chempy

ChemPy - Physical and Analytical Chemistry

ChemPy provides a systematic way to handle chemical entities and reactions. It can automatically balance complex redox reactions, solve systems of ordinary differential equations (ODEs) for kinetics, and calculate species distribution in equilibria.

When to Use

• Balancing chemical equations (including ionic and redox reactions).
• Simulating chemical kinetics (concentration vs. time) using ODE solvers.
• Calculating chemical equilibria and speciation (e.g., pH of a buffer).
• Handling physical constants and units in chemical calculations.
• Modeling ionic strength and activity coefficients (Debye-Hückel).
• Parsing chemical formulas and calculating molar masses.
• Generating LaTeX or HTML representations of chemical reactions.

Reference Documentation

Official docs: https://bjodah.github.io/chempy/
GitHub: https://github.com/bjodah/chempy
Search patterns: chempy.Reaction, chempy.ReactionSystem, chempy.balance_stoichiometry, chempy.kinetics

Core Principles

Chemical Entities

Represented as strings ('H2O', 'Fe+3') or Substance objects. ChemPy can parse these to determine composition and charge.

Reaction Systems

A collection of Reaction objects. This system can be converted into a mathematical model (ODE) where the rates are defined by mass-action kinetics or custom rate laws.

Units

ChemPy integrates with quantities or pint to ensure dimensional correctness, which is vital for calculating rates (e.g., M⁻¹s⁻¹).

Quick Reference

Installation

pip install chempy

Standard Imports

import numpy as np
import matplotlib.pyplot as plt
from chempy import Reaction, ReactionSystem, Substance
from chempy.util.parsing import formula_to_composition

Basic Pattern - Balancing a Reaction

from chempy import balance_stoichiometry

# 1. Define reactants and products
reac, prod = balance_stoichiometry({'H2', 'O2'}, {'H2O'})

# 2. Output coefficients
print(reac) # {'H2': 2, 'O2': 1}
print(prod) # {'H2O': 2}