# Chemical Forums

## Chemistry Forums for Students => Physical Chemistry Forum => Topic started by: Ice-cream on May 13, 2005, 07:49:24 AM

Title: rault's law, reaction enthalpy
Post by: Ice-cream on May 13, 2005, 07:49:24 AM
hey guys can i have some confirming plz

1. The vapour pressure of pure water at 25 degrees c is 23.8 mmHg. Determine the vapour pressure of water at 25 degrees C above a solution containing 33.2 g of urea (a nonvolatile, nonelectrolyte, MW = 60g/mol) dissolved in 75 g of water.

(i found no. of moles of urea = 0.5533 and no. of moles of water = 4.1667. since P(solution) = x(solvent) x Pure pressure (solvent), P(solution) =  21.01 mmHg.) does anyone agree with my answer?)

2. Calculate the reaction enthalpy in kJ for the formation of anhydrous aluminium chloride

2Al(s) + 3Cl2(g) --> 2AlCl3(s)

from the data:
2Al(s) + 6HCl(aq) --> AlCl3(aq) + 3H2(g)  delta H = -1049 kJ
HCl(g) --> HCl (aq)                               delta H = -73.5 kJ
H2(g) + Cl2(g) --> 2HCl(g)                     delta H = -185 kJ
AlCl3(s) --> AlCl3(aq)                            delta H = -323 KJ

(the answer i got was -1399kJ...does anyone agree?)

thanx
Title: Re:rault's law, reaction enthalpy
Post by: GCT on May 13, 2005, 12:59:48 PM
hey guys can i have some confirming plz

1. The vapour pressure of pure water at 25 degrees c is 23.8 mmHg. Determine the vapour pressure of water at 25 degrees C above a solution containing 33.2 g of urea (a nonvolatile, nonelectrolyte, MW = 60g/mol) dissolved in 75 g of water.

(i found no. of moles of urea = 0.5533 and no. of moles of water = 4.1667. since P(solution) = x(solvent) x Pure pressure (solvent), P(solution) =  21.01 mmHg.) does anyone agree with my answer?)
seems alright to me as long as mole fraction of water = your x