Chemical Forums
Chemistry Forums for Students => High School Chemistry Forum => Topic started by: mariam amro on September 18, 2015, 06:37:57 AM
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Hello, I got this question in the barron's SAT chemistry review book. But I am confused as to how to solve it.
Which of the following reactions will not occur spontaneously?
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I thought it will be C because Ag is one of the least reactive metals so it's unlikely to react with HCl. But the answer is Cu. Why?
Thank you for your help
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What method do you know to understand if a reaction occurs or not?
Can you describe (one by one) the reactions?
For example: the easiest one is the last one. What reaction is that? Do you think it's gonna be spontaneous?Why?
Be careful with Ag. You're not talking about the metal, but the Ag+ in solution. It's different!
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I thought it will be C because Ag is one of the least reactive metals so it's unlikely to react with HCl. But the answer is Cu. Why?
C is definitely not spontaneous - it involves transmutation of silver into aluminium!
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I thought it will be C because Ag is one of the least reactive metals so it's unlikely to react with HCl. But the answer is Cu. Why?
C is definitely not spontaneous - it involves transmutation of silver into aluminium!
I think it's a mistake! Maybe it's AgCl2 ;D
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Yes you're right the Al is a mistake it's supposed to be Ag
Ok for
A) it is zinc replacing hydrogen gas in an acid. This is spontaneous, because Zn is higher on activity series
B) The reaction of calcium carbonate and hydrochloric acid has positive entropy because a solid changes to a gas.
C) I don't understand what you said about Ag not being the same as Ag+
D) This is oxidation reduction, but I have no clue why it is or isn't spontaneous
E) Acid base neutralization so it is spontaneous.
Furthermore, I know that a spontanous reaction can either have positive entropy change or negative enthalpy change or both.
In this question we can't calculate enthalpy, so we are left with entropy.
Entropy increases if there are more moles of products than reactants, liquid or gas comes evolves from solid reactant. Yes?
Can you give me a hint as to what I am missing.
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C) I don't understand what you said about Ag not being the same as Ag+
You know what are redox reactions (at least you named some reactions as such), but you don't see a difference between metallic Ag and ionic Ag+?
Transmutation of Ag into Al is not the only problem with the reaction C, it is also not balanced and the formula on the right (AlCl2) doesn't make sense. I guess it was intended to be just AgCl.
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You wrote about the activity series for the Zn, what about Cu?
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Do you know how to use this table ??
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*MOD Edit -- remove monster quote*
Hi, Yes I do, I just never knew about the other arrow.
SO this basically says that a strong oxidizing agent will be a weak reducing agent and the opposite is true?
Thanks
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Not quite - the reduced form will be a weak reducing agent.
So e.g. Cl2 is a strong oxidising agent, Cl- is a weak reducing agent.
Li is a strong reducing agent, Li+ is a weak oxidising agent.