6.02 ChemLive
Exothermic and
Exothermic
Reactions
Exothermic Reactions
• Exothermic chemical reactions cause their
surroundings to warm up by giving off heat.
• Chemical bonds are formed during exothermic
reactions.
• Exothermic reactions are usually spontaneous.
– This is a reaction that takes place on its own without
an external force and another reaction needed to drive
it.
• Example: Lighting a match. When the head of the
match is struck, it results in the spontaneous
release of stored energy (heat) from the reactants
into the surroundings.
Potential Energy Diagram-Exothermic
• The reactants contain more stored energy than
the product because energy from external
sources is not required, but given off. This gives
the product more stability due to the lower
amount of energy needed.
Endothermic Reactions
• Energy is drawn in from the external
environment, causing its surroundings to loose
heat, or "cool down."
• Chemical bonds are broken with endothermic
reactions.
• Most endothermic reactions are not
spontaneous.
– A non spontaneous reaction is a reaction that doesn't
occur naturally and it normally tends to favor the
reactants of a chemical reaction.
• Example: Photosynthesis
– sunlight + 6CO2(g) + H2O(l) = C6H12O6(aq) +
6O2(g)
Potential Energy Diagram- Endothermic
• The endothermic chemical reaction creates
a product that has a higher energy level
than the original materials, causing the
reactant's stored energy to decrease.
Exothermic/Endothermic Examples
Exothermic Reactions
Endothermic Reactions
rusting iron
cooking an egg
condensation of rain from
water vapor
evaporation of water
formation of snow in clouds conversion of frost to water
vapor
making ice cubes
melting ice cubes
burning sugar
producing sugar by
photosynthesis
Measuring Heat
reaction
reaction
Exothermic reaction, heat
given off & temperature of
water rises
Endothermic reaction, heat
taken in & temperature of
water drops
6.02 Endothermic and Exothermic lab activity
• Hands-on Assignment Choices
–Choice One: Steel Wool and
Vinegar
–Choice Two: Baking Soda and
Vinegar
Choice One: Steel Wool and Vinegar
• Materials:
–
–
–
–
one piece of steel wool
vinegar
thermometer (if you have one)
glass jar with lid, or disposable plastic cup (not
polystyrene—also referred to as Styrofoam™)
with lid/plastic wrap
– newspaper (Use it to cover the countertop
next to the kitchen sink. This could get a little
messy!)
Choice One: Steel Wool and Vinegar
•
Procedure:
– Place the steel wool in a jar or cup and cover with vinegar.
– Let the steel wool soak in the vinegar for one minute.
– If you have a thermometer, measure the temperature of the vinegar and
steel wool.
– Squeeze the vinegar out of the steel wool and pour the vinegar from the
jar into the sink.
– Place the steel wool immediately back into the jar/cup and seal the lid.
You should be able to see it start rusting over the next few minutes.
– Place your hands on the outside of the container after sealing the lid and
record any temperature change that you observe.
– When you think the temperature change is complete, open the jar. If you
have a thermometer, measure the temperature of the steel wool.
– When you are done making observations, it is safe to dispose of the steel
wool in the trash. Be sure to wash the glass jar and thermometer before
putting them away.
Choice One: Steel Wool and Vinegar
Observations to help you with your 6.02 quiz that follows the activity:
1.What was the initial temperature in the jar______ degrees Celsius.
2.What was the temperature after the reaction? _____degrees Celsius.
3.What was the change in temperature? Increase or decrease?
4.Based on information from Part I and from observations, was this reaction
Exothermic or Endothermic?
An increase would be exothermic. A decrease would be endothermic
5.Are chemical bonds forming or breaking? Observation- What do you see
happening?
6.In this experiment, the acidic vinegar dissolved a protective coating off the steel
wool, allowing the oxidation of the steel to begin. This process is called
rusting. In this reaction, iron (III) is combined with oxygen gas to form iron
oxide.
Write the balanced chemical reaction for the rusting of iron. __Fe+__O2  __FeO3
Choice Two: Baking Soda and Vinegar
• Materials:
– one disposable plastic (not polystyrene—also referred
to as Styrofoam™) cup
– one disposable plastic spoon (plastic fork or knife may
be used)
– thermometer (if you have one)
– measuring cup and spoon
– newspaper (Use it to cover the countertop next to the
kitchen sink. This could get a little messy!)
– baking soda
– vinegar
Choice Two: Baking Soda and Vinegar
•
Procedure
– Measure two tablespoons of baking soda and pour it into the clean, dry
plastic cup.
– Measure out one cup of vinegar.
– If you have a thermometer, place it in the measuring cup of liquid and
write down the initial temperature.
– Grasping the plastic cup near the bottom with one hand, pour the liquid
into the plastic cup with your other hand.
– Continue to grasp the cup as you stir the solution gently with the plastic
spoon. Observe any temperature change felt through the plastic cup.
– If you have a thermometer, record the temperature change as you stir
the solution very gently.
– When you are done making observations, it is safe to pour the solution
down the sink and to dispose of the plastic cup and spoon in the trash.
Be sure to wash the measuring spoon, measuring cup, and thermometer
before putting them away.
Choice Two: Baking Soda and Vinegar
Observations to help you with your 6.02 quiz that follows the activity:
1.What was the initial temperature in the jar of vinegar?______ degrees Celsius.
2.What was the temperature after the reaction with baking soda? _____degrees Celsius.
3.What was the change in temperature? Increase or decrease?
4.Based on information from Part I and from observations, was this reaction Exothermic or
Endothermic?
An increase would be exothermic. A decrease would be endothermic
5.Are chemical bonds forming or breaking? Observation- What do you see happening?
6.In this experiment, the acidic vinegar reacted with baking soda producing sodium acetate
and carbonic acid. The carbonic acid quickly decomposes into carbon dioxide and
water.
The chemical reactions involved:
HC2H3O2 + NaHCO3 ===> NaC2H3O2 + H2CO3
H2CO3 ---> H2O + CO2
•You are ready to take
the 6.02 quiz