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💏intro to chemistry review

CnH2n+2

Written by the Fiveable Content Team • Last updated September 2025
Written by the Fiveable Content Team • Last updated September 2025

Definition

CnH2n+2 is a general chemical formula that represents a class of organic compounds known as alkanes, which are saturated hydrocarbons. The formula indicates that the compound has a carbon chain with n number of carbon atoms, and the number of hydrogen atoms is always 2n plus 2.

5 Must Know Facts For Your Next Test

  1. The CnH2n+2 formula applies to all members of the alkane homologous series, which includes compounds such as methane (CH4), ethane (C2H6), propane (C3H8), and so on.
  2. Alkanes have a tetrahedral arrangement of atoms around each carbon, with all carbon-carbon bonds being single bonds, resulting in a saturated structure.
  3. The number of hydrogen atoms in an alkane is always 2 more than twice the number of carbon atoms, as indicated by the 2n+2 in the formula.
  4. Alkanes are known for their high energy content, low reactivity, and use as fuels, solvents, and in the production of various chemicals.
  5. The simplest alkane is methane (CH4), which is the main component of natural gas and a potent greenhouse gas.

Review Questions

  • Explain the significance of the CnH2n+2 formula in the context of hydrocarbons.
    • The CnH2n+2 formula is the general formula for alkanes, a class of saturated hydrocarbons. It indicates that the number of hydrogen atoms in an alkane is always 2 more than twice the number of carbon atoms. This formula is significant because it allows for the prediction of the chemical structure and properties of alkanes, which are widely used as fuels, solvents, and in the production of various chemicals. The formula also helps to identify the homologous series of alkanes, where each member differs from the previous one by a CH2 group.
  • Describe the structural features of alkanes that are reflected in the CnH2n+2 formula.
    • The CnH2n+2 formula for alkanes reflects several key structural features. Firstly, the 'n' in the formula represents the number of carbon atoms in the molecule, indicating that alkanes can have varying chain lengths. Secondly, the '2n+2' part of the formula shows that the number of hydrogen atoms is always 2 more than twice the number of carbon atoms, reflecting the fully saturated nature of alkanes, where each carbon atom is bonded to the maximum number of hydrogen atoms. This tetrahedral arrangement of atoms around each carbon, with all carbon-carbon bonds being single bonds, results in the stable and unreactive nature of alkanes.
  • Evaluate the importance of the CnH2n+2 formula in understanding the properties and applications of alkanes.
    • The CnH2n+2 formula is crucial for understanding the properties and applications of alkanes. By knowing this formula, one can predict the number of carbon and hydrogen atoms in any alkane, which directly relates to its physical and chemical properties. For example, the formula explains why alkanes have high energy content and are commonly used as fuels, as well as their low reactivity due to the saturation of the carbon-carbon bonds. Additionally, the formula allows for the identification of the homologous series of alkanes, which helps in understanding their systematic nomenclature and predicting the properties of higher-order alkanes. Overall, the CnH2n+2 formula is a fundamental tool for chemists to comprehend the behavior and utility of this important class of hydrocarbons.