Exothermic and Endothermic Reactions
Name:
__________ Date __________
When a chemical reaction happens, there can be a net transfer of energy from the reactants into the surroundings (e.g.
air, water is in solution) or a net transfer of energy from the surroundings to the reactants causing a change in average
kinetic energy of the particles in the surrounding and a proportional change in the temperature.
Exothermic reactions/processes
In these reactions energy is transferred from the reaction system into the
surroundings. The average kinetic energy of the surroundings increases causing
the reaction mixture to increase in temperature and get warmer. Some examples
of exothermic reactions are:
• Burning ( combustion)
• sodium + chlorine makes table salt plus energy
• condensation of water vapor into water
Endothermic reactions/processes
In these reactions energy is absorbed from the surroundings. The average
kinetic energy of the surrounding decreases causing the reaction mixture to
get colder. Some examples of endothermic reactions are:
• photosynthesis (CO2 + H2O + energy to make sugar and O2)
• melting ice cubes
• cooking an egg
Exothermic and endothermic reactions are used extensively in everyday life
and in industry. Airbags, a safety device in modern cars, utilize an exothermic
reaction.
Use your notes and the text given here to decide whether each of these reactions/processes is exothermic or
endothermic:
Process or reaction
A heater
An air conditioner
When two chemical mix their temperature rises
A solid burns brightly and releases heat, light, and
sound
When two chemicals mix their temperature drops
Melting solid metal
Making ice cubes
Evaporation of water
Endothermic or Exothermic?