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Topic: Thermochemistry Problem?  (Read 2311 times)

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Offline mef131

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Thermochemistry Problem?
« on: November 15, 2009, 12:33:16 PM »
Brass has a density of 8.35 g/ cm^3 and a specific heat of 0.362 J/gC. A brass cube 19.00mm on edge is heated with a flame to a temperature of 95 degrees C. It is then immersed in 20.00 mL of water at 22 degrees C in an insulated container. Assuming the container absorbs no heat and that there is no heat loss, what is the final temperature of the water?

I know that heat lost by the brass is equal to heat gained by the water. So I found the volume of the brass cube and used that to find the mass. After that though, I'm stuck. What's the next step?

Offline ChmNerd111

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Re: Thermochemistry Problem?
« Reply #1 on: November 15, 2009, 04:21:39 PM »
Volume = (19)^3 =6859 mm^3 = 6.859 cm^3
Mass = d x V = 8.25 x 6.859 = 56.587 g
Is this the mass that you got?
Now what you need to do is use mass x specific heat x change in temp for the brass and set it equal to the opposite of the mass X specific heat x change in temp for the water. This is how you indicate that the heat lost by the brass is equal to the heat gained by the water. Your change in temperature is going to be (final temperature) - (initial temperature). I'll indicate final temp as X, because that is what we're trying to solve for. So...

56.587 x 0.362 ( x - 95.0 ) = - 20.0 x 4.186 ( x - 22.0 )

It's all algebra now. Solve for X. Remember your answer should be POSITIVE, because you're looking at the final temp of the water, NOT the brass. Hope that helped.

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