Chemical Changes

Q. Why is there no change in mass during chemical reactions?

Q. (1)

If you leave a piece of iron in the open for a few days, it acquires a film of brownish substance, called rust.​
(a) Do you think rust is different from iron?

(2)

If you leave a piece of iron in the open for a few days, it acquires a film of brownish substance, called rust.​

(b) Can you change rust back into iron by some simple method?

(3)

If you leave a piece of iron in the open for a few days, it acquires a film of brownish substance, called rust.​

(c) Do you think formation of rust from iron is a chemical change?

(4)

If you leave a piece of iron in the open for a few days, it acquires a film of brownish substance, called rust.​

(d) Give two other examples of a similar type of change.

Q.

Rusting of an article made up of iron is called :

1. Corrosion and it is a physical as well as chemical change

2. Dissolution and it is a physical change

3. Corrosion and it is a chemical change

4. Dissolution and it is a chemical change

Q.

The gas we use in the kitchen is called liquified petroleum gas (LPG). In the cylinder, it exist as a liquid. When it comes out from the cylinder it becomes a gas (Change – A) then it burns (Change – B). The following statements pertain to these changes. Choose the correct one.

1. Process – A is a chemical change

2. Process – B is a chemical change.

3. Both processes A and B are chemical changes.

4. None of these processes is a chemical change

Q. (1)
A student took a solution of copper sulphate in a beaker and put a clean iron nail into it and left it for about an hour.​

(a) What changes do you expect?

(2)
A student took a solution of copper sulphate in a beaker and put a clean iron nail into it and left it for about an hour.​

(b) Are these changes chemical in nature?

(3)
A student took a solution of copper sulphate in a beaker and put a clean iron nail into it and left it for about an hour.​

(c) Write a word equation for the chemical change, if any.

Q. A chemical change is involved in the image given below.

1. True
2. False

Q. Why is there no change in mass during chemical reactions?

Q. Burning of wood and rusting of iron bar are examples of ________ changes.

1. physical
2. chemical
3. temporary
4. periodic

Q.

Define rusting. What type of change is it?

Q.

Name the cause of change that takes place during the conversion of water into hydrogen and oxygen.

Q. State whether the following statements are true or false.
Condensation of steam is not a chemical change.

1. True
2. False

Q. Out of the following processes, which is/are chemical change(s)?

1. Cooking gas starts burning on ignition
2. Erosion of rocks takes place to form soil.
3. Iron article undergoes rusting.
4. Effervescense is formed on adding baking soda into a test tube containing dilute acid.

Q. Electrolysis involves ______ change.

1. chemical
2. electric
3. mechanical
4. physical

Q. Choose the example of chemical combination reaction from the following.

1. Coal burns in air
2. Water freezes on cooling
3. Oxygen and hydrogen react to give water
4. Ice melts on heating

Q. Give an example for each change that involves:(a) change in color, (b) evolution of a gas, and (c) production of sound