Explain the Ideal Gas?
The ideal gases are the ones that have elastic collisions between their molecules. There exist no intermolecular attractive forces in these ideal gases. Coming to reality, there is no such thing alike ideal gases. Gases simply exhibit the ideal behaviour under specific conditions of pressure and temperature.
Instead, when we speak about the ideal gases, the following assumptions can be taken into the consideration:
The ideal gases are combined of molecules that are in constant motion, and in random directions.
The ideal gas molecules behave as rigid spheres.
The total collisions are elastic.
The temperature of the gas is always directly proportional to the average kinetic energy of the molecules.
Pressure takes place because of the collision between the molecules to the container walls.
The Ideal Gas Law
Behaviour of an ideal gas
(Image to be added soon)
These gases obey three laws, which are given below:
Charles’ law – This law states that, at any constant pressure and the number of moles, the gas volume is directly proportional to its temperature. The derivative can be given as follows:
V∝ T
Boyle’s law – This law states that, at any constant temperature and the number of moles, the gas volume is inversely proportional to its pressure. The derivative can be given as follows:
V ∝ 1/p
Avogadro law – This law states that, at constant pressure and temperature, the gas volume is directly proportional to the number of its moles. The derivative can be given as follows:
V∝ n
Combining all these three laws, we get the result as follows:
V ∝ nT/p
V = R(nT/p)
Here R is given as the proportionality constant. By re-arranging the above equations we get the result as,
p V = n RT
Where R is called the universal gas constant and is the same for all gases. The above equation is referred to as the ideal gas equation. Thus, it can be said that at constant pressure and temperature, n moles of any gas will contain the same volume.
V = (nRT) / p
Here the terms, n, R, T, p, are constants and so, there will be a fixed volume for every gas under these conditions. This derived equation is applicable to any of the gas which approaches the ideal behaviour. And, the ideal gas law is otherwise called the equation of the state. This is because it defines the relationship between the 4 variables and describes the state of a given gas.
If we think about considering a case, where the pressure, volume, and temperature, varies from T1, V1, p1 - T2, V2, p2, then the resultant gas law can be written as follows:
(p1V1)/T1 = nR
In the same way,
(p1V1)/T1 = nR
=> (p1V1)/T1 = (p2V2)/T2
This is completely a useful equation and is also known as the combined gas law. If the 5 values are identified, then the 6th one can be calculated.
Characteristics of Ideal Gas
Let us look at a few of the important characteristics of an ideal gas:
They are made up of small particles, which are known as molecules and atoms. Also, currently, this condition is true for all the gases.
The particles themselves contain 0 volume, but the gas as a whole contains the volume. It means the particles present in the gas contains a negligible amount of volume. So, now, all the particles contain some amount of volume. However, the small it can be, and therefore, this condition is not true for all the gases.
The forces of attraction present between the particles of the gas are considered to be negligible. So, for sure, the forces of attraction are much feeble, but they do exist. Therefore, this condition is not true for all the gases.
The collisions present between the individual gas molecules are given as perfectly elastic. We also know that no collision is either perfectly inelastic or perfectly elastic. Therefore, this condition is not true for all the gases.
Always, the gas particles will be in a random motion. This is completely true because the particles of a gas are moving and hence the gas contains properties such as expansion. And, this is true for all the gases.
These are a few of the primary and important characteristics of ideal gases and also the reason they are either true or false in the case of real gases.
Properties of an Ideal Gas
An ideal gas contains a number of properties, where, the real gases often exhibit behaviour very close to that of ideal gases. A few of the properties of an ideal gas can be listed as follows:
An ideal gas has a large number of identical molecules.
When compared to the volume occupied by the gas, the volume occupied by the molecules themselves is negligible.
Also, the molecules obey Newton's laws of motion, and they travel in a random motion.
Finally, the molecules experience the forces only during collisions, where any collisions are completely elastic and can take a negligible amount of time.
FAQs on Ideal Gases and Factors Affecting Them
1. What is meant by an ideal gas in Chemistry?
An ideal gas is a hypothetical gas used in chemistry as a simplified model. It is defined as a gas whose particles occupy negligible volume and have no intermolecular forces of attraction or repulsion. An ideal gas perfectly obeys all gas laws, such as Boyle's Law and Charles's Law, under all conditions of temperature and pressure.
2. What are the four main factors or variables that affect the state of a gas?
The state of any gas is primarily determined by four interdependent variables. The key factors affecting gases are:
- Pressure (P): The force the gas exerts on the walls of its container.
- Volume (V): The space the gas occupies.
- Temperature (T): The measure of the average kinetic energy of the gas particles, expressed in Kelvin.
- Amount of Gas (n): The quantity of gas, measured in terms of moles.
3. What are the main assumptions made in the model of an ideal gas?
The model of an ideal gas is based on several key assumptions from the kinetic theory of gases:
- Gas particles themselves have negligible volume compared to the total volume of the container.
- There are no intermolecular forces of attraction or repulsion between the gas particles.
- All collisions between particles and with the container walls are perfectly elastic, meaning kinetic energy is conserved.
- The particles are in continuous, random motion.
4. How is the Ideal Gas Law expressed, and what does each term in the equation PV = nRT represent?
The Ideal Gas Law is a fundamental equation of state for an ideal gas, expressed as PV = nRT. Each term represents a specific factor:
- P stands for the pressure of the gas.
- V represents the volume it occupies.
- n is the number of moles of the gas.
- R is the universal gas constant, a value that is the same for all gases.
- T denotes the absolute temperature in Kelvin.
5. Why do real gases deviate from ideal gas behaviour?
Real gases deviate from ideal gas behaviour because the two primary assumptions for ideal gases are not perfectly true in reality. Firstly, real gas molecules do have a finite, non-negligible volume. Secondly, real gas molecules do experience intermolecular forces of attraction and repulsion. These factors become significant at high pressures and low temperatures, causing deviations from the Ideal Gas Law.
6. Under what specific conditions does a real gas behave most like an ideal gas, and why?
A real gas behaves most like an ideal gas under conditions of high temperature and low pressure. This is because:
- High temperatures provide the gas particles with enough kinetic energy to overcome the intermolecular forces of attraction between them.
- Low pressures ensure that the gas particles are far apart, making their individual molecular volume truly negligible compared to the total container volume.
7. What is the fundamental difference between an ideal gas and a real gas?
The fundamental difference is that an ideal gas is a theoretical concept where molecules are assumed to have zero volume and no intermolecular forces, making it a perfect follower of gas laws. In contrast, a real gas is any gas that actually exists, whose molecules have a finite volume and experience weak but measurable intermolecular forces, causing it to deviate from ideal behaviour.
8. What is a practical, real-world application of the Ideal Gas Law?
A common real-world application of the Ideal Gas Law is in the design and function of automotive airbags. During a collision, a chemical reaction is triggered to rapidly produce a specific amount (n) of nitrogen gas. Engineers use the PV = nRT equation to calculate the precise mass of reactants needed to inflate the airbag to the required volume (V) and pressure (P) at the high temperature (T) of the reaction, ensuring optimal safety.
9. What is the physical significance of the universal gas constant (R)?
The universal gas constant (R) is more than just a number; it represents the proportionality constant that links energy and temperature for a mole of gas particles. It signifies the amount of work done by one mole of an ideal gas when its temperature increases by one Kelvin at a constant pressure. It fundamentally connects the macroscopic properties of a gas (P and V) to its microscopic state (T and n).
