Chemistry ICSE Class 6 Important Questions Chapter 5 Changes Around Us
Practice Questions
Question 1.
What is pasteurization ? Who invented it ?
Answer:
Pasteurization is a process that involves heating a food substance to a specific temperature and then rapidly cooling it to a very low temperature, at which it is stored. This helps kill the germs and prevents the food spoilage. This method of food storage was invented by Louis Pasteur.
Question 2.
Name two changes that are desirable as well as undesirable.
Answer:
1. Burning of fuel is desirable for heating or cooking but undesirable when it causes air pollution.
2. Rain is a desirable change but excessive rain that causes floods is an undesirable change.
Question 3.
Mention characteristics of physical change and chemical change.
Answer:
Characteristics of a physical change :
- Generally, the change is temporary and reversible.
- No new substance is formed.
- The chemical composition of the original substance does not change.
- A physical change may cause changes in state, shape, size and colour of a substance.
Characteristics of a chemical change :
- Usually – the change is permanent and cannot be reversed by simple physical methods.
- One or more new substances are formed with composition and properties different from the original substances.
- A chemical change involves an exchange of energy in the form of heat and light.
Question 4.
How dissolving sodium chloride (common salt) in water is a physical change ?
Answer:
When sodium chloride is dissolved, a salt solution is obtained. On heating, the water evaporates and salt is left behind. So the process can be reversed and the chemical composition of water and salt does not change.
Question 5.
List the factors which effect the rate of evaporation.
Answer:
Evaporation increases with an increase in:
- temperature of the surroundings
- surface area of the liquid
- wind speed
- dryness of the air
Question 6.
What is catalyst ? Give example.
Answer:
Some chemical changes require the presence of another substance which does not undergo any change. Such a substance is called a catalyst. Example: Chlorophyll in plants is a catalyst. It helps change water and carbon dioxide to food and oxygen in presence of sunlight but itself does not get changed.
Question 7.
Fill in the blanks.
1. During a change, energy is either or ……………. in the form of heat, light, sound or any other form.
Answer:
During a change, energy is either released or absorbed in the form of heat, light, sound or any other form.
2. In a change of state from solid to liquid or from liquid to gas, heat energy is …………..
Answer:
In a change of state from solid to liquid or from liquid to gas, heat energy is absorbed.
3. In a change of state from liquid to solid or from gas to liquid, heat energy is …………..
Answer:
In a change of state from liquid to solid or from gas to liquid, heat energy is released.
4. Heat is …………… when evaporation of surgical spirit takes place.
Answer:
Heat is absorbed when evaporation of surgical spirit takes place.
5. Heat is …………. when water is added to quicklime.
Answer:
Heat is released when water is added to quicklime.
Question 8.
Give example of energy changes in a chemical change.
Answer:
Energy in the form of heat and light is released in chemical changes which involve burning of a substance.
Energy in the form of sunlight is absorbed in the process of photosynthesis, it being a chemical change.
ICSE Class 6 Chemistry Important Questions