# Lewis structure and thermochemistry problems

• staralfur
In summary: BaSO4.In summary, the conversation discusses the incorrect statements in the Lewis dot structure of HOClO2, with the answer being B. The conversation also touches on the concept of formal charge and the most abundant structure. Another question is asked about determining the qrxn per mole of BaSO4(s) formed in a reaction, with the correct answer being -26.4 kJ/mol. The conversation also includes a calculation error that is later corrected.
staralfur
Hi
I have a few questions that I have been working on but I don't get the right answer.

After drawing the Lewis dot structure of HOClO2, pick the incorrect statement of the following.
A. The oxygen bonded to the hydrogen has two lone pairs
B. the oxygens not bonded to hydrogen have three lone pairs
C. The O-Cl bonds are all double bonds.
D. The H-O bond is a single bond
E. Chlorine has a full octet.

I have been looking at this and I would have thought that this Lewis structure would be right as it has the lowest formal charge.
https://upload.wikimedia.org/wikipedia/commons/8/86/Chloric-acid-2D.pngThe The formal Charge for all the atoms would be zero.

If there are only single bonds between the two oxygen and chlorine the formal charge for each of the two oxygen bonded to chlorine would be: 6-6-(1/2)*2=-1
and for the chlorine it would be: 7-2-(1/2)*6=2

I would have thought that the incorrect answer is B and E also because the chlorine would then have an expanded octet.

Am I wrong?
Isn't the most abundant structure the one with the lowest formal charge?

I have another question.

Two solutions, 50.0 mL of 1.00M BaCl2(aq) and 50.0mL of 1.00M Na2SO4(aq), both initially at 21.5 ˚C, are added to a calorimeter with a total heat capacity, after the solutions are added, of 1.10 kJ/˚C and the temperature rises to 22.7˚C. Determine the qrxn per mole of BaSO4(s) formed in the reaction.

My solution:
0.05 moles of Ba2+ and 0.05 moles of SO42- make 0.05 mole of BaSO4(s).
q=n*c*∆T
q=0.1*1100*1.2=132 Joules per 0.05 moles of BaSO4(s) formed
132*1/(0.05)=2640 Joule/mole BaSO4.
What am i doing wrong here?

Last edited by a moderator:
staralfur said:
q=0.1*1100*1.2=132 Joules per 0.05 moles of BaSO4(s) formed
What's the point of multiplying by "0.1?"

A-E are not alternatives, so more than one of them can be right. And I think more than one is.

Bystander said:
What's the point of multiplying by "0.1?"
I thought it was 0.1 as 0.05+0.05=0.1 moles = total moles of reactants.
But I have figured this one out. it says the TOTAL heat capacity is 1100 joules so q=c*∆T = 1100*1.2=1320 Joules. So 1320 Joules for every 0.05 moles formed 1320*1/0.05=26400 Joules

## 1. What is a Lewis structure?

A Lewis structure is a diagram that represents the bonding between atoms in a molecule. It shows the arrangement of electrons and the connectivity of atoms in the molecule.

## 2. How do I draw a Lewis structure?

To draw a Lewis structure, follow these steps:

• Count the total number of valence electrons in the molecule.
• Determine the central atom and draw its skeleton structure.
• Add lone pairs of electrons around each atom until all valence electrons are used.
• Make sure all atoms have a full outer shell.
• If the central atom does not have an octet, you may need to form double or triple bonds to achieve stability.

## 3. What is thermochemistry?

Thermochemistry is the study of the energy changes that occur during chemical reactions and processes. It involves the measurement and calculation of heat and energy involved in chemical reactions and the relationship between energy and chemical bonds.

## 4. How do I solve thermochemistry problems?

To solve thermochemistry problems, you will need to use the following equations:

• q = mCΔT (for calculating heat transfer)
• ΔH = q/n (for calculating enthalpy change)
• ΔH = ΣH(products) - ΣH(reactants) (for calculating enthalpy change of a reaction)
• ΔH° = ΣH°(products) - ΣH°(reactants) (for calculating standard enthalpy change of a reaction)
You will also need to know the values for specific heat capacity (C), mass (m), and change in temperature (ΔT) for the substances involved in the reaction.

## 5. How do I determine the most stable Lewis structure?

To determine the most stable Lewis structure, you will need to follow the following guidelines:

• Atoms should have a full outer shell of electrons (except for hydrogen, which should have 2 electrons).
• Negative charges should be placed on the most electronegative atoms.
• Formal charges should be minimized.
• The structure with the lowest energy is the most stable.
Additionally, you can use the concept of resonance to determine the most stable Lewis structure, where multiple structures are possible and the actual structure is a combination of all resonance structures.

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