## 8.99: Enthalpy Values

Shannon Wasley 2J
Posts: 71
Joined: Fri Sep 29, 2017 7:06 am
Been upvoted: 1 time

### 8.99: Enthalpy Values

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 C, what is the nal 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.

I understand the steps, however, I do not understand where we obtain the values of the enthalpies of formation from. I went to Appendix 2A to find them, however I got a different answer than the solution manual for the enthalpy of reaction. I'm not sure whether I calculated wrong or if I am using the wrong values of enthalpies of formation. Can someone calculate the enthalpy of reaction using the enthalpies of formation for this problem?

Oscar Valdovinos 1I
Posts: 29
Joined: Fri Sep 29, 2017 7:05 am

### Re: 8.99: Enthalpy Values

I think the solution manual has a mistake in when calculating the enthalpy of formation, because i notice that the enthalpy for HCL was used twice in their equation.

Tiffany Dao 1A
Posts: 32
Joined: Fri Sep 29, 2017 7:05 am

### Re: 8.99: Enthalpy Values

Since they don't give you the enthalpy of formation of ZnCl2, you need to take it by parts. You need to use the one for Zn2+ and 2Cl-. Cl- is the same as HCl, hence the same number being used twice.

Return to “Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)”

### Who is online

Users browsing this forum: No registered users and 2 guests