SCIENCE CHAPTER 6 CHANGES AROUND US
Q.4 classify following in physical and chemical changes
Physical changes | Chemical changes |
Melting of an ice-cream Melting of wax Lighting of a bulb Formation of fog Formation of cloud | Baking of cake Burning a paper Boiling of egg Lighting of matchsticks Formation of coal Curdling of milk |
Q.5 Answer the following questions in short.
a.) list three main causes of change
Ans. 1) Pressure
2) Heat
3) Mixing
b) Give two examples of each of the following
i) Man-made changes – 1)Cooking
2)Making dams
ii) Reversible changes – 1) Melting ice
2) Water cycle
iii) Undesirable changes – 1) Earthquake
2) Rotting of food
c) State one difference between desirable changes and undesirable changes.
Q.6 Define the following
a) Irreversible changes :- A change that can not be reversed
Example :- cooking of food
b) Fast change :-changes those occur in short time are called fast changes.
Example :- floods ,burning of fossil fuels
c) Chemical changes :- A change in which both physical and chemical properties are altered and a new substance is formed ia called chemical changes. Example :- Rusting of iron
Q.7 Give reasons
Digestion is a chemical change as well as a physical change
In digestion process food is physically broken down by chewing and chemically broken down by digestive enzymes in the saliva and the acid in the stomach
Metals are used for making tools
Because metal melts on heating and contracts on cooling. That’s why its easy to mould metal in any shape
Q.8
a)How is the melting of wax is different from burning of wax?
Melting of wax is physical change because only physical state is changing from solid to liquid but burning of wax is chemical change because in burning, wax reacts with oxygen present in surroundings and forms carbon dioxide and ash.
b) How does mixing bring about a change? Explain with the help of a example.
When substances are mixed together, it can result either in a physical change or a chemical change. Example: If iron and sulphur are mixed, no chemical change occurs. But when the mixture is heated, it glows after some time and a black substance is formed which is different from iron and sulphur.
c) Why are gaps left between railway tracks?
Metal expands and contracts due to temperature changes. That’s why There is gaps between rail sections to allow for expansion and contraction of the metal in summer and winter due to temperature changes.
Q.11 HOTS( Higher Order Thinking Skills)
Why is the burning of LPG gas considered to be both physical and a chemical change ?
A change in which both physical and chemical changes occur is burning of LPG gas. Liquefied petroleum gas is filled in the cylinder in the form of a liquid. When these liquids come out of the cylinder in the form of vapors, physical change takes place. When these vapors are mixed with air and burn, chemical change takes place.
No comments:
Post a Comment