posted by Taylor on .
When 0.702 g of Ca metal is added to 200.0 mL of 0.500 M HCl(aq), a temperature increase of 114C is observed.
Assume the solution's final volume is 200.0 mL, the density is 1.00 g/mL, and the heat capacity is 4.184 J/gC.
(Note: Pay attention to significant figures. Do not round until the final answer.)
The molar heat of reaction, H rxn, for the reaction of
Ca(s) + 2H+(aq) Ca2+(aq) + H2(g)
q = mass water x specific heat water x delta T.
Then q/0.702 gives J/g and multiply by atomic mass Ca to get J/mol, then divide by 1000 to convert to kJ/mol.
But there is no water involved...
What do you think 0.500 M HCl(aq) is? That's 200 mL of 0.5 M HCl(aq) which is mostly water. Only 3.65 grams is HCl. And they specify that the density is 1.00 g/mL so that is 200 g for water. Also, the 4.184 J/g*C listed in the problem is the specific heat for WATER.
When I did the question, i noticed my answer had to be negative. why was that?
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