8.99

Moderators: Chem_Mod, Chem_Admin

Leah Savage 2F
Posts: 74
Joined: Fri Sep 29, 2017 7:06 am

8.99

Postby Leah Savage 2F » Mon Jan 22, 2018 3:41 pm

8.99 says: 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 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.

Can someone explain what equation and process to use for this problem?

Hannah Chew 2A
Posts: 76
Joined: Fri Sep 29, 2017 7:05 am
Been upvoted: 2 times

Re: 8.99

Postby Hannah Chew 2A » Mon Jan 22, 2018 4:26 pm

You first need to write a chemical reaction between HCl and zinc. This is also a limiting reactant problem, so you need to keep that in mind. Afterwards, you need to solve for the enthalpy of reaction using enthalpies of formation in the book. The energy released by the reaction can be found by multiplying the enthalpy of reaction by the # of moles found from the limiting reactant. This should give you -20.0kJ, which is also the q. You can solve for the final temperature by setting up q = mass x specific heat capacity x delta T, where delta T is the only unknown.

soniatripathy
Posts: 50
Joined: Thu Jul 13, 2017 3:00 am

Re: 8.99

Postby soniatripathy » Mon Jan 22, 2018 5:15 pm

Keep in mind that the question specifies that chloride ions are produced meaning that the products could not be ZnCl2 but rather Zn^2+ and 2Cl^-. This way you can use the information given in appendix 2 to calculate ∆Hrxn

Leah Savage 2F
Posts: 74
Joined: Fri Sep 29, 2017 7:06 am

Re: 8.99

Postby Leah Savage 2F » Mon Jan 22, 2018 5:30 pm

Which enthalpies of formation do you use?

Nickolas Manipud 1C
Posts: 60
Joined: Fri Sep 29, 2017 7:07 am

Re: 8.99

Postby Nickolas Manipud 1C » Mon Jan 22, 2018 8:52 pm

You would use the enthalpies of formation for Zn+, Cl-, Zn (solid), and H+

Leah Savage 2F
Posts: 74
Joined: Fri Sep 29, 2017 7:06 am

Re: 8.99

Postby Leah Savage 2F » Tue Jan 23, 2018 2:29 pm

Where does the solutions manual get 800 g to use in q=mc(delta T)?

Amy Zheng 2l
Posts: 57
Joined: Fri Sep 29, 2017 7:04 am

Re: 8.99

Postby Amy Zheng 2l » Tue Jan 23, 2018 9:15 pm

I think the manual got 800 gram from the idea that 1L of water is approx 1000g. So 800ml of solution would equate to 800 gram. In the question it states to treat it as the same density as water.


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 1 guest