Matter in Our Surroundings
Category : 9th Class
Matter in Our Surroundings
Chapter Overview
Science has been classified into different branches due to its enormous expansion and diversified fields. Chemistry is one of its important branch.
"Chemistry is the branch of science which deals with the study of structure, composition and properties of matter".
Thus, it is important to know about the matter and its classification.
Matter can be defined as, "Anything that occupies space, possesses mass, offers resistance and can be felt by one or more of our senses."
For example, air is matter, it can't be seen but its presence can be felt by us. Air has mass and occupy space. Gases like carbon-di-oxide, nitrogen mono-oxide etc. can't be seen but can be filled in cylinders. Their masses can be calculated by weighing them and their volume can be measured by the cylinders comprises of these gases. Thus, these gases are matter.
The massless substances like heat, sound, electricity, light, waves are not matter, similarly the vacuum is also not matter as these all do not have mass and do not occupy space.
Modern scientists classified the matter into two ways:
Physical Classification: According to this classification, matter is of three types:
(a) Solid, (b) Liquid, (c) Gas.
(ii) Chemical Classification: According to this classification, matter is classified as:
The various things around us exists in three forms. These are solid, liquid and gas. These three forms differ from one another with respect to their shapes, sizes, colours, hardness or fluidity.
Solid, liquid and gas are the three states in which the matter on the earth may exist.
Some examples of solid, liquid and gaseous state of matter present on earth are as follows:
Solid: Book, table, pen, chalk, blackboard, chair, coin, sugar, salt, ice, rice, pulses, grains, stones, iron, sand, gold etc.
Liquid: Water, oil, alcohol, milk, soft drink, chloroform, juice, petrol, kerosene oil etc.
Gas: Air around us as nitrogen, oxygen, hydrogen, carbon dioxide, ammonia, CNG (Compressed Natural Gas) etc.
It is quite obvious that these states of matter have been built from the constituent particles only. They differ with respect to the inter particle spaces as well as inter particle forces between.
In case when these are very strong, then the particles will be quite close to each other. However, if these are weaker then the particles constituting a particular matter will stay apart. These intermolecular forces are definitely responsible for the different states in which matter can exists i.e., solid, liquid and gaseous state.
4.1 Packing of Constituent particles and force acting on them
Let us discuss the packing of constituent particles and the force existing there in solid, liquid and gaseous state.
Fig. 4.1: Closely packed particles in solid state
(a) Solids: in solids the particles are closely packed. The inter particle spaces between them is about \[1\overset{\circ }{\mathop{A}}\,\] or \[{{10}^{-10}}\] m. There is a strong force of attraction between the particles of solid which holds them together. Thus, the position of particles in solid are fixed. Due to this strong force of attraction, solids have definite volume and cannot be compressed.
Thus, the form of matter, which possesses rigidity have definite volume, definite shape and incompressible in nature is known as solid.
(b) Liquids: in liquids particles are close together, but they are not as close as in solids, i.e., the particles are somewhat loosely packed. The inter particle space between them is in order of \[{{10}^{-7}}\]to \[{{10}^{-9}}\] m. There is strong inter particle force of attraction but not so strong as in solids. This force is quite strong which can keep the particles together but not strong enough to keep them in fixed position. So due to comparatively less strong inter particle forces, the particles of a liquid can move from one position to another within the liquid. Hence, the liquid have the property to flow.
Fig. 4.2 : Comparatively less close packing in liquids than in solids
Thus, the form of matter, which possesses fluidity, have definite volume but not definite shape and almost incompressible in nature, is known as liquids.
(c) Gases: In gases, the particles are much farther apart from one another as compared to solids and liquids. The inter-particle spaces between the particles are very large. So, the inter- particle forces of attraction are the weakest. Due to the weakest force of attraction the particles of gases are free to move in any direction i.e., they can move about in the whole space available to them. Gases neither have fix inter-particle spaces nor fix inter-particle force of attraction that's why gases do not have fix volume and fix shape. They acquire the shape of that container in which it is filled and acquire also the volume of that container where it is filled. Because of weakest force of attraction they have significant transitional, rotational and vibrational motion hence, particles of gases have maximum fluidity and highest compressibility.
Thus, the form of matter which possesses fluidity, neither definite shape nor definite volume and have highest compressibility is known as gases.
Properties of States of Matter
(A) Properties of Solids: In solids the constituent particles are held by strong force of attraction. Because of this the particles of solids are packed tightly. The solids are rigid and have high hardness. Some important properties of solids are as
(i) Solids have definite shape.
(ii) Solids have definite volume.
(iii) solids are almost incompressible.
(iv) solids are rigid.
(v) Particles of solids have negligible energy,
(vi) solids do not get diffused.
Fig. 4.3. Moving particles in gases
(B) Properties of Liquids: In liquids constituent particles are held less tightly as compared to the solids. Due to weaker inter-particle forces of attraction liquids have a nature to flow i.e., liquids possess fluidity. Some important features of liquids are as follows:
(i) Liquids do not have fixed shapes
(ii) Liquids show diffusion.
