Why Is the Sum of I2 to I5 Used in This Ionization Energy Calculation?

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Discussion Overview

The discussion revolves around the calculation of ionization energy for the process of ionizing a magnesium atom to form a Mg5+ ion. Participants are examining the use of specific ionization energies (I2 to I5) in this calculation and the application of Hess's Law.

Discussion Character

  • Homework-related
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions why the calculation uses the sum of I2, I3, I4, and I5, suggesting it should be I6 - I2 instead.
  • Another participant provides the reaction equations for each ionization energy (I1 to I6).
  • There is uncertainty about whether I1 should be included in the process, with some arguing it is not needed.
  • Participants discuss the nature of I6, with one clarifying that it represents the transition from Mg5+ to Mg6+.
  • There is a suggestion that both I1 and I2 may be necessary to go from Mg(0) to Mg2+.
  • Further clarification is sought on which reactions are required to progress from Mg+ to Mg5+.

Areas of Agreement / Disagreement

Participants express differing views on the inclusion of I1 in the calculation and the correct approach to determining the energy required for the ionization process. The discussion remains unresolved regarding the necessity of certain ionization energies and the correct application of Hess's Law.

Contextual Notes

There are limitations in the clarity of the relationships between the ionization energies and the specific process being analyzed, as well as the assumptions about the starting state of the magnesium atom.

Who May Find This Useful

Students studying ionization energy calculations, particularly in the context of chemistry and physical chemistry, may find this discussion relevant.

Hooke's Law
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Homework Statement



I1, = 786 kJ molG1 I5 = 16,091 kJ molG1
I2 = 1577 kJ molG1 I6 = 19,784 kJ molG1
I3 = 3232 kJ molG1 I7 = 23,766 kJ molG1
I4 = 4355 kJ molG1 I8 = 29,251 kJ molG1

Determine the energy required in kJ molG1 for the following process:
M(g)^+ ------> M^5+(g) + 4 e



The Attempt at a Solution



I saw the solution sheet and it says "E = 25,255 kJ/mol (Sum of I2, I3, I4 and I5) Use Hess’s Law"

But why is it I2 to I5 and I thought it should be (products - reactants)
which I thought is I6 - I2. Could someone explain to me?

Thanks
 
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Write reaction equation for each Ix.
 
I1 =M(g) ---> M^+(g) +e
I2= M+(g) ----> M2+ + e
I3 =M2+ ----> M3+ + e
I4 = M3+ ----> M4+ +e
I5 = M4+ ----> M5+ + e
I6 =M5+ ----M6 + +e

What's next?
 
Did I do them right?
 
OK, now, which reactions have to be combined?
 
I still don't understand. What I'm thinking is still I6 - I1...
 
I1 is about starting with Mg(0) - do you have Mg(0) in the process?
 
No, I1 won't be in the process.
 
What if I tell you that I6 is NOT Mg(0) -> Mg6+?
 
  • #10
Oh in my other previous post it should I6-I2. For I6 isn't it I6 =M5+ ----M6 + +e?
 
  • #11
Yes, I6 is Mg5+ -> Mg6+.

What reactions are needed to go from Mg(0) to Mg2+? Is I1 enough, or do you need I1 AND I2?
 
  • #12
I'm thinking I1 and I2 is needed.
 
  • #13
Yes, you need both. Now, which ones do you need to go from Mg+ to Mg5+?
 

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