Monday Rec., Hylan102 : LUSENET : UR General Chemistry : One Thread

To my monday 104 recitation students, I will hold an extra recitation next week as I told you I would if the exam was going to be on the 2nd. I will discuss it with you on Monday about scheduling it. Good Luck with studying.

-- Anonymous, February 23, 2000


can i come to you today, i hvae a question about numbers 30-32. Or if you like you could help me out over the net. Wwll, I really do not understand how to begin question number 30. Wuth question number 31, I don't underdtand how to calculate dShot. The same thing applies to question number 32. How do you calculate dS.

-- Anonymous, February 24, 2000

There is already an answer posted about number 31 and 32. Look and see if that helps you.

30. To find q you add together n*Cp*dT for ice, water, and vapor + dHfusion and and the dHvaporization. You should end up 56.8kJ.

at constant pressure q = dH

Work is only done when vaporiztion occurs and when vapor exands as temperature increases. So since w=P*dV, you must find V at 100C and 140C and the V of water.

Vwater = grams/density = (18g) / (1g/mL)= 18mL = 0.018L

V100C = (n*R*T) / P = 30.6L

V140C = (n*R*T) / P = 33.9L

Then w = -P*dV1 - P*dV2 = -3.43kJ

where dV1 = V100C-Vwater and V2 = V140C-V100C

dE = q + w = 53.4kJ

You find dS by added up the parts like you did for q where dS=n*Cp*ln(T2/T1), include fusion and vaporization where dS=dH/T. dS=163J/K

I hope this is helpful.

-- Anonymous, February 24, 2000

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