7th Edition 4.15

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Samantha Ito 2E
Posts: 64
Joined: Fri Sep 28, 2018 12:29 am

7th Edition 4.15

Postby Samantha Ito 2E » Wed Feb 06, 2019 10:50 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 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.

Does anyone know how to solve this?

705192887
Posts: 77
Joined: Fri Sep 28, 2018 12:18 am

Re: 7th Edition 4.15

Postby 705192887 » Thu Feb 07, 2019 9:52 am

Start out by balancing the equation: 2HCl + Zn --> H2 + ZnCl2
Find the limiting reactant (Zinc).
Now use Hess's law to find the Heat of the reaction (ΔHrxn), which is just the sum of the heats of formation of products minus the sum of the heats of formation of the reactants. This should give you the heat in kJ.
Now divide that KJ ]by the moles of zinc in the balanced equation (kJ/ mol Zn)
Use the number of moles of Zn that was put into HCl to eliminate the mol Zn. This gives the total heat that is involved in the reaction (negative, exothermic).
Since the answer is negative (-19.9995 kJ), so if the reaction lost heat, the HCl gained that heat (+19.9995)
equate this value to the formula mCpΔT.
the mass of the solution is found by 800ml x (1g/mL) since the solution's density is the same as water (given by problem)
Hope this helps!

Hai-Lin Yeh 1J
Posts: 89
Joined: Fri Sep 28, 2018 12:16 am
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Re: 7th Edition 4.15

Postby Hai-Lin Yeh 1J » Thu Feb 07, 2019 10:41 pm

Can you explain why you want to find the limiting reactant? What's different about this problem from others where you don't have to find the limiting reactant?


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