Endothermic and
exothermic reactions
Teacher : Claudia De Candido
Tutor: Elena Monti
ITC “O.Mattiussi” 2005/06
1
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.
2
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.
3
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.
4
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.
5
Time
4 class periods 50 min. each.
6
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.
7
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.
8
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.
9
Safety
Wear chemical splash goggles and
gloves to prepare the solutions.
10
Exo and endothermic
reactions
Exothermic reactions release heat
energy to the surroundings.
Endothermic reactions absorb heat
energy from the surroundings.
11
What types of reactions?
Answer the questions below to complete the puzzle and discover how
the 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.
2.
3.
4.
5.
6.
7.
8.
Material source of energy
Violent reaction
Change of state liquid-solid
Becoming liquid
Energy that changes temperature
You can measure this with the thermometer
To be on fire
Reaction with oxygen, usually accompanied by a
release of energy
9. Bubbling up with heat
10.Change of state gas- liquid
The reactions that release heat energy are called :
___ ___ ___ ___ ___ ___ ___ ___ ___ ___
12
Laboratory equipment
13
Answer the questions below to complete the puzzle and discover how the reactions that
give off heat energy are called.
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
FU E L
EXPLOSION
SOLI DIFICATION
MELTING
H E AT
TEMPERATURE
BURN
COMBUSTION
B O I LING
CONDENSATION
14
Cold and hot packs
How do instant hot and cold packs
work?
15
Hot pack
Pressing the bottom , the diaphragm breaks.
Calcium chloride dissolves in water and warms it.
The beverage gets warm.
16
Exothermic process
Heat flows into the surroundings from
the system in an exothermic process.
Surroundings
Energy
Hot pack
Temperature rises
17
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…….
18
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.
19
Endothermic process
Heat flows into the system from the
surroundings in an endothermic process.
Surroundings
Cold
pack
Energy
Temperature falls
20
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…….
21
Students’ worksheet
Fill in the blanks
a.Fill in the gaps
22
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)
23
b. Ask the questions below to the group in front of you (at least one
question 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?
24
c.Fill in the gaps.
d. Complete the table finding the missing words.
System
Salt
Heat
CaCl2
Cold pack
taken in
Temperature
rises
Reaction
endothermic
25
Question
What exothermic reactions or
endothermic reactions do you know?
26
Changes of state
Liquid
Vapor
requires energy.
This is the reason:
a) you cool down
after swimming
b) you use water to
put out a fire.
+ energy
27
Explosions
This reaction is exothermic!
28
Photosyntesis
This reaction is endothermic!
29
Combustions
These reactions are exothermic!
30
Changes in physical state
31
Giving reasons
Why does the system give off or take
in heat energy?
32
Energy Level Diagrams
Endothermic reactions
products
energy
reactants
The products are
higher in energy
than the reactants
energy taken in
is positive
time of reaction
33
The products are higher in energy
than the reactants.
In this case making the bonds gives
you less energy than breaking them.
34
Energy Level Diagrams
Exothermic reactions
energy
reactants
Energy given out
is negative
products
Time
of
reaction
The products are lower in
energy than the reactants
35
The products are lower in energy than
the reactants.
In this case making the bonds gives
you more energy than breaking them.
36
Ca Cl2 (s)
Ca Cl2 (aq)
Ca Cl2 (s)
energy
Heat
E <0
Heat given off is negative
Ca Cl2 (aq)
37
CH 4 + 2O 2  CO 2 + 2H 2 O + Heat
CH 4 + 2O 2
energy
Heat
E = - 812 kJ/mol
Heat given off is negative
CO 2 + 2 H 2 O
38
NH4NO3 (s)
NH4NO3 (aq)
NH4NO3 (aq)
energy
Heat
E>0
NH4NO3 (s)
Heat absorbed is positive
39
N 2 + O 2 + heat  2NO
2NO
energy
Heat
E = + 68 kJ/mol
N2 + O2
Heat absorbed is positive
40
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.
41
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.
42
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).
43
Crossword
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
44
45
46
47
Quick test
1. endothermic
2. heat energy
3. from the surroundings
4. with thermometer
5. (look at the diagram of an endothermic reaction)
6. exothermic
7. exothermic; reactants
8. exothermic
9. more
10. A 1; B 2; C 2
48
Missing words
System
Hot pack
Cold pack
Salt
CaCl2
NH4NO3
Heat
is given off
is taken in
Temperature
rises
falls
Reaction
exothermic
endothermic
49
50
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 the
energy used in ………….old bonds. It means that the…………. are at lower
energy than the reactants.
The difference in height represents the………….. given out (symbol – E = E
products - E reactants = negative ).
If the products contain more energy than the………….., heat is taken in from the
surroundings, the change is called endothermic and the difference in energy
is…………… (E > O = E products – E reactants ). In an…………… reaction,
the energy required to break old bonds is greater than the energy released
when new bonds are……………….
Word bank
Bonds
Breaking
Endothermic
Energy
Formed
Positive
Products
Reactants
Reactions
Released
Read in group and try to explain in simple way the diagrams below.
51
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.
52
Head packs
53
Glossary
Ammonium nitrate, calcium chloride: salts
Boil: to heat a liquid util it contains rising bubbles.
Bond: the electrical attractive force between the atoms
Combustion: the burning of fuels with oxygen.
Condensation: physical change from gas to liquid.
Endothermic reaction: absorbs heat energy from the surroundings.
Exothermic reaction: releases heat energy to the surroundings.
Explosion: violent reaction.
Fuels: substances able to burn, source of energy.
Heat: energy that is absorbed or released during a chemical reaction. The
temperature falls or rises.
Hot pack ( instant warm food), cold pack ( instant ice).
Melt : to become liquid by heating.
Photosynthesis: a reaction that plants use to produce sugar from carbon
dioxide and water. It requires sun energy.
Physical process: the matter changes only in size , shape or appearance.
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.
State of matter: solid , liquid, gaseous.
Surroundings: include the rest of universe.
System: specific part of the universe that is of interest in the study.
___
54