Changes Around ...

On lighting a candle, Paheli observed the following changes:

(i) Wax was melting.
(ii) Candle was burning.
(iii) The size of the candle was reducing.
(iv) Molten wax was getting solidified.

Among the above changes, those which can be reversed are

Study the dichotomous key and identify the type of change represented by W, X, Y, Z and U.

I. (i) Molten wax is poured into a round mould.
(ii) The candle formed is lighted up. Go to II
II. (i) Melting of wax
(ii) Burning of wax
III. (i) Solidification of the wax on cooling
(ii) Formation of flame

Consider the following statements regarding the physical and chemical changes, and choose the correct option from the table.

A. A physical change is always brought about by heating a substance.
B. A chemical change always involves a change in the state.
C. A chemical change may be reversed under suitable conditions.
D. A physical change is not always reversible.
E. A chemical change invariably results in the formation of a new substance.

	A	B	C	D	E
(1)	x	x			x
(2)		x	x		x
(3)	x	x
(4)		x			x

Which of the following statements are true when milk changes into curd?

(i) Its state is changed from liquid to semi-solid.
(ii) It changes colour.
(iii) It changes taste.
(iv) The change cannot be reversed.

Analyse the two statements given below and select the correct option.

Statement I: 2CO + O₂ 2CO₂ represents a balanced chemical equation.
Statement II: The number of atoms of each type on both the sides of the equation is equal.

Select the decomposition reactions from among the following:

(i)
(ii)
(iii)
(iv)

Rolling of chapati and baking of chapati are the changes that

A chemical change may involve

Paheli's mother made a concentrated sugar syrup by dissolving sugar in hot water. On cooling, crystals of sugar got separated.

This indicates a

Which of the following reactions correctly represents the balanced equation for the combustion of magnesium?

Which of the given changes can be reversed?

What is 'Z' in the given process?

Woollen yarn Z

If the sign '' is used in a chemical reaction, what does it indicate?

Which of the following changes can be reversed?

Which of the following reactions involves a physical change?

In a chemical reaction, _______ are produced as a result of a chemical change.

Which of the following is not a physical change?

Which of the following reactions is always exothermic?

Which of the following changes cannot be reversed?

Salt can be separated from its solution (salt dissolved in water) because