---
tags: [video, hyperframes, thermodynamics, real-gas, critical-point, teaching]
confidence: high
sources: [js/co2_data.js, js/physics.js, js/schedule.js, js/timeline.js, SCIENCE_QA.md]
last_updated: 2026-10-29
---

# HF-PCHEM-002 Storyboard

**Can Pressure Alone Turn a Gas into a Liquid?**
Compressing CO2 at two temperatures

1920 x 1080, 30 fps, 90 s, silent (built to be understood without narration). All on-screen text is English.
Made from the filled-in prompt template in `showcase/prompts/` (Part A: how to work; Part B: this video).

## System and numbers

| | A | B |
|---|---|---|
| Content | 1 mol CO2 | 1 mol CO2 |
| Bath (constant temperature) | 20 °C (below T_c = 31.0 °C) | 40 °C (above T_c) |
| Molar volume | 500 -> 55 cm³ mol⁻¹, then back to 120 in scene 5 | same piston schedule |
| Pressure | 37.2 bar -> 57.3 bar (droplets) -> flat -> 66.3 bar (all liquid); back to 57.3 bar in scene 5 | 41.6 -> 163.9 bar, smooth; 85.6 bar in scene 5 |
| Phase | gas -> gas + liquid -> liquid -> gas + liquid | gas -> supercritical fluid (a name only, past 73.8 bar) |

All values from the Span-Wagner reference equation of state (CoolProp), checked against NIST WebBook tables (SCIENCE_QA.md).

## Layout (scenes 1-5)

- Top bar: scene number and name (left); "Molecules: illustrative, not to scale" (right); thin progress line.
- Title zone: one statement per scene.
- Left card: two vertical cylinders with pistons, each in its water bath; under each, the live pressure, the constant temperature and a phase chip.
- Right card: pressure vs. molar volume diagram; both isotherms are traced live with a marker at the current state.
- Bottom zone: one caption per cylinder, or a centred explanation.

## Scene by scene

| Time | Scene | What happens on screen |
|---|---|---|
| 0-3.4 s | 1 The Question | Title "Can Pressure Alone Turn a Gas into a Liquid?" (on screen at frame 0), subtitle "Compressing CO2 at two temperatures". |
| 3.4-10 s | | Both cards rise in; molecules move in both cylinders; gauges 37.2 and 41.6 bar; setup line "1 mol of CO2 in each cylinder, same starting volume, each bath holds its temperature constant". |
| 10-16 s | 2 Squeeze Both | Title "Squeeze Both Slowly at Constant Temperature". Pistons move down together from 11 s. Captions: "Squeezing the gas raises the pressure." / "The pressure rises smoothly." |
| 16-23 s | | A reaches the saturated-vapor volume at 16.0 s: "Droplets at 57.3 bar. The pressure stays flat." A liquid layer with a surface grows at the bottom while the gauge stays at 57.3 bar; the diagram shows the flat step ("flat: liquid and vapor coexist"). B passes 73.8 bar at about 17.8 s: "Past 73.8 bar, B is called a supercritical fluid. Only the name changes: nothing happens there." |
| 23-30 s | | A all liquid at 23.0 s: "All liquid: pressure climbs, the piston hardly moves." (57.3 -> 66.3 bar for a 3% volume change). B: "No droplets at any pressure: one fluid all the way." Bottom right: "A ends as a liquid; B is dense but has no surface." |
| 30-36 s | 3 Pause and Predict | Molecules freeze, screen dims. Card: "PAUSE AND PREDICT / Same CO2, same squeeze. / Why did only the 20 °C sample turn into a liquid?" with a countdown ring. |
| 36-60 s | 4 The Critical Point | Title "The Critical Temperature of CO2: T_c = 31.0 °C". The diagram adds the coexistence region (shaded, "liquid + vapor") and isotherms at 10, 25 and 31.0 °C (dashed, T_c); the critical point is marked "31.0 °C, 73.8 bar". Notes in turn: "Below 31.0 °C every isotherm has a flat step." / "The step shrinks as the temperature rises and vanishes at the critical point." / "Above T_c no pressure can split CO2 into a liquid and a vapor." |
| 60-75 s | 5 Attraction versus Motion | Pistons move back to 120 cm³ mol⁻¹ (61-64.5 s): in A some liquid evaporates at 57.3 bar, leaving liquid and vapor with a visible (highlighted) surface; B is one uniform fluid at 85.6 bar. Notes: "Pull both pistons back a little." / "A liquid forms when attractions hold molecules together against their thermal motion." |
| 75-90 s | 6 Takeaway | Table: propane 96.7 °C, CO2 31.0 °C (pressure alone liquefies them at 20 °C: LPG cylinders, CO2 fire extinguishers); methane -82.6 °C, nitrogen -147.0 °C (cannot: cool first; methane boils at -161 °C, nitrogen at -196 °C). Large: "Pressure liquefies a gas only below its critical temperature." Closing line: "AI-Assisted Physical Chemistry Education". |

## Design notes

- Palette: white / light-blue background, navy text; blue for A (20 °C), warm orange for B (40 °C), violet for the critical isotherm and point.
- Molecules are dots of one colour; they encode position only. Their counts follow the lever rule, so the liquid and vapor dot densities differ by the real density ratio (about 4 at 20 °C).
- Minimum reading text is 22 px at 1080p (diagram labels); captions 26 px and up; titles 50-92 px.
- No sound. Narration, if added later, must be English.