Partial Pressure vs. Vapor Pressure — What's the Difference?
By Tayyaba Rehman — Published on November 12, 2023
Partial pressure is the pressure exerted by a specific gas in a mixture, while vapor pressure is the pressure exerted by a vapor in equilibrium with its condensed phase at a specific temperature.
Difference Between Partial Pressure and Vapor Pressure
Table of Contents
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Key Differences
Partial pressure relates to individual gas components within a mixture, denoting the pressure each gas would have if it occupied the entire volume alone. Vapor pressure, on the other hand, pertains to the pressure exerted by the vapor of a liquid or solid in equilibrium with its condensed phase.
Both concepts play pivotal roles in various scientific and industrial applications. Partial pressure is crucial for understanding gas mixtures, respiratory physiology, and more. Vapor pressure is essential for boiling, distillation, and understanding phase changes of substances.
Partial pressure can be calculated using Dalton's Law, which states that the total pressure of a gas mixture is the sum of the partial pressures of each component gas. Vapor pressure is determined experimentally and can be found in tables for specific substances at various temperatures.
In respiratory physiology, partial pressure explains the diffusion of gases in the lungs. In meteorology, vapor pressure aids in understanding humidity and dew point. Both are imperative in the study of thermodynamics and material properties.
The partial pressure of a gas in a mixture is influenced by its mole fraction and the total pressure. Vapor pressure is affected by the nature of the substance and the temperature. As temperature increases, the vapor pressure of a substance generally increases.
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Comparison Chart
Definition
Pressure of a specific gas in a mixture.
Pressure of a vapor in equilibrium with its liquid.
Determination
Calculated using Dalton's Law.
Determined experimentally for specific temperatures.
Influences
Mole fraction and total pressure.
Nature of the substance and temperature.
Applications
Gas mixtures, respiratory physiology.
Boiling, distillation, phase changes.
Relationship to Volume
Directly proportional to mole fraction.
Not related to volume but to temperature.
Compare with Definitions
Partial Pressure
The fraction of total pressure contributed by a specific gas.
Breathing at high altitudes involves lower partial pressures of oxygen, affecting our physiology.
Vapor Pressure
The pressure of a vapor above a liquid when there's no net evaporation.
The vapor pressure of ethanol is higher than that of water, making it more volatile.
Partial Pressure
The component of total pressure due to a specific gas.
The partial pressure of CO2 in the atmosphere is increasing due to human activities.
Vapor Pressure
A substance's intrinsic property defining its equilibrium pressure with its vapor.
Ice has a lower vapor pressure than liquid water at the same temperature.
Partial Pressure
A measure of the concentration of an individual gas in a mixture.
The partial pressure of helium in the balloon determines its buoyancy.
Vapor Pressure
The pressure exerted by a vapor in equilibrium with its liquid or solid phase.
Water's vapor pressure increases with temperature, leading to boiling.
Partial Pressure
Pressure exerted by one component in a gaseous mixture.
Nitrox diving relies on understanding the partial pressure of oxygen under various depths.
Vapor Pressure
A measure of a substance's volatility at a specific temperature.
Mercury has a significant vapor pressure, even at room temperature, leading to its vapor hazards.
Partial Pressure
The pressure a gas would exert if it were alone in a container.
In a mixture of oxygen and nitrogen, the partial pressure of oxygen is its individual contribution to the total pressure.
Vapor Pressure
Indicates the tendency of a substance to evaporate.
Gasoline's high vapor pressure makes it evaporate quickly on a hot day.
Common Curiosities
How is vapor pressure defined?
Vapor pressure is the pressure exerted by a vapor in equilibrium with its condensed phase at a specific temperature.
Does temperature affect vapor pressure?
Yes, vapor pressure generally increases with temperature for most substances.
How does one calculate partial pressure?
Partial pressure can be calculated using Dalton's Law based on the mole fraction and total pressure of the gas mixture.
What is partial pressure?
Partial pressure is the pressure exerted by a specific gas in a mixture.
How is vapor pressure related to boiling point?
When the vapor pressure of a liquid equals the atmospheric pressure, the liquid will boil. Hence, a substance's boiling point is the temperature at which its vapor pressure equals the external pressure.
Why do some liquids evaporate faster than others?
Liquids with higher vapor pressures at a given temperature will evaporate faster than those with lower vapor pressures.
Do both partial pressure and vapor pressure have the same units?
Yes, both are typically measured in units of pressure, such as atmospheres (atm), pascals (Pa), or millimeters of mercury (mmHg).
Can partial pressure be greater than the total pressure of a gas mixture?
No, partial pressure is always a fraction of the total pressure.
Can two different gases in a mixture have the same partial pressure?
Yes, two different gases can have the same partial pressure in a mixture if their concentrations and contributions to the total pressure are the same.
How are partial pressure and mole fraction related?
The partial pressure of a gas in a mixture is equal to its mole fraction multiplied by the total pressure of the mixture.
What happens to the vapor pressure of water as it is heated?
The vapor pressure of water increases as it is heated.
How does altitude affect partial pressure of atmospheric gases?
At higher altitudes, the total atmospheric pressure decreases, leading to a decrease in the partial pressures of its constituent gases, including oxygen.
Why do closed containers of liquid build pressure when heated?
Heating increases the vapor pressure of the liquid. In a closed container, the vapor cannot escape, causing a buildup of pressure inside the container.
Can the vapor pressure of a substance be changed?
While intrinsic to the substance, the vapor pressure is dependent on temperature. Therefore, by changing the temperature, one can alter the vapor pressure.
Is it possible for a solid substance to have a vapor pressure?
Yes, solids can have vapor pressures, though it is typically much lower than that of liquids. This phenomenon is evident when solids sublimate, turning directly from a solid to a gas.
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Tayyaba RehmanTayyaba Rehman is a distinguished writer, currently serving as a primary contributor to askdifference.com. As a researcher in semantics and etymology, Tayyaba's passion for the complexity of languages and their distinctions has found a perfect home on the platform. Tayyaba delves into the intricacies of language, distinguishing between commonly confused words and phrases, thereby providing clarity for readers worldwide.
