When 0.643 g of Ca metal is added to 200.0 mL of 0.500 M HCl(aq), a temperature increase of 105C 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)

The heat given off is mass (you are given 200.0ml*1.00g/ml) times heat capactity (given) times deltaTemp.

divide that by the moles of Ca metal.

check my thinking.

hey the answer was not correct. I multiplied the mass time the heat capacity times the delta temp and divided by the moles of Ca but it still didn't work

ok so you have the delta T is 105

make sure the Ca is the limiting reactants...

how many moles of Ca are there and how many moles of HCL?

okay after you find the limiting reactants then what do u do

1. The first thing that comes to mind, upon reading the question, is that you tried to report too many sifnificant figures in your answer. That means for you to be especially careful when the author says "pay attention to significant figures, do not round until the final step,"

2. I would like to know how you can get the temperature to rise in water above 100 degrees Celsius UNLESS you started off with an ice slush below zero. And that would mean taking the heat of fusion of ice into account but there is nothing in the problem to indicate that. I also note that this is carried out in 0.5 M HCl, instead of plain water, but the amount of HCl there is not enough to increase the boiling oint of water to 105. I think the problem is flawed.
Check my thinking.

200.0 x 4.184 x 10.7 x (1/1000)and divided by (0.655/40.078) and obtained 547.86075 which rounds to 548 kJ/mol to 3 s.f. (the 0.655 g has only 3 s.f. unless you omitted a final zero). So I don't think you've missed anything except you rounded the 0.0163 mols (0.655/40.078 = 0.0163431) and the problem specifically states to round AT THE END. So I left all of those numbers in my calculator and rounded at the end.

In the end, -548 kJ/mol.

Your thinking is correct. The problem seems to be flawed because it doesn't provide enough information to explain how the temperature can rise to 105 degrees Celsius without considering other factors such as the presence of ice or a different solvent. It's important to critically analyze the given information and consider any missing details that could affect the outcome of the problem.