Question

Complete and balance each combustion reaction. (a) \(\mathrm{C}_{2} \mathrm{H}_{6}(g)+\mathrm{O}_{2}(g) \longrightarrow\) (b) \(\mathrm{Ca}(s)+\mathrm{O}_{2}(g) \longrightarrow\) (c) \(\mathrm{C}_{3} \mathrm{H}_{8} \mathrm{O}(l)+\mathrm{O}_{2}(g)\) (d) \(\mathrm{C}_{4} \mathrm{H}_{10} \mathrm{~S}(l)+\mathrm{O}_{2}(g) \longrightarrow\)

Short answer

(a) 2C2H6(g) + 7O2(g) \rightarrow 4CO2(g) + 6H2O(g), (b) 2Ca(s) + O2(g) \rightarrow 2CaO(s), (c) C3H8O(l) + 5O2(g) \rightarrow 3CO2(g) + 4H2O(g), (d) 2C4H10S(l) + 13O2(g) \rightarrow 8CO2(g) + 10H2O(g) + 2SO2(g).

Step-by-step solution

Identify the Products

The products of combustion of a hydrocarbon or a compound containing carbon, hydrogen, and possibly other elements such as sulfur, will always be carbon dioxide (CO2) and water (H2O). If the compound contains sulfur, sulfur dioxide (SO2) will also be a product.

Write Down the Unbalanced Equations with Products

(a) \(C2H6(g) + O2(g) \rightarrow CO2(g) + H2O(g)\)(b) \(Ca(s) + O2(g) \rightarrow CaO(s)\)(c) \(C3H8O(l) + O2(g) \rightarrow CO2(g) + H2O(g)\)(d) \(C4H10S(l) + O2(g) \rightarrow CO2(g) + H2O(g) + SO2(g)\)

Balance Each Equation

Use coefficients to balance each element in the reaction. Begin with the carbon atoms, then hydrogen atoms, followed by sulfur if present, and finally balance the oxygen atoms since O2 can be adjusted as a diatomic molecule.

Balance the Equation for (a)

\(2C2H6(g) + 7O2(g) \rightarrow 4CO2(g) + 6H2O(g)\)

Balance the Equation for (b)

\(2Ca(s) + O2(g) \rightarrow 2CaO(s)\)

Balance the Equation for (c)

\(C3H8O(l) + 5O2(g) \rightarrow 3CO2(g) + 4H2O(g)\)

Balance the Equation for (d)

\(2C4H10S(l) + 13O2(g) \rightarrow 8CO2(g) + 10H2O(g) + 2SO2(g)\)

Key concepts

Chemical Equations

Chemical equations are symbolic representations of chemical reactions, illustrating the reactants transforming into products. They serve as a blueprint for scientists to understand the involved substances and their proportions, the type of reaction, and the conditions under which it occurs. A key aspect of chemical equations is their need for balance, adhering to the law of conservation of mass—that matter is neither created nor destroyed during a chemical reaction.

Stoichiometry

Stoichiometry is the calculation of reactants and products in chemical reactions. It is based on the balanced equations, reflecting the principle that atoms are merely rearranged during a reaction, not lost or gained. By performing stoichiometric calculations, one can predict the amounts of reactants needed and products formed. It's essential to first have a balanced chemical equation; without it, the stoichiometry will not reflect the true proportions of substances, leading to inaccurate results. Understanding stoichiometry is crucial in areas like chemistry and engineering, where precise measurements can determine the success or failure of processes and experiments.

Law of Conservation of Mass

The law of conservation of mass is a fundamental principle in chemistry, stating that in a closed system, the mass of reactants must equal the mass of products. This principle underpins the balancing of chemical equations, where the same number of each type of atom must appear on both sides of the equation. When balancing a combustion reaction, as shown in the given examples, you ensure that every carbon, hydrogen, oxygen, and any other atom is accounted for in the products, reflecting this inviolable law. This law also reinforces the understanding that atoms are conserved in their identity and quantity through chemical transformations, having profound implications for the predictability and consistency of chemical reactions.