Question on CHEM HW

Question

Hi I was attempting this problem earlier but I got it incorrect I would like to know where I went wrong.

Suppose you are investigating the reaction: M(s) + 2 HC|(aq) › MCl2(aq)+

H2(g).

You weigh out a 0.252 gram piece of metal and combine it with 60.5 mL of 1.00

M HCI in a coffee-cup calorimeter. If the molar mass of the metal is 49.36

g/mol, and you measure that the reaction absorbed 126 J of heat, what is the

enthalpy of this reaction in kJ per mole of limiting reactant?

Enter your answer numerically to three significant figures in units of kJ/mol.

Answer 1

M(s) + 2HCl(aq) ==> MCl2(aq) + H2(g) ... balanced equation

From the atomic mass of the metal and the mass that is weighed, we can find the moles of metal used:

mols M = 0.252 g x 1 mol / 49.36 g = 0.00511 mols M

mols HCl = 60.5 ml x 1 L / 1000 ml x 1.00 mol / L = 0.0605 mols HCl

So the limiting reactant is M since it takes 2 mol HCl per mol M and we have more than that amount of HCl

The rest is simple:

126 J / 0.00511 mols = 24,680 J / mol = 24.7 kJ / mole (3 sig.figs.)