Chemical Equations

Chemical equations represent chemical reactions and indicate the reactants, products, and their quantities.

Reactants are the starting substances in a chemical reaction and are often listed on the left side of the equation.
Products are the substances that are formed by the reaction, typically positioned on the right side of the equation.
The ‘+’ sign is used to separate individual reactants and products.
The ‘→’ symbol represents the direction of the reaction, from the reactants to the products.

Balancing Chemical Equations

Chemical equations must be balanced to comply with the law of conservation of mass, which states that mass cannot be created or destroyed.

Balancing a chemical equation involves ensuring that the same number of each type of atom is found on both the left-hand (reactants) and right-hand (products) side of the equation.
Balance chemical equations by identifying imbalances and then adjusting coefficients, the numbers placed in front of a compound or element.
Never change the subscripts to balance an equation as this will change the substance represented.

State Symbols in Equations

Chemical equations often include state symbols, which describe the physical state of each substance at reaction conditions.

The commonly used state symbols include: ‘(s)’ for solids, ‘(l)’ for liquids, ‘(g)’ for gases and ‘(aq) for aqueous solutions, i.e., substances dissolved in water.

Types of Chemical Reactions

Chemical reactions can be classified into distinct types including synthesis, decomposition, single and double displacement, and oxidation-reduction reactions.

A synthesis reaction involves two or more simple substances combining to form a more complex substance.
A decomposition reaction is the opposite of a synthesis reaction, where a complex substance breaks down into its more simple parts.
A single displacement reaction sees an element react with a compound and take the place of another element in it.
A double displacement reaction involves two compounds that exchange elements with each other to form two new compounds.
Oxidation-reduction reactions encompass all chemical reactions in which atoms have their oxidation state changed by either gaining electrons (reduced) or losing electrons (oxidised).

Thermochemical Equations

Thermochemical equations are balanced chemical equations that include the change in enthalpy (ΔH).

The change in enthalpy, represented as ‘ΔH’, indicates whether the reaction is exothermic (releases heat, ΔH < 0) or endothermic (absorbs heat, ΔH > 0).
Thermochemical equations often state conditions such as temperature and pressure, which can affect the movement of heat.