--- tags: [video, hyperframes, thermodynamics, first-law, adiabatic, teaching] confidence: high sources: [js/physics.js, js/schedule.js, js/timeline.js, SCIENCE_QA.md] last_updated: 2026-10-29 --- # HF-PCHEM-001 Storyboard **Why Does a Gas Cool Down Without Losing Heat?** Reversible Adiabatic Expansion vs. Free Expansion 1920 x 1080, 30 fps, 90 s, silent (built to be understood without narration). All on-screen text is English. ## System and numbers (identical start for both) | | A: Reversible adiabatic expansion | B: Adiabatic free expansion | |---|---|---| | Gas | 1 mol monatomic ideal gas (Ar), C_V,m = 3/2 R, gamma = 5/3 | same | | Start | 300 K, V₁, insulated walls | same, gas in the left half, vacuum in the right half | | Process | frictionless piston moves out quasi-statically as its external load is eased off, p_ext = p | partition pulled out, gas expands into vacuum, p_ext = 0 | | End | 2V₁, **189 K** | 2V₁, **300 K** | | q / w / dU | 0 / -1.38 kJ / -1.38 kJ | 0 / 0 / 0 | Sign convention throughout: **dU = q + w, w = work done on the gas** (stated on screen in scene 4). ## Layout (persistent through scenes 1-5) - Top bar: scene number and name (left), molecule colour legend "slow to fast" (right), thin progress line. - Title zone (y ~150): one statement per scene. - Two cards, A (blue accent) left and B (orange accent) right. Each card: system name, container (hatched insulated walls), thermometer with live T and dT, q = 0 chip, and one information module that changes by scene (speed distribution, P-V diagram, or energy bookkeeping). - Bottom zone: one caption per card, or a centred conclusion or equations. - Footnote (bottom edge, 13.2-82.6 s): "Molecules are illustrative: in A, their speeds are gently scaled to follow the ideal-gas temperature. B has no correction." (see SCIENCE_QA section 4). Piston vs. partition are drawn to be unmistakable: the piston is a thick navy block with a rod and handle that travels; the partition is a thin orange plate with a pull tab that slides up and out through a slot in the top wall. ## Scene by scene | Time | Scene | What happens on screen | |---|---|---| | 0-3.6 s | 1 The Question | Large title "Why Does a Gas Cool Down Without Losing Heat?" (already on screen at frame 0), subtitle "Reversible Adiabatic Expansion vs. Free Expansion". | | 3.6-12 s | | Title moves to the top. Both cards rise in with moving molecules (identical positions and velocities). Labels: "<- piston", "<- removable partition", "vacuum". Both show T = 300 K and the "q = 0 INSULATED" chip. Setup line: "Identical start: 1 mol of monatomic ideal gas (Ar) at 300 K, insulated walls, both end at twice the volume". Speed distributions appear, headed "Maxwell-Boltzmann (theory)" (the 3D curve for Ar at the displayed T, not a histogram of the dots). | | 12-13 s | 2 Two Expansions | Title "Two Different Expansions, Running at the Same Time". Tags "slow, quasi-static" (A) and "sudden, irreversible" (B). | | 13-27 s | | Both start at 13.0 s. A: piston moves out over 14 s; blue arrow "work done by the gas" while it moves (fades 0.6 s after it stops); cyan ripples where molecules strike the piston; T falls 300 -> 189 K along T V^(2/3) = const; distribution curve shifts left (dashed 300 K curve kept as reference); molecule colours drift toward blue. B: partition slides out in 0.5 s, the vacuum tint fades, molecules stream into the empty half; the thermometer keeps reading 300 K and a tag "not yet in equilibrium" stands in the dT slot for 4 s (13.0-17.0 s) while the gas is still streaming; distribution unchanged. | | 14.6-29.6 s | | Captions. A: "Gas performs work on its surroundings." / "Frictionless