Question

Which equation shows a physical change?

Pb(NO3)2 (aq) + 2KI(aq) _ 2KNO3(aq) + PbI2(s)

HCl(aq) + NaOH(aq) _ NaCl(aq) + H2O(l)

2H2O(l) _ 2H2(g) + O2(g)

H2O(g) _ H2O(s)

Answer 1

H2O(g) --> H2O(s)

This is the change of phase from gas to solid, which is a physical change.

The other equations correspond to chemical changes given that the origin subtances are forming different substances

Answer 2

Answer: The correct equation is
`H_2O(g)\rightarrow H_2O(s)`

Step-by-step explanation:

A physical change is defined as the change in which there is change in shape and size of the object and no change in the chemical composition of the substance. In this process, no new substance gets formed.

A chemical change is defined as the change in which chemical composition of the substance gets changed and new substance gets formed.

From the given options:

In first three options, new substances are getting formed and hence they are considered as a chemical change.

Only in last option, there is change in the physical state of matter that is change from gaseous state to solid state. No new substance is getting formed.

Hence, the correct equation is
`H_2O(g)\rightarrow H_2O(s)`