SEC. 3 CONTROLLING

CHEMICAL REACTIONS

Kitchen Chaos online activity

Every chemical reaction involves change of energy.

1.exothermic reaction= releases energy in form of heat

2.endothermic reaction= absorbs energy

activation energy• minimum amount of energy that has

to be added to start a reaction

Factors that

affectrate of

chemicalreactions

concentration surface area temperature catalyst inhibitor

amount of material in a given volume of another material

1. concentration=

2. surface area

3. temperature

4. catalysts=

lowers activation energy

– enzyme= biological catalyst

Elephant's Toothpaste • Materials• 16 oz. empty plastic soda bottle (preferably with a narrow neck such as those made by Coca-Cola) • 1/2 cup 20-volume hydrogen peroxide (20-volume is 6% solution, purchased from a beauty supply store) • Squirt of Dawn dish detergent • 3-4 drops of food coloring • 1 teaspoon yeast dissolved in ~2 tablespoons very warm water • Funnel • Foil cake pan with 2-inch sides • Lab goggles • Lab smock• 1. At each student's place: cake pan, plastic bottle, Dawn in small cup, food coloring, funnel, goggles and smock,

1/2 cup peroxide, dissolved yeast mixture. 2. Stand up bottle in the center of the cake pan. Put funnel in opening. Add 3-4 drops of food coloring to the peroxide and pour the peroxide through the funnel into the bottle. Show a water molecule diagram and a peroxide molecule diagram, pointing to the extra oxygen that will be set free. 3. Add the Dawn detergent to the peroxide in the bottle. 4. Pour the yeast mixture into the bottle and quickly remove the funnel. 5. The students can touch the bottle to feel any changes that take place. Observations

• The reaction creates foam that shoots up out of the bottle and pools in the pan. After a minute or so, it begins to come out in a moving stream that looks like toothpaste being squeezed our of a tube. The students can play with the foam as it is just soap and water with oxygen bubbles. The bottle will feel warm to the touch as this is an exothermic reaction. How does it work?

• Talk about the addition of the yeast as a catalyst which makes the peroxide molecule release the oxygen atom faster. The teacher who submitted this experiment claims to have done this with hundreds of students from kindergarten through fifth grade and some adults who all loved the experiment. It is very easy and safe to do again at home using regular hydrogen peroxide from the drugstore.

CATALYSTS

• A catalyst is like adding a bit of magic to a reaction.

• Reactions need a certain amount of energy to happen.

• If they don't have it, oh well, the reaction probably can't happen.

• A catalyst lowers the amount of energy needed so that a reaction can happen easier.

5. inhibitor

• decreases rate of reaction

INHIBITORS

• Works exactly the opposite of catalysts.• Slow the rate of reaction. Sometimes they

even stop the reaction completely.• You might be asking, "Why would anyone

need those?" You could use an inhibitor to make the reaction slower and more controllable.

• Without them, some reactions could keep going and going and going. If they did all of the molecules would be used up. That would be bad, especially in your body.

inhibitor

• decreases rate of reaction

factors that affect rate of chemical reactions:

1. Concentration

2. Surface area

3. Temperature

4. Catalysts (enzymes)

5. Inhibitors

catalysts=

lowers activation energy

endothermic reaction

type of reaction that absorbs energy

enzyme

biological catalyst

• exothermic reaction

type of reaction that releases energy in the form of heat

activation energy• minimum amount of energy that has

to be added to start a reaction

Exothermic reaction

Endothermic reaction

endothermic & exothermic reactions

Prediction Observation Endothermic or

Exothermic

calcium chloride

(CaCl2) & water

magnesium sulfate

(MgSO4) & water

Questions (write the questions)

1. What is the temperature before and after each reaction?

2. Which reaction was endothermic? Why?

3. Which reaction was exothermic? Why?

4. Are the results of mixing the MgSO4 and the water a chemical change or a physical change? Explain.

1. _____ Fe + _____ S _____ FeS2. _____ H2 + _____ Cl2 _____ HCl3. _____ Mg + _____ O2 _____ MgO4. _____ O2 + _____ H2 _____ H2O5. _____ HgO _____ Hg + _____ O2

Balance the following equations. Tell what kind ofreaction it is (synthesis, decomposition, replacement)

Question: How does surface area affect the reaction speed of an

object?

Information: L x W X # of surfacesHypothesis: If the surface area

increases, then the speed of the reaction will increase.

Variables: shape or size of tablet (independent)

size (type) of cup amount of water temp. of water age of the tablet

& ingredients

Time Crushed tablet

Whole tablet