Question

0.103 g of Zn(s) is combined with 50.0 mL HCl in a reaction vessel, the temperature changes from 22.5oC to 23.7oC. What is the ΔHof for the Zn2+(aq). Use q = CmΔT, the C for liquid water (4.18 J/g oC), and the density of 1.0 g/mL to calculate the mass of HCl.

Answer 1

Given:

0.103 grams of Zinc (solid) 
50 ml of HCl
Density of HCl = 1.0 g/mL
Initial Temperature (Ti) = 22.5 C
Final Temperature (Tf) = 23.7 C

Solve for the mass of HCl:

50 mL * 1.0 g/mL = 50 g

Assume that the Cp for HCl is similar to the Cp of water:

q = mCpdT
   = mCp (Tf - Ti) 
   = 50 g * 4.18 J/gC * (23.7 - 22.5)
q = 250.8 J = H