A pressure-temperature (P-T) phase diagram showing the boundaries between solid, liquid, and gas phases of a substance. The diagram includes the triple point where all three phases coexist and the critical point beyond which the liquid-gas distinction vanishes. This is one of the most fundamental diagrams in chemistry and physics, essential for understanding phase transitions and states of matter.
""" anyplot.ai
phase-diagram-pt: Thermodynamic Phase Diagram (Pressure-Temperature)
Library: letsplot 4.10.1 | Python 3.13.13
Quality: 91/100 | Updated: 2026-06-08
"""
import os
import numpy as np
import pandas as pd
from lets_plot import (
LetsPlot,
aes,
element_blank,
element_line,
element_rect,
element_text,
flavor_high_contrast_dark,
flavor_high_contrast_light,
geom_area,
geom_line,
geom_point,
geom_text,
ggplot,
ggsize,
labs,
layer_tooltips,
scale_color_manual,
scale_x_continuous,
scale_y_log10,
theme,
theme_minimal,
)
from lets_plot.export import ggsave
LetsPlot.setup_html()
# Imprint palette — canonical order (hybrid-v3)
IMPRINT_PALETTE = ["#009E73", "#C475FD", "#4467A3", "#BD8233", "#AE3030", "#2ABCCD", "#954477", "#99B314"]
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"
INK_MUTED = "#6B6A63" if THEME == "light" else "#A8A79F"
# Phase region fill colors — theme-adaptive subtle backgrounds
FILL_GAS = "#FFF8E1" if THEME == "light" else "#302C00"
FILL_SOLID = "#EDE9F8" if THEME == "light" else "#1E1930"
FILL_LIQUID = "#E0F2F1" if THEME == "light" else "#00302E"
# Water phase diagram — physically accurate (Clausius-Clapeyron equations)
# Triple point: 273.16 K, 611.73 Pa | Critical point: 647.1 K, 22.064 MPa
triple_t, triple_p = 273.16, 611.73
critical_t, critical_p = 647.1, 22.064e6
# Solid-gas boundary (sublimation curve)
temp_solid_gas = np.linspace(200, triple_t, 80)
L_sub = 51059.0
R = 8.314
pressure_solid_gas = triple_p * np.exp((L_sub / R) * (1 / triple_t - 1 / temp_solid_gas))
# Liquid-gas boundary (vaporization curve — triple point to critical point)
temp_liquid_gas = np.linspace(triple_t, critical_t, 100)
L_vap = 40660.0
pressure_liquid_gas = triple_p * np.exp((L_vap / R) * (1 / triple_t - 1 / temp_liquid_gas))
# Solid-liquid boundary (melting curve — negative slope, water anomaly)
temp_solid_liquid = np.linspace(200, 273.16, 80)
pressure_solid_liquid = triple_p + (temp_solid_liquid - triple_t) * (-13.5e6)
pressure_solid_liquid = np.clip(pressure_solid_liquid, triple_p, 1e9)
# DataFrames for boundary curves
df_sublimation = pd.DataFrame(
{"temperature": temp_solid_gas, "pressure": pressure_solid_gas, "boundary": "Solid–Gas (Sublimation)"}
)
df_vaporization = pd.DataFrame(
{"temperature": temp_liquid_gas, "pressure": pressure_liquid_gas, "boundary": "Liquid–Gas (Vaporization)"}
)
df_melting = pd.DataFrame(
{"temperature": temp_solid_liquid, "pressure": pressure_solid_liquid, "boundary": "Solid–Liquid (Melting)"}
)
df_boundaries = pd.concat([df_sublimation, df_vaporization, df_melting], ignore_index=True)
# Phase region fill areas
gas_temp = np.concatenate([temp_solid_gas, temp_liquid_gas])
gas_pressure_upper = np.concatenate([pressure_solid_gas, pressure_liquid_gas])
df_gas_fill = pd.DataFrame({"temperature": gas_temp, "ymax": gas_pressure_upper, "ymin": 0.01, "phase": "Gas"})
df_solid_fill = pd.DataFrame(
{"temperature": temp_solid_liquid, "ymax": 2e9, "ymin": pressure_solid_liquid, "phase": "Solid"}