(iii) Liquids occupy fixed volume.
(iv) Liquids have properly to flow but do not have rigidly.
(v) Liquids have lesser density.
(vi) Liquids show diffusion.
(vii) On increasing temperature the kinetic energy of particles of liquids increases due to which the rate of diffusion also increases.
(C) Properties of Gases - In gases, the particles are much farther apart from one another as compared to solids and liquids. The inter-particle spaces or distance between the particles of gases are very large. The inter-particle forces of attraction between the particles of gas is negligible.
So, the motion in the particle of gases are high. Some important properties of gases are as follows :
(i) Gases do not have fixed shape and volume.
(ii) Gases have maximum fluidity and least rigidity.
(iii) Gases are highly compressible.
(iv) Density of gases are low.
(v) Kinetic energy of gases is high.
(vi) Pressure due to gaseous particles.
(vii) Diffusion of gases is very fast.
(viii) Gases expand on heating.
Comparison of General Properties of Solids, Liquids and Gases
The differences between solids, liquids and gases are as follows:
|
|
Property |
Solid |
Liquid |
Gas |
|
1. |
Shape and volume |
Definite shape and volume |
Indefinite shape but definite volume Weak |
Indefinite shape as well as volume Very weak |
|
2. |
Inter-particle forces of attraction |
Very strong |
definite volume Weak |
|
|
3. |
Density (mass/ volume) |
High |
Lesser than solid while greater than gas |
Very low density |
|
4. |
Inter-particle spaces |
Very small, particles are closely packed |
Comparatively large. Particles are loosely packed |
Very large, Particles are very loosely packed. |
|
5. |
Compressibility |
Negligible |
Very small |
High |
|
6. |
Rigidity and fluidity |
Very hard and rigid but not fluid |
Less rigid but have fluidity |
Compressible, least Rigid but highly fluid |
|
7. |
Diffusion |
Negligible |
Slow |
Very fast |
|
8. |
Molecular motion or kinetic energy |
Very low |
Comparatively high |
Very high |
|
9. |
Surface |
Many number of surfaces |
Only one upper surface |
No surface |
|
10. |
Particle motion |
Particle only vibrate about its position |
Particles show transitional, rotational and vibrational motion. |
Particles have maximum freedom. It shows transitional, vibrational and rotational motion. |
These three state of matter in terms of inter-particle spaces can be illustrated with the help of fig. 1.4.
(a) 
(b) 
(c) 
Fig. 4.4: a, b and c show the magnified schematic pictures of the three states of matter. The motion of the particles can be seen and compared in the three states of matter.
In our daily life we use celsius scale of temperature for measuring the temperature.
Hence, the common unit of temperature is degree celsius which is used to measure melting points, boiling points etc. Degree celsius is written as \[{}^\circ C\]in short. The melting point of ice on celsius scale is \[0{}^\circ C\](zero degree celsius) while the boiling point of water on celsius scale is \[100{}^\circ C\](hundred degree celsius).
Instead of celsius scale for temperature measurement, two other scales are also known today. The scales are - Kelvin scale and Fahrenheit scale. Kelvin scale used for measuring is also known as absolute scale is used-by the scientists for the research work. Kelvin is the SI unit of temperature which is denoted by the symbol 'K.
The relation between Celsius scale and Kelvin scale is as follows-
Temperature in Kelvin scale = Temperature in Celsius scale + 273
\[T(K)=t{{(}^{o}}C)+273\]
With the help of above given relation celsius temperature can be converted into Kelvin temperature.
Fahrenheit scale is another scale of temperature. It is denoted by\[\left( {}^\circ F \right)\]. The freezing point of water in Fahrenheit scale is \[32{}^\circ F\]while the boiling point of water in Fahrenheit scale is\[212{}^\circ F\].
There are three states of matter i.e., solid state, liquid state and gaseous state. For example, water can exist in three states of matter:
(a) Ice, as solid
(b) Water, as liquid
(c) Water vapours, as gas.
These three states of water can be obtained easily in our daily life. For example, Ice (solid phase) can be obtained from refrigerator, liquid water can be obtained from tap while steam (gaseous phase) can be obtained from boiling water.
At lower temperatures water exists in solid state i.e., in ice form at \[0{}^\circ C\]or below it while at room temperature water exists in liquid state and at \[100{}^\circ C\]water exists in gaseous state that is in the form of steam.
Thus, inter conversion of matter can be achieved in the following two ways -
(1) By changing temperature
(2) By changing pressure.
