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Endothermic and exothermic reactions

Teacher : Claudia De CandidoTutor: Elena MontiITC “O.Mattiussi” 2005/06

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Menu

Exothermic and endothermic reactions.Experiments: hot pack and cold pack.Questions about observing and comparing.Energy level diagrams.Quick test, crosswords, fill in the blanks.

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Objectives

In this unit the students will: identify endothermic or exothermic processes

through temperature changes;learn about the energy level diagrams and the

difference in energy between products and reactants;

understand the meaning of the E positive or negative;

make predictions about reactions, known the energy level diagrams or E.

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Skills

Knowledge of the new words and the new concepts.Accurate explanation of energy level diagrams.Prediction of behaviour through the acquainted

knowledge.

Grade Level : second classes - secondary school.

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Evaluation

During the lessons the students can evaluate their understanding and their improvements through activities single or in group.

Assessment: fill in the blanks,speaking (questions),quick test,matching exercise.

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Time

4 class periods 50 min. each.

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Suggestions

What the students need to do:Ask, ask, ask if you don’t understand.During the experiments follow instructions carefully.Take notes and take part in the lessons.Practice and revise even when we don’t tell you.

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Procedures

Before showing the menu and the objectives, performing some reactions and give students a puzzle to discover the topic.

Perform some experiments using hot packs and cold packs. The students can hold these systems in their hands to see and feel that the reaction takes place.

Introduce the concept of endo/exothermic processes showing slides.Repeat the experiments with chemicals , measuring the temperature.

The students will make notes and answer the questions.Ask the students to give examples of different kinds of exothermic

processes (combustion, explosions ) and endothermic processes (melting ice , photosynthesis).

Introduce the energy diagrams for both of reaction and discuss the energy of reactants and products, the convention used to write the heat taken in and given out.

Summarise all the features of these reactions.Do exercises and gather the worksheets.

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Resources required

Hot pack and cold pack, ammonium nitrate, calcium chloride, water.

Thermometer, beaker, stick. Projector, computer, power point

presentation about exothermic and endothermic reactions.

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Safety

Wear chemical splash goggles and gloves to prepare the solutions.

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Exo and endothermic reactions

Exothermic reactions release heat energy to the surroundings.Endothermic reactions absorb heat energy from the surroundings.

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What types of reactions?

Answer the questions below to complete the puzzle and discover howthe reactions that give off heat energy are called.You may use the glossary for help.

1. _ _ _2. _ _ _ _ _ _ _ _3. _ _ _ _ _ _ _ _ _ _ _ _ _4. _ _ _ _ _ _5. _ _ _6. _ _ _ _ _ _ _ _ _ _7. _ _ _8. _ _ _ _ _ _ _ _ _9. _ _ _ _ _ _10. _ _ _ _ _ _ _ _ _ _ _

1. Material source of energy2. Violent reaction3. Change of state liquid-solid4. Becoming liquid5. Energy that changes temperature6. You can measure this with the thermometer7. To be on fire8. Reaction with oxygen, usually accompanied by a

release of energy9. Bubbling up with heat10.Change of state gas- liquid

The reactions that release heat energy are called :

___ ___ ___ ___ ___ ___ ___ ___ ___ ___

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Laboratory equipment

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Answer the questions below to complete the puzzle and discover how the reactions thatgive off heat energy are called.

1. F U E L2. E X P L O S I O N3. S O L I D I F I C A T I O N4. M E L T I N G5. H E AT6. T E M P E R A T U R E7. B U R N8. C O M B U S T I O N9. B O I L I N G10. C O N D E N S A T I O N

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Cold and hot packs

How do instant hot and cold packs work?

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Hot pack

Pressing the bottom , the diaphragm breaks.Calcium chloride dissolves in water and warms it.The beverage gets warm.

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EnergySurroundings

Exothermic process

Heat flows into the surroundings from the system in an exothermic process.

Temperature rises

Hot pack

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Hot pack

We will repeat the process in a beaker with calcium chloride ( 25 g CaCl2) + water (25 ml) and a thermometer.We will record the initial temperature of the water and the temperature after the dissolution of the salt.Observation:a temperature rise of…….

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Cold pack

Water and ammonium nitrate are kept in separate compartments.Pressing the wrapper, the ammonium nitrate dissolves in water and absorbs heat.The pack becomes cold.

It is used to treat sports injuries.

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Cold pack

Energy

Surroundings

Endothermic process

Heat flows into the system from the surroundings in an endothermic process.

Temperature falls

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Cold pack

We will repeat the process in a beaker with ammonium nitrate ( 25 g NH4NO3) + water (25 ml) and a thermometer.We will record the initial temperature of the water and the temperature after the dissolution of the salt.Observation:a temperature drop of…….

