ)
8. Average molar enthalpy for reaction 2 = ∆H2 = ____________ kJ
Page J-6 Chem 111 Lab: Thermochemistry—Report Form
(c) Calculate ∆H5 , the Molar enthalpy forMgO(s) + 2 H+(aq) ! Mg2 +(aq) + H2 O(aq)
This uses data from PART 2 of the experiment.Run 1 Run 2
9. Mass of MgO reacting __________ __________
10. Moles of MgO reacting __________ __________
11. Mass of HCl used __________ __________ (assume density = 1.0 g/mL)
12. Total mass of solution __________ __________ (g MgO + g HCl)
13. Temperature change observed __________ __________
14. Heat evolved by your mass of MgO (J) __________ __________
q = -(total mass)(sp. ht.)(∆T) (here sp. ht. = 4.18 J/g-deg and q is negative)
15. Molar enthalpy change, ∆H5 (kJ) __________ __________
∆H5 ( kJ / mol) = q from line 14 ( J )
( g MgO / 40. 3 g•mol− 1 ) ( 1000 J / kJ)
16. Average molar enthalpy for reaction 5 = ∆H5 = ____________ kJ
(d) Calculation of the molar enthalpy of formation of MgO(s), ∆H1
∆H2 = ___________________________ kJ
∆H3 = ___________________________ kJ (recall that ∆H3 = -∆H5)
∆H4 = ___________________________ kJ (molar enthalpy of formation of liquid H2O; to
∆H1 = ___________________________ kJ = molar enthalpy of formation of MgO(s)
Actual value of ∆Hf[MgO(s)] (entered by your instructor) = _______________________ kJ/mol
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