Why does Cu2+ react with I- to give CuI?

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In summary: The Ksp will tell you how much of a catalyst is needed to make the reaction go faster, and the Nernst equation will tell you how much energy is needed to make the reaction go faster.
  • #1
phantomvommand
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Why does Cu2+ react with I- to give CuI?
According to my teacher,
2Cu2+ + 2I- <--> 2Cu+ + I2-- reaction 1, Ecell < 0
2Cu+ + 2I- --> 2CuI (s) -- reaction 2
Fall in [Cu2+] due to reaction 2 leads to forward reaction in reaction 1 being favoured (by LCP), so Ecell becomes more positive, and thus reaction 1 is now spontaneous and the reaction proceeds fully to form CuI(s).
But doesn't [I-] in reaction1 also fall due to reaction 2? Why does LCP apply, and why does it shift equilibrium rightwards?
 
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  • #2
phantomvommand said:
CuI (s)

That's already an answer, but additionally: check the Ksp.
 
  • #3
Borek said:
That's already an answer, but additionally: check the Ksp.
I understand that CuI will form. But I was thinking that the reaction would stop after running out of (the very little) Cu+ to precipitate away, since no more Cu+ is formed due to the non-spontaneous reaction 1. I am thinking no more Cu+ forms because LCP doesn't favour either side of reaction one, since both Cu+ and I- are used up in reaction 2.
 
  • #4
phantomvommand said:
Fall in [Cu2+] due to reaction 2 leads to forward reaction in reaction 1 being favoured (by LCP),
That should be "fall in [Cu+] due to reaction 2" - not [Cu2+].
Because CuI has very low solubility, the concentration of Cu+ is very small. Essentially, as soon as you make any Cu+, it is removed by precipitation, so reaction 1 continues to go rightwards.
 
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  • #5
mjc123 said:
That should be "fall in [Cu+] due to reaction 2" - not [Cu2+].
Because CuI has very low solubility, the concentration of Cu+ is very small. Essentially, as soon as you make any Cu+, it is removed by precipitation, so reaction 1 continues to go rightwards.
yes, apologies for the typo. So reaction 1 goes rightwards because the effect of a fall in [Cu+] is much greater than for [I-], given the extremely low [Cu+], so LCP still favours the rightward direction? Or does it go rightwards 'by chance', ie the reaction continues when some Cu+ is formed again by chance
 
  • #6
No "chance". It's an equilibrium; leftward and rightward reactions are both occurring all the time. The very low [Cu+] means the rate of the leftward reaction is low.
 
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  • #7
mjc123 said:
No "chance". It's an equilibrium; leftward and rightward reactions are both occurring all the time. The very low [Cu+] means the rate of the leftward reaction is low.
I think you are saying that [Cu+] forms due to the rightward reaction (which exists, but just happens to a very small extent). And then the [Cu+] is precipitated away. I would agree with this.
But does the LCP argument still stand though? That for the same fall in amount of Cu+ and I- due to reaction 2, the effect of the fall is much greater for [Cu+] due to the extremely low quantities, and so the rightward reaction is favoured, in addition to the already existing (but very slow) rightward reaction. I ask this because my teacher explicitly said the Ecell 'turns positive' for reaction 1 due to the forward reaction now being favoured by LCP.
 
  • #8
Yes. You can quantify this using the Ksp and the Nernst equation.
 
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FAQ: Why does Cu2+ react with I- to give CuI?

Why does Cu2+ react with I- to give CuI?

Cu2+ reacts with I- to give CuI because of the difference in electronegativity between copper and iodine. Copper has a higher electronegativity than iodine, meaning it has a stronger pull on electrons. This causes the copper to attract the electrons from the iodine, forming a bond and resulting in the formation of CuI.

What is the chemical equation for the reaction between Cu2+ and I-?

The chemical equation for the reaction between Cu2+ and I- is Cu2+ + 2I- → CuI.

Is this reaction spontaneous?

Yes, this reaction is spontaneous. This is because the overall energy of the system decreases when the reaction occurs, meaning it is thermodynamically favorable.

Can other halides, such as Cl- or Br-, also react with Cu2+ to form a compound?

Yes, other halides can also react with Cu2+ to form compounds. However, the reactivity and resulting compound may differ depending on the halide used.

What is the role of Cu2+ in this reaction?

Cu2+ acts as the oxidizing agent in this reaction, meaning it accepts electrons from the iodine. This results in the formation of CuI and the reduction of Cu2+ to Cu.

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