Question

Zinc metal reacts with hydrochloric acid according to the following balanced equation. Zn(s)+2HCl(aq)→ZnCl2(aq)+H2(g) When 0.106 g of Zn(s) is combined with enough HCl to make 50.6 mL of solution in a coffee-cup calorimeter, all of the zinc reacts, raising the temperature of the solution from 21.5 ∘C to 24.4 ∘C. Find ΔHrxn for this reaction as written. (Use 1.0 g/mL for the density of the solution and 4.18 J/g⋅∘C as the specific heat capacity.)

Answer 1

volume of solution= 50.6 ml, density of the solution = 1 g/ml

mass of the solution = Volume* density= 50.6*1= 50.6 gm

since there is a temperature rise, the reaction is exothermic.  

so enthalpy change = - mass of solution* specific heat* temperature difference= -50.6*4.184*(24.4-21.5)=-614 joules

this much heat is liberated due to the reaction Zn+ 2HCl---->ZnCl2+ H2

mole of Zn used =mass/atomic weight= 0.106/65.38=0.0016

hence enthalpy change = -614/0.0016 J/mole of Zinc=378778.5 J/mole = 378.7785 KJ/mole