chap 10 chem AM

Question

If the molar heat capacity of 1.00 M HCl is the same as that for water [c_P = 75.3 J/(mol∙°C)], what is ΔH_rxn?

Answer 1

Mg(s) + 2HCl(aq) ==> MgCl₂(aq) + H2(g) ... balanced equation

mols Mg present = 2.06 g Mg x 1 mol/24.3 g = 0.0848 mols

mols HCl present = 96.6 ml x 1 L / 1000 ml x 1.00 mol/L = 0.0966 mols

Since it takes 2 mols HCl for each mol Mg, HCl is limiting.

Use q = mC∆T

q = heat = ?

m = mass = 0.0966 mols

C = 75.3 J/molº

∆T = change in temperature = 8.4º

q = (0.0966 mol)(75.3 J/molº)(8.4º)

q = 61.1 J