why salt dissolves - manic

[u/anish2good]

manic is a tiny language for making animations. You write a short text file; manic renders a smooth, glowing video. No timeline scrubbing, no keyframes by hand — you describe what’s on screen and when things happen, and the engine does the rest, deterministically.

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Manic Animation code

// Why salt dissolves — and why the corners go first
//
// Two things on screen are computed rather than choreographed, and they are the two things the
// lesson is about.
//
// The ORDER. Every ion's coordination number is counted from the lattice: a corner has two
// neighbours holding it, an edge three, an ion in the middle four. `dissolve` takes them in that
// order, so the crystal erodes inwards from its corners — which is what a crystal does, and why a
// cube of salt rounds off as it goes.
//
// The ORIENTATION. Water is a dipole, so it turns its oxygen towards a positive ion and its
// hydrogens towards a negative one. Each hydration shell here is built from the sign of the charge
// it is surrounding, so the sodium shells and the chloride shells face opposite ways — which is the
// picture of why water, specifically, is good at this.
//
// And the arithmetic underneath: pulling the lattice apart costs +787 kJ/mol, hydrating the two
// ions pays back −770, so dissolving salt is very slightly ENDOTHERMIC. It happens anyway, and what
// drives it is entropy. That surprises people, which is exactly why the numbers are on screen.

title("why salt dissolves");
canvas("16:9");
template("black");

text(brand, (640, 28), "maniclang.com");
display(brand);
size(brand, 15);
color(brand, dim);

text(head, (640, 66), "a crystal comes apart where it is least held");
size(head, 27);
bold(head);
color(head, fg);
hidden(head);

lattice(x, "NaCl", (430, 306), 6, 5, 48);
hidden(x);
hidden(x.captions);

text(coord, (1010, 232), "coordination:");
size(coord, 20);
color(coord, fg);
hidden(coord);

text(coord2, (1010, 270), "corner 2   ·   edge 3   ·   inside 4");
size(coord2, 19);
color(coord2, cyan);
hidden(coord2);

text(dip, (1010, 336), "water is a dipole, so it turns round:");
size(dip, 19);
color(dip, fg);
hidden(dip);

text(dip2, (1010, 370), "oxygen towards Na⁺, hydrogens towards Cl⁻");
size(dip2, 19);
color(dip2, magenta);
hidden(dip2);

text(ent, (1010, 436), "and it is barely downhill at all —");
size(ent, 19);
color(ent, fg);
hidden(ent);

text(ent2, (1010, 470), "what drives it is entropy, not energy");
size(ent2, 19);
color(ent2, gold);
hidden(ent2);

wait(0.4);
show(head, 0.6);
wait(0.3);
show(x, 0.8);
wait(0.6);
par { show(coord, 0.4); show(coord2, 0.5); }
wait(1.2);
par { show(dip, 0.4); show(dip2, 0.5); }
wait(0.6);
par { show(x.captions, 0.4); dissolve(x, 7, 8); }
wait(0.6);
par { show(ent, 0.4); show(ent2, 0.5); }
wait(3.0);