AP Chemistry Problem





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Discus: SAT/ACT Tests and Test Preparation: October 2003 Archive: AP Chemistry Problem
By Mo222 (Mo222) on Saturday, October 04, 2003 - 12:40 pm: Edit

When 5.00 mL of ethyl alcohol, C2H5OH(l) (d=.789 g/cm^3) us burned in a bomb calorimeter, the temperature in the bomb rises from 19.75 to 28.67 degrees celcius. The heat capacity of the calorimeter is 13.24 kJ/C. Calculate q for the combustion of 1 mol of ethyl alcohol.

By Mo222 (Mo222) on Saturday, October 04, 2003 - 05:23 pm: Edit

HELP

By Mo222 (Mo222) on Saturday, October 04, 2003 - 05:53 pm: Edit

Q = C_cal * /\T
Q = (13.24 kJ/C)(28.67 C - 19.75 C)
Q = 118 kJ

5.00 mL * ( 1 cm^3 / 1 mL )*(.789 g / cm^3)* ( 1 mol / 46.07 g) = 0.0856 mol C2H5OH

1 mol *(118 kJ / .0856 mol) = 1380 kJ

Okay I got it... Now I just don't know why its actually -1380 kJ....

By Mo222 (Mo222) on Saturday, October 04, 2003 - 06:01 pm: Edit

Oh ok, its because the 118 kJ is aborbed by the bomb, but released by the ethyl alcohol...I get it now...


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