LCPS Core Experience |Chemical Reactions Investigation ONE
Chemical Reactions
Stu de nt No tes
OBJECTIVES
Students will:
 investigate the relationship between reactants and products.
 investigate an exothermic reaction.
 investigate an endothermic reaction.
LINK
1. How can you tell if an energy change has taken place in a chemical reaction?
The temperature increases or ___________. The substance gives off _______ or gets colder.
Background
Chemical reactions usually have two or more chemicals called reactants that are different
from one another. The reactants interact during the chemical reaction to form one or more
products. These are substances that are different from the reactants and from each other. The
reactants and products in a chemical reaction can be written as chemical formulas using
letters to represent elements.
All chemical reactions can be written as equations that are like sentences. The reactant and
product formulas are like the words in a sentence. In an equation, the reactants and products
are separated by an arrow (→). When reading a chemical equation, the word yield is used for
the arrow symbol (→). The chemical equation is then read by saying that the interaction of
the reactants yields the products.
In a chemical reaction, the chemical bonds that hold the atoms of the reactants together are
broken and reformed in a different arrangement to form the products. Breaking and reforming
these bonds occurs when the reactants react with each other. The different arrangement of
atoms can be seen by the different formulas that represent the reactants and products.
When all of the reactants are consumed in a chemical reaction, they no longer exist in their
original form. All the atoms originally found in the reactants can now be found in the
products. Atoms and molecules react with each other in specified ratios in order for a
chemical reaction to take place. The balanced chemical equation that represents each
chemical reaction stipulates the relative numbers of reactants and products. In a chemical
reaction every atom that is part of the reactants is part of the products.
Background (continued)
Chemical reactions are classified into two broad types: ones in which energy is released
(exothermic) and ones in which energy is absorbed (endothermic). A clue that a chemical
reaction has taken place is a transfer of energy.
Chemical Reactions Investigation ONE
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LCPS Core Experience |Chemical Reactions Investigation ONE
EXPERIMENT
In this investigation, you will be investigating an endothermic reaction and an exothermic
reaction.
Lesson One: Measuring Energy Change in a Chemical Reaction
1. Obtain the materials for Lesson One. You will be investigating the following chemical
reaction.
Yeast
2H2O2

2H2O
+
O2
Hydrogen
peroxide
Water
Oxygen
2. Measure 30 mL of hydrogen peroxide using a 50 mL graduated cylinder. Pour the hydrogen
peroxide into a 250 mL Erlenmeyer flask.
3. Put a thermometer into the flask and wait two minutes to allow the thermometer to reach the
temperature of the hydrogen peroxide. During the time you are waiting, measure 2 g of
yeast with the balance.
4. Record the starting temperature ______________. One person should keep track of the
time. Another person should keep track of the temperature. You will be measuring the
temperature every 30 seconds.
5. Add the yeast to the beaker and immediately record the temperature in Table A, this is time
zero, while gently stirring the contents of the flask. Continue to record the temperature in
Table A every 30 seconds for 3 minutes.
6. Did the temperature increase or decrease? __________________
7. Was energy taken in or released in the reaction? ___________________
8. Pour the mixture down the drain and rinse out the flask with water. Rinse the thermometer
off.
Chemical Reactions Investigation ONE
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Name: _______________________________________ Block: ____________ Date: _____________
LCPS Core Experience | Chemical Reactions Investigation TWO
Lesson Two: Measuring Energy Change in a Chemical Reaction
Materials Per Lab Group for Lesson Two
1. Obtain the materials for Lesson Two. You will be investigating the following chemical
reaction.
heat
NaHCO3
+
CH3COOH 
CH3COONa +
H2O +
CO2
Baking
Soda
Acetic
Acid
Sodium
Acetate
Water
Carbon
Dioxide
2. Put a thermometer into the flask and wait two minutes to allow the thermometer to reach the
temperature of the vinegar. During the time you are waiting, measure 2 g of baking soda
with the balance. Refer to the procedural toolbox Using a Weigh Dish.
3. Record the starting temperature ____________.
4. Add the baking soda to the vinegar and immediately record the temperature, as time zero in
Table A as you swirl the contents of the flask. Continue to record the temperature every 30
seconds as you observe the reaction for 3 minutes.
5. Did the temperature increase or decrease? ____________________________
6. Was energy taken in or released in the reaction? _____________________
7. Pour the mixture down the drain and rinse out the flask with water. Rinse the thermometer.
Table A: The Effect of a Chemical Reaction on the Temperature of a Solution
Lesson One:
Lesson Two:
Hydrogen Peroxide
Vinegar and Baking
and Yeast Reaction
Soda Reaction
0
Time (min)
Temperature ( C)
Temperature (0C)
0
0.5
1.0
1.5
2.0
2.5
3.0
Chemical Reactions Investigation ONE
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LCPS Core Experience | Chemical Reactions Investigation ONE
Graph: Use the data from Table A to plot a graph of time vs. temperature for both solutions on
the same graph paper.
a. Use a different color for each set of data..
b. Determine which variable is the independent variable and which is the dependent variable.
STOP AND DISCUSS
LEARNING REVIEW
List three things you learned about energy, endothermic and exothermic reactions.
a. ___________reactions absorb energy, which means that the temperature would decrease.
b. ___________ reactions release energy, which means that the temperature would increase.
c. ____________ reactions are either exothermic or endothermic.
Chemical Reactions Investigation ONE
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LCPS Core Experience | Chemical Reactions Investigation ONE
EVALUATION
1. Which reaction was endothermic? Write the chemical equation.
NaHCO3
+ _____________

CH3COONa + _______
+
CO2
2. Why did you select this reaction as the endothermic reaction?
The reaction is endothermic because the temperature ____________ during the reaction.
Therefore, energy was absorbed during the reaction.
3. Which reaction was exothermic? Write the chemical equation.
2H2O2

2H2O
+
_______
4. Why did you select this reaction as the exothermic reaction?
The reaction is exothermic because the temperature ____________during the reaction,
therefore energy was given off during the reaction.
Chemical Reactions Investigation ONE
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