Show work or include as much as explanation as needed to support the calculation

Question

Show work or include as much as explanation as needed to support the calculation. If you write just the final answer, you will not get full credit. Round off answer to correct SF. Zinc metal reacts with hydrochloric acid according to the equation: Zn(s) + 2HCl(aq) rightarrow ZnCl_2(aq) + H_2(g) When 0.183 g Zn metal combined with 58.0 mL of hydrochloric acid in a coffee-cup calorimeter, the initial temperature of 22.5 deg C increases to a maximum of 24.2 deg C. Assuming the density of the solution is 1.00 g/mL and its specific heat is 4.184 J/g deg C, calculate the delta H for the reaction per mole of zinc.

Explanation / Answer

Zn (s) + 2 HCl (aq) ---------->ZnCl2 (aq) + H2 (g)

Step-1 Calculate the moles of Zn

Molar mass of Zn = 65.38 g /mol

Moles of Zn = Weight of Zn/ Molar mass of Zn

(0.183) / (65.38 g /mol) = 0.002799 mol Zn

Step-2 Calculate H of Zn

q = m CT

q = heat energy gained or lost by a substance

m = mass = 58ml x 1g/ml = 58 g

C= specific heat = 4.184 J/g·ºC as

T = change in temperature = 24.20 C – 22.50C = 1.7 0C

q = 58g x 4.184 J/g·C x 1.7 0C = 412.54 J

q rxn = - 412.54 J

H = (- 412.54 J) / (0.002799 mol)

= - 147388. 35 J/mol

= -1.47 x 10^2 kJ/mol

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