Reaction in a Bag
An exothermic reaction occurs when the energy used to break the bonds
in the reactants (the starting stuff) is less than the energy released when
new bonds are made in the products (the stuff you end up with). This extra
energy is given off as heat and there is a temperature rise around the
surroundings of the reaction.
Combustion is an example of an exothermic reaction- you can feel the
heat given off if you get too close!
The reactants have more energy than the end products. It also indicates
that the enthalpy change is negative as heat is lost to the surroundings
resulting in a temperature increase.
Investigation 1
What might happen if you put calcium chloride, baking soda, and water in a zip bag?
CaCl2 + 2NaHCO3 + H2O
CaCO3 + 2NaCl + 2H2O + CO2
Reactants
Products
Procedure
1. Person 1, at the table measure one level spoonful of calcium chloride and one level spoonful
of baking soda into the zip bag on one side and seal that side of the baggie.
2. Person 2, measure 50mL of water in the graduated cylinder.
3. Person 3, use your finger to dent in the middle of the baggie so that the calcium chloride and
baking soda mixture are on one side.
4. Person 4, slowly pour the water in the baggie on the opposite side trying to keep it separate
from the CaCl2 and NaHCO3.
5. Person 1, immediately zip the bag closed.
6. All students observe as the group members take turns holding and gently shaking the bag.
Observe what happens and answer the questions below.
Questions
1. What are the reactants in this investigation?
2. What are the products in this investigation?
3. Is matter conserved in this reaction?
4. Was this reaction a physical or chemical reaction? Explain how you know.
5. Was this reaction an endothermic or exothermic reaction? Explain how you know.
6. What did you find out by doing the reaction in the bag that you couldn’t find out if the
reaction occurred in a cup?
Reaction in a Bag
An endothermic reaction occurs when the energy used to break the bonds in
the reactants is greater than the energy given out when bonds are formed in
the products. This means that overall the reaction takes in energy, therefore
there is a temperature decrease in the surroundings. Electrolysis is an example
of an endothermic reaction but you can create one easily in the kitchen just
by dissolving salt or sugar in water. If you use cold water and lots of salt you
can even make ice-cream.
Similarly, this endothermic chart shows that the reactants start off with less
energy this time and the end products have absorbed energy. Clearly shown in the diagram,
enthalpy change of the reaction is positive because energy is being taken in from the surroundings
which results in a temperature decrease.
Investigation 2
What might happen if you put citric acid, baking soda, and water in a zip bag?
C6H8O7 + 3NaHCO3 + H2O
Na3C6H5O7 + 4H2O + 3CO2
Reactants
Products
Procedure
1. Person 1, at the table measure one level spoonful of citric acid and one level spoonful of
baking soda into the zip bag on one side and seal that side of the baggie.
2. Person 2, measure 50mL of water in the graduated cylinder.
3. Person 3, use your finger to dent in the middle of the baggie so that the citric acid and baking
soda mixture are on one side.
4. Person 4, slowly pour the water in the baggie on the opposite side trying to keep it separate
from the C6H8O7 and NaHCO3.
5. Person 1, immediately zip the bag closed.
6. All students observe as the group members take turns holding and gently shaking the bag.
Observe what happens and answer the questions below.
Questions
1. What are the reactants in this investigation?
2. What are the products in this investigation?
3. Is matter conserved in this reaction?
4. Was this reaction a physical or chemical reaction? Explain how you know.
5. Was this reaction an endothermic or exothermic reaction? Explain how you know.
6. What did you find out by doing the reaction in the bag that you couldn’t find out if the
reaction occurred in a cup?