# Why do gases not have definite volume?

Gases are one of the three physical states of matter, the other two being liquids and solids. Unlike solids and liquids, gases do not possess a definite volume, which means they can expand and contract to fill any available space. This can be explained by several factors.

Firstly, gases are composed of tiny, rapidly moving particles that are spread out with large spaces in between. Unlike solids or liquids, gases are not held together by strong intermolecular forces between particles. Instead, the particles are in a state of constant motion, colliding with each other and with the walls of their container.

Secondly, gases are highly compressible. This means that when pressure is applied, the volume of the gas decreases. For example, if a gas is compressed inside a cylinder, it will occupy a smaller space, and if the pressure is released, the gas will expand to fill the container completely. This property allows gases to be stored and transported in compressed form.

Thirdly, gases are affected by temperature. As the temperature of a gas increases, the average kinetic energy of its particles also increases. This results in a greater number of collisions between particles and with the container walls, causing the gas to expand and occupy a larger volume.

The lack of a definite volume in gases is due to the fact that their particles are highly mobile, not held together by strong intermolecular forces, highly compressible, and affected by temperature. These characteristics of gases make them useful in many applications, such as heating and cooling, as well as fuel for combustion engines.

## Is gas volume definite or definite?

Gas volume is not definite or fixed. It can change based on temperature, pressure, and the amount of gas present. The volume of a gas is directly proportional to the number of particles present, which can change if additional gas is added or if some gas particles escape. Additionally, the behavior and movement of gas particles can impact their volume.

According to the kinetic theory of gases, gas particles are in constant motion and can exert pressure on the container walls they are in. Heating a gas causes its particles to move more quickly and collide more frequently, increasing the pressure and therefore changing the volume. Similarly, reducing the pressure on a gas can increase its volume.

Thus, gas volume is not definite, but rather flexible and dependent on various factors.

## Why gases can be compressed?

Gases can be compressed because they are made up of molecules that are spread out and in constant motion. The space between gas particles is much greater than in solids or liquids, which means there is a lot of space available for these particles to move around. When pressure is applied to a gas, such as by squeezing it into a smaller volume or increasing the atmospheric pressure, the gas molecules are forced closer together, which reduces the amount of space they have to move.

As a result, the gas molecules become more densely packed together, allowing for the gas to be compressed. This process is reversible, meaning that when the pressure is released, the gas molecules will regain their previous amount of space and expand. This is why gases are able to fill up any container they are placed in and take on its shape.

The compressibility of gases can also be attributed to the gas laws, specifically Boyle’s law, which states that the pressure of a gas is inversely proportional to its volume at a constant temperature. This means that as the volume of a gas is reduced, the pressure will increase proportionately. This relationship between pressure and volume allows for gases to be compressed to much smaller volumes than they occupy in their natural state.

It is important to note that not all gases can be compressed equally. Some gases, such as helium or neon, have a low compressibility because their particles are already closer together and have less space to move around. Other gases, such as hydrogen or nitrogen, have a higher compressibility, making them useful in applications such as fuel storage or gas cylinders.

The compressibility of gases is a result of their molecular composition and the amount of space available for their particles to move. This property has a range of practical applications, from fuel storage to refrigeration, and is governed by gas laws such as Boyle’s law.

## Why is it possible to compress gases but not solids?

The ability to compress a substance depends on a number of factors, including the nature of the material itself and the conditions under which it is being compressed. When it comes to gases and solids, there are fundamental differences in their physical properties that make compression possible for one and not the other.

Gases are made up of individual molecules that are in constant motion and do not have a fixed shape or volume. This means that if the pressure on the gas is increased, the molecules can be pushed closer together, decreasing the volume of the gas. Since the volume of the gas is proportional to the number of gas molecules present, the pressure and volume are inversely related according to the ideal gas law, PV=nRT.

As the volume decreases, the pressure increases to maintain the same temperature according to the ideal gas law. This is the reason gases can be compressed into smaller volumes.

On the other hand, solids are made up of closely-packed atoms or molecules that are held together by strong intermolecular forces, such as ionic, covalent, or metallic bonds. These forces create a rigid, fixed structure that is difficult to compress. When a force is applied to a solid, its shape may change, but its volume does not.

