Domain: Natural Science — Chemistry
Target concept: Zinc particles reacting with dilute acid, comparison of initial gas generation rate

Video generation prompt: Two identical transparent beakers contain equal amounts of zinc granules; dilute hydrochloric acid is added simultaneously, with the concentration of hydrochloric acid in the left beaker being higher than that in the right.

Evaluation guide:
Target concept: Initial reaction rate of Zn + HCl is directly proportional to [H⁺], demonstrated via real-time visual proxy of H₂ bubble nucleation frequency and density. Minimum mechanistic assumptions: (1) Reaction occurs heterogeneously at Zn surface; (2) Bubble formation requires local H₂ supersaturation; (3) Nucleation rate ∝ [H⁺]; (4) Identical granule mass = identical total surface area (validated by uniform size/density). Phased storyline: (Phase 1: Baseline) Two still beakers, identical zinc beds, labeled acid concentrations visible. (Phase 2: Trigger) Simultaneous acid addition, droplets impact with identical splash morphology. (Phase 3: Causal onset) Within 0.3 s, bubbling initiates *only at granule surfaces* in both; left shows immediate multi-site nucleation, right shows delayed, mono-site onset. (Phase 4: Rate divergence) 0.8–2.0 s: left sustains dense, fine bubble stream; right produces sparse, coarse bubbles; thermal shimmer emerges *only* above left. (Phase 5: Verification) By 2.5 s, left bubble frequency is ≥2.5× right, quantifiable, unambiguous, and causally anchored to concentration label. Visibility constraints: Orthogonal front view, no occlusion, lighting optimized for bubble transparency and surface reflectivity; perspective must allow direct comparison of bubble density per unit granule area, with no foreshortening or parallax.

Manual:
I. Basic Demonstration Information
Demonstration Title: Zinc Granules Reacting with Dilute Hydrochloric Acid — Comparison of Initial Gas Generation Rate
Subject: Natural Science - Chemistry - Reaction Kinetics
Demonstration Purpose: To visually compare the initial rate of hydrogen gas evolution when identical masses of zinc granules react with dilute hydrochloric acid of different concentrations; to establish the direct relationship between reactant concentration and initial reaction rate; to train observation of heterogeneous gas-evolution kinetics through visual proxies (bubble frequency, nucleation density, rise dynamics).

II. Demonstration Carrier/Equipment
Core Carrier: Two identical transparent cylindrical glass beakers (100 mL, borosilicate, wall thickness ≥1.2 mm); zinc granules (99.9% pure, 3–5 mm diameter, matte gray metallic luster, no oxide layer); dilute hydrochloric acid (left beaker: 6.0 mol/L; right beaker: 2.0 mol/L; both freshly prepared, colorless, clarified).
Auxiliary Equipment: Calibrated disposable droppers (1 mL, ±0.05 mL accuracy); waterproof concentration labels ('6 M HCl' on left beaker base, '2 M HCl' on right); white matte background board; LED ring light (5600 K, shadow-free); standard video camera able to clearly resolve bubble motion at normal frame rates; digital timer display (optional, embedded in corner).

III. Demonstration Content Description
Layout: Place beakers side-by-side on level surface, centered in frame, 10 cm apart. Fill each with 30 mL acid *before* adding zinc. Then add *equal masses* (1.00 ±0.05 g) of zinc granules to both beakers simultaneously using tweezers. Wait 5 s for settling. Then add *identical volumes* (5.0 ±0.1 mL) of *same-batch* dilute HCl to both beakers *in perfect unison* (hands mirror each other, droppers released at identical moment).
State Control: Ensure granules rest on beaker bottom without clumping; acid must be still (no swirl) pre-addition; room temperature 22–25℃ to avoid convection interference.
Comparison Baseline: Use identical granule batches; verify mass equality with analytical balance pre-demonstration; confirm acid concentrations via titration report (provided as metadata, not shown).

IV. Observation of Core Phenomena
Initial Bubble Onset: Within 0.3 s of acid contact, discrete bubbles nucleate *exclusively at zinc surface* in both beakers.
Rate Contrast (0–2 s): Left (6 M) shows many bubbles emerging rapidly from multiple granule sites; right (2 M) shows noticeably fewer and slower bubbles, mostly from one or two dominant sites; bubble streams in left are dense, fine, and rapidly coalescing; in right, bubbles are larger, isolated, and slower-rising.
Thermal Signature: At 1.5 s, faint but measurable air shimmer appears *only above left beaker*, widening gradually — evidence of localized exothermicity.
Stability & Causality: No bubbling before acid contact; no bubbles in acid-only regions; all bubbles rise vertically with natural Brownian deviation; cessation of bubbling in right beaker lags left by ≥3 s — confirming sustained rate difference.

V. Summary of Key Knowledge Points and Principles
Core Concept Definition: Initial reaction rate is the instantaneous rate at t→0, directly proportional to reactant concentration for elementary steps; here, Zn(s) + 2H⁺(aq) → Zn²⁺(aq) + H₂(g) is surface-limited, so rate ∝ [H⁺].
Kinetic Principle: Higher [H⁺] increases frequency of effective collisions between H⁺ ions and active Zn sites → more nucleation centers → higher bubble frequency and faster H₂ release.
Visual Proxy Logic: Bubble frequency ≈ relative rate; nucleation site density ≈ active surface coverage; bubble size distribution reflects local supersaturation (smaller bubbles = higher [H⁺]); thermal shimmer confirms ΔH < 0 and differential power dissipation.
Further Knowledge: Rate also depends on surface area (granule size), temperature, and catalysts; this demo isolates concentration as sole variable — all else held constant.

