# What are chemical reactions?

May 25, 2014

Chemical reactions are when new substances are formed. Substances that react together are called reactants, and the substances formed are called products. The products will have different properties to the reactants. A chemical reaction can be identified by, for example, by bubbles appearing (gas being produced), cloudiness of a solution, a change of colour, an explosion, heat given out, or a change of smell.

Chemical Equations are a basic mathematical statement showing the molecules involved as reactants and the outcomes known as products.

There are 6 basic forms of chemical equations.

Synthesis is a reaction of two atoms or molecules combining to form one product.

$A + B \to A B$
$2 {H}_{2} + {O}_{2} \to 2 {H}_{2} O$

Decomposition is the breakdown of one molecule into component parts.

$A B \to A + B$
$2 K C l {O}_{3} \to 2 K C l + 3 {O}_{2}$

Single Displacement reactions exchange one element with a molecule.

$A B + C \to C B + A$
$C a C {l}_{2} + M g \to M g C {l}_{2} + C a$

Double Displacement reactions exchange two molecules.

$A B + C D \to A D + C B$
$N a C l + K N {O}_{3} \to N a N {O}_{3} + K C l$

Combustion reactions burn a hydrocarbon in oxygen to produce water and carbon dioxide.

$C H + O \to C {O}_{2} + {H}_{2} O$
${C}_{3} {H}_{8} + 5 {O}_{2} \to 3 C {O}_{2} + 4 {H}_{2} O$

and

Neutralization reaction combine an acid and a base to neutralize into salt and water.

$H A + B O H \to B A + {H}_{2} O$
$H C l + N a O H \to N a C l + {H}_{2} O$