Q5 of 19 Page 13

Do all substances change from solid to liquid and liquid to gas on heating? Explain.

No. Some Solids do not convert into liquid eg Naphthalene balls, woods. It depends on the molecular energy of the solid. Bond Dissociation energy of naphthalene balls particles are very low that’s why it does not convert into liquid. Woods have tightly packed structure. Dry ice is a frozen CO2 at -78.50C CO2 particles have weak wan der val forces. That’s why it converts into gas from solid state.



Fig.7


More from this chapter

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3

"When sugar is dissolved in water there is no increase in volume". Is it true or false?

 4

Is there any change in mass when a substance changes its state? Explain with example.

 6

Define the following terms:

a) melting point


b) boiling point


c) evaporation

 7

Correct the following statements.

a) Water boils at 100°C under atmospheric pressure. 14 Matter Around us


b) a liquid evaporates above its boiling point


c) solids have the largest inter-particle space.


d) gases have the strongest inter-particle forces.