Question

Aluminum metal reacts with hydrochloric acid to produce hydrogen gas and aluminum chloride (write a balanced equation). When 1.357 g of Al(s) is combined with 100.0 mL of 3.00M HCl (aq) in a coffee cup calorimeter, all of the aluminum reacts, raising the temperature of the solution from 21.5oC to 38.4oC. Find ΔHrxn in kJ/mol H2. Assume the density of the solution is 1.00 g/mL and the heat capacity is 4.184 J/goC. Attach a sheet of paper to show your work.

Answer 1

volume of solution = 100 mL

mass of solution = 100 g

specific heat = 4.184 J / g oC

temperature rise = 38.4 - 21.5 = 16.9 oC

Q = m Cp dT

   = 100 x 4.184 x 16.9

Q = 7070.96 J

moles of Al = 1.357 / 27 = 0.05026

moles of HCl = 100 x 3 / 1000 = 0.3

2 Al +   6 HCl    ------------> 2 AlCl3   + 3 H2

2          6                                                3

0.05026     0.3

ΔHrxn = - Q / n

           = - 7070.96 x 10^-3 / 0.05026

ΔHrxn = - 140.7 kJ/mol