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: pygal 3.1.0 | Python 3.13.13
Quality: 90/100 | Updated: 2026-06-08
"""
# Ensure we import the installed pygal package, not this file
import importlib.util
import os
import sys
import xml.etree.ElementTree as ET
import cairosvg
import numpy as np
pygal_spec = importlib.util.find_spec("pygal")
if pygal_spec and pygal_spec.origin != __file__:
import pygal
from pygal.style import Style
else:
_cwd = os.getcwd()
sys.path = [p for p in sys.path if os.path.abspath(p) != _cwd]
try:
import pygal
from pygal.style import Style
finally:
sys.path.insert(0, _cwd)
THEME = os.getenv("ANYPLOT_THEME", "light")
PAGE_BG = "#FAF8F1" if THEME == "light" else "#1A1A17"
INK = "#1A1A17" if THEME == "light" else "#F0EFE8"
INK_MUTED = "#6B6A63" if THEME == "light" else "#A8A79F"
# Imprint palette — theme-independent categorical colors
IMPRINT_PALETTE = ("#009E73", "#C475FD", "#4467A3", "#BD8233", "#AE3030", "#2ABCCD", "#954477", "#99B314")
# Water phase diagram (physically accurate constants)
triple_t = 273.16 # K
triple_p = 611.73 # Pa
critical_t = 647.1 # K
critical_p = 22.064e6 # Pa
R = 8.314 # J/(mol·K)
# Sublimation curve (Solid-Gas): from 200 K to triple point
sublimation_temps = np.linspace(200, triple_t, 80)
L_sub = 51059 # J/mol — sublimation enthalpy of water
sublimation_pressures = triple_p * np.exp((L_sub / R) * (1 / triple_t - 1 / sublimation_temps))
# Vaporization curve (Liquid-Gas): from triple point to critical point
vaporization_temps = np.linspace(triple_t, critical_t, 100)
L_vap = 40700 # J/mol — vaporization enthalpy of water
vaporization_pressures = triple_p * np.exp((L_vap / R) * (1 / triple_t - 1 / vaporization_temps))
# Melting curve (Solid-Liquid): water has anomalous negative slope
melting_pressures = np.logspace(np.log10(triple_p), np.log10(critical_p * 5), 80)
melting_temps = triple_t - (melting_pressures - triple_p) * 7.5e-8
# Pressure formatter — handles scalar and (x, y) tuple passed by pygal's XY formatter
def fmt_p(v):
p = v[1] if isinstance(v, (list, tuple)) else v
return f"{p / 1e6:.1f} MPa" if p >= 1e6 else (f"{p / 1e3:.1f} kPa" if p >= 1e3 else f"{p:.1f} Pa")
# Title: 46 chars < 67 baseline → no scaling needed, use default 66
title = "phase-diagram-pt · python · pygal · anyplot.ai"
custom_style = Style(
background=PAGE_BG,
plot_background=PAGE_BG,
foreground=INK,
foreground_strong=INK,
foreground_subtle=INK_MUTED,
colors=IMPRINT_PALETTE,
font_family="DejaVu Sans, Helvetica, Arial, sans-serif",
title_font_family="DejaVu Sans, Helvetica, Arial, sans-serif",
title_font_size=66,
label_font_size=56,
major_label_font_size=44,
value_font_size=36,
legend_font_size=44,
legend_font_family="DejaVu Sans, Helvetica, Arial, sans-serif",
label_font_family="DejaVu Sans, Helvetica, Arial, sans-serif",
major_label_font_family="DejaVu Sans, Helvetica, Arial, sans-serif",
value_font_family="DejaVu Sans, Helvetica, Arial, sans-serif",
stroke_width=5,
opacity=0.92,
opacity_hover=1.0,
guide_stroke_color=INK_MUTED,
guide_stroke_dasharray="6,6",
tooltip_font_size=36,
tooltip_font_family="DejaVu Sans, Helvetica, Arial, sans-serif",
tooltip_border_radius=8,
)
chart = pygal.XY(
width=3200,
height=1800,
style=custom_style,
title=title,
x_title="Temperature (K)",
y_title="Pressure (Pa)",
show_legend=True,
legend_at_bottom=True,
legend_box_size=22,
dots_size=2,
stroke=True,
show_x_guides=True,
show_y_guides=True,
logarithmic=True,
explicit_size=True,
truncate_legend=-1,
spacing=20,
margin=40,
margin_bottom=120,
margin_left=220,
margin_right=160,
tooltip_fancy_mode=True,
tooltip_border_radius=8,
interpolate="cubic",
interpolation_precision=200,
xrange=(180, 720),
print_values=False,
human_readable=True,
x_value_formatter=lambda x: f"{x:.0f} K",
value_formatter=fmt_p,
y_labels=[1, 100, 1e4, 1e6, 1e8],
y_label_rotation=0,
)
# Series 1–3: phase boundary curves — Imprint positions 1 (green), 2 (lavender), 3 (blue)
sublimation_points = [
{"value": (float(t), float(p)), "label": f"Sublimation: {t:.0f} K, {fmt_p(p)}"}
for t, p in zip(sublimation_temps[::4], sublimation_pressures[::4], strict=True)
]
chart.add(
"Solid ↔ Gas (Sublimation)",
sublimation_points,
show_dots=False,
stroke_style={"width": 8, "linecap": "round", "linejoin": "round"},
formatter=fmt_p,
)
vaporization_points = [
{"value": (float(t), float(p)), "label": f"Vaporization: {t:.0f} K, {fmt_p(p)}"}
for t, p in zip(vaporization_temps[::5], vaporization_pressures[::5], strict=True)
]
chart.add(
"Liquid ↔ Gas (Vaporization)",
vaporization_points,
show_dots=False,
stroke_style={"width": 8, "linecap": "round", "linejoin": "round"},
formatter=fmt_p,
)
melting_points = [
{"value": (float(t), float(p)), "label": f"Melting: {t:.2f} K, {fmt_p(p)}"}
for t, p in zip(melting_temps[::4], melting_pressures[::4], strict=True)
]
chart.add(
"Solid ↔ Liquid (Melting)",
melting_points,
show_dots=False,
stroke_style={"width": 8, "linecap": "round", "linejoin": "round"},
formatter=fmt_p,
)