Effect of Change of Temperature
The order of inter particle force of attraction in the three states of matter is as follows:
gas < liquid < solid
On increasing temperature the inter particle force of attraction decreases because the kinetic energy of particles increases due to which motion of particles increases hence, force of attraction decreases. Thus, we can say that on increasing temperature solid state can be changed into liquid and liquid can be changed into gaseous state.
i.e., \[Solid\xrightarrow[{}]{heat}Liquid\xrightarrow[{}]{heat}Gas\]
Similarly, on decreasing temperature the motion of particle decreases i.e., kinetic energy decreases due to which force of attraction between particles increases hence, gas can be changed into liquid state while liquid can be changed into solid state.
\[Gas\xrightarrow[{}]{cool}Liquid\xrightarrow[{}]{cool}Solid\]
This can be understood more clearly by these topics:
(i) Solid to Liquid state (Melting): As discussed earlier that when heat is supplied to solid, its temperature increases and hence, kinetic energy of its constituent particles increases due to which their motion increases. If the temperature is further increased then the energy supplied in the form of heat overcomes the force of attraction between the particles and hence, one state is changed into another state, i.e., solid can be changed into liquid state.
For example-The melting point of ice is \[0{}^\circ C\]or 273.16 K. The melting point of rhombic sulphur is \[95{}^\circ C\]or 368 K, melting point of wax is \[63{}^\circ C\]or 336 K etc.
(ii) Liquid to Gaseous state (Latent heat of Vaporisation) : 'The' amount of heat energy that is required to change 1 kg of a liquid into vapours at atmospheric pressure at its boiling point is called Latent heat of Vapourisation."
(iii) For example: The latent heat of vapourisation of water at \[100{}^\circ C\] is\[~22.5\times {{10}^{5}}\] Joule per kilogram. It means that \[~22.5\times {{10}^{5}}\] Joules heat is absorbed by one kilogram of water at its boiling point \[(100{}^\circ C)\] when it changes into gaseous state at \[100{}^\circ C\] and will have more energy than the particles of water at the same temperature. Thus, steam is more effective than boiling water for heating purposes. It can be understood as, the burns caused by steam are much more severe than those caused by boiling water though both have same temperature of\[100{}^\circ C\]. It is due to the fact that steam contains more energy in the form of latent heat, than boiling water.
Gaseous State to Liquid State (Condensation)
The process of conversion of gas or vapours to a liquid by cooling is called as condensation.
In other words, we can say that the process of conversion of matter from a more random state to a less random state is called as condensation.
For example, when we cool steam by lowering its temperature then it is converted into liquid water because on cooling the kinetic energy of particle decreases due to which their motion slow down and they come more closer together until they start being attracted to each other. In this way, gaseous state changes into liquid state. Actually, condensation process is reverse of boiling or vapourisation. For example, the boiling point of water is \[100{}^\circ C\] at one atmospheric pressure while the condensation temperature of steam is also \[100{}^\circ C\] at one atmospheric pressure.
Thus, Solid State\[\underset{cool}{\overset{heat}{\longleftrightarrow}}\]Liquid State \[\underset{cool}{\overset{heat}{\longleftrightarrow}}\]Gaseous State
(iv) Solid State to Gaseous State (Sublimation): "Sublimation is a process during which a solid on heating, changes directly into the vapour phase without passing through the liquid state."
Therefore, Solid \[\underset{cool}{\overset{heat}{\longleftrightarrow}}\] Vapour (or Gas)
The solid substance which undergoes sublimation is known as sublime while the solid which is obtained by cooling the vapours of solid is called sublimate. The examples of solids which undergo sublimation on heating are naphthalene, camphor, dry ice (solid\[C{{O}_{2}}\]), iodine, ammonium chloride, mercury (II) chloride, anthracite, benzoic acid etc.
The phenomenon of change of liquid into the vapour state at any temperature below the boiling point of the liquid is called evaporation:
Factors affecting Evaporation:
(i) Surface Area
(ii) Temperature
(iii) Strength of inter-particle forces
(iv) Humidity
(v) Speed of wind
(vi) Nature of Liquid
Fig. 7.1: Interchange of Three States
Difference between Boiling and Evaporation
In both cases i.e., in boiling and in evaporation liquid form is converted into gaseous form yet, there is a large difference between these two process. The difference is as follows:
|
|
Evaporation |
|
Boiling |
|
(1) |
It occurs spontaneously at all temperatures. |
(1) |
When vapour pressure of liquid becomes equal to atmospheric pressure, boiling occurs. |
|
(2) |
Evaporation is a surface phenomenon. |
(2) |
Boiling is the phenomenon of entire liquid and takes place in the form of bubbles inside the liquid phase. |
|
(3) |
Evaporation is slow process. |
(3) |
Boiling is fast process. |
|
(4) |
Evaporation always causes cooling. |
(4) |
No cooling is caused during boiling. |
|
(5) |
Evaporation of liquid takes place of its own. |
(5) |
It occurs only when liquid is heated. |
Gases > Liquids > Solids
Gas > Liquids > Solid
Gas > Liquid > Solid
(a) Temperature
(b) Surface area
(c) Humidity
(d) Wind speed
Solid \[C{{O}_{2}}\]is known as dry ice.
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