6.02 ChemLive Exothermic and Exothermic Reactions

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6.02 ChemLiveExothermic and Exothermic Reactions
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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.
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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.

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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)

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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.

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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
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Measuring Heat
Exothermic reaction, heat given off temperature
of water rises
Endothermic reaction, heat taken in temperature
of water drops
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6.02 Endothermic and Exothermic lab activity

• Hands-on Assignment Choices
• Choice One Steel Wool and Vinegar
• Choice Two Baking Soda and Vinegar

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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 polystyrenealso 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!)

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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.

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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.
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• 2.What was the temperature after the reaction?
  _____degrees Celsius.
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• 3.What was the change in temperature? Increase or
  decrease?
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• 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
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• 5.Are chemical bonds forming or breaking?
  Observation- What do you see happening?
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• 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

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Choice Two Baking Soda and Vinegar

• Materials
• one disposable plastic (not polystyrenealso
  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

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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.

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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.
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• 2.What was the temperature after the reaction
  with baking soda? _____degrees Celsius.
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• 3.What was the change in temperature? Increase or
  decrease?
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• 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
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• 5.Are chemical bonds forming or breaking?
  Observation- What do you see happening?
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• 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 gt NaC2H3O2 H2CO3
• H2CO3 ---gt H2O CO2

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• You are ready to take the 6.02 quiz