Question

The major use of alkanes has been in _________ reactions, as a source of heat and light.

Short answer

The major use of alkanes has been in combustion reactions, as a source of heat and light.

Step-by-step solution

Identify the type of reaction alkanes undergo

Alkanes are hydrocarbons. They undergo combustion reactions in the presence of oxygen (O2) to produce heat and light.

Fill in the blank

The missing term is "combustion" so the completed sentence is: "The major use of alkanes has been in combustion reactions, as a source of heat and light."

Key concepts

Combustion Reactions

Combustion reactions are a type of chemical process where a substance combines with oxygen to release energy in the form of light and heat. This reaction is exothermic, meaning it releases more energy than it consumes. Alkanes, which are the simplest type of hydrocarbons consisting of carbon and hydrogen, readily undergo combustion.

In a typical combustion reaction involving an alkane, the carbon and hydrogen atoms in the molecule react with oxygen (O2) from the air to form carbon dioxide (CO2) and water (H2O). The general formula for the combustion of an alkane is:
\[ C_nH_{2n+2} + \frac{3n+1}{2} O_2 \rightarrow n CO_2 + (n+1) H_2O \]
where \( n \) is the number of carbon atoms in the alkane molecule.

Hydrocarbons

Hydrocarbons are organic molecules consisting solely of carbon (C) and hydrogen (H) atoms. They are categorized into different groups based on their structure and bonding, such as alkanes, alkenes, and alkynes. Alkanes have single bonds and are known for their saturated nature, meaning they hold the maximum number of hydrogen atoms.

They are generally unreactive except for combustion and substitution reactions. Alkanes have a wide range of applications, especially as fuels. Methane (CH4), propane (C3H8), and butane (C4H10) are common examples of alkanes often used for heating and cooking. The properties of hydrocarbons like boiling point and solubility depend on their molecular size and structure.

Chemical Reactions in Chemistry

Chemical reactions are processes that convert one set of chemical substances to another. They are governed by the laws of conservation of mass and energy, which dictate that matter and energy cannot be created or destroyed in a reaction.

Reactions are categorized by the changes they involve, such as synthesis, decomposition, single replacement, double replacement, and combustion. Chemists analyze reactions by writing balanced chemical equations, which show the reactants and products along with their stoichiometric coefficients. Understanding how various factors like temperature, pressure, concentration, and catalysts affect reaction rates is crucial in fields ranging from industrial manufacturing to environmental science.