Chapter 7, Problem 11STP

Interpretation Introduction

Interpretation:

A balanced chemical equation corresponding to the combustion of propane gas needs to be presented.

Concept Introduction:

• A chemical reaction is represented in terms of a chemical equation with the reactants on the left and the products on the right.

  $\text{Reactants }\to \text{ Products}$

• A balanced chemical equation is one in which the number of atoms of various elements on the reactants side is equal to that on the product side. It depicts the stoichiometry of a given reaction.

• The equations are balanced in two steps:

1) Balance the atoms by matching the number of atoms of each type on the reactants and product side.

2) Adjust the coefficients to the smallest whole number. A coefficient of '1' is implied and therefore not explicitly written.

Answer to Problem 11STP

  ${\text{C}}_3{\text{H}}_8{\text{(g) + 5O}}_{\text{2}}\text{(g) }\to {\text{ 3CO}}_2{\text{ (g) + 4H}}_{\text{2}}\text{O(g)}$

Explanation of Solution

The given equation involves the reaction between propane gas and oxygen to form carbon dioxide gas and water vapor. The reactants and products are:

Reactants:

  $\begin{array}{l}{\text{Propane, gas - C}}_3{\text{H}}_8(\text{g})\\ {\text{Oxygen, gas - O}}_{\text{2}}\text{ (g)}\end{array}$

Products:

  $\begin{array}{l}{\text{Carbon dioxide, gas - CO}}_2\text{(g)}\\ {\text{Water vapor - H}}_{\text{2}}\text{O (g)}\end{array}$

Unbalanced equation:

  ${\text{C}}_3{\text{H}}_8{\text{(g) + O}}_{\text{2}}\text{(g) }\to {\text{ CO}}_2{\text{ (g) + H}}_{\text{2}}\text{O(g)}$

The above equation is not balanced since the number of C, H and O atoms on the reactants side is 3, 8 and 2 respectively while that on the products side is 1, 2 and 3. In order to balance the above equation, multiply O₂ by 5, CO₂ by 3 and H₂O by 4 to get:

  ${\text{C}}_3{\text{H}}_8{\text{(g) + 5O}}_{\text{2}}\text{(g) }\to {\text{ 3CO}}_2{\text{ (g) + 4H}}_{\text{2}}\text{O(g)}$

Conclusion

Therefore, 1 mole of propane reacts with 5 moles of oxygen to form 3 moles of carbon dioxide and 5 moles of water vapour.