This is because the intermolecular forces resist any attempt to change the volume of the solid. Thus, it is not possible to compress solids to any significant extent.

The ability to compress a substance depends on its physical properties and the conditions under which it is being compressed. While gases can be compressed due to their individual, non-rigid molecules, solids are not compressible because of their tightly-packed, fixed structures held together by strong intermolecular forces.

## Why gases do not liquify on compression only?

The process of liquification occurs when a gas is subjected to a combination of low temperature and high pressure, which causes the gas molecules to come closer together and lose kinetic energy. The attraction between the molecules then becomes strong enough to overcome the kinetic energy of the molecules, resulting in a liquid phase.

However, simply compressing a gas is not enough to achieve liquification because compression only increases the pressure, but not necessarily the temperature. As a gas is compressed, its volume decreases and its pressure increases, but the temperature of the gas may remain relatively constant. This is known as adiabatic compression.

In order to achieve liquification, the temperature of the gas must also be lowered in addition to increasing the pressure. This is because the energy of the gas molecules is directly related to their temperature – as the temperature decreases, the gas molecules move more slowly and are more likely to come together to form a liquid.

Therefore, a combination of high pressure and low temperature is necessary for the gas molecules to be brought close enough together to form a liquid phase. Additionally, the specific properties of the gas, such as its critical temperature and pressure, must also be taken into account in determining whether it is possible to achieve liquification through compression alone.

While compression can increase the pressure of a gas, it cannot cause liquification without also reducing the temperature to a point where the kinetic energy of the molecules is low enough for them to come together and form a liquid phase.

## Why liquids can flow but are not compressible?

Liquids, like gases, have the ability to flow and take the shape of their containers. However, unlike gases, liquids are not compressible. This is because the molecules in liquids are packed closer together than in gases, and the intermolecular forces between the molecules are stronger. These forces are primarily due to Van der Waals forces, dipole-dipole forces, and hydrogen bonding.

When pressure is applied to a liquid, the molecules are unable to compress and move closer together. Instead, the intermolecular forces in the liquid counteract the pressure, keeping the molecules at a fixed distance from each other. This makes liquids highly resistant to compression, and their volume cannot be reduced easily, even under high pressures.

On the other hand, fluids, including liquids, can flow and take the shape of their containers. This is because the molecules in liquids move past each other due to the kinetic energy they possess. However, their movement is limited by the intermolecular forces present in the liquid. As a result, liquids will flow more slowly than gases and are said to have a higher viscosity.

The nature of the intermolecular forces in liquids makes them resistant to compression, making them useful in applications where a liquid is required to maintain its volume or pressure, such as in hydraulic systems. At the same time, their ability to flow makes them useful in a variety of applications from transportation of fluids to medical applications.

## Why gases do not liquefy above their critical temperature?

Gases do not liquefy above their critical temperature because at this point, the liquid and gas phases become indistinguishable from each other. Above the critical temperature, the gas cannot be condensed into a liquid regardless of the pressure applied. This is due to the fact that the critical temperature is the temperature above which there is not enough difference in energy between the gas and liquid phases to allow them to coexist as separate phases.

At a molecular level, the transition from gas to liquid involves the molecules coming closer together as the temperature decreases. In a gas, the molecules are highly energetic and move around rapidly, colliding with one another and bouncing off the walls of the container. As the temperature decreases, the energy of the gas molecules becomes less and less, causing them to move at slower speeds and eventually come closer together.

At some point, the interactions between the molecules become strong enough to form a liquid, and the gas condenses into a liquid phase.

The critical temperature is the highest temperature at which a gas can be liquefied, regardless of the pressure applied. Above this temperature, the energy of the molecules is too high for them to come together to form a separate liquid phase. Instead, the gas phase remains homogenous, with properties like density and viscosity that approach those of a liquid.

The critical temperature varies for different gases and depends on their specific molecular properties, such as size and shape. For example, larger, more complex molecules generally have higher critical temperatures than smaller, simpler molecules because they have more intermolecular forces holding them together.

