Question

Write the balanced chemical reaction for the following reaction:
Zinc $+$ silver nitrate $\to$ Zinc nitrate $+$ silver

Answer 1

A balanced chemical equation obeys the law of conservation of mass i.e., mass can neither be created nor be destroyed during a chemical reaction and the total mass of the elements or molecules present on the left i.e., reactant side must be equal to the net mass of elements or molecules present on the product side.

Complete answer:
As the balancing of a chemical reaction is governed by the law of conservation of mass, so in the equation the number of atoms of each element in the product must be equal to the number of elements in the reactant. The steps to balance the given chemical equation are as follows:
Given word equation: Zinc $+$ silver nitrate $\to$ Zinc nitrate $+$ silver
Step-1: Convert the given chemical names into chemical formulae and represent the word equation in its equivalent chemical equation:
$Zn + AgN{O_3} \to Zn{(N{O_3})_2} + Ag$
Step-2: Evaluating the number of atoms of each element in the reactant and product as per following table:

Element	Reactant	Product	Balanced
$Zn$	$1$	$1$	Yes
$Ag$	$1$	$1$	Yes
$N$	$1$	$2$	No
$O$	$3$	$6$	No

Step-3: The number of nitrogen atoms and oxygen atoms in the reactant are not equal to the number of atoms in the product. To achieve balance, the coefficients of the chemical equation must be changed as needed. As the number of atoms of N and O in the product are twice that in reactant. Therefore, we need to add 2 as a coefficient of silver nitrate. The reaction will be as follows:
$Zn + 2AgN{O_3} \to Zn{(N{O_3})_2} + Ag$
Step-4: Evaluating the number of atoms of each element in the reactant and product in the new chemical reaction as per following table:

Element	Reactant	Product	Balanced
$Zn$	$1$	$1$	Yes
$Ag$	$2$	$1$	No
$N$	$2$	$2$	Yes
$O$	$6$	$6$	Yes

Step-5: Number of silver atoms in the reactant is twice the number of atoms in the product. So, 2 will be added as a coefficient of silver in the product. The chemical reaction will be as follows:
$Zn + 2AgN{O_3} \to Zn{(N{O_3})_2} + 2Ag$
Step-6: Evaluating the number of atoms of each element in the reactant and product in the new chemical reaction obtained in previous step as per following table:

Element	Reactant	Product	Balanced
$Zn$	$1$	$1$	Yes
$Ag$	$2$	$2$	Yes
$N$	$2$	$2$	Yes
$O$	$6$	$6$	Yes

As the number of atoms of each element exactly balances the number of elements in the product. Therefore, the balanced chemical reaction for given equation is as follows:
$Zn + 2AgN{O_3} \to Zn{(N{O_3})_2} + 2Ag$

Note:
Remember that the formula subscripts define the identity of the compound or elements, so while balancing a chemical reaction these values cannot be altered because it can change the qualitative meaning of the equation. Also, in some cases it is convenient to use fractions instead of integers as intermediate coefficients within the process of balancing a chemical equation.