SCIENCE · INVESTIGATE AND EXPLAIN

Distinguish equilibrium vapor pressure from evaporation speed

Use a supplied temperature relation while keeping phase and reference assumptions explicit.

Learning outcome: Compare20 and40 kJ/mol at280,320,360 K. Retain pressure ratios and identify the reversal around the common reference. Explain boiling at a specified external pressure without a real heating trial.

Starting recap

Review the electron and formal-charge budget, bond multiplicity, signed interaction energies and the distinction between a model and a measured property.

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

Try

Every supplied curve has P=20 kPa at320 K. A larger enthalpy parameter produces a steeper temperature dependence, not a universally lower pressure at every temperature.

Open the experiment

Predict

If two curves share a reference pressure, can increasing the enthalpy parameter lower pressure both above and below the reference temperature?

Your prediction and reason

Experiment

Compare20 and40 kJ/mol at280,320,360 K. Retain pressure ratios and identify the reversal around the common reference. Explain boiling at a specified external pressure without a real heating trial.

Distinguish equilibrium pressure from evaporation rate

Worked teaching model · synthetic values · Fictional liquid with equilibrium P0=20 kPa at T0=320 K. Supplied ln(P/P0)=−ΔHvap/R(1/T−1/T0), R=8.314 J/(mol K), constant positive enthalpy and ideal vapor. Assumes liquid remains present and no phase transition within range. Not real substance data or a vessel/heating protocol.

Vaporization enthalpy parameter: 30 kJ/mol Temperature: 320 K

Reset keeps your prediction, captures and practice history.

Axes rescale. Connected samples represent the supplied continuous parameter relationship; stems denote discrete pairs or steps, not a time trajectory.

Numerical plot coordinates

temperature (K)	equilibrium vapor pressure (kPa)
280	3.994235
285	5.007519
290	6.229106
295	7.691574
300	9.430869
305	11.48644
310	13.90134
315	16.72234
320	20
325	23.78872
330	28.14681
335	33.13649
340	38.82389
345	45.27909
350	52.57603
355	60.7925
360	70.01006

Calculated evidence under the declared representation
Quantity	Value	Unit
Equilibrium vapor pressure	20	kPa
Reference pressure	20	kPa
Pressure ratio to reference	1	ratio
Pressure-temperature parameter	3608.371	K

Equilibrium pressure and the rate of evaporation are different questions.

At the same reference temperature all these stipulated curves share 20 kPa; a larger enthalpy parameter changes their temperature dependence, not an unconditional pressure ranking. Boiling occurs when equilibrium vapor pressure matches external pressure. A sealed equilibrium needs both condensation and evaporation; an empty liquid phase invalidates the specified coexistence model.

Equilibrium pressure and the rate of evaporation are different questions.

Observation to attach to a capture

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

Understand

Equilibrium contains motion

A liquid in contact with its vapor can reach a dynamic equilibrium in a closed system: evaporation and condensation continue but balance on average. Vapor pressure refers to that equilibrium under specified conditions. It is not the same as how quickly an open puddle disappears, which also depends on airflow, exposed area and transport of vapor away from the surface.

Use a declared relation

The workbench supplies ln(P/P0)=−ΔHvap/R(1/T−1/T0), with P0=20 kPa at T0=320 K and R=8.314 J/(mol K). Convert the enthalpy parameter from kJ/mol to J/mol. The relation assumes approximately constant enthalpy, ideal vapor and liquid–vapor coexistence within the chosen range. It is not a universal equation through freezing, a critical point or exhaustion of the liquid.

Read the reference correctly

At T=T0, the reciprocal-temperature difference is zero, so P=P0 for every selected enthalpy parameter. Above the reference temperature, the exponent is positive and a larger positive parameter gives a larger pressure ratio. Below the reference, it gives a smaller ratio. The crossing is intentional: both the reference pressure and temperature dependence were independently stipulated.

Predict a changed reference comparison

At360 K with a20 kJ/mol parameter, the exponent is about0.8353, giving P≈46.1 kPa. Doubling the parameter doubles the exponent, not the pressure, giving roughly106.3 kPa. This mathematical comparison does not establish that an actual substance with stronger attractions must have greater vapor pressure; a real cross-substance comparison cannot silently hold the same reference pressure while changing everything else.

Connect to boiling and molecular identity

Boiling occurs when equilibrium vapor pressure reaches the external pressure. Changing external pressure can change the boiling temperature without changing molecular identity. Vaporization usually separates molecules rather than breaking their internal covalent bonds. A numerical pressure match is a model result, not an instruction to heat or seal material. Retain the equilibrium boundary and the independent reference assumptions alongside every inferred temperature or pressure.

Sources and evidence boundary

Conceptual sources checked 30 October 2026: Phase transitions and vapor pressure. 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.

Which assumptions fail if the liquid is exhausted or the enthalpy varies strongly with temperature?

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: Separate donor identity, acceptance and contact geometry Next: Balance solvation gains against interactions that must be disrupted

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.