VI. Demonstration Precautions
Zinc Purity: Use freshly etched or acid-washed granules to remove passivating oxide layer — verified by pre-test showing immediate bubbling in 1 M HCl.
Acid Handling: Wear goggles; use fume hood if scaling up — H₂ is flammable, but 5 mL volume poses negligible risk in open demo.
Timing Rigor: Practice simultaneous addition until hand synchronization error is minimal; use metronome or audio cue if needed.
Lighting: Avoid backlighting that obscures bubble transparency; use diffuse frontal lighting to maximize bubble contrast against liquid.
Video Duration: Record 5 s total (t=−0.5 s to t=+4.5 s relative to acid contact), focusing on 0–2.5 s window where rate difference is maximal and unambiguous.

Prompt Grounding rubric:
level_1: No beakers are shown, or only one beaker appears, or neither beaker contains any visible zinc granules, or the acid is poured into only one beaker or into the two beakers more than a second or so apart, or there's no visual sense of a left/right pair at all.
level_2: Two beakers are present and similar in shape and size, but zinc granules are missing from one or both, or the acid is added to the two beakers noticeably out of sync, or neither beaker carries any concentration label or other visual cue that could tell the two acids apart, or the beakers aren't sitting side by side on the same surface.
level_3: Two matching transparent beakers sit side by side, each holding a similar amount of visible metallic zinc granules at the bottom, and dilute hydrochloric acid is poured into both within a moment of each other, but neither beaker carries a concentration label or other cue, so a viewer can't tell from the setup alone which acid is meant to be stronger.
level_4: The two beakers, zinc amounts, and near-simultaneous acid addition all match level 3, and in addition the left beaker is marked with a legible label identifying it as the higher-concentration acid, distinguishing it from the right; this level is about the setup being correctly labeled and staged, not about how the liquids end up bubbling.
level_5: Two beakers of matching size and appearance sit side by side on the same surface, each holding a visually similar amount of zinc granules; dilute hydrochloric acid is added to both at essentially the same instant via matching pouring or dropper motions; the left beaker is clearly and legibly labeled as the higher-concentration acid and the right as the lower-concentration one; and the camera holds a steady, unobstructed, straight-on view of both beakers throughout, regardless of whatever bubbling follows.

Scientific and Causal Correctness rubric:
level_1: No bubbling appears in either beaker after the acid is added, or bubbles show up before the acid ever touches the zinc, or bubbles drift sideways or downward, or the zinc seems to vanish instantly with no bubbling at all, or the liquid takes on some unnatural color.
level_2: Bubbling appears in both beakers, but the left (higher-concentration) beaker doesn't visibly bubble any faster or more densely than the right (they look about the same, or the right beaker actually bubbles more), giving no sense that the higher concentration is driving a faster reaction.
level_3: The left beaker shows visibly more bubbling activity than the right shortly after the acid is added, consistent with its higher acid concentration, but the contrast is subtle or takes a few seconds to become clear, and bubbles in both beakers only ever start after the acid actually touches the zinc.
level_4: Within a couple of seconds of the acid being added, the left beaker is clearly producing bubbles faster and in greater numbers than the right; bubbling stays confined to the zinc surfaces in both beakers and never appears before contact, so a viewer can tell at a glance that the left reaction is running noticeably faster.
level_5: From nearly the moment the acid touches the zinc, the left beaker bubbles noticeably more densely and rapidly than the right, and this gap holds up or even grows over the following several seconds rather than fading; bubbles in both beakers rise only from the zinc surfaces and never appear before contact, and neither beaker shows any color change, cloudiness, or residue beyond the expected zinc-acid reaction.

Spatiotemporal Consistency rubric:
level_1: A beaker or the zinc granules inside it change size, shape, or position between shots with no cause, the acid appears to pour upward or bubbles shoot downward, the whole reaction seems to jump from just-added to fully finished within a single moment, the pouring tool is drawn at a scale that couldn't fit the beaker, or the lighting around the beakers suddenly swings from bright to dark (or vice versa) with no cause tied to the reaction.
level_2: The two beakers sit at different heights or angles from each other, the acid is poured from a noticeably different height or speed into each, bubbles drift or tilt at odd angles, there's a long pause between the acid landing and the first bubble, or the hand doing the pouring moves in a jerky, unnatural way.
level_3: Both beakers stay level and stable, the acid is added with similar tools and motion in both, but the timing between the two pours is slightly off, the bubbles rise mostly straight up but look a touch too uniform in size, or a hand briefly blocks part of one beaker during the pour.
level_4: Both beakers are shown from the same steady, straight-on angle without distortion, the acid falls and lands naturally in each, bubbles rise smoothly upward from the zinc surfaces without stalling or jumping, the hand withdraws cleanly after pouring so both beakers stay fully visible, and the lighting stays even throughout with no flicker.
level_5: Both beakers keep an identical, undistorted framing from start to finish, the acid pours and lands the same natural way in both, bubbles rise continuously and only ever upward with plausible-looking changes in speed as they ascend, and the lighting and camera position never shift or stutter for the whole clip.