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)

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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