Limiting Reactants (Section) Consider the mixture of ethanol, C2H5OH, and 0I shown in the accompanying diagram.: (a) Write a balanced equation for the combustion reaction that occurs between ethanol and oxygen (b) Which reactant is the limiting reactant? (c) How many molecules of C02, H20, C2H50H, and 02 will be present if the reaction goes to completion?
Solution 75 Combustion reaction :A combustion reaction is a major class of chemicalreactions. Combustion usually occurs when a hydrocarbon reacts with oxygen to produce carbon dioxide and water. In the more general sense,combustion involves a reaction between any combustible material and an oxidizer to form an oxidized product. (a) The combustion reaction between ethanol and oxygen is shown as follows: The equation is not the balanced chemical equation. To balance the carbon atoms multiply the carbon dioxide molecule on the product side by 2. Also, multiply the water molecule on the product side by 3 to balance the hydrogen atoms. Then the equation becomes as follows: Multiply oxygen molecule on reactant side by 3 to balance the oxygen atoms. Then, the equation becomes a balanced chemical equation as follows: Step 2 of 3 (b) From the diagram given in the question, it is clear that there are 2 molecules of ethanol and 7 molecules of oxygen present in the reaction mixture. From the balanced chemical equation, it can be concluded that 1 molecule of ethanol requires 3 molecules of oxygen to give the products. Thus, for 2 molecules of ethanol requires 6 molecules of oxygen to give the products. Thus, in the reaction mixture the only reactant left is 1 molecule of oxygen. Hence, the limiting reagent is ethanol.