Name:
Period:
Endothermic and Exothermic Reactions Lab
Purpose
This is the test of two reactions to determine if they are endothermic or exothermic reactions.
Introduction
All chemical reactions take in some energy and give off some energy. The difference between those two
amounts is the heat of reaction. When the amount of energy given off is more than the amount taken in, the heat
of reaction is negative (the products have less energy than the reactants did). When the reaction takes in more
heat than it give off, the heat of reaction is positive (the products have more energy than the reactants).
A reaction in which thermal energy is given off is called an exothermic reaction. The products are lower in
thermal energy than the reactants. This lost energy is transferred to the surroundings and can be measure by the
increase in temperature of those surroundings. Many other reactions absorb heat from their environment. A
reaction in which thermal energy is absorbed is endothermic. The products are higher in thermal energy (as
measure by their temperature) than the reactants. The type of reaction can be determined from the change in
temperature as well as from the slope on a graph of temperature vs. time. A negative slope means the reaction in
endothermic. A positive slope means the reaction is exothermic.
Materials
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SPARK or GLX
stainless steel temperature probe
electric balance
250mL beaker
Styrofoam beaker
100mL graduated cylinder
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0.5M HCL
1.5M Citric Acid
Magnesium metal strip
steel wool
NaHCO3 (sodium bicarbonate)
water
Procedure
1.
Turn on the SPARK or GLX and hook up the temperature probe. Get your instrument set up to show a
graph of temperature verses time.
2.
Before continuing on to the next step, draw the shape of the temperature vs. time graph you would expect
to see for an exothermic reaction in your data. Get you teachers’ signature before continuing. Do not warn
any other groups to get the signature.
3.
Put 30.0mL of 1.5M citric acid into the Styrofoam beaker. Put the temperature probe in the acid.
4.
Weigh out 10.0g of sodium bicarbonate (baking soda).
5.
Begin to record data on your device. After about 20s of recording just the temperature of the acid, add the
baking soda to the citric acid. Gently stir the solution with the temperature probe to ensure good mixing.
6.
Record data until the temperature reading has stabilized or beings to go the other direction. Stop recording.
7.
Fill in the necessary information on Table 1 in the Data section. Sketch your data in Graph 2. Label the
graph as an endothermic or exothermic reaction.
8.
Pour the remaining contents down the drain. Make sure to rinse your Styrofoam beaker with water to
remove any remaining chemicals.
9.
Put 30.0mL of 0.5M HCl into the Styrofoam beaker with the temperature probe.
10. Clean the magnesium metal with steel wool to remove any oxidation.
11. Begin to record data on you device. After about 20s, add the clean strip of magnesium metal to the acid
solution. Gently stir the solution with the temperature probe to ensure good mixing.
12. Record data until the temperature reading has stabilized or begins to go the other direction. Stop recording.
13. Fill in the necessary information on Table 1 in the Data section. Sketch your data in Graph 3. Label the
graph as an endothermic or exothermic reaction.
14. Pour the remaining liquid down the drain. Any remaining magnesium strip should be retrieved with
tweezers and put into the trash. Make sure to rinse your Styrofoam beaker with water to remove any
remaining chemicals.
Data
Graph 1
Table 1
Item
Minimum Temperature
Maximum Temperature
Change in Temperature
Baking Soda/Citric Acid
Magnesium/Hydrochloric Acid
Graph 2
Graph 3
Conclusion Questions
1.
Which reaction had a negative temperature change? Does that mean that the reaction is endothermic or
exothermic? Explain using your graph.
2.
Which reaction had a positive temperature change? Does that mean that the reaction is endothermic or
exothermic? Explain using your graph.
3.
For each reaction, describe three things that indicate a chemical reaction was taking place.
4.
Which reaction had the faster reaction rate? Explain your answer.