SCIENCE · INVESTIGATE AND EXPLAIN

Keep phase and reaction extent in a formation-enthalpy account

Apply products-minus-reactants with explicit coefficients, standard references and physical states.

Learning outcome: Compare water phases at fixed fuel parameter, then change the fuel parameter alone. Retain the stoichiometric formation sum and heat for.0200 mol reaction.

Starting recap

Review signed energy transfers, dimensional consistency, reaction coefficients, state functions and phase/structural evidence boundaries.

All lessons are open directly. Your saved experiments remain when you leave and return.

Try

With supplied fuel formation−275, CO2−394 and liquid water−286 kJ/mol, reaction enthalpy is2(−394)+3(−286)−(−275)=−1371 kJ/mol fuel.

Open the experiment

Predict

Does replacing liquid product water by water vapor leave the same reaction enthalpy?

Your prediction and reason

Experiment

Compare water phases at fixed fuel parameter, then change the fuel parameter alone. Retain the stoichiometric formation sum and heat for.0200 mol reaction.

Keep reaction coefficients and product phases in formation enthalpy

Worked teaching model · synthetic values · C2H6O(l)+3O2(g)→2CO2(g)+3H2O(selected phase). Rounded supplied formation enthalpies CO2−394, water(l)−286, water(g)−242 and O2 reference0 kJ/mol. Fuel value varied hypothetically; no claim all variants are real ethanol measurements. Same reference temperature and standard-state convention.

Stipulated fuel formation enthalpy: -275 kJ/mol Product water:0=liquid,1=gas: 0 phase

Reset keeps your prediction, captures and practice history.

Calculated evidence under the stated assumptions
Quantity	Value	Unit
Product formation sum	-1646	kJ/mol reaction
Reactant formation sum	-275	kJ/mol reaction
Reaction enthalpy	-1371	kJ/mol fuel
Heat for0.0200 mol fuel	-27.42	kJ
Three-water phase-change difference	132	kJ/mol reaction

Products minus reactants includes stoichiometric factors and the declared physical states.

The zero for O2 refers to the chosen standard elemental reference, not zero internal energy or zero bond energy. Replacing three liquid waters by gaseous waters raises the reaction enthalpy by132 kJ/mol reaction in this supplied table. A molar reaction value must be multiplied by actual reaction extent to obtain sample heat.

Retain the system, phase and structural assumptions with every number. Supplied or calculated evidence is not actual calorimetry, chemical handling or X-ray operation.

Products minus reactants includes stoichiometric factors and the declared physical states.

Observation to attach to a capture

Captures preserve recipes and replay their calculated results. They are synthetic model evidence, not physical measurements.

Understand

Define the thermochemical equation

The packet uses C2H6O(l)+3O2(g)→2CO2(g)+3H2O in the selected product phase. A thermochemical equation includes states as well as formulas and coefficients. Changing liquid water into water vapor changes an endpoint even though the atom balance is identical.

Apply formation enthalpies consistently

Reaction enthalpy is the sum of product formation enthalpies multiplied by their coefficients minus the corresponding reactant sum. With supplied CO2−394, liquid water−286 and fuel−275 kJ/mol, products total−1646 and reactants−275. The difference is−1371 kJ per mole of fuel reacted as written.

Interpret a reference zero

The selected elemental O2 standard reference has formation enthalpy zero by convention. It does not have zero internal energy, zero entropy or zero energy needed to break its bond. A standard formation reaction creates one mole of a specified substance from reference elements; the zero convention is a consistent bookkeeping origin, not a claim that nature contains an absolute energy-free oxygen state.

Compare product phases

The supplied gaseous water value is−242 rather than−286 kJ/mol. Three waters therefore raise the product sum by3×44=132 kJ/mol reaction. At the same fuel parameter, the gas-water reaction is less exothermic by that amount. Comparing a gas-phase bond-energy estimate with liquid-water formation data without this correction mixes different reactions.

Scale to a sample

For a stipulated extent.0200 mol with liquid products, heat under the appropriate constant-pressure/only-PV-work assumptions is−27.42 kJ. The molar value is not itself the heat of every sample. The fuel formation parameter is varied hypothetically to test the ledger, not presented as multiple measured values for one real ethanol state. Retain the reference temperature, phase choices and actual extent before interpreting an energy result as a material property.

Sources and evidence boundary

Conceptual sources checked 30 October 2026: Standard formation enthalpy. All prose, cases, code and diagrams are original. The supplied models are not measured structures, a performed laboratory investigation or certification of independent mastery. No chemical handling, heating, pressure vessel or cryogenic experiment is requested. Retain predictions, contrasting evidence and a changed-case explanation.

Apply

Public practice checks a specific claim. It does not establish independent mastery.

Why does zero standard formation enthalpy for reference O2 not mean zero bond energy or internal energy?

Your explanation and limitations

Continue

Completion requires a saved prediction, at least one capture and a reflection. Presence checks do not grade your reasoning.

Skipping retains experiments and awards no mastery.

Previous: Test an enthalpy network instead of averaging incompatible paths Next: Distinguish average bond energies from a reaction-specific enthalpy

Save a science backup or import one

Science work is stored locally in this browser, separately from mathematics and AI. It does not sync automatically. Use this science-only backup; this checkout's older all-subject export does not include science.

A legacy file is available only when the complete snapshot fits the 36 MB limit. For larger snapshots, prepare a complete file set below; never discard notebooks to make a smaller file.

Choose a science backup (maximum 36 MB)

Matching imported notebook drafts replace their current drafts. Omitted lessons and known first attempts remain. Export your current work first if you want to retain both drafts.

Complete file sets and course backups

A file set can hold more work than one science file. Keep its manifest and every part together. Each file is limited to 36 MB. This format needs this version of LearnAI or a compatible newer version; older versions can use only the legacy single-file backup above.

Export scope

The set includes every saved science course and global continuation at this moment. Later edits need a new export. A conflicting tab exports its own visible work, which may differ from saved work in another tab.

Choose the manifest and all parts together

0 file(s) selected. File order and filenames do not determine identity. Missing, changed or conflicting parts block the entire restore; no good part is applied by itself.

Science storage: loading. No account or remote computation is required.