Endothermic & Exothermic Reactions

Thermochemistry

Endothermic &
Exothermic Reactions

Endothermic

Reaction

● An endothermic reaction is a chemical that
absorbs heat from the surrounding

● Heat energy change to chemical energy
● Surrounding temperature decreases
● Products of reactions become cool
● Breaking bond
● Thermometer reading decreases

Examples of Endothermic Reaction

1) Baking cookies ● The flour and other ingredients used in
creating the cookie dough are heated in
the oven

● They absorb the heat making chemical
reactions happen

● Hence, endothermic reaction has taken
place while baking cookies

Examples of Endothermic Reaction

2) Ice pack

● In the bag, there are two components: water
and ammonium nitrate.

● When the bag is broken up, water and
ammonium nitrate mix.

● The endothermic reaction makes the water
colder and the bag feel frosty

Examples of Endothermic Reaction

3) Photosynthesis ● Photosynthesis is an endothermic
reaction, meaning that it takes in
energy.

● In this case, it takes in energy from
the sun, carbon dioxide and water
into itself.

● It creates glucose and oxygen.
● The glucose is used and the oxygen is

repelled.
● Hence, endothermic reaction has

taken place

Exothermic

Reaction

● An exothermic reaction is a chemical
reaction that releases heat to the
surrounding

● Chemical energy change to heat energy
● Surrounding temperature increases
● Product of reactions become hot
● Formingbond
● Thermometer reading increases

Examples of Exothermic Reaction

1) Hot pack ● Hot pack contains water and anhydrous sodium
chloride powder which is separated into two
compartments

● When the hot pack is squeezed, the thin
membrane between the two compartments will
break and the anhydrous sodium chloride
powder will dissolve in water

● Heat energy will be released and exothermic
reaction will take place

Examples of Exothermic Reaction

2) Making of ice cubes

● When water freezes into ice cubes, the energy is
released in the form of heat.

● When water molecules begin to freeze, their
particles come close and forms a new bond.

● As in exothermic reaction, the energy released is
more when new bonds are formed than the
energy required when bonds break.

● So, ice cube formation is an exothermic process.

Examples of Exothermic Reaction

3) Firework ● The explosion of fireworks is an
exothermic reaction.

● The fuel oxidizes (burns) quickly,
causing a great buildup in pressure
that eventually leads to solids and
gases bursting across the sky in
colorful patterns.

Difference of Endothermic &
Exothermic Reaction

Endothermic Exothermic
Absorbs heat to the surrounding Releases heat to the surrounding
Heat energy change to chemical energy Chemical energy change to heat energy
Surrounding temperature decreases Surrounding temperature decreases
Products of reactions become cool Products of reactions become hot
Breaking bond Forming bond
Thermometer reading decreases Thermometer reading increases
Examples: melting, boiling, frying an egg, cake Examples: freezing, condensation, neutralisation,
baking, photosynthesis respiration,firework display

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