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by Marcelo Brito.
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[ What is an ideal gas? ]
How are pressure, volume, temperature and number of gas molecules related?
Gas are tricky. They are filled with billions of high-energy gas molecules that can collide and possibly interact.
Because real gases are difficult to describe exactly, scholars have developed the ideal gas concept as an approximation to help model and predict the behavior of real gases.
The term ideal gas refers to a hypothetical gas composed of molecules that obey certain rules.
- The molecules of an ideal gas are neither attracted nor repelled.
- The only interactions between molecules in an ideal gas are elastic collisions
when molecules collide with each other or with the walls of the container.
- Molecules are punctual (they do not have physical dimensions).
[ What is elastic collision? ]
The term elastic collision refers to a collision in which kinetic energy is not transformed into other forms of energy during the collision.
In other words, kinetic energy can be exchanged between colliding objects, such as molecules, but the total kinetic energy before the collision is equal to the total kinetic energy after the collision.
A collision between two automobiles, in which kinetic energy is converted to heat and sound, resulting in two dented bumpers, would not be elastic.
In the case of ideal gases, in theory, all their molecules have the same mass.
[ What would the molecules of an ideal gas look like? ]
An ideal gas molecule takes up no volume.
A gas occupies a volume because the molecules expand over a large area of space.
However, an ideal gas molecule is approximated as a point particle that has no volume and takes up no space.
It may sound too idealistic to be true, but it is.
There is no exact ideal gas, but there are some gases that are close enough that the ideal gas concept is a very useful approximation in many situations.
In fact, many of the gases we are interested in are practically ideal at temperatures close to room temperature and pressures close to atmospheric pressure.
At very high gas pressures (e.g. hundreds of times atmospheric pressure) or very low temperatures (e.g. -200 °C), significant deviations from the ideal gas law may occur.
[ What is the molar form of the ideal gas law? ]
In the ideal gas, T(temperature) is related by a simple equation called the ideal gas law.
The simplicity of this relationship is an important reason why gases are generally considered ideal, unless there is a specific reason to do otherwise.
PV=nRT
where:
P is the pressure of the gas,
V is the volume occupied by the gas,
T is the temperature of the gas,
R is the gas constant,
n is the number of moles (molecules) of the gas.
Perhaps the most confusing aspect of applying the ideal gas law is being careful about using the correct units.
When using the universal perfect gas constant: R=8.31 J/(K・mol)
P = Pa (Pascal)
V = m³ (cubic meters)
T = K (Kelvin)
When using the universal perfect gas constant: R=0.082 (L・atm)/(K・mol)
P = atm (atmospheres)
V = L (liters)
T = K (Kelvin)
Note: 1 atm is approximately 10⁵ Pa (Pascal)
1 m³ = 1000 L (liters)
[ Chosen language: Javascript ]
User Interaction: 2D Graphic Animation.
The animation in Javascript simulates the movement of molecules of an Ideal Gas inside a closed container.
2D simulation using "canvas".
See the source code of the page: