A student measures three reactions with a coffee-cup calorimeter to verify Hess's law for the dissolution of NaOH and reaction with HCl: (1) NaOH(s) -> NaOH(aq), delta H1 = -44.5 kJ/mol (2) NaOH(s) + HCl(aq) -> NaCl(aq) + H2O(l), delta H2 = -100.0 kJ/mol (3) NaOH(aq) + HCl(aq) -> NaCl(aq) + H2O(l), delta H3 = ? Reactions (1) and (2) used 2.00 g of NaOH each; (3) used 50.0 mL of 1.00 M NaOH and 50.0 mL of 1.00 M HCl. Combine results to predict delta H3.
From Hess's law, what is the predicted delta H3?
- A
+55.5 kJ/mol
- B
-144.5 kJ/mol
- Ccheck_circle
-55.5 kJ/mol
- D
-22.3 kJ/mol
Explanation
Reaction (3) = (2) - (1): delta H3 = -100.0 - (-44.5) = -55.5 kJ/mol.