Reactions

A reaction has reactants, an arrow, and products. Conditions sit in bracketed groups immediately after the arrow.

Arrow types

Arrow	Kind	Use
->	:forward	Net forward reaction
<-	:reverse	Net reverse reaction
<=>	:equilibrium	Equilibrium (Haber, acid/base)
<->	:resonance	Resonance structures

Basic reactions

2H_2 + O_2 -> 2H_2O

$2{\mathrm{H}}_2+{\mathrm{O}}_2\to 2{\mathrm{H}}_2\mathrm{O}$

HCl + NaOH -> NaCl + H_2O

$\mathrm{H}\mathrm{Cl}+\mathrm{Na}\mathrm{O}\mathrm{H}\to \mathrm{Na}\mathrm{Cl}+{\mathrm{H}}_2\mathrm{O}$

CH_4 + 2O_2 -> CO_2 + 2H_2O

$\mathrm{C}{\mathrm{H}}_4+2{\mathrm{O}}_2\to \mathrm{C}{\mathrm{O}}_2+2{\mathrm{H}}_2\mathrm{O}$

Reactants and products are each a +-separated list of molecules. The + operators are stripped from the model; the renderer reinserts them.

Equilibrium with conditions

The Haber process — nitrogen and hydrogen over an iron catalyst at elevated temperature:

N_2 + 3H_2 <=>[Fe][400°C] 2NH_3

${\mathrm{N}}_2+3{\mathrm{H}}_2\underset{\mathrm{Fe}}{\overset{\text{400°C}}{\rightleftharpoons }}2\mathrm{N}{\mathrm{H}}_3$

The first bracketed group [Fe] is the above condition (catalyst). The second bracketed group [400°C] is the below condition (temperature). Both are captured as Reaction#conditions.

The MathML renderer emits the arrow as an <munderover>:

<munderover>
  <mo>⇌</mo>
  <mtext>Fe</mtext>
  <mtext>400°C</mtext>
</munderover>

One-sided conditions

Only the above condition:

A <=>[H_2O] B

$\mathrm{A}\stackrel{{\mathrm{H}}_2\mathrm{O}}{\rightleftharpoons }\mathrm{B}$

Only the below:

A <=>[Δ] B

$\mathrm{A}\stackrel{\text{Δ}}{\rightleftharpoons }\mathrm{B}$

(Use the second form when the condition is energy/heat, by convention placed below the arrow.)

Spectators and ionic equations

Ag^+ + Cl^- -> AgCl

${\mathrm{Ag}}^{+}+{\mathrm{Cl}}^{-}\to \mathrm{Ag}\mathrm{Cl}$

Ions on either side are full Molecule instances with their charge captured on the relevant atom. Round-trip is exact.

What’s not yet in v1

• Reversible resonance is supported; tautomerism arrows are not.
• Multi-step reactions (chained arrows) require explicit Reaction nodes per step.
• Rates and stoichiometry validation are out of scope for the parser — a separate linter pass can verify balancing.