In a coffee cup calorimeter, 1.50 g of Mg(s) is dissolved in 100.0 mL of excess

Question

In a coffee cup calorimeter, 1.50 g of Mg(s) is dissolved in 100.0 mL of excess hydrochloric acid solution originally at 20.00. If the final temperature of the solution is 88.9?, determine the ?? for the reaction below in units of kJ/mol Mg. (Assume that the specific heat capacity of the solution is 4.18 J/g'C, and that the total mass of the solution is 100.0 g. Also, assume that none of the heat is lost to the calorimeter.) Mg(s) 2HCl(aq) ? MgCl2(aq) H2(g) ??-??? + + a) -467 kJ/mol b) -28.8 kJ/mol c) 71.9 kJ/mol d) -122 kJ/mol e) -57.6 kJ/mol

Explanation / Answer

q = m*s*DT

m = total mass of solution = 100 g

s = specific heat of solution = 4.18 j/g.c

DT = 88.9 - 20 = 68.9 C

q = 100*4.18*68.9

= 28.8 kj

No of mol of Mg reacted = w/Mwt

                = 1.5/24.3

                = 0.0617 mol

DHrxn = -q/n

      = - 28.8/0.0617

      = -467 kj/mol

answer: a

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