Do gases have a definite volume

Complete step by step answer:
We have learnt the lower sections of our classes about the states of matter which are of 3 forms. But, currently scientists consider four states of matter among which one is a man made.
- The three states of matter well known are solids, liquids and gases
- Among these states of matter we are familiar with their definitions as,
Solids are the ones who have rigid structure and which have a definite volume and shape.
Liquids are those which flow in a particular direction and these are having no definite shape and this actually takes the shape of the container.
The third state of matter is that gases are those matters in which the molecules are not held together but they are moving in the random directions. Therefore, these do not have a definite shape.
- Here, solids and liquids have definite shape and mass and similarly even gases have only definite mass because mass of a substance is not dependent on their shape.
- Therefore, gases take the shape of the container and occupy the complete volume of that particular container.
- Thus, the correct answer to this question is that gases have definite mass but no definite volume and shape.
So, the correct answer is “Option A”.

Note: There can be a confusion with the options containing density but note that density changes along with the change in volume even if mass is the same throughout because density is the ratio of mass by volume.

Question 3 Objective Type Questions

Q3) Give reasons for the following.

1. Gases have no definite shape or volume.
2. Liquids have one free upper surface only.
3. Globules of mercury kept in a petri dish, which is shaklen slowly, come together forming a big globule.
4. A crystal of iodine on slow heating in a closed flask, turns into vapours and fills the complete flask.
5. An empty tumbler lowered into a glass beaker containing water, on tilting shows bubbles of air coming out, but when not tilted, no bubbles are seen.

Solution :

1. Gases do not have a definite shape or volume because the molecules in gases are very loosely packed, they have large intermolecular spaces and hence they move around. The force of attraction between molecules is also very less, as a result gases acquire any shape or any volume.
2. Liquids have one free surface because they do not have a definite volume but a shape bounded by the container they are in, so the top surface of the container is the only free surface it has.
3. The formation of big globules is because of the forces of attraction existing between the molecules.
4. The particles of solid are closely packed and occupy less space while particles of gases are loosely packed and occupy the complete space available.
5. When the empty tumbler is tilted, the air inside the tumbler comes out and bubbles of air are seen. The air inside the tumbler was occupying space inside the beaker. When the tumbler is not tilted, the air inside does not come out, hence no bubbles are seen.

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(a) Solids have definite shape and definite volume because the molecules in solid are closely packed and in fixed positions. The molecules can vibrate but do not move around which keeps the shape and volume definite.

(b) Liquids have no definite shape but definite volume because the molecules in liquid are not so closely packed and they have space between them. The molecules can move around and the forces of attraction between molecules is less as compared to solids, so the liquid takes the shape of the container and volume is definite.

(c) Gases do not have a definite shape or volume because the molecules in gases are very loosely packed, they have large intermolecular spaces and hence they move around. The force of attraction between molecules is also very less, as a result gases acquire any shape or any volume.

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1. Why is the state of water different in each picture?
2. Matter and its States
   1. Liquid
   2. Gas
   3. Solid
   4. Plasma
3. Summary
4. Review

 

Figure \(\PageIndex{1}\) (Credit: Iceberg: Courtesy of Rear Admiral Harley D. Nygren, NOAA; Beach: User:Wicki/Wikimedia Commons; Volcano: Courtesy of E. Klett, ​​​​​​​US Fish and Wildlife Service; Source: Iceberg: http://commons.wikimedia.org/wiki/File:Ice_berg.jpg(opens in new window); Beach: http://commons.wikimedia.org/wiki/File:Ocean_Spokojny.JPG(opens in new window); Volcano: http://commons.wikimedia.org/wiki/File:Dds40-097_large.jpeg(opens in new window); License: Public Domain)

Why is the state of water different in each picture?

Water can take many forms. At low temperatures (below \(0^\text{o} \text{C}\)), water is a solid. When at "normal" temperatures (between \(0^\text{o} \text{C}\) and \(100^\text{o} \text{C}\)), it is a liquid. At temperatures above \(100^\text{o} \text{C}\), water is a gas (steam).

The state of water depends on the temperature. Each state (solid, liquid, and gas) has its own unique set of physical properties.

Matter and its States

Matter typically exists in one of three states: solid, liquid, or gas. There is a fourth state of matter called plasma, which rarely exists on earth, but we will omit this from our current discussion. The state a given substance exhibits is also a physical property. Some substances exist as gases at room temperature (oxygen and carbon dioxide), while others, like water and mercury metal, exist as liquids. Most metals exist as solids at room temperature. All substances can exist in any of these three states.

Liquid

Liquids have the following characteristics:

• No definite shape (takes the shape of its container).
• Has definite volume.
• Particles are free to move over each other, but are still attracted to each other.

A familiar liquid is mercury metal. Mercury is an anomaly. It is the only metal we know of that is liquid at room temperature. Mercury also has an ability to stick to itself (surface tension), which is a property that all liquids exhibit. Mercury has a relatively high surface tension, and this makes it very unique. Here you can see mercury in its common liquid form.

Figure \(\PageIndex{2}\): Mercury. (Courtesy of the EPA; Source: http://commons.wikimedia.org/wiki/File:Mercury-element.jpg(opens in new window); License: Public Domain)

If we heat liquid mercury to its boiling point of \(357^\text{o} \text{C}\), and contain it under the right pressure conditions, we would notice all particles in the liquid state go into the gas state.

Gas

Gases have the following characteristics:

• No definite shape (takes the shape of its container).
• No definite volume.
• Particles move in random motion with little or no attraction to each other.
• Highly compressible.

Solid

Solids are defined by the following characteristics:

• Definite shape (rigid).
• Definite volume.
• Particles vibrate around fixed axes.

If we were to cool a sample of liquid mercury to its freezing point of \(-39^\text{o} \text{C}\), and had it contained under the right pressure conditions, we would notice all of the liquid particles would go into the solid state.

As you can see in the video, mercury can be solidified when its temperature is brought to its freezing point. However, when returned to room temperature conditions, mercury does not exist in solid state for long, and returns back to its more common liquid form.

Plasma

Plasma is a state of matter that resembles a gas but has certain properties that gases do not have. Like a gas, plasma consists of particles of matter that can pull apart and spread out, so it lacks a fixed volume and a fixed shape. Unlike a gas, plasma can conduct electricity and respond to a magnetic field. That’s because plasma consists of electrically charged particles called ions, instead of uncharged particles such as atoms or molecules.

Plasma are defined by the following characteristics:

• particles are charged ions and free electrons
• no definite shape
• no definite volume
• conducts electricity
• responds to magnetic field

Summary

• Three states of matter exist: solid, liquid, and gas.
• Solids have a definite shape and volume.
• Liquids have a definite volume, but take the shape of their container.
• Gases have no definite shape or volume.

Review

1. How many states of matter are there?
2. What is a solid?
3. What is a liquid?
4. What is a gas?

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Has gas have definite volume?

Gases have no definite shape or volume.

Why does a gas have no definite volume?

In gases, the particles are very loosely packed and the intermolecular force of attraction is very weak. So the gas molecules can break loose easily from any boundary and can fill up any space. Hence, they do not have any definite volume.

Does gas have a definite mass and volume?

- Thus, the correct answer to this question is that gases have definite mass but no definite volume and shape.

Do gases have a definite mass?

Gases do not have a definite shape but have a definite mass.