# chemistry

that's a little vague.
Are you dealing with ideal gases? If so you would use the formula PV=nRT

P = pressure
V = volume of container
n = moles (grams/molar mass)
R = gas constant (0.0821)
T = temperature

sorry about that go read Jon's post we have the same homework we don't get what the person said

Couldn't you make it a little easier than having us scroll through an HOPE we find one by Jon. I found one that deals with Pb and water and asking for the final T. What did you use for specific heat of lead and specific heat of water? That may be the error. Post your work here and we can find the error for you.

the specific heat for Pb=.1276 and water is 4.18

Suppose a piece of lead with a mass of 14.9g at a temperature of 92.5c is dropped into an insulated container of water. The mass of water is 165g and its temperature before adding the lead is 20.0c. What is the final temperature of the system?

chemistry - bobpursley, Thursday, March 15, 2007 at 3:37pm
The sum of the heats gained is zero (some will absorb heat)
ml*cl*(Tf-92.5) + mw*Cw*(Tf-20)=0
solve for Tf.

I have copied the problem I think you are talking about to this location. Post your work and I can find your error. The 4.18 J/g*c for water is correct and I found 0.129 for lead but your value rounded would be 0.128 and I don't think it would make that much difference.

my book has Pb=.1276 but whatever this is all I have
(165g)(Tf-20.0)(4.18j/g.c)=
(14.9g)(100.0-Tf)(129j/g.c

thats from the equation q=(m)(T)(Cp)

Check the problem numbers again.
The original post I THOUGHT you were talking about gave 92.5 and not 100 for th initial T of Pb. But, you also should have set it up, if you had followed Bob Pursley's suggestion, as
165(Tf-20.0)(4.18) + 14.9(Tf-92.5)=0
I get final T about 20.2.

thats correct I was thinking of another problem thanks for the answer but how did you get 20.2?

Just do the algebra. Post your work and I can find your error.

165 x 20.0 x 4.18= 13794
14.9 x 92.5= 1378.25

You just multiplied some numbers. In doing so, you omitted half the problem. Where is the unknown?
I don't intend to work the problem for you. But here is what you SHOULD have done to get you started.

165*4.18*(Tf-20.0) + 14.9*0.1276*(Tf-92.5)=0

689.7Tf - 13794 + 1.901Tf - 175.86=0
Solve for Tf.

I got it. I cant thank you enough this was a really confusing problem.

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