PADI Divemaster Certification Practice Exam

What is partial pressure in a gas mixture?

1. The total pressure exerted

2. The pressure exerted by a single gas

3. The average pressure of all gases

4. The pressure equilibrium in a closed system

The correct answer is: The pressure exerted by a single gas

Partial pressure refers specifically to the pressure exerted by an individual gas within a mixture of gases. In a gas mixture, each gas contributes to the total pressure, and the partial pressure of a specific gas is the pressure that gas would exert if it occupied the entire volume by itself at the same temperature. This concept is crucial in diving, especially when discussing the effects of gases like oxygen and nitrogen under pressure during descent and ascent. It is fundamental to understanding concepts such as the treatment of gas narcosis and oxygen toxicity, as these effects are based on the partial pressures of the respective gases at various depths. The notion of partial pressure allows divers to make informed decisions regarding gas mixtures and their behavior, contributing directly to safe diving practices and the management of potential risks associated with changes in pressure while underwater.