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a.Fill in the gaps

Students’ worksheetFill in the blanks

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Complete the sentences below observing your system and using the correct word.

The system is similar to ………………(hot /cold pack)

The salt which dissolves in water is……………The heat energy is ……………………..(given off/

taken in)The temperature ………………. (falls/rises). In

fact the initial temperature was ……..and the final temperature is……………

The reactions is ………………….. (endothermic/exothermic)

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b. Ask the questions below to the group in front of you (at least onequestion a person) and write the answers.

What salt did you dissolve in water?What does the temperature do?Was the heat given off or taken in from the surroundings ?Was the reaction endothermic or an exothermic?

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c.Fill in the gaps.

d. Complete the table finding the missing words.

System Salt Heat Temperature ReactionCaCl2 rises

Cold pack taken in endothermic

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Question

What exothermic reactions or endothermic reactions do you know?

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Liquid Vaporrequires energy.This is the reason:a) you cool down

after swimming b) you use water

to put out a fire.

+ energy

Changes of state

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Explosions

This reaction is exothermic!This reaction is exothermic!

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Photosyntesis

This reaction is endothermic!This reaction is endothermic!

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Combustions

These reactions are exothermic!These reactions are exothermic!

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Changes in physical state

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Giving reasons

Why does the system give off or take in heat energy?

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Energy Level DiagramsEndothermic reactions

energy

time of reaction

energy taken in is positivereactants

products

The products are higher in energy than the reactants

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The products are higher in energythan the reactants.In this case making the bonds gives you less energy than breaking them.

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Energy Level DiagramsExothermic reactions

energy

Time of reaction

reactants

products

Energy given out

is negative

The products are lower in energy than the reactants

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The products are lower in energy than the reactants.In this case making the bonds gives you more energy than breaking them.

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en

erg

y

Heat

E <0Heat given off is negative

Ca Cl2 (s) Ca Cl2 (aq)

Ca Cl2 (s)

Ca Cl2 (aq)

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CH + 2O CO + 2H O + Heat4 2 2 2

CH + 2O 4 2

CO + 2 H O 2 2

en

erg

y

Heat

E = - 812 kJ/molHeat given off is negative

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en

erg

y Heat

E>0Heat absorbed is positive

NH4NO3 (s)

NH4NO3 (aq)

NH4NO3 (s) NH4NO3 (aq)

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N + O2 2

en

erg

y Heat

2NO

N + O 2NO2 2 + heat

E = + 68 kJ/molHeat absorbed is positive

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Exothermic reactions

The products have less energy than the reactants.The energy is given out to the surroundings.Ep - Er = E <O The temperature goes up.

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Endothermic reactions

The products have more energy than the reactants.The energy is taken in from surroundings.Ep - Er = E >O The temperature goes down.

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Direction energy

Every energy measurement has three parts:

1. a unit ( Joules of calories);2. a number how many;3. a sign to tell direction (negative –

exothermic, positive- endothermic).

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Across 3. Able to burn 7. The electrical attractive force between the atoms 9. Substance that changes in a reaction 10. Specific part of the universe that is of interest in the study. 11. Ammonium nitrate and calcium chloride 12. The burning of fuels 13. The new substances in a reaction Down 1. A reaction which absorbs energy 2. It increases in an exothermic reaction 4. A reaction which releases energy 5. Energy that is absorbed or released during a chemical reaction 6. This is the main endothermic plant process in nature 8. Chemical change

Crossword

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Q uick test

1 . W hat so rt o f reaction takes in energy ?

2 . W hen am m onium nitrate disso lves w hat sort o f energy is taken in ?

3 . W here does the energy com e from ?

4 . H o w do you m easure the tem pera tu re ?

5 . D raw an energy leve l d iagram fo r an endo therm ic reaction and thequantity o f energy taken in .

6 . W hat k ind o f reac tions a re burn ing fue ls and exp losions?

7 . A reac tion has E = - 45 kJ . Is it an exo therm ic o r endo therm ic reac tion ? W hich substances(reac tan ts o r p roducts) have the h ighest energy ?

8 . W hat k ind o f reac tion does the d iagram below represen t?

