Interconversion of States Melting Boiling Sublimation - UNSOLVED PRACTICE SET

Q7. Define melting point and boiling point. How do they differ from freezing point and condensation point?

Q8. Why does the temperature remain constant during melting even though heat is being supplied?

Q9. What is sublimation? Give two examples of substances that sublime.

Q10. Distinguish between evaporation and boiling.

Q11. Why does a pressure cooker cook food faster than an open vessel?

Q12. What happens to the boiling point of water when salt is added to it? Explain why.

Q13. Explain the process of melting at the molecular level. Why does the temperature remain constant during phase change? Describe what happens to the arrangement and energy of particles during melting.

Q14. Explain the process of boiling. How does it differ from evaporation? Discuss the factors that affect the boiling point of a liquid.

Q15. Describe the process of sublimation with examples. Explain why some substances sublime while others do not, and discuss the conditions that favour sublimation.

Q16. The melting point of ice is 0°C and its latent heat of fusion is 334 J/g.

(a) Calculate the heat required to melt 50 g of ice at 0°C.

(b) Calculate the heat required to convert 50 g of ice at −10°C to water at 20°C. (Specific heat capacity of ice = 2.1 J/g°C, specific heat capacity of water = 4.2 J/g°C)

(c) Draw a heating curve showing temperature vs time for this process.

Q17. The boiling point of water at 1 atm is 100°C. The latent heat of vaporization is 2260 J/g.

(a) Calculate the heat required to convert 100 g of water at 100°C to steam at 100°C.

(b) Calculate the total heat required to convert 100 g of ice at 0°C to steam at 100°C.

(c) If this heat is supplied by a 1 kW heater, calculate the time required for each stage.

Q18. In your school science lab, a student investigates the interconversion of states.

(a) She places 20 g of ice at 0°C in a beaker and heats it gently. The ice melts completely in 10 minutes. Calculate the rate of heat supply if the latent heat of fusion of ice is 334 J/g.

(b) She then takes 10 g of naphthalene balls (used in Indian homes to protect clothes from moths) and leaves them in an open dish. After a week, they have disappeared without any liquid residue. Explain this observation and calculate how much heat would be required to sublime 10 g of naphthalene if its latent heat of sublimation is 400 J/g.

(c) The student uses the example of making tea in her kitchen. She heats 500 mL of water from 25°C to 100°C in an electric kettle of 1500 W. Calculate the time required and the cost if electricity costs ₹6 per unit (1 unit = 1 kWh).

(d) A classmate asks why water pipes sometimes burst in winter in hilly regions of India like Shimla or Kashmir. Explain using the concept of freezing and the anomalous expansion of water.

(e) In the Indian context, discuss how traditional methods of food preservation (like making papad, drying mangoes to make amchur, or making ghee) use the interconversion of states. Explain the science behind each method.