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Gas and liquid along with solids make up the different states of matter. Matter is defined as a collection of particles which has mass and also occupies space. These different states of matter exist in nature because of the differences in their molecules. For example, solids possess a very definite size and shape. On the other hand, liquids are comparatively more flexible and will therefore take up the shape of the container they are contained in. As for gases, they diffuse in the environment in order to fill up the available volume completely.
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| Table of Content |
Key Takeaways: Matter, Solid, Liquid, Gas, Volume, Mass.
What is Gas?
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Gas is characterised by its inherent ability to have a structure wherein it lacks a definite shape and size. Gases take up the shape of the containers in which they are placed. Among all the states of matter, the energy of the gas is the highest. The force of attraction between the molecules is minimum in the case of gases. Furthermore, the molecular arrangement in gas is sparsely arranged; however, it has the characteristic of being random in nature.
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The points pertaining to the features of gases can be summarised as follow:
- Gases do not possess any exact volume or shape.
- They have very little intermolecular force of attraction. The atoms and molecules move freely and are separated from each other.
- Rotatory, Vibratory and Translatory motions can be easily observed in the case of gases.
- Gases possess the highest compressibility and thermal expansion among all the states of matter.
- Gases can be converted into liquids via the process of condensation. Example of gas: Oxygen
What is Liquid?
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Liquid has a definite value of volume. However, it has no definite shape. Liquid possesses a medium amount of energy. There is a sparse arrangement of molecules in a liquid. The force of attraction between the molecules of a liquid is medium in nature. Furthermore, the molecules predominantly move around in Brownian motion.
A container is specifically needed to store liquids as it has a definite volume but lacks a fixed shape.
The points pertaining to the features of liquids can be summarised as follow:
- Liquids have a constant volume and are capable of changing their shape according to the vessel they are put into by flowing.
- In a fluid, atoms, and molecules adhere loosely. Here, the particles of the liquid roam around but also exist side-by-side.
- Liquids are mechanically weaker than solids but stronger than gases.
- Liquids can be changed into solids through the process of solidification and into gases through the process of evaporation.
- Compressibility, as well as thermal expansion of liquids, is higher than solids.
Example of liquid: Water
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Difference between Gas and Liquid
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As it is commonly observed, both liquids as well as gases are fluids, which implies that they have the potential to flow. However, there are numerous variables upon which these two matters are differentiated from each other.
| Parameters of Comparison | Gas | Liquid |
|---|---|---|
| Definition | Gas has no definite shape or size. However, it confines to the shape of the container it is placed in. | Liquid has a definite volume, but it does not have any definite shape. |
| Energy Possessed | High. | Medium. |
| Molecular Arrangement | Sparsely Arranged. | Less sparsely arranged. |
| Attraction between the molecules | Minimum. | Medium. |
| Movement of Molecules | Movement of random, free and stagnant in nature. | Brownian motion. |
| Storage | They are required to be stored in an air-tight or sometimes pressurized closed container. | A normal container can be used for storage. |
| Compression | Easily Compressed. | Not easily compressed, it needs energy for the process. |
| Direction of Flow | Flows in all directions. | Flows from a region which is high to a region which is at a lower level. |
| Intermolecular space | Large spaces. | Less as compared to gases. |
| Speed of Sound | Lowest in comparison to all the states of matter. | Speed is faster then gas but is comparatively slower than solids. |
| Shape, size, volume | No fixed shape or volume. | Definite volume but it lacks fixed shape. |
Things to Remember
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- Matter exists in the environment in four forms, namely, solids, liquids, gases, and plasma.
- The intermolecular forces are at play between the particles of any matter. These forces are different from the electrostatic forces which exist between the two oppositely charged ions.
- Liquids don’t have any fixed shape, nor do they occupy any fixed volume. However, they are slightly compressible and can easily take the shape of their containers.
- Gases don’t have any fixed shape, nor do they occupy any fixed volume. However, gaseous substances are highly compressible and occupy the shape of their containers by taking up the entire volume of the container.
- The force of interaction between the gas molecules are almost negligible and are almost independent of their chemical nature.
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Sample Questions
Ques 1. Calculate the total number of electrons which are present in 1.4 g of dinitrogen gas. [3 marks]
Ans.
Molecular mass of N2 = 28g
28 g of N2 has No. of molecules = 6.022 x 1023 1.4 g of
N2 has No. of molecules = 6.022 x 1023 x 1.4 g/28 g
= 3.011 x 1022 molecules.
Atomic No. of Nitrogen (N) = 7
1 molecule of N2 has electrons = 7 x 2 = 14
3.011 x 1022 molecules of N2 have electrons
= 14 x 3.011 x 1022
= 4.215 x 1023 electrons.
