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Malia Shitabata 1F
Posts: 127
Joined: Sat Aug 17, 2019 12:17 am


Postby Malia Shitabata 1F » Tue Feb 11, 2020 6:42 pm

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 25ºC, 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.

Why do we find q in kJ per mole of Zn but then solve q=mC∆T using the parameters for HCl? Why aren't they both for HCl or both for Zn and how do you know which one to use?

Zaynab Hashm 2I
Posts: 110
Joined: Wed Sep 11, 2019 12:15 am
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Re: 4.15

Postby Zaynab Hashm 2I » Thu Feb 13, 2020 9:57 pm

when calculating ΔH(rxn), we find that all except for ΔH(zinc) in the products is not in its most stable state and therefore not equal to 0.

zinc is also the limiting reagent in that reaction, after finding ΔH(rxn) multiply it by moles of zinc which you can find by dividing by molar mass of zinc.

then you use the equation q = mCΔT for the whole system to find ΔT, rearrange equation to solve for ΔT (use ΔH for q).

lastly, use ΔT to find the final temperature because you are given the initial temperature which is 25°C.

hope this helps!

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