Solve eight original mixed cases, explain the assumptions, then compare feedback and revise.
These public tasks combine ledgers, representations and changed conditions. They sample Unit 2 reasoning; they are not a secure exam, full-unit mastery score, unseen assignment or practical-lab assessment. Your existing six Unit 1 cases keep their own counts and history.
Write a reason before recording. First/latest responses and up to three attempts remain saved with known exposure. Your explanation stays editable after feedback and is not a locked first-attempt explanation. A nonempty explanation is not automatically correct. Older imports preserve existing first responses and known exposure.
0/8 attempted; 0/8 first responses match the keys. These counts award no completion or mastery and do not alter existing achievements.
Separate force, separation work and a barrier
An original potential packet sets U(infinity)=0. At a selected separation U=−2 eV and dU/dr=−4 eV/Å. Enter the signed external quasistatic work in eV to separate the pair to infinity. In your explanation give the force direction using F=−dU/dr, and explain why neither number establishes an activation barrier or reaction rate.
Quantity / representation
Packet value
Selected potential
−2 eV
Local derivative
−4 eV/Å
Reference potential at infinity
0 eV
Write a reason before recording. This checks only that text is present, not its correctness. Your explanation stays editable and is not a locked first-attempt report.
0/3 attempts retained. No feedback exposure is recorded.
Combine charge and distance changes
For an original isolated unlike-ion model U=kq1q2/r, both charge magnitudes double while separation becomes 1.5 times the original. Enter the new/old magnitude ratio |Unew|/|Uold|, to at least six decimal places if needed. Explain the energy sign and why this does not determine a real solid’s stability or the force ratio.
Quantity / representation
Packet value
Charge product multiplier
4
Separation multiplier
1.5
Potential model
U=kq1q2/r
Write a reason before recording. This checks only that text is present, not its correctness. Your explanation stays editable and is not a locked first-attempt report.
0/3 attempts retained. No feedback exposure is recorded.
Repair a balanced electron budget that fails a shell
Construct CH2O with central C bonded to two H and one O. A proposed graph has all three bonds single, three lone pairs on O and none on C/H. The valence budget is 12 electrons. Which repair retains the budget and satisfies the ordinary C/O octets and H duets? Explain the original carbon count and formal charges after repair.
Quantity / representation
Packet value
Original bonds
H–C, H–C, C–O
Original lone pairs
O:3; C:0; each H:0
Valence electrons
4+2(1)+6=12
Write a reason before recording. This checks only that text is present, not its correctness. Your explanation stays editable and is not a locked first-attempt report.
0/3 attempts retained. No feedback exposure is recorded.
Connect a learner graph to domains and overlaps
An original neutral N-centered graph has three N–H single bonds and one N lone pair. Enter the number of electron domains around N. Then name the electron-domain geometry, molecular shape, local sp label within the introductory model, and sigma/pi counts. State why counting only nuclei gives the wrong domain count.
Quantity / representation
Packet value
Bond domains
Three single N–H bonds
Nonbonding domains
One N lone pair
Requested count
All electron domains at N
Write a reason before recording. This checks only that text is present, not its correctness. Your explanation stays editable and is not a locked first-attempt report.
0/3 attempts retained. No feedback exposure is recorded.
Test cancellation after changing shape
Two stipulated equal bond vectors each have magnitude one arbitrary unit and point outward from a central atom. Their included angle changes from 180° to 120°. Enter the magnitude of their sum in the 120° case. Explain both the initial cancellation and why this bond-vector model alone is not a measured molecular dipole.
Quantity / representation
Packet value
Each bond contribution
1 arbitrary unit
New included angle
120°
Useful identity
|u+v|²=|u|²+|v|²+2|u||v|cos θ
Write a reason before recording. This checks only that text is present, not its correctness. Your explanation stays editable and is not a locked first-attempt report.
0/3 attempts retained. No feedback exposure is recorded.
Separate a wire ranking from a bonding claim
An original wire packet at one temperature gives target resistivity three times the reference, target length twice the reference, and target area eight times the reference. Enter the target/reference resistance ratio. Explain whether the result establishes ionic bonding or a specific substitution-site arrangement, and name an additional observation needed for either claim.
Quantity / representation
Packet value
ρtarget/ρreference
3
Ltarget/Lreference
2
Atarget/Areference
8
Write a reason before recording. This checks only that text is present, not its correctness. Your explanation stays editable and is not a locked first-attempt report.
0/3 attempts retained. No feedback exposure is recorded.
Reject the frequency-only energy inference
An original diatomic isotope comparison has target/reference reduced mass 1.5 and harmonic-frequency ratio 0.8. Enter the inferred local stiffness ratio under ω proportional to √(k/μ). Explain why 0.64 is incomplete and why the corrected value still does not give a dissociation-energy ratio or statistical significance.
Quantity / representation
Packet value
Reduced-mass ratio
1.5
Harmonic-frequency ratio
0.8
Coefficient uncertainty
Not supplied
Write a reason before recording. This checks only that text is present, not its correctness. Your explanation stays editable and is not a locked first-attempt report.
0/3 attempts retained. No feedback exposure is recorded.
Combine empirical steps before assigning uncertainty
Use the selected NIST CODATA gas formation enthalpies shown below at 298.15 K. Combine CO2→CO+O and CO→C+O. Enter the conservative endpoint half-width in kJ/mol for the total atomization, treating each source ± value as an input bound. Also derive the central total, the mean per bond, and explain why adding the two separate step-bound widths double-counts a cancelled reference.
Quantity / representation
Packet value
CO₂(g)
−393.51 ±0.13 kJ/mol
CO(g)
−110.53 ±0.17 kJ/mol
C(g)
716.68 ±0.45 kJ/mol
O(g)
249.18 ±0.10 kJ/mol
Write a reason before recording. This checks only that text is present, not its correctness. Your explanation stays editable and is not a locked first-attempt report.
0/3 attempts retained. No feedback exposure is recorded.
Retain a report for a human review
The report includes your current explanation drafts and retained first/latest answers, labeled separately. It includes comparison reasoning only for already exposed cases. Preparing a report does not submit it to anyone or establish independent review.
Source and transfer boundaries
Cases 1–7 use original stipulated packets. Case 8 selects historical NIST CODATA gas formation enthalpies at 298.15 K from CO₂, CO, C(g) and O(g). The enthalpy lesson explains their definitions and bounds.
A reviewer should inspect your species/phase ledger, geometry and carrier reasoning, uncertainty assumptions and distinction between model and measurement. Ask for an unfamiliar case and a separately judged explanation. Saved text and numeric agreement alone cannot supply that judgment.
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