Science [1 Marks Each] M.C.Q.

The losing of magnetic property is only a physical change as there is no change in the chemical composition of the substance.

All the above are correct.

All other changes are irreversible.

Sugar crystals on heating form new substance caramel and water vapour. Hence, it is a chemical change.

Heartbeat.

Melting of ice and freezing of ice.

Burning of fuels is an example of chemical change.

A change in composition occurs when coal is burnt in air. So, it is a chemical change.

Heat energy is given out.

Change in states.

While fixing the metal rim, it is heated. It becomes slightly larger in size and can be fixed into the wooden wheel. On cooling, it contracts and fits tightly on to the wheel.

When petrol it comes into contact with our skin, it absorbs our body heat and evaporates. It is an endothermic reaction.

Charcoal burning is a chemical change.

Melting of ice.

The low temperature in a refrigerator prevents food from getting spoiled.

It has undergone a chemical change. A new substance (ammonia gas) having different properties is formed. It is an endothermic change requiring high temperature and pressure.

Physical change.

Cooking, as cooked food is different in composition than uncooked food.

Formation of flower from bud.

Are irreversible changes.

In both evaporation and melting heat is absorbed so both of them are endothermic changes.

The burning of a match stick is a fast reaction.

When antacid tablet is dropped in water, it fizzes and form carbon dioxide gas which is a chemical change.

Changes which occur again and again after fixed intervals of time are known as periodic changes. For example, change of day and night, occurrence of full moon, beating of heart, oscillation of pendulum of clock, high and low tides in sea, etc. Changes which do not repeat themselves at regular intervals are called non-periodic changes. You cannot predict when will they reoccur. For example, occurrence of earthquake, accidents, sneezing, rusting of iron, growing of a tree, etc.

Endothermic change.

All the metals expand on heating.

Both occurrence of tides and opening of a morning glory flower are periodic changes.

In both types of changes (i.e. reversible change and physical change) we can get back the original substance by reversing the conditions.

Irreversible change.

Physical change.

The process of heating a liquid to high temperature and rapidly cooling it in order to kill bacteria is called pasteurization.

Iron expands on heating and contracts on cooling. This is a physical change.

Heat is released when you burn petrol. So, it is an exothermic reaction.

Bread is baked.

Change of colour is a physical change.

 All the given changes occur in a physical change.

A chemical reaction in which heat energy is liberated is called an exothermic reaction.

Molten ice cream when cooled gives ice-cream again.

On heating the iron rim, it expands first, then on cooling it contracts and fits onto the wooden wheel.
Note: Expansion occurs on heating whereas contraction occurs on cooling.

The occurrence of days and nights is a natural, periodic change.

On boiling tea, steam is formed. So, due to pressure of steam the cover of tea kettle flew away.

Activation energy.

Irreversible change.

A glass cup falls from the counter and shatters on the ground.

All the above.