Question

The addition of hydrochloric acid to a silver nitrate solution precipitates silver chloride according to the reaction: AgNO3(aq)+HCl(aq)→AgCl(s)+HNO3(aq) When you combine 90.0 mL of 0.150 M AgNO3 with 90.0 mL of 0.150 M HCl in a coffee-cup calorimeter, the temperature changes from 23.49 ∘C to 24.47 ∘C

Calculate ΔHrxn for the reaction as written. Use 1.00 g/mL as the density of the solution and C=4.18J/g⋅∘C as the specific heat capacity.

Answer 1

Number of moles of AgNO3 , n = Molarity x volume in L

                                             = 0.150 M x 0.090 L

                                              = 0.0135 mol

Mass of AgNO3 , m' = number of moles x molar mass

                        = 0.0135 mol x 170 (g/mol)

                              = 2.295 g

Number of moles of HCl , n = Molarity x volume in L

                                        = 0.150 M x 0.090 L

                                       = 0.0135 mol

Mass of HCl , m = number of moles x molar mass

                         = 0.0135 mol x 36.5 (g/mol)

                          = 0.493 g

Therefore total mass = 2.295 + 0.493 = 2.788 g

Heat released , Q = mcdt

Where

m = total mass = 2.788 g

c = specific heat capacity of solution = 4.18 J/goC

dt = cahnge in temperature = 24.47-23.49 = 0.98 oC

Plug the values we get Q = 11.42 J

This is the heat released for 0.0135 mole of HCl

For 1 mole of HCl the heat released = 11.42 / 0.0135 = 846 J

Therefore the enthalpy change = -846 J