Download Exothermic and Endothermic Reactions

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Chemistry
MODULE
Exothermic and Endothermic
Reactions
In most chemical reaction energy is taken in or given out, often under the form of heat.
According to the way energy changes reactions are divided into exothermic and
endothermic.
When a reaction releases energy it is said to be exothermic, the prefix “exo” meaning
“out”: the energy generated is transferred to the surroundings and the products obtained
by the reaction have less energy than the reactants used to give them. This process can
be summarized as follows:
reactants Ü products + heat energy
Mixing together iron and sulphur easily shows that energy is given out: the mixture
glows without heating it.
The combustion of fuels is the most obvious example of exothermic reaction, combustion resulting by the combination of oxygen with hydrocarbons, alcohols or other
fuels. Similarly, respiration in our body cells is an example of exothermic reaction providing the energy for warmth and movement.
When a reaction takes in energy it is said to be endothermic, the prefix “endo” meaning “inside”: the reactants will subtract energy from the surroundings for the reaction
to go ahead and the products obtained have more energy than the reactants. This
process can be summarized as follows:
reactants + heat energy Ü products
Photosynthesis, which takes in energy from sunlight, electrolysis, where energy is provided in form of electricity, and the reactions occurring in food during cooking are all
examples of endothermic reactions.
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Match the word and its definition.
energy
reaction
reactant
product
exothermic
endothermic
a
b
c
d
e
f
TIP
The unit for energy is
the joule (J) as in
physics
a chemical reaction where heat is produced
form of power present in all physical things
a process in which a chemical change occurs
a substance involved in a chemical reaction
a chemical reaction where heat is absorbed
the result of a process
Answer the following questions.
1 What does the prefix “exo” mean? ..................................................................................................................................................................................................
2 What does the prefix “endo” mean? .............................................................................................................................................................................................
3 What is an exothermic reaction? ........................................................................................................................................................................................................
4 What is an endothermic reaction? ...................................................................................................................................................................................................
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5 What is the unit for energy? .......................................................................................................................................................................................................................
6 Can you give some more example of endothermic or exothermic reactions? .................................................
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© Ulrico Hoepli Editore S.p.A. 2004
Claudia Radini, Valeria Radini - Dental topics
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