The substances present at the beginning of a chemical reaction are called reactants. The substances formed by a chemical reaction are called products.
Reactants --> Products
During a chemical reaction, bonds between atoms in the reactants are broken and new bonds are formed in the products. When natural gas is burned. Bonds between the carbon and the hydrogen atoms in methane are broken. Bonds between oxygen atoms are broken. New bonds are formed between hydrogen and oxygen in water vapor.
CH4 + 2 02 --> C02 + 2 H2O
Methane + Oxygen --> Carbon Dioxide + Water
In the previous example:
CH4 + 2 02 --> C02 + 2 H2O
4. Reactants Products
C 1 1
O 4 4
H 4 4
Every chemical reaction absorbs or releases energy (as heat or light). Energy is needed to break and create bond between atoms. The energy can be calculated by summing the energy released by the broken bonds, minus the energy absorbed by the created bonds. So:
If the chemical reaction releases energy is called exothermic reaction, the energy of the broken bonds is bigger than the energy of the created bonds.
If the chemical reaction absorbs energy is called endothermic reaction, the energy of the created bonds is bigger than the energy of the broken bonds.
Energy Reaction = Energy broken bonds – Energy created bonds
Energy = (4 Energy C-H + 2 Energy O-O) – (2 Energy C-O + 4 Energy H-O)
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