CHANGES IN 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. some of these changes are beneficial to us while some are not. Changes can be defined as alteration in physical and chemical properties of matter which give a new shape and properties of matter which give a new shape and properties to it . Changes may involve different kinds of alterations in shape, size, colour, state, composition etc.

 

                                                                 Classification of changes

NAME OF THE CHANGE CHARACTERISTICS EXAMPLE DIAGRAM
i)Natural change It occurs in nature on their own. i)Change of day and night;

ii)Growth of living organism;

iii)Flowering of plant;

iv)Change in weather.

ii) Man-made change This change is brought and controlled by human. i)Burning of wood;

ii)Formation of curd;

iii)Drying of cloth.

Iii) Periodic change It occurs after a fixed interval of time.l i)Phenomenon of day and night;

ii)Swinging of pendulum;

iii)Heart beat;

iv)Recurrence of full moon and new moon.

iv) Non-periodic change These changes do not repeat themselves at regular intervals of time. i)Occurrence of land slide and earth quake;

ii)Rusting of iron;

iii)Burning of fuel;

iv)Breaking of glass.

v) Desirable change Changes which are useful to us. i)Ripening of fruit;

ii)Drying of cloth;

iii)Cooking of food;

iv)Preparation of curd from milk.

vi)Undesirable change The changes which are harmful to us. i)Flooding of river;

ii)Spoilage of food;

iii)Eruption of volcano;

iv)Earthquake.

vii)Fast change The changes which occur within a very short time. i)Burning of match stick;

ii)Bursting of inflated balloon;

iii)Bursting of cracker.

viii) Slow change The changes which take longer duration of time for their completion. i)Rusting of iron;

ii)Freezing of water;

iii)Germination of seed;

iv)Growth of plant.

ix) Reversible change The change which can be reversed by reversing the condition. i)Evaporation of water;

ii)Melting of ice;

iii)Sublimation;

iv)Glowing of bulb.

x) Irreversible change The change which cannot be reversed even by changing condition. i)Burning of paper;

ii)Ageing of living things;

iii)Rusting of iron;

iv)Growth of plant.

xi)Physical change A reversible, temporary change where no new element or compound is formed. i)Melting of ice;

ii)Breaking of chalk;

iii)Tearing of paper.

xii)Chemical change The change which is irreversible and new substance is formed. i)Burning of wood;

ii)Rusting of iron;

iii)Curdling of milk.

 

Physical change brings change in 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 are changed.  Physical properties as well as chemical properties are changed.
ii)Molecular composition It remains unchanged It gets changed.
iii)New substance Not formed New substance is formed.
iv)Type Temporary and reversible Permanent and irreversible.
v)Requirement of energy No or very small amount of energy is either absorbed or evolved. 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

 

                                                  CONDITIONS FAVOURING A CHEMICAL CHANGE

  • Certain conditions which favours a chemical change are described below:
  • Contact between the reacting reacting substances- Reacting substances should be brought in contact like paper and fire.
  • 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-di-oxide.
  • Heat- Some chemical changes occur only on heating like iron powder and sulphur does not react in normal temperature but when this mixture is heated then iron sulphide is formed.

                                                     Fe + S = FeS

  • 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.
  • 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 INVOVES ENERGY

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 ; e.g. when Ammonia Chloride or urea is dissolved in water, energy is absorbed.

 

2)EXOTHERMIC CHANGES ( exo means out and thermic means heat) The change during which heat enegy is evolved is called exothermic change.

It is a reaction where heat is liberated ; e.g. during cooking of food and slaking of lime, the heat is evolved.

 

                             EXPLANATION OF PHYSICAL  AND CHEMICAL CHANGE

  • Dissolution of solid in a liquid is a physical change: Sugar is sweet. It is dissolved 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. In this way, the sugar is easily   recovered from the solution by simple method (crystalline).                                     Therefore, the dissolution of sugar in water is a physical change.
  • Sublimation is a physical change: During sublimation, a solid substance when heated 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 . The  sublimation is a type of change which can easily be reversed by  temperature change. Therefore, sublimation is a physical change.

 

  • Melting of butter is a chemical change:  Butter is an emulsion of fat and water. When, butter is heated the emulsion breaks up and fat get separated from water to form layers. The fat layer which is usually called ghee  is separated.   Ghee and butter are different in properties. We, cannot get back butter from Therefore, melting of butter is a chemical change.
  • Cooking of food is a chemical change: During cooking 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.

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