Latent Heat Fusion and Vaporisation - UNSOLVED PRACTICE SET
Chapter: Matter in Our Surroundings | Topic: Latent Heat Fusion and Vaporisation
LATENT HEAT FUSION AND VAPORISATION - UNSOLVED PRACTICE SET
Topic: Latent Heat Fusion and Vaporisation
SECTION NAME
Q1. Which of the following correctly defines the latent heat of fusion?
- Heat required to raise the temperature of 1 kg of a substance by 1°C
- Heat required to change 1 kg of a solid into liquid at its melting point without any change in temperature
- Heat required to change 1 kg of a liquid into gas at its boiling point
- Heat required to change the temperature of ice from 0°C to 100°C
Q2. During the boiling of water in a pressure cooker, what happens to the temperature of water once it starts boiling vigorously?
- It keeps increasing continuously
- It decreases gradually
- It remains constant at 100°C (at normal pressure)
- It fluctuates between 90°C and 110°C
Q3. Why does a wet cloth feel cooler on your body on a hot summer day?
- Water absorbs heat from the cloth
- Water evaporates and absorbs latent heat of vaporisation from your body
- The cloth blocks sunlight
- Water releases heat to your body
QQ4. The latent heat of vaporisation of water is 2260 kJ/kg. What does this value signify?
- 2260 kJ of heat is needed to boil 1 kg of water from 0°C to 100°C
- 2260 kJ of heat is needed to convert 1 kg of water at 100°C to steam at 100°C
- 2260 kJ of heat is released when 1 kg of steam condenses to water at 0°C
- 2260 kJ of heat is needed to melt 1 kg of ice at 0°C
Q5. In which of the following processes is latent heat involved?
- Heating water from 20°C to 50°C
- Cooling hot tea from 80°C to 60°C
- Melting of ice cubes in a glass of lemonade
- Warming your hands near a heater
Q6. When steam at 100°C comes in contact with your skin, it causes a more severe burn than boiling water at 100°C. What is the reason for this?
- Steam has more kinetic energy than boiling water
- Steam first releases latent heat of vaporisation while condensing, and then the water at 100°C releases heat as it cools
- Steam is lighter than water and penetrates deeper into the skin
- Steam contains impurities that cause burns
Short Answer Questions
Q7. Define latent heat of fusion and latent heat of vaporisation. Why is the word "latent" used to describe these quantities?
Q8. Explain why the temperature remains constant during the melting of ice, even though heat is continuously being supplied.
Q9. On a hot day, a student places a few ice cubes in a glass of water. She notices that the ice cubes melt, but the temperature of the water remains at 0°C until all the ice has melted. Explain this observation using the concept of latent heat.
Q10. During the winter season in hilly areas of India, farmers spray water on fruit trees at night to protect them from frost. How does this practice help? Explain in terms of latent heat.
Q11. A student heats a beaker containing ice and water mixture on a Bunsen burner. He records the temperature every 30 seconds and plots a graph. What would be the shape of the temperature-time graph during the phase change from ice to water? Sketch and describe the expected graph.
Q12. Why does sweating help cool down our body during physical exercise or on a hot day? Explain the role of latent heat of vaporisation in this process.
Long Answer Questions
Q13. Explain the process of boiling and evaporation. How are they different from each other? Discuss the role of latent heat of vaporisation in both processes with a suitable example from daily life.
Q14. Describe an experiment to demonstrate the concept of latent heat of fusion. Include the materials required, procedure, observations, and conclusion. How does this experiment help you understand why ice at 0°C is more effective in cooling a drink than water at 0°C?
Q15. When 1 kg of steam at 100°C condenses to form water at 100°C, it releases 2260 kJ of heat. Using this information, explain why steam burns are more dangerous than hot water burns. Also, discuss one practical application of this property of steam in an industry or household setting in India.
Numerical and Application-Based Problems
Q16. Calculate the amount of heat required to convert 2 kg of ice at 0°C into water at 0°C. Given: Latent heat of fusion of ice = 336 kJ/kg.
Q17. 500 g of water at 20°C is heated until it completely changes into steam at 100°C. Calculate the total heat energy required for this process.
Given: Specific heat capacity of water = 4.2 J/g°C, Latent heat of vaporisation of water = 2260 J/g.
Q18. In a school science fair, a student demonstrates that 100 g of steam at 100°C, when condensed and cooled to water at 20°C, releases a large amount of heat. Calculate the total heat released during this entire process.
Given: Latent heat of vaporisation = 2260 J/g, Specific heat capacity of water = 4.2 J/g°C.