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Endothermic and Exothermic
Reactions
Endothermic and Exothermic
Reactions
Physical ChangePhysical Change
• change in size, shape, color, or state of matter
Chemical ReactionsChemical Reactions
• process in which one or more substances are changed into others. Chemical reactions are accompanied by a loss or gain of energy.
• Indicators of chemical changes are evident.
Indicators:•Temperature change•Odor change•Formation of a precipitate
And sometimes…•Color change
Activation Energy Activation Energy
•the smallest amount of energy needed to make a substance react
ExothermicExothermic
• energy (heat, light, electrical, etc.) is given off; surroundings usually feel warmer
- ex. Combustion, evaporation of water
Cellular RespirationCellular RespirationCellular respiration allows organisms to use (release) energy stored in the chemical bonds of glucose (C6H12O6). The energy in glucose is used to produce ATP. Cells use ATP to supply their energy needs. Cellular respiration is therefore a process in which the energy in glucose is transferred to ATP.
This is an example of an exothermic reaction.
Exothermic DiagramExothermic DiagramEnergy level
Reaction progress
Activation energy
Energy given out
by reactionUsing a catalyst might lower the
activation energy
© Teachable . Some rights reserved. http://teachable.net/res.asp?r=1910
Reactants
Products
SaltSalt
An example of an exothermic reaction is the mixture of sodium metal and chlorine gas which yields table salt.
2Na(s) + Cl2(g) 2NaCl(s) + energy
EndothermicEndothermic
• A chemical reaction in which energy is absorbed; surroundings usually feel cooler
- ex. Cold packs, melting ice
Endothermic Diagram
Endothermic Diagram
Energy
Reaction progress
Activation energy Energy
absorbed by reaction
© Teachable . Some rights reserved. http://teachable.net/res.asp?r=1910
Reactants
Products
How do cold packs work?How do cold packs work?
The outer pouch contains water. The inner pouch contains ammonium-nitrate.
When you “pop” the inner pouch, the chemical reaction absorbs heat energy from the surroundings. This is an endothermic reaction.
The temperature of the solution falls to about 35 F for 10 to 15 minutes.
PhotosynthesisPhotosynthesis
During photosynthesis, plants absorb the energy from the sun to convert carbon dioxide and water into glucose and oxygen. This is an example of an endothermic reaction.
sunlight + 6CO2 + 6H2O C6H12O6 + 6O2
True or False
Chemical reactions always produce heat
F
Chemical reactions can release or
absorb heat, but can also create
light, sound, or electricity!
True or False
Heat can be lost, destroyed
or just disappear
F
Heat energy is transferred from one object to another, or is transferred to another form of energy, but never disappears.
Law of Conservation of Energy
True or False
Color change is always a physical property
F
Color is a physical property.
Color is a physical property.
Color change can be the result
of a chemical change.
Set up your Lab Notebook like this:
Set up your Lab Notebook like this:
________________ Experiment(You’ll fill in the blank after the experiment.)Citric acid solution temperature: _____
Citric acid + NaHCO3 temperature:___
Reaction time: ___________________
ExperimentExperiment
Procedures:
1.Pour 25 mL citric acid solution in a Styrofoam cup. Use a thermometer or other temperature probe to record the initial temperature.
ExperimentExperiment
2. Stir in 15g baking soda (sodium bicarbonate). Track the change in temperature as a function of time.
This means you will start a timer when you add the baking soda. Stop the timer when the temperature no longer changes.
ExplainExplain
1. Describe what happens when baking soda and citric acid are mixed.
2. What are evidences of chemical change?
ExplainExplain
3. Is this an endothermic or exothermic reaction?
How do you know?
Set up your Lab Notebook like this:
Set up your Lab Notebook like this:
___________ Experiment (You’ll fill in the blank after the experiment.)
Jar temperature: _____
Temperature of steel wool soaked in vinegar: ________
ExperimentExperiment
Procedures:
1. Place the thermometer in the jar and close the lid. Allow about 5 minutes for the thermometer to record the temperature, then open the lid and remove the thermometer. Take a reading.
ExperimentExperiment
2. Soak a piece of steel wool in vinegar for 1 minute.
3. Squeeze the excess vinegar out of the steel wool.
ExperimentExperiment
4. Wrap the wool around the thermometer and place the wool/thermometer in the jar, sealing the lid.
5. Allow 5 minutes, then read the temperature and compare it with the first reading.
ExplainExplain
Is this an endothermic or exothermic reaction? How do you know?
Clean-UpClean-Up
Experiment 1:
Pour citric acid and baking soda solution into the sink while running water.
Rinse the cup. Place it back at your station for the next class.
Replenish any materials necessary for next period.
Experiment 2:
Place steel wool in the trash.
Wipe out jar with paper towel.
Replace thermometer in jar and close the lid.
Replenish any materials necessary for next period.