Question

Write a balanced molecular equation describing each of the following chemical reactions.

(a) Solid calcium carbonate is heated and decomposes to solid calcium oxide and carbon dioxide gas

(b)Gaseous butane reacts with diatomic oxygen gas to yield gaseous carbon dioxide and water vapor

(c)Aqueous solution of magnesium chloride and sodium hydroxide react to produce solid magnesium hydroxide and aqueous sodium chloride

(d) Water vapor reacts with sodium metal to produce solid sodium hydroxide and hydrogen gas.

Short answer

1. \(CaC{O_3}\xrightarrow{\Delta }CaO + C{O_2}\)

2. \(2{C_4}{H_{10}}\left( g \right) + 13{O_2}\left( g \right) \to 8C{O_2}\left( g \right) + 10{H_2}O\left( g \right)\)
3. \(MgC{l_2}\left( {aq} \right) + 2NaOH\left( {aq} \right) \to Mg{\left( {OH} \right)_2}\left( s \right) + 2NaCl\left( {aq} \right)\)
4. \(2{H_2}O\left( g \right) + Na\left( s \right) \to 2NaOH\left( s \right) + {H_2}\left( g \right)\)

Step-by-step solution

Consider all the elements in reaction (a)

The reaction has equal numbers of atoms in the reactant and products of the reaction. Hence balancing is not required.

\(CaC{O_3}\xrightarrow{\Delta }CaO + C{O_2}\)

Draw the balancing table to check:

Element	Reactant	Product	Balanced? yes
Ca	1×1	1×1	1=1
C	1×1	1×1	1=1
O	1×3	1×1+1×2	3=3

Consider the elements in reaction (b)

Calculate the atoms in the reactants and products of the given reaction. Use small integer coefficients for the formula to balance the equation.

\(2{C_4}{H_{10}}\left( g \right) + 13{O_2}\left( g \right) \to 8C{O_2}\left( g \right) + 10{H_2}O\left( g \right)\)

Draw the balancing table to check: Vary coefficients, not subscripts in the formula.

Element	Reactant	Product	Balanced? yes
C	2×4	8×1	8=8
H	2×10	10×2	20=20
O	13×2	8×2+10×1	26=26

Consider the elements in the reaction (c)

Calculate the type and numbers of atoms in the reactants and products of the reaction. Use integer coefficients of the formula; subscripts are kept constant.

\(MgC{l_2}\left( {aq} \right) + 2NaOH\left( {aq} \right) \to Mg{\left( {OH} \right)_2}\left( s \right) + 2NaCl\left( {aq} \right)\)

Draw the balancing table to check: Vary coefficients, not subscripts in the formula

Element	Reactant	Product	Balanced? yes
Mg	1×1	1×1	1=1
Na	2×1	2×1	2=2
Cl	2×1	2×1	2=2
O	2×1	1×2	2=2
H	2×1	1×2	2=2

Determine the elements in reaction (d)

Calculate the types and numbers of atoms in the reactants and products of the reaction. Use coefficients of the formula, but subscripts cannot be changed.

\(2{H_2}O\left( g \right) + 2Na\left( s \right) \to 2NaOH\left( s \right) + {H_2}\left( g \right)\)

Draw the balancing table to check:

Element	Reactant	Product	Balanced? yes
Na	2×1	2×1	2=2
H	2×2	2×1+1×2	4=4
O	2×1	2×1	2=2