Question

Name the two products of the complete combustion of hydrocarbons. What is the other reactant, and how do the products change when this reactant is in short supply?

Short answer

The products are CO_2 and H_2O with oxygen as the reactant. In short supply of oxygen, CO and soot form.

Step-by-step solution

Definition of Complete Combustion

Complete combustion of hydrocarbons refers to the chemical reaction where the hydrocarbon reacts completely with oxygen, producing specific products.

Identify the Reactants and Products

During the complete combustion of hydrocarbons, the primary reactant that combines with the hydrocarbon is oxygen ( O_2 ). The products of this reaction are carbon dioxide ( CO_2 ) and water ( H_2O ).

Understanding Short Supply of Oxygen

When oxygen is in short supply, the combustion is incomplete. This leads to the formation of carbon monoxide ( CO ) and, potentially, even elemental carbon (soot) in addition to water.

Key concepts

Chemical Reaction

A chemical reaction involves the transformation of one or more substances into different substances. It usually occurs with a change in energy, such as heat being released or absorbed. In the context of hydrocarbons, a complete combustion chemical reaction is a process where hydrocarbons react with oxygen. Hydrocarbons, which are compounds made of hydrogen and carbon, completely oxidize to form new products. This type of reaction is fundamental in understanding energy generation, as it releases energy when the bonds in the hydrocarbons break and new bonds form in the products.

• Combustion reactions are exothermic, meaning they release heat.
• A balanced chemical equation represents both the reactants and products in stoichiometric proportions.

Understanding the nature of these reactions helps in grasping how fuels like gasoline and natural gas power engines and heating systems.

Oxygen Reactant

Oxygen is a key reactant in the complete combustion of hydrocarbons. In fact, without oxygen, combustion cannot occur. Oxygen is a diatomic molecule, meaning each molecule contains two atoms, denoted as \(O_2\).In a complete combustion reaction, the hydrocarbon (the fuel) is totally consumed and converted into carbon dioxide and water by reacting with oxygen. This relationship highlights the importance of oxygen in the process.

• The ratio of reactants must be appropriate to ensure complete combustion occurs.
• Typically, hydrocarbons require a large amount of oxygen to combust completely.

Without sufficient oxygen, the combustion process is incomplete, which leads to different chemical outcomes.

Carbon Dioxide

Carbon dioxide is one of the main products of the complete combustion of hydrocarbons. It is a colorless, odorless gas that plays a critical role in the Earth's atmosphere. In the balanced chemical equation of complete combustion, each carbon atom of the hydrocarbon is converted to one \(CO_2\) molecule. This process is vital in many applications.

• In engines, it is a sign of efficient fuel utilization and complete energy release.
• In environmental sciences, it is a focus point due to its role in the greenhouse effect.

Understanding how carbon dioxide is formed and its implications can aid in developing strategies for reducing emissions.

Water

Water is the second product formed during the complete combustion of hydrocarbons. This product appears as vapor when the reaction occurs at high temperatures, such as in internal combustion engines. In chemical terms, each hydrogen atom in the hydrocarbon combines with oxygen to form \(H_2O\). This reaction highlights the conversion of hydrogen energy to water vapor energy.

• The amount of water produced is proportional to the hydrogen content in the fuel.
• The presence of water can be harnessed in certain energy recovery systems.

Apart from being a simple byproduct, this formation process is essential for studying thermodynamics and energy conservation principles.

Incomplete Combustion

Incomplete combustion occurs when there is not enough oxygen to convert all the carbon in a hydrocarbon into carbon dioxide. This results in the formation of unwanted byproducts like carbon monoxide \(CO\)and sometimes even soot, which consists of elemental carbon. This type of combustion is less desirable due to several reasons.

• It produces less energy compared to complete combustion.
• It releases carbon monoxide, a toxic gas dangerous to health.

Incomplete combustion can be mitigated by ensuring an adequate supply of oxygen to the reaction environment, illustrating the importance of maintaining the right conditions for combustion processes.