piston, load eased off slowly: p_ext = p at every step". B: "No work is done against external pressure." / "Expands into vacuum: p_ext = 0". | | 30-37.4 s | 3 Predict and Reveal | Molecules freeze (pause), screen dims. Card: "PAUSE AND EXPLAIN / Both processes are adiabatic. / Why are their temperature changes different?" with a 5 s countdown ring. | | 37.4-41 s | | The question stays as the title, motion resumes. Reveal: A card glows blue, "Temperature decreases, 300 K -> 189 K"; B card glows orange, "Temperature remains constant, 300 K -> 300 K (ideal gas)". dT chips appear (-111 K, 0 K). | | 41-49.3 s | | Modules switch to P-V diagrams. A: reversible adiabat drawn as a continuous curve from i to f, ending on the 189 K isotherm below the 300 K isotherm. B: only the initial and final states are plotted (both on the 300 K isotherm); no line connects them: "No equilibrium path". | | 49.7-52.4 s | 4 The First Law | Gas fades, both systems reset to the identical initial state, "Replay" badge. Title: "The First Law dU = q + w (w = work done on the gas)". | | 51-62.5 s | | Energy modules. Headers "Work done by the gas" (A) and "Expansion against vacuum" (B). Row "q = 0" pops in for both at 52 s. Replay starts at 53.5 s (both together); B shows "not yet in equilibrium" in its dT slot 53.5-57.5 s. Internal-energy bar for A shrinks in step with the piston (3.74 -> 2.36 kJ, live), B bar stays full (3.74 kJ, unchanged). Row "w < 0" (live value to -1.38 kJ) vs "w = 0, p_ext = 0" at 55 s; row "dU < 0" vs "dU = 0" at 59.5 s. Thermometers and dT update live from the same clock; the live w is shown as (shown U - shown U1), so the panel adds up on screen. Bottom zone (51.6-63.0 s) has a guiding line: "Replay: watch the **internal-energy bars** as both gases expand." | | 63.6-69.6 s | | Conclusion: "With q = 0 in both systems, dU = w." / "Only the gas that does work loses internal energy." | | 70-82.6 s | 5 The Molecular Picture | Title "Internal energy and temperature are linked." Speed distributions return. Equations: "Ideal gas, constant C_V (monatomic: C_V,m = 3/2 R): dU = n C_V,m dT" (71 s) and "Mean translational kinetic energy per molecule: k> = 3/2 k_BT" (73 s). v_rms markers and k> readouts: 3.91 x 10^-21 J (A, 189 K) vs 6.21 x 10^-21 J (B, 300 K). Five molecules per box get velocity arrows: their speeds differ and keep changing through collisions. Notes: "Speeds still vary widely; the distribution shifts lower." / "...the distribution is unchanged." | | 83-90 s | 6 Takeaway | Two summary cards. "Reversible Adiabatic Expansion: q = 0, w < 0, dT < 0" and "Ideal-Gas Free Expansion: q = 0, w = 0, dT = 0". Large: "Adiabatic Does Not Mean Isothermal." Closing line: "AI-Assisted Physical Chemistry Education". | ## Design notes - Palette: white / light-blue background, navy text, cyan accents, blue for A (cooling), warm orange for B (unchanged). Thermometer and curve colour run orange (300 K) -> violet -> blue (189 K). - Molecules are 3D hard spheres in a thin slab seen from above (positions and velocities in x, y, z; the screen shows x and y). Colour encodes the in-plane speed of that molecule (same scale for both boxes), so the shift of the whole population is visible while the spread of speeds stays visible too. Velocity arrows (scene 5) show the stored in-plane velocity of the frame. Collisions depend on the 3D separation, so discs that overlap on screen need not touch. In A the speeds are scaled a little each frame toward the ideal-gas temperature, and the footnote says so. - Minimum reading text is 24 px at 1080p; titles 44-92 px; equations 54-76 px. - No sound. Narration, if added later, must be English.