# Landmark points — series order controls legend swatch via palette cycling.
# Series 4 → palette[3] = ochre #BD8233 → Critical Point (no per-point override needed)
# Series 5 → palette[4] = matte red #AE3030 → Triple Point (no per-point override needed)
chart.add(
f"Critical Point ({critical_t} K, {fmt_p(critical_p)})",
[
{
"value": (float(critical_t), float(critical_p)),
"label": f"Critical Point — liquid-gas distinction vanishes\n{critical_t} K, {fmt_p(critical_p)}",
}
],
dots_size=18,
stroke=False,
formatter=fmt_p,
)
chart.add(
f"Triple Point ({triple_t} K, {triple_p:.0f} Pa)",
[
{
"value": (float(triple_t), float(triple_p)),
"label": f"Triple Point — all three phases coexist\n{triple_t} K, {triple_p:.0f} Pa",
}
],
dots_size=18,
stroke=False,
formatter=fmt_p,
)
# SVG post-processing: frame removal, phase region labels, callout annotations
svg_string = chart.render(is_unicode=True)
root = ET.fromstring(svg_string)
ns = "http://www.w3.org/2000/svg"
# Remove default chart frame border via CSS override
style_elems = root.findall(f".//{{{ns}}}style")
frame_css = "\nrect.background { stroke: none !important; stroke-width: 0 !important; }"
if style_elems:
style_elems[0].text = (style_elems[0].text or "") + frame_css
# Phase region labels — semi-transparent, color-coded by boundary membership
phase_labels = [
{"text": "SOLID", "x": "600", "y": "580", "size": "52", "color": IMPRINT_PALETTE[2], "opacity": "0.35"},
{"text": "LIQUID", "x": "1370", "y": "400", "size": "52", "color": IMPRINT_PALETTE[1], "opacity": "0.35"},
{"text": "GAS", "x": "1890", "y": "1050", "size": "52", "color": IMPRINT_PALETTE[0], "opacity": "0.35"},
{"text": "SUPERCRITICAL", "x": "2730", "y": "155", "size": "36", "color": IMPRINT_PALETTE[3], "opacity": "0.30"},
{"text": "FLUID", "x": "2730", "y": "193", "size": "36", "color": IMPRINT_PALETTE[3], "opacity": "0.30"},
]
for lbl in phase_labels:
el = ET.SubElement(root, f"{{{ns}}}text")
el.set("x", lbl["x"])
el.set("y", lbl["y"])
el.set(
"style",
f"font-family:DejaVu Sans,Helvetica,Arial,sans-serif;"
f"font-size:{lbl['size']}px;fill:{lbl['color']};font-weight:700;"
f"letter-spacing:4px;opacity:{lbl['opacity']};text-anchor:middle;",
)
el.text = lbl["text"]
# Callout annotations for thermodynamic landmarks
# Triple point: approx SVG (760, 1040) — callout to upper-right
# Critical point: approx SVG (2640, 250) — callout to lower-left
callouts = [
# (x_dot, y_dot, x_end, y_end, x_txt, y_txt1, y_txt2, label, sublabel, anchor)
(760, 1040, 860, 960, 875, 954, 994, "Triple Point", "273.16 K · 611.73 Pa", "start"),
(2640, 250, 2510, 320, 2495, 314, 354, "Critical Point", "647.1 K · 22.064 MPa", "end"),
]
for x_d, y_d, x2, y2, x_t, y_t1, y_t2, label, sublabel, anchor in callouts:
g = ET.SubElement(root, f"{{{ns}}}g")
ln = ET.SubElement(g, f"{{{ns}}}line")
ln.set("x1", str(x_d))
ln.set("y1", str(y_d))
ln.set("x2", str(x2))
ln.set("y2", str(y2))
ln.set("style", f"stroke:{INK_MUTED};stroke-width:2;opacity:0.7;")
t1 = ET.SubElement(g, f"{{{ns}}}text")
t1.set("x", str(x_t))
t1.set("y", str(y_t1))
t1.set(
"style",
f"font-family:DejaVu Sans,Helvetica,Arial,sans-serif;"
f"font-size:36px;fill:{INK};font-weight:600;text-anchor:{anchor};",
)
t1.text = label
t2 = ET.SubElement(g, f"{{{ns}}}text")
t2.set("x", str(x_t))
t2.set("y", str(y_t2))
t2.set(
"style",
f"font-family:DejaVu Sans,Helvetica,Arial,sans-serif;"
f"font-size:30px;fill:{INK_MUTED};font-weight:400;text-anchor:{anchor};",
)
t2.text = sublabel
modified_svg = ET.tostring(root, encoding="unicode")
cairosvg.svg2png(
bytestring=modified_svg.encode("utf-8"), write_to=f"plot-{THEME}.png", output_width=3200, output_height=1800
)
chart.render_to_file(f"plot-{THEME}.html")
Part of Thermodynamic Phase Diagram (Pressure-Temperature) on anyplot.ai.