Problem 8.99

Angela 1K
Posts: 80
Joined: Fri Sep 29, 2017 7:05 am

Problem 8.99

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 solutions is 25C, what is the final temperature of this solution?

The solutions manual solves for the enthalpy of the equation like this:

$\Delta Hr=-153.89kJ/mol+2(-167.16 kJ/mol)-2(-167.16kJ/mol)-0=-153.89kJ/mol$

I'm not quite sure where those values come from.

Thanks.

Anh Nguyen 2A
Posts: 36
Joined: Fri Sep 29, 2017 7:05 am
Been upvoted: 1 time

Re: Problem 8.99

2HCl(aq) + Zn(s) -> Zn2+(aq) + 2Cl-(aq) + H2(g)
The products of this reaction Zn2+, 2Cl-) and H2(g) . The enthalpy of formation of H2 is 0, Zn2+ is -153.89 and 2Cl- is 2(-167.16)
=> Enthalpy of formation of the product = (-153.89) + 2(-167.16)
The reactants are 2HCl(aq) and Zn(s). The enthalpy of formation of Zn is 0 and 2HCl(aq) is 2(-167.16)
=> Enthalpy of formation of the reactant = 2(-167.16)
Enthalpy of reaction = products - reactants = (-153.89) + 2(-167.16) - 2(-167.16) = -153.89 (kJ/mol)
The enthalpy of formation values are given in appendix 2A at the end of the textbook.

Mishta Stanislaus 1H
Posts: 45
Joined: Fri Sep 29, 2017 7:04 am

Re: Problem 8.99

On the test will the enthalpy of formation values be provided in the problem or do we have to memorize?

Dylan Mai 1D
Posts: 70
Joined: Sat Jul 22, 2017 3:00 am

Re: Problem 8.99

I think for something like this we would be provided values

Magdalena Palavecino 1A
Posts: 54
Joined: Fri Sep 29, 2017 7:04 am

Re: Problem 8.99

In the previous explanation for this question, how is the ZnCl2 separated? Should we say they are separated into their ionized versions and calculate the enthalpies of each? Isn't the product ZnCl2 and we should use bond enthalpies of two ZnCl bonds? And how is the enthalpy of formation of 2Cl something, is they are two separate molecules? Is is because it is diatomic and takes energy to break them apart?

Magdalena Palavecino 1A
Posts: 54
Joined: Fri Sep 29, 2017 7:04 am

Re: Problem 8.99

How does calculating limiting reactant impact this problem?

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

Re: Problem 8.99

The limiting reactant determines the amount of energy released by the reaction which will help us determine the final temperature

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