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.
""" anyplot.ai
line-reaction-coordinate: Reaction Coordinate Energy Diagram
Library: seaborn 0.13.2 | Python 3.13.14
Quality: 89/100 | Updated: 2026-06-24
"""
import os
import matplotlib.pyplot as plt
import numpy as np
import pandas as pd
import seaborn as sns
from scipy.interpolate import PchipInterpolator
# Theme tokens — Imprint palette
THEME = os.getenv("ANYPLOT_THEME", "light")
PAGE_BG = "#FAF8F1" if THEME == "light" else "#1A1A17"
ELEVATED_BG = "#FFFDF6" if THEME == "light" else "#242420"
INK = "#1A1A17" if THEME == "light" else "#F0EFE8"
INK_SOFT = "#4A4A44" if THEME == "light" else "#B8B7B0"
BRAND = "#009E73" # Imprint position 1 — first (and only) data series
EA_COLOR = "#AE3030" # Imprint position 5 — semantic red for activation barrier
DH_COLOR = "#4467A3" # Imprint position 3 — blue for enthalpy change
sns.set_theme(
context="notebook",
style="ticks",
rc={
"figure.facecolor": PAGE_BG,
"axes.facecolor": PAGE_BG,
"axes.edgecolor": INK_SOFT,
"axes.labelcolor": INK,
"text.color": INK,
"xtick.color": INK_SOFT,
"ytick.color": INK_SOFT,
"grid.color": INK,
"grid.alpha": 0.15,
"legend.facecolor": ELEVATED_BG,
"legend.edgecolor": INK_SOFT,
},
)
# Data — single-step exothermic reaction: Ea = 70 kJ/mol, ΔH = −30 kJ/mol
reactant_energy = 50.0
transition_energy = 120.0
product_energy = 20.0
control_x = np.array([0.0, 0.12, 0.22, 0.35, 0.47, 0.59, 0.72, 0.82, 0.90, 1.0])
control_y = np.array(
[
reactant_energy,
reactant_energy,
reactant_energy + 2,
85,
transition_energy,
85,
product_energy + 5,
product_energy,
product_energy,
product_energy,
]
)
reaction_coord = np.linspace(0, 1, 500)
spline = PchipInterpolator(control_x, control_y)
energy = spline(reaction_coord)
df = pd.DataFrame({"Reaction Coordinate": reaction_coord, "Potential Energy (kJ/mol)": energy})
# Key state markers evaluated on the spline
key_x = np.array([0.10, 0.47, 0.88])
key_states = pd.DataFrame({"Reaction Coordinate": key_x, "Potential Energy (kJ/mol)": spline(key_x)})
# Figure-level seaborn API — relplot for consistent figure layout management
g = sns.relplot(
data=df,
x="Reaction Coordinate",
y="Potential Energy (kJ/mol)",
kind="line",
color=BRAND,
linewidth=2.5,
height=4.5,
aspect=16 / 9,
)
g.figure.set_dpi(400)
g.figure.set_facecolor(PAGE_BG)
ax = g.axes.flat[0]
ax.set_facecolor(PAGE_BG)
# Seaborn scatter layer marking reactant, transition state, and product positions
sns.scatterplot(
data=key_states,
x="Reaction Coordinate",
y="Potential Energy (kJ/mol)",
color=BRAND,
s=80,
zorder=5,
legend=False,
ax=ax,
)
ax.fill_between(reaction_coord, energy, alpha=0.08, color=BRAND, zorder=2)
# Horizontal dashed reference lines at reactant and product energy levels
ax.hlines(reactant_energy, xmin=-0.02, xmax=0.18, color=INK_SOFT, linestyle="--", linewidth=1.2, alpha=0.6)
ax.hlines(product_energy, xmin=0.82, xmax=1.02, color=INK_SOFT, linestyle="--", linewidth=1.2, alpha=0.6)
# Species labels — direct annotation on chart
ax.text(0.02, reactant_energy + 3, "Reactants\n(50 kJ/mol)", fontsize=9, fontweight="bold", color=INK, va="bottom")
ax.text(
0.98, product_energy - 3, "Products\n(20 kJ/mol)", fontsize=9, fontweight="bold", color=INK, va="top", ha="right"
)
ax.text(
0.47,
transition_energy + 2,
"Transition State\n(120 kJ/mol)",
fontsize=9,
fontweight="bold",
color=INK,
va="bottom",
ha="center",
)
# Activation energy arrow (Ea)
ea_x = 0.13
ax.annotate(
"",
xy=(ea_x, transition_energy),
xytext=(ea_x, reactant_energy),
arrowprops={"arrowstyle": "<->", "color": EA_COLOR, "lw": 2.0, "shrinkA": 0, "shrinkB": 0},
)
ax.text(
ea_x - 0.02,
(reactant_energy + transition_energy) / 2,
f"$E_a$ = {transition_energy - reactant_energy:.0f} kJ/mol",
fontsize=8,
color=EA_COLOR,
fontweight="bold",
ha="right",
va="center",
bbox={"boxstyle": "round,pad=0.3", "facecolor": ELEVATED_BG, "edgecolor": "none", "alpha": 0.9},
)
# Enthalpy change arrow (ΔH)
dh_x = 0.82
ax.annotate(
"",
xy=(dh_x, product_energy),
xytext=(dh_x, reactant_energy),
arrowprops={"arrowstyle": "<->", "color": DH_COLOR, "lw": 2.0, "shrinkA": 0, "shrinkB": 0},
)
ax.text(
dh_x - 0.02,
(reactant_energy + product_energy) / 2,
f"$\\Delta H$ = {product_energy - reactant_energy:.0f} kJ/mol",
fontsize=8,
color=DH_COLOR,
fontweight="bold",
ha="right",
va="center",
bbox={"boxstyle": "round,pad=0.3", "facecolor": ELEVATED_BG, "edgecolor": "none", "alpha": 0.9},
)
# Style
title = "line-reaction-coordinate · python · seaborn · anyplot.ai"
ax.set_xlabel("Reaction Coordinate", fontsize=10, color=INK)
ax.set_ylabel("Potential Energy (kJ/mol)", fontsize=10, color=INK)
ax.set_title(title, fontsize=12, fontweight="medium", color=INK)
ax.tick_params(axis="both", labelsize=8, colors=INK_SOFT)
sns.despine(ax=ax)
ax.spines["left"].set_color(INK_SOFT)
ax.spines["bottom"].set_color(INK_SOFT)
ax.set_xlim(-0.02, 1.02)
ax.set_ylim(0, 145)
ax.set_xticks([])
ax.xaxis.grid(False)
ax.yaxis.grid(True, alpha=0.15, linewidth=0.8, color=INK)
g.tight_layout()
plt.savefig(f"plot-{THEME}.png", dpi=400, facecolor=PAGE_BG)
Part of Reaction Coordinate Energy Diagram on anyplot.ai.