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

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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

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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.