Characteristics of matter
INTRODUCTION:
Substances undergo a wide variety of changes. Many changes take place in nature, for example, the change of weather, the change of a plant into a tree, the formation of cloud, the change of a child into an adult etc, which terms as characteristics of matter. Some of these changes are beneficial to us while some are not. Changes may involve different kinds of alterations in shape, size, color, state, composition etc.
Classification of changes in characteristics of matter
Physical change brings change in the physical state but chemical change brings a permanent change in chemical state. Here is a comparative study of these two changes ….
| KEY CHARACTER | PHYSICAL CHANGE | CHEMICAL CHANGE |
i)Change of properties |
Only physical state and physical properties changes. | Physical properties as well as chemical properties changes. |
ii)Molecular composition |
Unchanged | Changed. |
iii)New substance |
Not formed | New substance forms. |
iv)Type |
Temporary and reversible | Permanent and irreversible. |
v)Requirement of energy |
Absorption or evolve of very small amount of energy. | Relatively large amount of heat is either absorbed or evolved. |
vi)Example |
i)Tearing of paper;
ii)Stretching of rubber band; iii)Glowing of bulb. |
i)Burning of candle;
ii)Curdling of milk; iii)Cooking of food. |
vii)Diagram |
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CONDITIONS FAVORING A CHEMICAL CHANGE IN CHARACTERISTICS OF MATTER
- Certain conditions which favors a chemical change are described below:
- Contact between the reacting reacting substances- Reacting substances should be brought in contact like paper and fire.
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Medium-
Many chemical changes need a medium like dry lime does not react with carbon-di-oxide by lime water turns milky in presence of carbon-dioxide.
Fe + S = FeS
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Light-
Certain chemical changes take place only in the presence of light like photosynthesis in green plants which occurs in presence of sunlight.
6CO2 + 12H2O——-–sunlight and chlorophyll————> C6 H12 O6 + 6H2O + 6O2
- Electricity: Some chemical changes can be brought about with the help of electricity, like acidulated water is decomposed into hydrogen and oxygen when electricity is passed through it.
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Pressure:
An increase in pressure may lead to chemical change like some type of cracker explode when struck with a hammer.
-
Catalyst:
The presence of a suitable catalyst increases the rate of reaction like when Manganese di oxide is mixed with potassium Chlorate rate of evolving oxygen is increased.
2KClO3 —-Mno2 —->2KCl + 3O2
CHANGES INVOLVES ENERGY IN CHARACTERISTICS OF MATTER
1)ENDOTHERMIC CHANGES ( endo means in and thermic means heat): It is a type of change where cooling can be deserved.
GLUCOSE + HEAT FROM THE SURFACE OF TONGUE ————> COOLING EFFECT OF TONGUE.
An endothermic change is the one in which the cooling is observed. Evaporation causes cooling because during evaporation the liquid absorbs heat from the surrounding ;
2)EXOTHERMIC CHANGES ( exo means out and thermic means heat) The change during which heat enegy is evolved is called exothermic change.
EXPLANATION OF PHYSICAL AND CHEMICAL CHANGE
- Dissolution of solid in a liquid is a physical change: Sugar is sweet. We can dissolve in water easily. So the sugar solution tastes sweet that means sugar on dissolution has not lost its basic properties.
If the solution of sugar is concentrated by heating and then cooled; it gives back the crystals of sugar which tastes sweet. Therefore, the dissolution of sugar in water is a physical change. It is a characteristics of matter. -
Sublimation which is a characteristics of matter is a physical change: During sublimation, if we heat a solid substance it changes into vapour form, and the vapour on cooling gives back the substance in solid form.
During the change of state, there is no change in the composition and chemical properties of the substance . Therefore, sublimation is a physical change.
- Melting of butter is a chemical change: Butter is an emulsion of fat and water. Ghee and butter are different in properties. We, cannot get back butter from Therefore, melting of butter is a chemical change found in characteristics of matter.
- Cooking of food is a chemical change: During cooking in characteristics of matter many chemical reactions take place within the food material. The taste and the chemical structure also change. It is not possible to get back the raw food or flour from the cooked food and making of chapatti , all are chemical change.
PROBLEMS RELATED TO CHARACTERISTICS OF MATTER
Qs1: Name a porous solid.
Ans1: Clay which is a porous solid is a characteristics of matter.
Qs2: How is ice changed into water?
Ans2: In characteristics of matter ice changes into water by melting by adding heat.
Qs3: Name the temperature at which a liquid gets converted into solid.
Ans3: Condensation which is also a characteristics of matter.
Qs4: Name to substances which undergo sublimation on heating.
Ans4: Camphor and Ammonium chloride can undergo sublimation.
Qs5: Name a material that can exist as solid, liquid and gas.
SHORT QUESTION
Ans5: Water can exist as solid in ice, liquid in water and gas in steam.
Qs6: Which of the two, germination of seeds or burning or bursting of a cracker is a fast change?
Ans6: Bursting of cracker is a fast change.
Qs7: How is a change useful to us?
Ans7: Physical and chemical changes bring various benefits like, change of day and night, ripening of fruit, digestion of food, germination of seed, preparation of curd from milk.
Qs8: Give one example of the periodic change?
Ans8: Changing of season.
Qs9: In which change there is evolve of change? Ans9: Exothermic change.
Qs10: In which type of change, only the physical properties of the substance change?
Ans10: Physical change.
Qs11: Give one example of change which includes a desirable change, chemical change as well as slow and irreversible change.
Ans11: Formation of curd.
Qs12: When urea is dissolved in water taken in a test tube, the test tube cools down. What type of change is this?
Ans12: Endothermic change.
Qs13: Name some undesirable change.
Ans13: Burning of forest, bursting of cracker, flooding of a river, earthquake, eruption of volcanoes, spoiling of foodstuff, souring of milk.
Qs14: Classify weathering of a rock in as many ways as possible.
Ans14: Weathering of a rock can be classified as:
Undesirable change
Slow change
Non-periodic change
Irreversible change.