Question

How can I balance synthesis reactions?

Answer 1

Hint: Balancing of an equation is a method to introduce coefficients on either side of a reaction equation so that the number of atoms on both sides of the equation becomes the same.

Complete step by step answer:
A synthesis reaction is defined as a reaction in which more than two substrates react with each other to form a new product. For the reaction between two reactants A and B which combine with each other to generate a product C, the reaction is expressed by the equation
$A + B \to C$
The above reaction is a one way reaction so an arrow pointing towards the right hand side is used. If the reaction is an equilibrium reaction then double headed half arrows are used. In that case the reactants are combined to products and the products are reverting back to the reactants. The equilibrium reactions are shown as
$A + B \rightleftharpoons C$
The balancing of an equation is required to know the amounts of individual reactants used in a reaction. This indicates how much amount of A reacts with how much amount of B. Also it gives the information about the exact amount of product formed in a reaction.
Steps for writing a balanced reaction are as follows:
a. write the reactants and the product on either side of the equation.
b. count the number of atoms on both sides of the equation.
c. multiply the respective atom by a coefficient number to match it on both sides
Let us consider the synthesis of ammonia molecules from hydrogen and nitrogen gas. The basic equation between the combining gaseous reactants is as follows
${N_2}(g) + {H_2}(g) \to N{H_3}(g)$
The reaction is an unbalanced reaction as the number of nitrogen and hydrogen atoms are not equal on both sides of the equation. The number of nitrogen atoms is \[2\] as nitrogen is diatomic gas and the number of hydrogen atoms is \[2\] as hydrogen is also a diatomic gas. But the product ammonia is composed of \[1\] nitrogen and \[4\] hydrogen atoms.
Thus to balance the atoms the hydrogen atoms is to be multiplied by a coefficient \[3\] and the product ammonia molecule is to be multiplied by a coefficient \[2\].
Thus the balanced equation of ammonia synthesis is
${N_2}(g) + 3{H_2}(g) \to 2N{H_3}(g)$

Note:
The balanced chemical equation leads to exact stoichiometry of the reactants and products. Knowing the stoichiometry enables to determine the exact amount of reactants used and products formed during a reaction.