Question

# Zinc metal reacts with hydrochloric acid according to the following balanced equation. Zn(s)+2HCl(aq)→ZnCl2(aq)+H2(g) When 0.107 g...

Zinc metal reacts with hydrochloric acid according to the following balanced equation. Zn(s)+2HCl(aq)→ZnCl2(aq)+H2(g) When 0.107 g of Zn(s) is combined with enough HCl to make 51.6 mL of solution in a coffee-cup calorimeter, all of the zinc reacts, raising the temperature of the solution from 22.2 ∘C to 24.3 ∘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

Answer - We are given, mass of Zn = 0.107

density = 1.00 g/mL , volume of solution = 51.6 mL, so

mass of solution = 51.6 g , ti = 22.2oC, tf = 24.3oC

We know formula for calculating the heat

q = m*C* Δt

= 51.6 g * 4.184 J/goC*(24.3 – 22.2)oC

= 453.4 J

= 0.4534kJ

We know, ∆H = -q

= - 0.4534 kJ

Now we need to calculate the moles of Zn

Moles of Zn = 0.107 g/65.39 g.mol-1

= 0.00164 moles

So, for 0.00164 moles of Zn = - 0.4534kJ

then for 1 moles of Zn = ?

= - 277.1 kJ/mol

∆Hrxn = - 277.1 kJ/mol

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