Gases do not liquefy above their critical temperature due to the lack of a distinguishable difference between the gas and liquid phases. The critical temperature is the point at which the energy of the gas molecules is too high for them to condense into a liquid phase, resulting in a homogenous gas-like state.

The critical temperature varies for different gases and is determined by their molecular properties.

## Why some gases are most difficult to liquify?

Some gases are more difficult to liquify than others because of various factors such as their molecular size, intermolecular forces, and critical temperature.

One of the most critical factors that affect the liquefying ability of gases is their molecular size. Gases that have a larger molecular size tend to have weaker intermolecular forces than smaller gases, making it challenging to liquefy them. This is because the intermolecular forces between the gas molecules are insufficient to overcome the kinetic energy of the gas molecules, which causes them to remain in a gaseous state.

Another crucial factor that affects the liquefying ability of gases is the strength of the intermolecular forces. Gases with strong intermolecular forces require lower temperatures and higher pressures to liquefy because the attractive forces between the molecules are greater. For example, noble gases such as helium and neon have weak intermolecular forces and are, therefore, challenging to liquefy.

The critical temperature of a gas also plays a significant role in its ability to liquefy. This temperature is the highest temperature at which a gas can be liquefied regardless of the pressure applied. Gases with high critical temperatures, such as hydrogen, are more challenging to liquefy than those with low critical temperatures since they require very low temperatures to reach saturation pressure.

Additionally, some gases, such as helium, have very low boiling points and require extremely low temperatures for liquefaction. For example, helium has a boiling point of -268.9°C, which means it must be cooled to near absolute zero to become liquid.

Several factors can make it challenging to liquefy gases, including their molecular size, intermolecular forces, critical temperature, and boiling point. Gases that possess any of these characteristics are often difficult to liquify and remain as gases even under high pressures and low temperatures.

Understanding these factors is essential for various fields, such as cryogenics and chemical engineering industries, which require liquefied gases for many applications.

## Why high pressure can liquefy gases?

The process of liquefying gases involves reducing the temperature and/or increasing the pressure of the gas until it reaches a critical point where the gas transforms into a liquid state. High pressure plays a crucial role in this process as it compresses the gas molecules together, reducing the space between them and increasing their chances of colliding with each other.

This collision between gas molecules generates thermal energy, which in turn increases the internal energy and temperature of the gas.

At high pressure, the intermolecular forces between the gas molecules become stronger, and they start attracting each other. As a result, the molecules lose their kinetic energy and start to slow down, eventually to the point where the intermolecular forces hold them together in a liquid state. This is why gases that are typically found at room temperature and pressure, such as nitrogen and oxygen, can be liquefied at lower temperatures and higher pressures.

When the gas is compressed into a smaller volume, its molecules also tend to come closer together, which makes it easier for them to interact and form bonds with each other. This is what happens when high pressure is applied to gases like CO2, which liquefies at a relatively low pressure of around 5-7 atmospheres at room temperature.

High pressure is a critical factor in the liquefaction process of gases as it compresses the molecules together, increasing their intermolecular forces and facilitating the formation of a liquid state. Understanding the effects of temperature and pressure on gas molecules is essential in various industrial applications, including refrigeration, liquefied natural gas (LNG) production, and gas separation processes.

## What kind of shape does a gas have?

Gas does not have a defined shape or volume, as it is composed of individual particles that are constantly moving and have no set arrangement. The behavior of gas is governed by the kinetic theory, which states that gas particles are in constant motion and occupy all available space uniformly. This means that gas will take the shape of any container that it is placed in, as it expands to fill the available volume.

Additionally, gas particles are capable of compressing and expanding, making it a highly versatile substance that can be used in a variety of applications. Due to its unique properties, gas plays a vital role in many industries and is widely used for heating, cooling, and propulsion purposes. while gas does not have a set shape or volume, its dynamic properties make it a valuable and versatile substance that has countless applications in science and industry.

### Resources

1. Gases have no definite shape or volume. – Lido Learning
2. Why do gases have neither a fixed shape nor a fixed volume ?
3. Why do gases have no definite volume and they can … – Quora
4. Why does a gas have no definite shape and no definite volume?
5. Classifying Matter According to Its State—Solid, Liquid, and Gas