Classify the different type of changes that occurs around you
Answers
A change can be defined as an alteration in the physical and chemical properties of matter due to the effect of some kind of energy. Changes take place continuously. Changes in weather, growth in living things, cooking of food, etc, are some of the common changes we see around us.
Changes can be classified in many ways:
Natural and man-made changes:
Some changes occur in nature. They are called natural changes. Our heart is beating continuously. Change in seasons occurs in nature. These changes are examples of natural changes.
Man-made changes:
Some changes are made by human beings. They are called man-made changes.
Slow and fast changes
Some changes take place slowly. They are called slow changes. Growth of plants is a slow change.
Some changes takes place fast. They are called fast changes. Burning of paper is a fast change.
Periodic and non-periodic changes:
Changes which are repeated after regular intervals are called periodic changes. The occurrence of day and night and even the change of periods in your school are examples of periodic changes.
Changes which do not take place periodically, such as freezing of water to form ice, are non-periodic changes.
Desirable and undesirable changes:
Some changes are useful to us. They are called desirable changes. Some changes are not useful to us. They are called undesirable changes. If our food gets spoiled, it is an undesirable change.
Reversible and irreversible changes:
On heating, ice melts and converts into water. Water on cooling, changes into ice at 0°C. This type of change in which a substance can be brought back to its original form is called a reversible change.
A change is said to be irreversible if the substance cannot be brought back to its original form. Rusting of iron and growth of a plant are examples of irreversible changes.
Physical and chemical changes:
A change is said to be physical if no new substances are formed. Physical changes are temporary and can easily be reversed to give back the substances in their previous form. Freezing of water is an example of a physical change.
A change is said to be chemical if new substances with different properties are formed. Chemical changes are permanent and cannot be reversed to give back the substances in their previous form. Burning of paper is an example of a chemical change.
Whatever be the nature of changes they can broadly be categorized as physical or chemical changes.
Both physical and chemical changes are vital to life. We are alive because every minute there is a change going on in our body. Respiration, digestion and photosynthesis in plants are examples of some very important changes.
Physical Changes:
You are familiar with the physical properties of matter. Any change in the physical properties of a substance will result in a physical change.
To bring about a physical change some external force or energy has to be applied. Press a cardboard box and its shape changes. Heat water and it evaporates. Freeze water and it solidifies, and loses its transparency.
Characteristics of a physical change:
Physical changes have some common features.
1. Physical changes are temporary and can be easily reversed. If you cool a saturated solution of sugar in a refrigerator, you will see that sugar crystals are obtained back. Let us understand this characteristic of physical changes through, another example.
Conditions favouring a chemical change:
Chemical changes are always accompanied by some external indications such as production of heat or light, precipitation, change in colour or appearance, etc.
Different conditions are necessary to bring about chemical changes in different substances. Some conditions, which, in general, favour a chemical change, are as follows.
1. Contact:
A chemical reaction between two substances takes place when they are in close contact with each other. For example, as soon as a piece of sodium comes in contact with water, a reaction takes place to give hydrogen and sodium hydroxide. However, sodium and water do not react with each other if they are not in contact.
2. Solution:
In some cases, chemical reactions occur only when the solutions of the reactants are mixed together. For example, baking soda powder and tartaric acid crystals do not react when they are mixed. But, a vigorous reaction occurs when tartaric acid crystals are added to a solution of baking soda.
3. Heat:
Heating is necessary for some chemical reactions. For example, iron and sulphur, when mixed, do not react unless heated. The study of chemical changes occurring due to heat is called thermo chemistry.
4. Light:
A number of chemical reactions take place only in the presence of light. Photosynthesis is a chemical reaction, which cannot take place at night. A photographic plate is affected only when exposed to light. The study of such reactions is called photochemistry
PHYSICAL CHANGE - in physical change, the substance will have a change in its physical properties like state, temperature etc
eg - burning of paper
CHEMICAL CHANGE - in chemical change, the substavnce will have a change in its chemical properties like texture, color, smell, taste etc.
eg - Ripening oof friuts