. The variation of vapour pressure of different liquids with temperature is shown in figure


(i) Calculate graphically boiling points of liquids A and B

(ii) If we take liquid C in a closed vessel and heat it continuously. At what temperature will it boil? 

(iii) At high altitude, atmospheric pressure is low (say 60 mm Hg). At what temperature liquid D boils? 

(iv) Pressure cooker is used for cooking food at hill station. Explain in terms of vapour pressure why is it so? 


Best Answer

Answer: (i) Boiling point of A = approximately 315 K, B = approximately 345 K 

(ii) Will not boil 

(iii) approximately 313 K 

(iv) A liquid boils when vapour pressure becomes equal to the atmospheric pressure. Water boils at low temperature on hills because atmospheric pressure is low. Therefore even at low temperature vapour pressure becomes equal to atmospheric pressure. 


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