Reaction Coordinate Energy Diagram — Makie.jl

A reaction coordinate diagram plots potential energy against reaction progress, showing the energy landscape of a chemical transformation. The smooth curve traces the path from reactants through the transition state (energy maximum) to products, clearly depicting the activation energy barrier and overall enthalpy change. This fundamental chemistry visualization is essential for understanding reaction kinetics and thermodynamics.

Reaction Coordinate Energy Diagram rendered with Makie.jl

Renders

Julia source (Makie.jl)

# anyplot.ai
# line-reaction-coordinate: Reaction Coordinate Energy Diagram
# Library: makie 0.22.10 | Julia 1.11.9
# Quality: 90/100 | Created: 2026-06-24

using CairoMakie
using Colors
using Random

Random.seed!(42)

const THEME       = get(ENV, "ANYPLOT_THEME", "light")
const PAGE_BG     = THEME == "light" ? colorant"#FAF8F1" : colorant"#1A1A17"
const ELEVATED_BG = THEME == "light" ? colorant"#FFFDF6" : colorant"#242420"
const INK         = THEME == "light" ? colorant"#1A1A17" : colorant"#F0EFE8"
const INK_SOFT    = THEME == "light" ? colorant"#4A4A44" : colorant"#B8B7B0"
const INK_MUTED   = THEME == "light" ? colorant"#6B6A63" : colorant"#A8A79F"
const IMPRINT_PALETTE = [
    colorant"#009E73", colorant"#C475FD", colorant"#4467A3", colorant"#BD8233",
    colorant"#AE3030", colorant"#2ABCCD", colorant"#954477", colorant"#99B314",
]
const BRAND = IMPRINT_PALETTE[1]

# Data — single-step exothermic reaction
E_r  = 50.0   # reactant energy level (kJ/mol)
E_ts = 120.0  # transition state energy (kJ/mol)
E_p  = 20.0   # product energy level (kJ/mol)

x_peak = 0.38  # transition state position on [0, 1]
sigma  = 0.14  # Gaussian half-width controls barrier sharpness

n_pts = 300
x_vals = collect(LinRange(0.0, 1.0, n_pts))
linear_baseline = E_r .+ (E_p - E_r) .* x_vals
barrier_height = E_ts - (E_r + (E_p - E_r) * x_peak)
energy = linear_baseline .+ barrier_height .* exp.(-(x_vals .- x_peak).^2 ./ (2 * sigma^2))

E_a     = Int(E_ts - E_r)  # activation energy = 70 kJ/mol
delta_H = Int(E_p - E_r)   # enthalpy change = -30 kJ/mol

# Figure
title_str = "line-reaction-coordinate · julia · makie · anyplot.ai"

fig = Figure(
    size            = (1600, 900),
    fontsize        = 14,
    backgroundcolor = PAGE_BG,
)

ax = Axis(
    fig[1, 1];
    title              = title_str,
    titlesize          = 20,
    titlecolor         = INK,
    xlabel             = "Reaction Coordinate",
    ylabel             = "Potential Energy (kJ/mol)",
    xlabelsize         = 14,
    ylabelsize         = 14,
    xticklabelsize     = 12,
    yticklabelsize     = 12,
    xlabelcolor        = INK,
    ylabelcolor        = INK,
    xticklabelcolor    = INK_SOFT,
    yticklabelcolor    = INK_SOFT,
    xtickcolor         = INK_SOFT,
    ytickcolor         = INK_SOFT,
    backgroundcolor    = PAGE_BG,
    topspinevisible    = false,
    rightspinevisible  = false,
    leftspinecolor     = INK_SOFT,
    bottomspinecolor   = INK_SOFT,
    xgridvisible       = false,
    ygridvisible       = true,
    ygridcolor         = RGBAf(INK.r, INK.g, INK.b, 0.12),
    xticklabelsvisible = false,
    xticksvisible      = false,
)

# Reaction energy curve
lines!(ax, x_vals, energy; color = BRAND, linewidth = 3.5)

# Horizontal dashed reference lines at reactant and product energy levels
hlines!(ax, E_r; color = INK_MUTED, linewidth = 1.2, linestyle = :dash)
hlines!(ax, E_p; color = INK_MUTED, linewidth = 1.2, linestyle = :dash)

# Axis limits — extra right margin for annotation labels
xlims!(ax, -0.05, 1.20)
ylims!(ax, E_p - 15.0, E_ts + 30.0)

# Labels: reactants, transition state, products
text!(ax, 0.04, E_r + 6.0;
      text  = "Reactants\n50 kJ/mol",
      color = INK, fontsize = 13, align = (:left, :bottom))
text!(ax, x_peak, E_ts + 8.0;
      text  = "Transition State ‡\n120 kJ/mol",
      color = INK, fontsize = 13, align = (:center, :bottom))
text!(ax, 0.94, E_p + 6.0;
      text  = "Products\n20 kJ/mol",
      color = INK, fontsize = 13, align = (:right, :bottom))

# Activation energy (Eₐ) double-headed arrow: from reactant level to transition state
x_ea = 0.62
arrows!(ax, [x_ea], [E_r], [0.0], [E_ts - E_r]; color = INK, linewidth = 1.5)
arrows!(ax, [x_ea], [E_ts], [0.0], [-(E_ts - E_r)]; color = INK, linewidth = 1.5)
text!(ax, x_ea + 0.03, (E_r + E_ts) / 2.0;
      text  = "Eₐ = $(E_a) kJ/mol",
      color = INK, fontsize = 12, align = (:left, :center))

# Enthalpy change (ΔH) double-headed arrow: between reactant and product levels
x_dh = 0.85
arrows!(ax, [x_dh], [E_p], [0.0], [E_r - E_p]; color = INK, linewidth = 1.5)
arrows!(ax, [x_dh], [E_r], [0.0], [-(E_r - E_p)]; color = INK, linewidth = 1.5)
text!(ax, x_dh + 0.03, (E_r + E_p) / 2.0;
      text  = "ΔH = $(delta_H) kJ/mol",
      color = INK, fontsize = 12, align = (:left, :center))

# Save
save("plot-$(THEME).png", fig; px_per_unit = 2)

Part of Reaction Coordinate Energy Diagram on anyplot.ai.

Other implementations