9 . E rase the incorrec t w ord in th is sen tence :

In exo therm ic reactions the p roducts have m ore /less energy than the reac tants

10 . Is energy absorbed (1 ) o r re leased (2 ) in each of the fo llow ing:

___A . Ice to liqu id w ater___B . W ater vapor to ra in

___C . W ater to ice

rea ctants

p roducts

E nerg y

tim e

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Quick test1. endothermic2. heat energy3. from the surroundings4. with thermometer5. (look at the diagram of an endothermic reaction)6. exothermic7. exothermic; reactants8. exothermic9. more10. A 1; B 2; C 2

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Missing words

System Salt Heat Temperature ReactionHot pack CaCl2 is given off rises exothermicCold pack NH4NO3 is taken in falls endothermic

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E n e rg y ch a n g e s

C h e m ica l re a c tio n s ca n b e d iv id e d in to tw o ty p e s : th o s e w h ich ca u s e a r is e inte m p e ra tu re a n d th o s e w h ich ca u s e a fa ll in te m p e ra tu re .W e h a v e a s p e c ia l n a m e fo r th e s e ty p e s o f re a c tio n s :

D e c id e w h ich re a c tio n is e x o th e rm ic o r e n d o th e rm ic a n d if th e te m p e ra tu re r is e so r fa lls .

R e a c tio n s E x o th e rm ic / E n d o th e rm ic T e m p e ra tu re o fth e s u r ro u n d in g sr is e s / fa lls

E x p lo d in g b o m b

F o rm a t io n o f s n o w

E v a p o ra t in g w a te r

C o o k in g fo o d

C o n d e n s a t io n o f ra in

M e lt in g ic e

C o m b u s t io n o f a c a n d le

N u c le a r fi s s io n

B a k in g b re a d

P h o to s y n th e s is

e x o t h e r m i c r e a c t i o n s h e a t i s g i v e n o u t t h e t e m p e r a t u r e i n c r e a s e se n d o t h e r m i c r e a c t i o n s h e a t i s t a k e n i n t h e t e m p e r a t u r e d e c r e a s e s

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Energy level diagrams

Fill in the gaps. Use the words the Word Bank below.Look at the energy level diagrams for help.

During a chemical reaction, old bonds are broken and new ……… are formed.Energy must be supplied to break existing bonds and is ……….. when new bonds are formed.In exothermic………., the energy released in bond formation is greater than theenergy used in ………….old bonds. It means that the…………. are at lowerenergy than the reactants.The difference in height represents the………….. given out (symbol – E = Eproducts - E reactants = negative ).If the products contain more energy than the………….., heat is taken in from thesurroundings, the change is called endothermic and the difference in energyis…………… (E > O = E products – E reactants ). In an…………… reaction,the energy required to break old bonds is greater than the energy releasedwhen new bonds are……………….

Word bankBondsBreakingEndothermicEnergyFormedPositiveProductsReactantsReactionsReleased

Read in group and try to explain in simple way the diagrams below.

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Heat pads

A heat pad contains a solution which exists as a liquid at a temperature minor than the melting point. Bending a metal disk inside the crystallisation process starts. The heat of the solidification is given out.The supercooled solution is sodium acetate and water.Boiling the solid, you melt it back to the liquid state.

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Head packs

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GlossaryAAmmmmoonniiuumm nniittrraattee,, ccaallcciiuumm cchhlloorriiddee:: ssaallttssBoil: to heat a liquid util it contains rising bubbles.Bond: the electrical attractive force between the atomsCombustion: the burning of fuels with oxygen.Condensation: physical change from gas to liquid.EEnnddootthheerrmmiicc rreeaaccttiioonn:: aabbssoorrbbss hheeaatt eenneerrggyy ffrroomm tthhee ssuurrrroouunnddiinnggss..EExxootthheerrmmiicc rreeaaccttiioonn:: rreelleeaasseess hheeaatt eenneerrggyy ttoo tthhee ssuurrrroouunnddiinnggss..Explosion: violent reaction.Fuels: substances able to burn, source of energy.Heat: energy that is absorbed or released during a chemical reaction. Thetemperature falls or rises.HHoott ppaacckk (( iinnssttaanntt wwaarrmm ffoooodd)),, ccoolldd ppaacckk (( iinnssttaanntt iiccee))..

Melt : to become liquid by heating.Photosynthesis: a reaction that plants use to produce sugar from carbondioxide and water. It requires sun energy.PPhhyyssiiccaall pprroocceessss:: tthhee mmaatttteerr cchhaannggeess oonnllyy iinn ssiizzee ,, sshhaappee oorr aappppeeaarraannccee..Products: the new substances in a reaction.Reactants: substances that change in a reaction.Reaction: chemical change.Solidification: physical change from liquid to solid.Stir: to mix a solution.SSttaattee ooff mmaatttteerr:: ssoolliidd ,, lliiqquuiidd,, ggaasseeoouuss..Surroundings: include the rest of universe.System: specific part of the universe that is of interest in the study.

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