Question

Classify the following as slow or fast change:
(i) Bearing of heat
(ii) Change of seasons
(iii) Burning of paper
(iv) Weathering of rocks
(v) Melting of wax
(vi) Cooking of food
(vii) Burning of wax
(viii) Melting of ice creams
(ix) Curdling of milk
(x) Formation of day and night.

Answer 1

Hint: As we know that the changes can be classified according to the rate of change as slow, fast or moderate. The change of matter depends upon the physical and chemical conditions. There are also physical changes and chemical changes such as rusting of iron is slow it is a chemical change.

Step by step answer:
The fast changes are those changes in which matter does not take time (less than an hour). As the matter comes to contact with anything it starts to change its shape, size or colour or react with another compound or molecule and gives product fast.
The slow changes are the reverse of fast changes. It takes more than a day.
(i) Bearing of heat- it is a fast change because heat when generated from any process it suddenly expands in the surrounding.
(ii) Change of seasons- it is a slow change as the seasons come after a month.
(iii) Burning of paper- it is also a chemical reaction. Paper reacts very fast with oxygen and changes to ash. So, it is a fast change.
(iV) Weathering of rocks-it is a slow change. This process is also called physical change as the rocks are broken into pieces.
(v) Melting of wax- it is also a fast process as we can see at our home when we burn candles the wax melts and reacts with oxygen.
(vi) Cooking of food-it is also a fast change as it does not take much time to cook.
(vii) Burning of wax-it is also a fast change as the melted wax evaporates and reacts with oxygen.
(viii) Melting of ice creams- it is a fast change. As we know that ice absorbs the surrounding temperature and melts into liquid.
(ix) Curdling of milk- it is the slow change as the curdling of milk takes four or five hours to change the state of milk into curd.
(x) Formation of day and night-it is also a slow change. Our earth rotates very slowly around its axis.

Note: There are many slow changes which take billions of years to change its state such as coal, petroleum oil, formation of diamond from graphite. These are natural changes and require very high temperature, high pressure