Chapter 9, Problem 3STP

Interpretation Introduction

Interpretation: The number of moles of oxygen required for every 1 mole of ethane during the reaction between them needs to be determined.

Concept introduction:The ratio of mass of substance to its molar mass is said to be number of moles of that substance.

The ratio of amount of any two compounds involved in a chemical reaction in terms of mole is said to be mole ratio, and used as a conversion factor between reactants and products.

Answer to Problem 3STP

The correct answer is option (c): $\text{3}\text{.5}$ .

Explanation of Solution

An exothermic reaction that is where energy is produced in the reaction by reacting compound with oxygen which results in the formation of water and carbon dioxide is said to be combustion reaction.

The general combustion reaction for hydrocarbon is:

  ${\text{C}}_x{\text{H}}_y\left(\text{g}\right)\text{ + }\left(\text{x + }\frac{y}{4}\right){\text{O}}_{\text{2}}\left(\text{g}\right)\stackrel{\text{Δ}}{\to }{\text{xCO}}_{\text{2}}\left(\text{g}\right)\text{ + }\frac{y}{2}{\text{H}}_{\text{2}}\text{O}\left(\text{g}\right)$

The molecular formula for ethane is ${\text{C}}_{\text{2}}{\text{H}}_{\text{6}}$ .

Using this molecular formula, the chemical equation for complete combustion of ethane will be:

  ${\text{C}}_{\text{2}}{\text{H}}_{\text{6}}\left(\text{g}\right)\text{ + 3}{\text{.5O}}_{\text{2}}\left(\text{g}\right)\stackrel{\text{Δ}}{\to }{\text{2CO}}_{\text{2}}\left(\text{g}\right)\text{ + }3{\text{H}}_{\text{2}}\text{O}\left(\text{g}\right)$

From the balanced chemical reaction, the mole ratio of ethane and oxygen is 1:3.5 that means 1 mole of ethane reacts with 3.5 moles of oxygen.

Hence, the number of moles of ${\text{O}}_2(g)$ required for every 1 mole of ethane is 3.5.