Energy changes during a Reaction: Exothermic, Endothermic
Initial Publication Date: August 11, 2008
Summary
This is a demonstration done to introduce energy changes during reactions, and to promote discussion regarding exo and endothermic reactions, enthalpy, spontaneity, system and surroundings.
CollapseLearning Goals
Students will make accurate observations.
Students will differentiate between exo and endothermic reactions.
Students will learn the difference between system and surroundings during a reaction.
Students will infer how conservation of energy applies during an exo or endothimic reaction.
Vocabulary:
exothermic
endothermic
system
surroundings
enthalpy
spontaneity
Students will differentiate between exo and endothermic reactions.
Students will learn the difference between system and surroundings during a reaction.
Students will infer how conservation of energy applies during an exo or endothimic reaction.
Vocabulary:
exothermic
endothermic
system
surroundings
enthalpy
spontaneity
Context for Use
This activity (demonstration) could be used as an introduction to heat in chemistry during a stoichiometry unit, or during intro to spontaneous reactions.
Time needed: 10 minutes for demo-complete 50 minute for discussion.
Materials:
Large water bottle (from water dispenser)
Use blast shield for bottle experiment.
wood square(approx.5 cm x 5 cm) or any flat, wooden, light object
Time needed: 10 minutes for demo-complete 50 minute for discussion.
Materials:
Large water bottle (from water dispenser)
Use blast shield for bottle experiment.
wood square(approx.5 cm x 5 cm) or any flat, wooden, light object
Description and Teaching Materials
These demos should be set up at the front of the room or at a lab table. Two different demos exhibit heat loss or gain.
Demo 1:
Materials:
blast shield
Large water jug - (can get from water company)
Methanol
Lit match on end of tongs
Instructions:
1. Swirl small amount of methanol in jug ( approx. 5-7 ml)
2. Roll jug to disperse and vaporize methanol.
3. Pour out any liquid remaining after spinning jug a few times.
4. Turn out lights - ignite with match held with tongs.
Make observations
Demo 2:
Materials:
250 ml beaker
water squirt bottle
wood piece
6 grams of Barium Hydroxide
3 grams of Ammonium Thiocyanate
glass stirring rod
Instructions:
1. Squirt small amount of water on wood block.
2. Place beaker on wood.
3. Mix dry materials in beaker until slushy.
4. Wait a few minutes
5. Lift beaker (wood should be frozen to beaker)
Make observations
Demo 1:
Materials:
blast shield
Large water jug - (can get from water company)
Methanol
Lit match on end of tongs
Instructions:
1. Swirl small amount of methanol in jug ( approx. 5-7 ml)
2. Roll jug to disperse and vaporize methanol.
3. Pour out any liquid remaining after spinning jug a few times.
4. Turn out lights - ignite with match held with tongs.
Make observations
Demo 2:
Materials:
250 ml beaker
water squirt bottle
wood piece
6 grams of Barium Hydroxide
3 grams of Ammonium Thiocyanate
glass stirring rod
Instructions:
1. Squirt small amount of water on wood block.
2. Place beaker on wood.
3. Mix dry materials in beaker until slushy.
4. Wait a few minutes
5. Lift beaker (wood should be frozen to beaker)
Make observations
Teaching Notes and Tips
Discussion for demo #1 can lead to many topics including what the products will be and why this can't immediately be done in the same jug. Let students feel the jug-it will be warm. Use tongs to make sure no liquid is still in the jug as it will burn and weaken the container.
Demo 2
Larger amounts of reactants will create more ice formation and the beaker can lift larger piece of wood.
Previous thermite reaction is too dangerous for a room setting.
Demo 2
Larger amounts of reactants will create more ice formation and the beaker can lift larger piece of wood.
Previous thermite reaction is too dangerous for a room setting.
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Assessment
Student discussion should lead to differentiate between system and surroundings and direction of heat flow. Students will also write equations with heat and be able to solve stoichiometry problems. Group problems
Standards
IIA7-Interactions between particles
IIB1-Chemical reactions using words and symbols
IIC5-Conservation of Energy during physical and chemical reactions
IIB1-Chemical reactions using words and symbols
IIC5-Conservation of Energy during physical and chemical reactions