)
df_liquid_fill = pd.DataFrame(
{"temperature": temp_liquid_gas, "ymax": 2e9, "ymin": pressure_liquid_gas, "phase": "Liquid"}
)
# Special points — triple point and critical point
df_points = pd.DataFrame(
{
"temperature": [triple_t, critical_t],
"pressure": [triple_p, critical_p],
"label": ["Triple Point\n(273.16 K, 611.73 Pa)", "Critical Point\n(647.1 K, 22.06 MPa)"],
"point_type": ["Triple Point", "Critical Point"],
}
)
# Phase region labels
df_labels = pd.DataFrame(
{"temperature": [225.0, 450.0, 450.0], "pressure": [5e7, 5e8, 500.0], "text": ["SOLID", "LIQUID", "GAS"]}
)
# Boundary curve colors — first 3 Imprint palette positions
boundary_colors = IMPRINT_PALETTE[:3]
anyplot_theme = theme(
plot_background=element_rect(fill=PAGE_BG, color=PAGE_BG),
panel_background=element_rect(fill=PAGE_BG),
panel_grid_major=element_line(color=INK_SOFT, size=0.3),
panel_grid_minor=element_blank(),
axis_title=element_text(size=12, color=INK),
axis_text=element_text(size=10, color=INK_SOFT),
axis_line=element_line(color=INK_SOFT),
plot_title=element_text(size=16, color=INK, margin=[0, 0, 8, 0]),
legend_text=element_text(size=10, color=INK_SOFT),
legend_title=element_text(size=12, color=INK),
legend_background=element_rect(fill=ELEVATED_BG, color=INK_SOFT),
legend_position="bottom",
)
plot = (
ggplot()
# Subtle phase region fills
+ geom_area(data=df_gas_fill, mapping=aes(x="temperature", y="ymax"), fill=FILL_GAS, alpha=0.6, inherit_aes=False)
+ geom_area(
data=df_solid_fill, mapping=aes(x="temperature", y="ymax"), fill=FILL_SOLID, alpha=0.5, inherit_aes=False
)
+ geom_area(
data=df_liquid_fill, mapping=aes(x="temperature", y="ymax"), fill=FILL_LIQUID, alpha=0.5, inherit_aes=False
)
# Phase boundary curves with interactive tooltips (lets-plot distinctive)
+ geom_line(
data=df_boundaries,
mapping=aes(x="temperature", y="pressure", color="boundary"),
size=1.2,
tooltips=layer_tooltips().line("@boundary").line("T = @temperature K").line("P = @pressure Pa"),
)
# Special points with diamond markers
+ geom_point(
data=df_points,
mapping=aes(x="temperature", y="pressure"),
color=INK,
size=4,
shape=18,
inherit_aes=False,
tooltips=layer_tooltips().line("@point_type"),
)
# Triple point annotation
+ geom_text(
data=df_points.iloc[[0]],
mapping=aes(x="temperature", y="pressure", label="label"),
color=INK,
size=6,
nudge_x=50,
nudge_y=0.5,
label_padding=0.3,
inherit_aes=False,
)
# Critical point annotation
+ geom_text(
data=df_points.iloc[[1]],
mapping=aes(x="temperature", y="pressure", label="label"),
color=INK,
size=6,
nudge_x=-55,
nudge_y=0.7,
label_padding=0.3,
inherit_aes=False,
)
# Phase region labels — bold, subdued
+ geom_text(
data=df_labels,
mapping=aes(x="temperature", y="pressure", label="text"),
color=INK_MUTED,
size=9,
fontface="bold",
alpha=0.85,
inherit_aes=False,
)
+ scale_color_manual(values=boundary_colors)
+ scale_y_log10()
+ scale_x_continuous(breaks=[200, 300, 400, 500, 600, 700])
+ labs(
x="Temperature (K)",
y="Pressure (Pa)",
title="phase-diagram-pt · python · letsplot · anyplot.ai",
color="Phase Boundary",
)
+ theme_minimal()
+ (flavor_high_contrast_light() if THEME == "light" else flavor_high_contrast_dark())
+ anyplot_theme
+ ggsize(800, 450)
)
ggsave(plot, f"plot-{THEME}.png", path=".", scale=4)
ggsave(plot, f"plot-{THEME}.html", path=".")
Part of Thermodynamic Phase Diagram (Pressure-Temperature) on anyplot.ai.