Ideal Gas Model and Behavioral Patterns of Real Gases

Let’s understand the difference in properties of solid, liquid, and gas. These three are interchangeable states of matter. Solids.Solid is that state of matter which has a fixed shape because all its atoms are tightly bonded to each other. Atoms do not move freely. Because of its fixed shape, its volume is also fixed. The intermolecular force between the particles of solids is maximum. Therefore, the intermolecular space between the particles of solids is minimum.

The distance between the particles of solids is small. This is because the particles are compactly arranged nearby to each other. These tightly packed intermolecular space particles give solids high densities. Atoms in solids are bonded by strong bonds. That is why solids are not compressible.Do you know what compressibility is?.Compressibility, is the measure of how much a given volume of matter decreases, when placed under pressure. If we put pressure on solids, there is essentially no change in the volume.

Let’s take an example. Here we see a brick. It has a definite shape and a fixed volume. Atoms are arranged in a definite manner. It can not be compressed because it does not have any free intermolecular space. That's why brick has high density. Let’s take another example.Sand is also solid as it has a fixed shape and volume. Its density is high. Upon applying pressure its volume does not decrease in volume. Therefore it is not compressible.

Liquids.Liquid particles are in close-contact. Their intermolecular space is less than of gases. That's why it has a definite volume. But liquid particles can move freely. Therefore they do not have a definite shape. Liquids flow and fill the lower portion of the container, taking its shape. However, this does not change the volume. Liquid particles can move and glide past one another very easily. Therefore they take the shape of the part of the container that they occupy. The particles of liquid remain nearby to each other. Therefore, there is only a small rise in volume in liquids compared to solids. What do you think of liquid density and compressibility?.

The same mass of liquid will have a slightly greater volume than solids. This is the reason a liquid has a slightly lower density than its solid state. But liquids have much higher density than the density of its corresponding gaseous state.Although particles are randomly arranged they are tightly packed. This gives liquids high densities but slightly lower than the solids. Compressibility is a change in volume with a rise in pressure. So liquids volume decreases on applying pressure. But this happen in a very small fraction. The particles of liquid are packed, but a little loosely, so can be compressed. Hence liquids are slightly compressible.

Example 1.Water is liquid with fixed volume but with a definite shape. If it is placed in a glass it takes shape of the glass. If it is placed in the bottle it takes shape of the bottle. It has a high density. Milk is also compressible but change or decrease in volume is very low.Example 2.Blood is also liquid it does not have a shape and contains the shape of arteries that it occupies. It has a density of 1g/m which is high than any grass. it is also compressible.

Gases.A gas has maximum intermolecular space. This is why it does not have a definite volume. Because its particles are not tightly packed, they move freely. Therefore, a gas does not have a definite shape. A gas take the shape of the container it they occupies. In most cases, there are no attractive forces between particles. This means a gas has nothing to hold a specific shape or volume.

Density is the mass taking up a unit volume at specific pressure and temperature. A gas has a negligible density. It is 1000 times lower than the density of solid or liquid. Therefore gases typically have exceptionally low densities.Gases are highly compressible because most of the volume of gas is composed of large amounts of space between the gas particles. By applying pressure the volume of gases decreases.

Examples.Let’s take soda for example. In sodas, there is carbon dioxide gas. This gas also takes shape of a bottle and volume where there is no liquid soda. It has a low density and is resides in a soda bottle by compression.Did you know that WiFi cables contain helium gas? This helium gas in WiFi cables take the shape and volume of the cable it occupies. It has the lowest density and reside in those cables in compressed form.

The ideal gas equation.The ideal gas equation is formulated as PV=nRT. It is also called the ideal gas law. It is the equation of a hypothetical ideal gas. It indicates an approximation of the behavior of many gases under many conditions. There are some limitations to it too. It is a combination of empirical laws such as Charles's law and Boyle's law. It helps us in describing gases under particular conditions. It is applied to find the volume and density of gases.

This equation is also used to inter-convert between molar amounts and volumes in a chemical reaction equation.An ideal gas is a hypothetical gas that is not seen in reality. Its purposed is to simplify calculations. In an ideal gas scenario, gas molecules or particles move freely in all directions with the elastic collision between them. In ideal gas conditions, there is no loss of energy when particles collide with each other.

In reality, there is no such ideal gas. All real gases try to achieve ideal gas properties at low enough density. Molecules of gas are so far from each other and do not interact, which helps in a low-density case. So ideal gas hypothesis is used to understand real gases. If we want to study gases, we need a standard gas. Using it we compare all other gases and study their properties. Let's say we want to study hydrogen, nitrogen, oxygen, helium, or any other gas. We take one mole of that gas and put it in a container. We also maintained its temperature and pressure. Then at low density, small measurement differences also disappear.

It is proved that at low densities real gases tend to behave as an ideal gas and obey 1 universal law known as the ideal gas law.This law is presented by an equation called the ideal gas equation.PV=nRT. Here P is the pressure and V is the volume of ideal gases. n represents the moles of an ideal gas. T is temperature and R is the gas constant. R has a fixed value of 8.3144(48)JK⁻¹mol⁻¹.

There are several limitations to the ideal gas law. It is only applicable when the density is low. At high densities, real gases deviate from the ideal gas law. In ideal gas equation, n stands for the total moles of gas particles in a given mixture. While in the equation of states of ideal gas there is a relation between simple properties that are very generic. The simple equation of state of gas is known as the ideal gas equation of state.Can you calculate volume or pressure from ideal gas equation?.

Example 1.What will be the volume of gas taken up by 5 grams of carbon dioxide at standard temperature and pressure? First, write the ideal gas equation and re-arrange it to determine the volume. V=nRT/P. Then we calculate as seen here.Example 2.Let's see another example of finding temperature. In this 0.8 moles of oxygen gas occupies 15 liters of 2 atmospheres.To determine temperature let's rearrange the ideal gas equation. T = PV/nR