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Effects of change in temperature on the state of matter:
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Melting |
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When a solid is heated, its molecules begin to gain energy and vibrate. Gradually, they break free and begin to disperse resulting in the melting of the substance. Thus the solid converts into liquid through the process of melting. The temperature at which a substance melts is known as the melting point. The melting point of a substance depends upon the pressure. The melting point of a substance increases with the increase in pressure. Therefore the melting point of a solid is always considered at one atmospheric pressure. |
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Sublimation |
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Some substances transform directly into gases without first converting into the liquid state on heating and similarly they convert into the solid state from the gaseous state on cooling. This type of conversion is known as sublimation. For instance, when dry ice is heated, it converts directly into vapor instead of converting into liquid first. In these cases the gases are known as the sublime substances and the solid that they convert into; on cooling; are known as the sublimates. |
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Evaporation |
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When a liquid is heated, the molecules from its surface start to break away to form vapors. This gradual change is known as evaporation. The rate of evaporation depends upon the humidity and the temperature that it is heated on. Higher the temperature, higher the rate of evaporation is. Humidity and the rate of evaporation are inversely proportional to each other. As we know that the evaporation takes place at the surface level of liquids, the larger the surface of the liquid exposed, the greater will be the rate of evaporation.
During evaporation the temperature of the liquid drops. This is because some molecules in the liquid possessing lower kinetic energy (as compared to the molecules at the surface possessing higher kinetic energy) lower the average kinetic energy of the molecules in the liquid state.
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Boiling |
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Boiling is very similar to evaporation. In boiling, bubbles appear on the surface of the liquid and they rise up to evaporate. Boiling point is the point where the temperature of the liquid remains constant till it converts into vapors.
Boiling point of a liquid changes with a change in the atmospheric pressure. Therefore, the boiling point of a liquid is always considered at one atmospheric pressure. Impurities dissolved in a liquid increase its boiling point and lower its freezing point. |
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Freezing |
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When a liquid is cooled constantly, it gradually freezes. Just like when water is cooled, it freezes to form ice. The freezing point of a liquid is also considered at one atmospheric pressure. Freezing is also known as solidification.
NOTE: when gases are heated, the intermolecular space within increases and the volume of the gas increases. This decreases the attraction between the molecules. This results in the expansion of the gas. |
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Effects of change in pressure on the state of matter: |
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A change in the pressure does not affect the solids much as the inter-molecular space is already low. However, the gases are affected by a change in the atmospheric pressure.
Condensation
Condensation is the conversion of the gases into liquids. On increasing the pressure on gases, the inter-molecular space decreases and the attraction between the molecules increases thereby liquefying the gas.
NOTE: condensation cannot take place with increased temperatures. The temperatures also need to be lowered along with increasing the pressure for complete condensation.
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CHANGES IN MATTER:
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On the application of energy, matter undergoes certain changes. These changes are broadly classified into physical and chemical changes.
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PHYSICAL CHANGES
Matter undergoes a physical change when its shape, size, or state is altered but no change occurs in its chemical composition. In this case, no new substance is formed. The change brought about in this case is usually reversible i.e. the original substance can be obtained again. When we crush a can, we are causing a physical change. When we cool water to form ice, that too is a physical change because the basic substance remains the same only its state changes. Physical changes are brought about by the forces of temperature, pressure and motion.
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CHEMICAL CHANGES
Chemical change in a substance occurs when the substance is altered chemically. It usually results in the formation of at least one new substance. Also, the newly formed substance has different properties from the original substance. Some examples of chemical changes are combustion, electrolysis, tarnishing and oxidation. Chemical changes usually result in color change, precipitation, gas production, temperature change and changes in properties.
NOTE: heating a sugar cube is a physical change because the basic thing is still sugar but burning a sugar cube is a chemical change because the chemical bond within is broken.
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| BASIS |
PHYSICAL CHANGES |
CHEMICAL CHANGES |
| FORMATION OF A NEW SUBSTANCE |
No new substance is formed |
At least one new substance is formed |
| PRODUCTION OF ENERGY |
The substance does not produce energy |
The substance often produces energy |
| CHANGE IN PROPERTIES |
Only physical properties change, chemical ones do not |
Both physical and chemical properties change |
| ATOMIC CHANGE |
Atoms are not rearranged |
Atoms are rearranged into different molecules |
| ABILITY TO REVERSE |
Generally easy to reverse |
Not reversible without further reaction |
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