CHEMICAL EQUATIONS

Chemical equations is the representation of chemical reaction in terms of the symbols and formulas of the elements and compounds involved. The substances that participate in the reaction, i.e., reactants, are written on the left-hand side, while the products of the reaction are written on the right-hand side. Reactants and products are linked together by an arrow symbol (               ) whose head points towards the products. However, a reversible reaction is one which can be made to proceed in either direction under suitable conditions. The reactants can form products, so also the products can also form reactants. Reversible reactions is denoted by the symbol (            ). Chemical reactions are represented in form of equations, which show the reactants and products in any given chemical reaction. For example, the reaction of aqueous hydrogen chloride and aqueous sodium hydroxide is represented by the equation:  HCl(aq) + NaOH(aq)     NaCl(aq) + H2O(l). While a reversible reaction is NH4Cl(s)       HN3(g)  +  HCl(g)

Balancing Chemical Equations

All chemical equations must be balanced to comply with the law of conservation of mass. For example, to balance the equation for the reaction involving the combustion of ammonia gas in air, the following steps should be followed:

Step 1: The reactants (LHS) are NH3 and O2, while the products (RHS) are NO and H2O 

NH3(g)  + O2(g)   →  NO(g) + H2O(g)

Step 2: Place a 4 in front of NH3 and a 6 in front of H2O. There are now 12 hydrogen atoms on both sides of the equation.

4NH3(g)  + O2(g)   →      NO(g) + 6H2O(g)

Step 3: Place a 4 in front of NO to balance with the 4 nitrogen atoms of the LHS of the equation.

4NH3(g)  + O2(g)   →     4NO(g) + 6H2O(g)

Step 4: Place a 5 in front of O2. An “atom count” shows that the equation is balanced.

4NH3(g)  + 5O2(g) →  4NO(g) + 6H2O(g)

An equation must be balanced. A balanced equation contains the same number of atoms of the elements of the compounds on both sides of the equation.

The equation must also show the physical states of the reactants and the products i.e. whether in aqueous solution or gaseous or solid state.

When balancing a chemical reaction, the following must be remembered

1. Equations must be balanced through the use of coefficients in front of the formular and not by changing the subscript numbers within the formulae 
2. Common gases such as Hydrogen, Oxygen, Nitrogen and Chlorine in the free state are diatomic e.g. H2, O2, N2, and Cl2.
3. Other elements such as Sodium, Potassium, Copper and Iron in the Free State are represented by their atomic symbols e.g. Na, K, Cu and Fe
4. In simple chemical reactions, radicals remain unchanged during the reactions.

Information Provided by a Chemical Equation

1. The stoichiometry of the reaction (i.e. the relationship between the amounts of the reactants and the products) in terms of mole ratio and the mass ratio of the reactants and products.
2. The molar mass of each compound from the relative atomic masses of elements forming the compound
3. The relative volume of reactants and products if gaseous (1 mole occupies 22.4dm3 at s.t.p)
4. The reactants and products involved
5. Which reactants are in excess in a mixture of known amount of reactant and how much.
6. The state of matter of the reactants and products as indicated by the state symbols (s) for solid, (l) for liquid, (g) for gas and (aq) for aqueous solution.

Information Not provided by a chemical equation

1. The physical state, such as colours, of the reactants and products
2. The conditions of the reaction i.e. whether the solutions are concentrated or diluted, heat change.
3. The speed of the reaction.

Evaluation

Balance the equations below:

1. NaOH (aq) + HCl (aq)   →      NaCl(aq)   +   H2O(l)
2. KClO3(s) →   KCl(s)   +   O2 (g)
3. NaOH(aq) +  CO2(g)   →      Na2CO3(s)   +   H2O(l)
4. C(s) +  H2O(g)   →     CO(s) +  H2(g)
5. BaCl2(aq) + H2SO4(aq)  →  BaSO4(s) +  HCl (aq)
6. NH3(g) +  O2(g)   →     H2O(g) +  N2(g)
7. Al(OH)3(s) +  HNO3(aq)   →       Al(NO3)3(aq) +  H2O(l)
8. H2SO4(aq) + KOH(aq)   →     K2SO4(aq)  +  H2O(l)
9. NH3(g) + O2(g)   →       NO(g)   +  H2O(g)
10. ZnCO3(s) +  HCl(aq)   →     ZnCl2(aq)  +  H2O(l)  + CO2(g).
11. CaCO3(s) +HCl(aq)  →     CaCl2(s) + H2O(l) + CO2(s)
12. CO2(g) + NaOH(aq)  →     Na2CO3(aq) + H2O(l)