Effect of Temperature and Pressure on States - UNSOLVED PRACTICE SET

Q7. Why does water boil at a lower temperature at high altitudes like in Shimla or Darjeeling?

Q8. Explain how a pressure cooker works. Why is it especially useful in hilly regions?

Q9. What is the triple point of a substance? Why is the triple point of water defined as 273.16 K?

Q10. Why does skating on ice become difficult if the temperature is very low?

Q11. What is the effect of increasing pressure on the melting point of ice? Is this behaviour typical of all substances?

Q12. Why does CO₂ not exist as a liquid at atmospheric pressure?

Q13. Explain the effect of temperature and pressure on the states of matter using a phase diagram. Discuss the significance of the triple point and critical point.

Q14. Explain why the melting point of ice decreases with increasing pressure, while the melting point of most other substances increases with pressure. Use Le Chatelier's principle in your explanation.

Q15. Discuss the working of a pressure cooker. How does it increase the boiling point of water, and why does this reduce cooking time?

Q16. The normal boiling point of water is 100°C at 1 atm (101.325 kPa). The enthalpy of vaporization is 40.7 kJ/mol.

(a) Using the Clausius-Clapeyron equation, calculate the boiling point of water at 0.8 atm (approximate pressure at an altitude of 2000 m).

(b) Calculate the boiling point of water in a pressure cooker where the pressure is 2 atm.

(c) If pasta requires 10 minutes to cook at 100°C, estimate the cooking time at the pressure cooker temperature (assume cooking rate doubles for every 10°C rise).

Q17. The triple point of water is at 0.01°C and 611.7 Pa. The critical point is at 374°C and 22.1 MPa.

(a) Convert the triple point temperature to Kelvin.

(b) Explain why water cannot exist as a liquid above 374°C regardless of pressure.

(c) If the atmospheric pressure on Mars is about 600 Pa, predict whether liquid water can exist on Mars and explain your reasoning.

Q18. In your school science project, a student investigates the effect of pressure on boiling.

(a) She heats water in a flask and stops when it boils at 100°C. She then seals the flask and inverts it, pouring cold water over it. The water begins to boil again. Explain this phenomenon in terms of vapour pressure and boiling point.

(b) She calculates that at Mount Everest (altitude 8848 m, pressure ≈ 0.33 atm), water boils at about 70°C. Explain why it is difficult to cook potatoes or rice at this altitude, and how mountaineers overcome this problem.

(c) The student then studies the phase diagram of CO₂. At 1 atm, CO₂ sublimes at −78.5°C. Explain why CO₂ is called 'dry ice' and why it is used in stage shows and for preserving ice cream in India.

(d) A classmate suggests that if we increase pressure enough, we can make water boil at 200°C. Is this possible? Explain using the concept of the critical point.

(e) In the Indian context, discuss how traditional cooking methods (like using a handi or degchi with a tight lid) implicitly use the principle of increased pressure to cook food faster, and compare this with modern pressure cookers.