Vapor Pressure: What Affects Gasoline Evaporation?

In summary, Dalton's law states that the total pressure of a mixture of ideal gases is equal to the sum of the partial pressures of the individual gases in the mixture. This means that the vapour pressure of a gas is dependent upon the temperature and the individual component's partial pressure.
  • #1
Ask1122
52
0
Hi all,

I have a question on vapor pressure. As far as I understood, a liquid will flashes into gas when the absolute pressure it is experiencing (in a pipe / in the atmosphere) is lower than the liquid's vapor pressure (assuming temperature is constant).
Everyone knows that gasoline forms a vapor cloud when it is released into the atmosphere. But a lots of sources I came across on the internet states that the vapor pressure of gasoline ranges between 20kPa - 80 kPa at room temperature on average, so if that is true, how does gasoline form a vapor in the atmosphere?

Thank you~
 
Physics news on Phys.org
  • #2
The way I have understood it, is that temperature is just an average. Some of the molecules will have enough energy by chance to escape as vapor at any temperature. The numbers you state are average, and if the average is high enough for vaporization, you get a large scale effect, ie boiling.
 
  • #3
Ask1122 said:
Hi all,

I have a question on vapor pressure. As far as I understood, a liquid will flashes into gas when the absolute pressure it is experiencing (in a pipe / in the atmosphere) is lower than the liquid's vapor pressure (assuming temperature is constant).
Everyone knows that gasoline forms a vapor cloud when it is released into the atmosphere. But a lots of sources I came across on the internet states that the vapor pressure of gasoline ranges between 20kPa - 80 kPa at room temperature on average, so if that is true, how does gasoline form a vapor in the atmosphere?

Thank you~

Well then, how does water from a vapour in air at room temperature?
The vapor pressure of water at 20 deg C or room temperature is 17.5 mm Hg, yet liquid water still evaporates at atmospheric pressure.

But boiling water at 100 deg C has a vapour vapor pressure is 760.0 mm Hg - ie atmospheric pressure.

The vapour pressure is a function of temperature. If you put a substance in a closed container, an equilibrium will be reached after some time where the pressure of the gas of the substance in the container reaches a value depending upon the temperature. That is the vapour pressure at that temperature. Since gasoline is not a pure substance its vapour pressure varies depending upon its volatile constituents.

Here is an excerpt fom Wiki regarding dalton's Law
Dalton's law of partial pressuresMain article: Dalton's law
The partial pressure of an ideal gas in a mixture is equal to the pressure it would exert if it occupied the same volume alone at the same temperature. This is because ideal gas molecules are so far apart that they don't interfere with each other at all. Actual real-world gases come very close to this ideal.

A consequence of this is that the total pressure of a mixture of ideal gases is equal to the sum of the partial pressures of the individual gases in the mixture as stated by Dalton's law.[2] For example, given an ideal gas mixture of nitrogen (N2), hydrogen (H2) and ammonia (NH3):

where:
= total pressure of the gas mixture
= partial pressure of nitrogen (N2)
= partial pressure of hydrogen (H2)
= partial pressure of ammonia (NH3)

It takes some time to get your head around all of this vapour pressure stuff I know.
 

1. What is vapor pressure?

Vapor pressure is the measure of the pressure exerted by a gas when it is in equilibrium with its liquid or solid state at a specific temperature. In the case of gasoline, it is the pressure exerted by the evaporated gas above the liquid fuel.

2. How does temperature affect vapor pressure of gasoline?

As temperature increases, the vapor pressure of gasoline also increases. This means that more gasoline molecules will evaporate, resulting in a higher concentration of gas in the air above the liquid. This is why gasoline evaporates faster in warmer temperatures.

3. What other factors can affect vapor pressure of gasoline?

In addition to temperature, the composition of the gasoline can also affect its vapor pressure. Gasoline with a higher percentage of volatile compounds will have a higher vapor pressure. Other factors such as atmospheric pressure and humidity can also play a role in gasoline evaporation.

4. How does vapor pressure affect the performance of a car?

Vapor pressure is important in maintaining the proper fuel-air mixture in a car's engine. If the vapor pressure of gasoline is too low, the fuel may not evaporate sufficiently, resulting in a lean mixture and poor engine performance. On the other hand, if the vapor pressure is too high, it can cause vapor lock, where the fuel vaporizes before reaching the engine and disrupts the fuel flow.

5. Can vapor pressure of gasoline be controlled?

Yes, the vapor pressure of gasoline can be controlled by adjusting its composition, such as the percentage of volatile compounds, and also by using additives to lower or raise the pressure. Refineries and fuel companies carefully monitor and adjust the vapor pressure of gasoline to ensure optimal performance and safety.

Similar threads

  • Mechanics
Replies
10
Views
3K
  • Mechanics
2
Replies
39
Views
5K
Replies
31
Views
9K
Replies
27
Views
5K
Replies
6
Views
1K
Replies
7
Views
16K
Replies
6
Views
2K
Back
Top