Suppose that following the procedure of Experiment T (Enthalpy and Entropy Chang

Question

Suppose that following the procedure of Experiment T (Enthalpy and Entropy Changes) you had reacted a 0.950 g sample of MgO with 60.0 mL of 1.2 M HCl according to the reaction MgO(s) + 2H^+(aq) rightarrow Mg^2+(aq) + H_2O DeltaH = ? kJ/mol The initial and final temperatures were 20.0degreeC and 43.0degreeC respectively. If you assume that the specific heat capacity of the solution was 4.184 J/degree-g, and that the density of the solution was 1.00 g/mL, what should you report for DeltaH (in kJ/mol) for reaction (1): (a) 214 kJ/mol (b) -214 kJ/mol (c) 245 kJ/mol (d) -245 kJ/mol (e) 5.8 kJ/mol

Explanation / Answer

HRxn = -Q/n

Q= m*Cp*dT =60.95*4.18(43-20) = 5859.733 J

n = MV = 1.2*60 = 72 mmol = 72*10^-3 = 0.072 mol of HCl

n = mass/MW = 0.95/40.3044 = 0.039 = 0.02357 mol of MgO

excess of HCl so

Hrxn = -5859.733/(0.02357) = 248609.800594 J/mol = -248.609 kJ/mol

nearest answer is D

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