EXPERIMENT 10 – ENDOTHERMIC AND EXOTHERMIC REACTIONS
Name__________________Per _____
Many chemical reactions give off energy. Chemical reactions that release energy are called exothermic reactions.
Some chemical reactions absorb energy and are called endothermic reactions. You will study one exothermic and
one endothermic reaction in this experiment.
In Part I, you will study the reaction between citric acid solution and baking soda. An equation for the reaction is:
→ 3 CO2(g) + 3 H2O(l) + Na3C6H5O7(aq)
H3C6H5O7(aq) + 3 NaHCO3(s) 
In Part II, you will study the reaction between magnesium metal and hydrochloric acid. An equation for this
reaction is:
→ H2(g) + MgCl2(aq)
Mg(s) + 2 HCl(aq) 
Another objective of this experiment is for you to become familiar with using the LabQuest and Logger Pro
program.
MATERIALS
Vernier Temperature Probe
PC Computer
100-mL graduated cylinder
Balance
weighing paper
goggles
Styrofoam cup
250-mL beaker
citric acid, H3C6H5O7, solution (1.0M)
baking soda, NaHCO3
hydrochloric acid, HCl, solution (0.75M)
magnesium, Mg (0.1g)
PROCEDURE
1.
Obtain and wear goggles.
Part I Citric Acid plus Baking Soda
2. Place a Styrofoam cup into a 250 mL beaker
as shown in Figure 1. Measure out 30 mL of
citric acid solution into the Styrofoam cup.
Place the Temperature Probe into the citric
acid solution. The chemicals and
Styrofoam cup should be placed as far
away as possible from the keyboard and
LabQuest interface box.
3. Turn on the computer and the LabQuest Interface.
Figure 1
a. Use chemstu as the Username and chemistry as the Password.
b. Double-click on Logger Pro 3.8.4, go to File, Open, Chemsitry with Vernier, and 01-Endo-Exothermic.
c. When the Sensor Confirmation screen pops up, change Sensor to Direct Connect Temp, then click Connect.
d. Check that the vertical axis has temperature scaled from -10 to 40 degrees Celsius. The horizontal axis
has time scaled from 0 to 300 seconds. The live reading should show room temperatuUH in Celsius.
122010
10-1
EXPERIMENT 10 – ENDOTHERMIC AND EXOTHERMIC REACTIONS
4. Weigh out about 10 g of solid baking soda on a piece of weighing paper.
5. The temperature probe must be in the citric acid solution for at least 30 seconds before this step. Tap
Collect (green button) to begin data collection. After about 20 seconds have elapsed, add the baking soda
to the citric acid solution. During data collection, continuously stir the solution with the temperature
probe to ensure good mixing. Collect data until a minimum temperature has been reached and the
readings begin to increase. You can tap Stop (red button) to end data collection or let the computer
automatically end after 300 seconds.
6. Dispose of the reaction products in the sink. Rinse out the cup and graduate with tap water.
7. To analyze your data: (Note: If buttons are not available, click on the graph.)
a. Click the STAT button on the toolbar. In the statistics box that appears on the graph, several statistical
values are displayed including minimum and maximum. Record the maximum and the
minimum temperature onto your data table. Close the statistics box by clicking the X in the upperleft corner of the box.
b. Make a sketch of the general shape of the curve for Part I on the axes provided at the end of your
lab write-up.
8. Find the Data button. Click on it and choose Clear All Data. Proceed to step 9.
Part II Hydrochloric Acid Plus Magnesium
9. Measure out 30 mL of HCl solution into the Styrofoam cup. Place the Temperature Probe into the HCl
solution. Note: The Temperature Probe must be in the HCl solution for at least 30 seconds before doing
Step 10. CAUTION: Hydrochloric acid is caustic.
10. Obtain a piece of magnesium metal from your instructor.
11. Tap Collect to begin data collection. After about 20 seconds have elapsed, add the Mg to the HCl
solution. Continuously stir the solution with the Temperature Probe to ensure good mixing. Caution: Do
not breathe the vapors. You can tap Stop (red button) to end data collection or let the computer automatically
end.
12. Dispose of the reaction products in the sink. Rinse the graduate and cup with tap water.
13. To analyze your Part II data, repeat Steps 7a and 7b above.
14. When you have finished, tap the Data button and choose Clear All Data. Select File and Exit. Do not save
changes. Shut down the computer and turn off the LabQuest interface.
DATA AND CALCULATIONS
Part I
Part II
Final Temperature, t2
°C
°C
Initial Temperature, t1
°C
°C
Temperature change, Δt
°C
°C
122010
10-2
EXPERIMENT 10 – ENDOTHERMIC AND EXOTHERMIC REACTIONS
PROCESSING THE DATA
1. Calculate the temperature change, Δt, for each reaction by subtracting the initial temperature, t1, from the final
temperature, t2 (Δt = t2 – t1).
For questions 2 and 3, fill in the blanks with the words; warmer, colder, lost or gained.
2. In Part 1, the (water) solution became ________, hence energy was _______ .
Therefore, the reactants _______ energy as they formed products.
Write the word energy on the correct side of the equation below.
______ + H3C6H5O7(aq) + 3 NaHCO3(s) → 3 CO2(g) + 3 H2O(l) + Na3C6H5O7(aq) +_______
Is this an endothermic or exothermic reaction? _________
____
3. In Part 2, the (water) solution became ________, hence energy was _______ .
Therefore, the reactants _______ energy as they formed products.
Write the word energy on the correct side of the equation below.
→ H2(g) + MgCl2(aq) +___________
_________ +Mg(s) + 2 HCl(aq) 
____
Is this an endothermic or exothermic reaction? _________
_
4. For each reaction, describe three ways you could tell a chemical reaction was taking place.
Endothermic Reaction
a. ____________________________________________________________________
b. ____________________________________________________________________
c. ____________________________________________________________________
Exothermic Reaction
d. ____________________________________________________________________
e. ____________________________________________________________________
f. ____________________________________________________________________
Part I
Part II
122010
10-3