Ques 2. A particular mix of gases, namely, dihydrogen and dioxygen at one bar pressure, contains around 20% by weight of dihydrogen in the mix. Find the partial pressure of dihydrogen. [3 marks]
Ans.
As the mixture H2 and O2 contains 20% by weight of dihydrogen, therefore, if H2 = 20g, then O2 = 80g
Ques 3. The critical temperatures of CO2 and CH4 are 31.1°C and -81.9°C respectively. Which of these two gases has presence of a stronger intermolecular force and why? [2 marks]
Ans. It has been a common observation that higher the critical temperature of the gas, more easily will the gas be able to get liquefied. This implies that greater the intermolecular forces of attraction, the easier it will be to compress the gas into a liquid. Thus, Co2 has stronger intermolecular forces than CH4 as a consequence of its higher critical temperature.
Ques 4. What are ideal and real gases? Out of CO2 and NH3, which is expected to demonstrate higher deviation from the ideal gas behaviour? [2 marks]
Ans.
Ideal Gas: It refers to a gas that strictly follows Boyle’s law, Charles’ law and Avogadro law strictly. Furthermore, it is also assumed that intermolecular forces of attraction are not present between the molecules of an ideal gas.
Real Gases: It refers to the gases which deviate from the ideal gas behaviour.
Out of the two gases given, NH3 is expected to show more deviation. Since NH3 is polar in nature, it can be liquified easily and demonstrate deviation from the behaviour of an ideal gas.
Ques 5. State and explain Dalton’s law of partial pressures. Is it possible to apply Dalton’s law of partial pressures to a mixture of gases such as carbon monoxide and oxygen? [3 marks]
Ans:
Dalton’s law of partial pressure: In a condition, wherein any two or more non-reacting gases are tightly enclosed in a vessel, in such as case, the total pressure of the gaseous mixture then becomes equal to the sum of the partial pressures that each gas will exert when they are enclosed separately in the same vessel at a particular constant temperature.
P= P1 + P2 + P3
Here, P refers to the total pressure of the three gases A, B, and C which are enclosed in a container.
Furthermore, P1 , P2 and P3 refers to the partial pressures of these three gases when they are enclosed separately in the same vessel at a given temperature but one by one.
No, the law cannot be applied to the gas mixture. This is because carbon monoxide and oxygen readily combine to form another gas, namely carbon dioxide and the law can be applied only to the non-reacting gases. Therefore, the law won’t be applicable.
Ques 6. Calculate the minimum pressure which will be required to compress 500 dm3 of air at 1 bar to 200 dm3 at 30°C? [3 marks]
Ans.
Given, Initial pressure, p1 = 1 bar
Initial volume, V1 = 500 dm3
Final volume, V2 = 200 dm3
As the temperature remains constant, the final pressure (P2) can be determined using Boyle's law.
According to Boyle's law,
P1V1=P2V2
1 bar x 500 dm3 = P2 x 200 dm3 or P2=500/200 bar=2.5 bar
Ques 7. A 120 mL capacity vessel contains a certain amount of gas at 35°C and 1.2 bar pressure. Subsequently, the gas is transferred to another vessel which contains the volume of 180 mL at 35°C. Calculate the new pressure? [3 marks]
Ans.
V1= 120 mL, P1=1.2 bar,
V2 = 180 mL, P2 = ?
As temperature remains constant, P1V1 =
P2V2
(1.2 bar) (120 mL) = P2 (180mL)
Ques 8. Density of a gaseous oxide at 2 bar, at 0°C is the same as that of dinitrogen at 5 bar. Calculate the molecular mass of the gaseous oxide? [3 marks]
Ans.
Using the expression, d =MP/RT , at the given temperature and density,
M1P1 = M2P2 (as R is constant)
(Gaseous oxide) (N2)
Or
M1 x 2 = 28 x 5(Molecular mass of N2 = 28 u)
or M1 = 70u
Ques 9. Drainex (drain cleaner) contains small bits of aluminium which further reacts with caustic soda in order to produce dihydrogen gas. Calculate volume of dihydrogen at 20 °C and one bar which will be released when 0.15g of aluminium reacts with caustic soda? [3 marks]
Ans.
The chemical equation for the reaction is
2 Al + 2 NaOH + H?0 → 2 NaAlO? + 3H? (3 x 22400 mL At N.T.P)
2 x 27 = 54 g.
54 g of Al at N.T.P release
H2 gas = 3 x 22400 0.15 g of Al at N.T.P release
Ques 10. Calculate the pressure which will be exerted by a mixture of 3.2g of methane and 4.4g of carbon dioxide which are contained in a 9 dm3 flask at a temperature of 27 °C. [3 marks]
Ans.
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