The ratio of the number of moles of a particular gas in a mixture to the total number of moles in the mixture is called the?

• A. Mole fraction
• B. Partial pressure
• C. Total pressure
• D. Entropy

Answer: (A)

This question tests your understanding of mole fraction in gas mixtures. The mole fraction of a component is defined as the number of moles of that component divided by the total number of moles in the mixture: X = n_component / n_total. This ratio is dimensionless and ranges from 0 to 1, representing how much of the mixture is made up of that gas. In ideal gas behavior, it also connects to pressure: the partial pressure of a component equals its mole fraction times the total pressure (P_i = X_i P_total), meaning the gas contributes to the total pressure in proportion to its share of moles. This concept is helpful for predicting how a mixture behaves without needing masses or volumes.

Partial pressure is a pressure value for a component, not a ratio; total pressure is the sum of all partial pressures; entropy measures disorder, not a ratio of moles.