Connect thermodynamic direction, circuit evidence and charge
Solve eight original cases linking entropy, free energy, rate, dissolution, coupled steps and electrochemical evidence.
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Repair an elemental-entropy error
For fictional A2(g)+2B(g)→2AB(g), use assigned standard molar entropies 180, 140 and 160 J/(mol K), respectively. Enter ΔrS° in J/(mol reaction K). Explain why setting the elemental reactant values to zero would be invalid.
Quantity / representation
Packet value
Temperature
All values share one specified reference temperature
Values
A2:180; B:140; AB:160 J/(mol K)
Status
Stipulated reference packet, not a newly measured reaction
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Find a direction crossover with consistent units
A hypothetical process has ΔH°=−30 kJ/mol and ΔS°=−60 J/(mol K), held constant over the considered range. Enter the positive crossover temperature in K. Explain which side favors the forward standard-state direction and name a limitation of extending the result.
Quantity / representation
Packet value
Equation
ΔG°=ΔH°−TΔS°
Approximation
No heat-capacity variation or phase transition included
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Distinguish kinetic evidence from equilibrium evidence
A reaction mixture has independently established Q<K at the observed temperature, but no detectable conversion occurs during a short observation. Which explanation is compatible with both observations? Identify an additional measurement needed to support it.
Quantity / representation
Packet value
Thermodynamics
The actual forward reaction is favored because Q<K
Observation
No detectable conversion during the stated interval
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Avoid confusing low solubility with zero dissolution
For an ideal 1:1 salt with solid present, ΔG°diss is positive and Ksp is small. The prepared unsaturated solution has Q below Ksp. Which conclusion follows? Explain the role of finite solid inventory and activity assumptions.
Quantity / representation
Packet value
Actual-state test
ΔrG=RT ln(Q/Ksp)
Phase
Solid initially present
Assumption
Compatible dimensionless ion activities
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Cancel a shared intermediate before summing
Original steps are A+X→I with ΔG=+35 kJ/mol and I+Y→B+X with ΔG=−50 kJ/mol at compatible conditions. Enter the total free-energy change per mole of A converted, then write the net reaction and explain why an unrelated exergonic process is not enough.
Quantity / representation
Packet value
First step
A+X→I; +35 kJ/mol
Second step
I+Y→B+X; −50 kJ/mol
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Scale a balanced equation without scaling voltage
A balanced three-electron reaction has E°=+0.400 V. Multiply the complete reaction equation by two. Enter the new E° in V, then explain how n, ΔG° and K change.
Quantity / representation
Packet value
Relationship
ΔG°=−nFE°
Operation
Double every coefficient in the complete reaction
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Identify the missing current path
A schematic galvanic cell has the specified favorable redox chemistry and an intact wire, but its ionic connection is blocked. Which diagnosis is supported? Identify where oxidation occurs and how an open-circuit voltage differs from current.
Quantity / representation
Packet value
Circuit
Electronic path intact; ionic path interrupted
Excluded
Short transients, leakage and competing reactions
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Infer charge from a deposited amount
A fictional run deposits 0.00500 mol of metal M through M²⁺+2e−→M at 100% current efficiency. Use F=96485.33212 C/mol e−. Enter required charge in C, then determine how the charge changes at 80% current efficiency and distinguish that assumption from collection loss.
Quantity / representation
Packet value
Deposited amount
0.00500 mol M
Electron requirement
2 mol e− per mol M
Current efficiency
100% for the requested numerical response
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Source and model boundaries
The original packets align with AP Chemistry Unit 9, checked 30 October 2026. All numbers are assigned teaching inputs. They are not official examination items, conducted laboratory measurements or proof of learning effectiveness.
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