## HW 4.15

Hannah Lee 2F
Posts: 117
Joined: Thu Jul 11, 2019 12:15 am

### HW 4.15

Hydrochloric acid oxidizes zinc metal in a reaction that produces hydrogen gas and chloride ions. A piece of zinc metal of mass 8.5 g is dropped into an apparatus containing 800.0 mL of 0.500 m HCl(aq). If the initial temperature of the hydrochloric acid solution is 25 8C, what is the final temperature of this solution? Assume that the density and molar heat capacity of the hydrochloric acid solution are the same as those of water and that all the heat is used to raise the temperature of the solution.

Based on the solutions manual, why does it matter which species is the limiting reactant? How would it change the answer if HCl was the limiting reactant instead of Zn?

Sanjana Munagala_1j
Posts: 103
Joined: Sat Aug 24, 2019 12:17 am
Been upvoted: 1 time

### Re: HW 4.15

If I am not mistaken, if HCl was the limiting reactant, then all of the Zinc would not dissolve which affects the amount of moles of Zinc that are used when determining the standard enthalpy of the reaction. After calculating the enthalpy of the reaction, you get that answer as per mole of the reaction or per mole of Zinc. However, because it was given that you have 8.5g of Zinc, you use this in order to get the enthalpy of the reaction for that given amount of Zinc. If HCl was the limiting reactant, then you would use a number that is probably lower than 8.5g after doing limiting reactant stoichiometry.

Hope that helps!