a. dHrxn = (n*dHf of products) - (n*dHf of reactants)
You know dHf HCl and ZnCl2. Remember dHf H2 gas and Zn solid are zero.
Substitute and solve for the dH rxn. The approx answer is -150 kJ/mol but that's just a close estimate.
b, 1 mol Zn (about 65.4 g Zn) produces approx -150 kJ so we convert for grams needed for 123 kJ.
That's 65.4 g x (-123/-150) = ?
Post your work if you get stuck.
A piece of zinc reacts completely with hydrochloric acid, HCl(aq), to produce an aqueous solution of zinc chloride, ZnCl2(aq), and hydrogen gas.
a. Use the data shown below to determine the enthalpy of reaction per mole of zinc.
▲Hf of HCl(aq) = –167.2 kJ/mol
▲Hf of ZnCl2(aq) = –488.2 kJ/mol
Zn(s) + 2HCl(aq) → ZnCl2(aq) + H2(g)
b. What mass of zinc must be used for 123 kJ of heat energy to be given off?
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