All chemical reactions start with the reactants having some sort of
energy activation that results in the bonding of the two material's
molecules and forms a new product.
THE DIFFERENCE BETWEEN EXOTHERMIC AND ENDOTHERMIC CHEMICAL REACTIONS
The most common form of energy is heat; either the chemical
reaction will cause the product to give off heat, or
The easiest way to start to understand the differences between
endothermic and exothermic reactions can be derived from their names.
"Endo" means "to draw into," and "Exo" means "to give off."
* Endothermic reactions draw heat in from their surroundings.
* Exothermic reactions give heat off to their surroundings.
* In a chemical equation, "energy" appears on the left side in an endothermic
reaction and on the right
side in an exothermic reaction
ENDOTHERMIC PROPERTIES EXPLAINED
* Energy is drawn in from the external environment, causing its
surroundings to loose heat, or "cool down."
* The endothermic chemical reaction creates a product that has a
higher energy level than the original materials, causing the reactant's
stored energy to decrease. (In scientific terms, the reactants have
"less total enthalpy" than the product.)
* The resulting product of the reaction is less stable because, the
higher the energy bond, the less strength its molecules possess.
* Most endothermic reactions are not spontaneous.
EXOTHERMIC PROPERTIES EXPLAINED
* Exothermic chemical reactions cause their surroundings to warm up
by giving off heat.
* The reactants contain more stored energy than the product because
energy from external sources is not required, but given off. This gives
the product more stability due to the lower amount of energy needed.
(In this case, the reactants have a "greater total enthalpy" than the
* Exothermic reactions are usually spontaneous.
SIMPLE EXAMPLES OF ENDOTHERMIC AND EXOTHERMIC CHEMICAL REACTIONS
- Endothermic = Photosynthesis. Energy in the form of light
from the sun is used by plants to make sugar. ENERGY + CO2
+ H2O => C6H12O6
- Endothermic = breaking apart Mercury oxide. HgO
+ ENERGY=> Hg + O2
- Exothermic = When the head of the match is
struck, it results in the spontaneous release of stored energy (heat)
from the reactants into the surroundings. The flame that is produced
has a lower level of energy than the match and the striking surface
because the reaction is giving off stored energy and not required to
draw energy in from its surroundings.
- Exothermic = making Mercury oxide. Hg + O2
Chemical reactions are all about energy and randomness. Some
reactions occur as the result of entropy, which is a facet of random,
spontaneous bonding, but even if a spontaneous reaction between
chemicals would not normally occur, one can be created, if enough
energy is applied.