Question

When a fuel is bumed in the air, what is typically the limiting reactant?

Short answer

In a combustion reaction, the fuel is typically the limiting reactant.

Step-by-step solution

Understanding Combustion

Combustion, or burning, is a high-temperature exothermic redox chemical reaction between a fuel and an oxidant, which produces heat and light. The most common example of combustion is fire. In most cases, in the presence of sufficient oxygen, fuels are completely oxidized, yielding carbon dioxide and water as products.

Identifying Reactants in Combustion

In a combustion reaction, the fuel and oxygen (from the air) are reactants. Common fuels include hydrocarbons, like gasoline and natural gas, which are compounds of carbon and hydrogen.

Determining The Limiting Reactant

In a combustion reaction, the fuel is typically the limiting reactant. There is an abundance of oxygen in the air (approximately 21% of the earth's atmosphere is oxygen). On the other hand, the fuel, be it gasoline, wood, etc., is often present in a smaller quantity. Therefore, the fuel is typically consumed completely in the reaction, determining the amount of products that form.

Key concepts

Limiting Reactant

In chemical reactions, a limiting reactant is the substance that is entirely consumed first. Once it is used up, the reaction cannot continue, and no more products can be formed. This concept is crucial because it determines the maximum amount of product that can be created from a given set of reactants. In combustion reactions, the limiting reactant is often the fuel. This is because, although oxygen is necessary for the reaction, it is abundant in the air. Consequently, the fuel, which could be a hydrocarbon, is typically the first to be fully consumed, defining the extent of the reaction.

Oxidation

Oxidation is a central aspect of combustion reactions. It refers to the chemical process where a substance loses electrons. In the context of a combustion reaction, the fuel undergoes oxidation by reacting with oxygen. When hydrocarbons burn in oxygen, their carbon atoms are oxidized to carbon dioxide and hydrogen atoms to water. This process releases energy, mostly in the form of heat and light, which is why combustion is exothermic.
Understanding oxidation is key to comprehending how energy is released during the reaction, making it a foundational concept in studying chemical reactions.

Hydrocarbons

Hydrocarbons are compounds made primarily of carbon and hydrogen atoms. They serve as a crucial source of energy owing to their high-energy combustibility. Common hydrocarbons include methane, propane, gasoline, and natural gas. These substances are significant in combustion reactions as they react with oxygen to produce carbon dioxide and water, releasing a significant amount of energy.
In the ecosystem of chemical reactions, hydrocarbons are vital players in energy production processes, ranging from small-scale household appliances to powering vehicles and even generating electricity in power plants.

Chemical Reactions

Chemical reactions are processes where substances, known as reactants, change into new substances, called products. A combustion reaction is a type of chemical reaction particularly noted for its exothermic nature, releasing energy as it occurs. This makes combustion indispensable in numerous real-world applications, like heating and powering engines.
During a combustion reaction, hydrocarbons are oxidized by oxygen, resulting in new molecules such as carbon dioxide and water. These reactions are guided by principles such as the conservation of mass and energy, reinforcing the interconnection of science and everyday life.