Homework Help: chemistry

Posted by christine on Monday, October 25, 2010 at 1:13pm.

Metal Specific Heat (J/g-C)
Al (s) 0.900
Au(s) 0.129
Cu(s) 0.385
Fe(s) 0.444
Hg(l) 0.139
H2O(l) 4.184
C2H5OH(l) 2.46

Using the above table, determine the final temperature if 713.6J is released from a 48.2g sample of copper initially at 93.8o C.

i keep coming up withthe wrong answer for this
i am getting 1822.111
-713.6=28.2(.385)(Tf-93.8)
i am getting 1822.111
but when i punch it back into the equation its wrong
please help

chemistry - DrBob222, Monday, October 25, 2010 at 1:56pm
I don't get 1822.11 no matter how I do it. First, are you using 28.2 g for the metal? The problem states 48.2 g
-713.6 = 48.2*0.385(Tf-93.8) and I get something like 55.3 C. If I check that number, I get this.
q = mass x sp. h. x (Tf-Ti)
q = 48.2 x 0.385 x (55.3-93.8)
q = 48.2 x 0.385 x (-38.5)
q = -714.4 (the small difference is caused by rounding the final T to three s.f. My calculator reads 55.345 and that rounds to 55.3 to 3 s.f. If I used 55.345 I get
q = 48.2*0.385*(55.345-93.8)
q = 48.2*0.385*(-38.455) = -713.61 which is very close.

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