If 10–4 dm3 of water is introduced into a 1.0 dm3 flask to 300 K, how many moles of water are in the vapour phase when equilibrium is established?

(Given : Vapour pressure of H2O at 300 K is 3170 Pa ; R = 8.314 J K–1 mol–1)

(1) 5.56 x 10–3 mol 

(2) 1.53 x 10–2 mol 

(3) 4.46 x 10–2 mol 

(4) 1.27 x 10–3 mol

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1 Answers

(4)

n = PV/RT = 

= 128 x 10-5 moles

= (3770 x 10-5atm x 1L/0.0821 L atm k-1mol-1 x 300K) = 1.27 x 10-3 mol

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