Balance Chemical Equations | Interactive Chemistry model

Balancing challenge

Choose a reaction

Not balanced yet — compare the atom counts below.

Reactants

Products

Element	Reactant atoms	Product atoms	Check

Strategy: Start with an element that appears in only one substance on each side. Balance one element at a time, then recheck all elements. Leave hydrogen and oxygen until later when they occur in several compounds.

Check Chemical Equations with Python

A computer can check an equation by storing the number of each type of atom in every molecule, multiplying those counts by the coefficients, and comparing totals on the two sides.

# Example:
# CH4 + O2 -> CO2 + H2O

# Atom counts in each molecule
molecules = {
    "CH4": {"C": 1, "H": 4},
    "O2":  {"O": 2},
    "CO2": {"C": 1, "O": 2},
    "H2O": {"H": 2, "O": 1}
}

# Try changing these coefficients
reactants = {
    "CH4": 1,
    "O2": 2
}

products = {
    "CO2": 1,
    "H2O": 2
}


def count_atoms(side):
    totals = {}

    for formula, coefficient in side.items():

        for element, atoms in (
            molecules[formula].items()
        ):
            totals[element] = (
                totals.get(element, 0)
                + coefficient * atoms
            )

    return totals


left_atoms = count_atoms(reactants)
right_atoms = count_atoms(products)

print("Reactants:", left_atoms)
print("Products: ", right_atoms)

if left_atoms == right_atoms:
    print("Equation is BALANCED")
else:
    print("Equation is NOT balanced")

# Balanced methane combustion:
#
# CH4 + 2O2 -> CO2 + 2H2O
#
# Left:
# C = 1, H = 4, O = 4
#
# Right:
# C = 1, H = 4, O = 4

Conservation of Atoms

The Python model does not need to know how to perform the reaction. It only checks whether the number of atoms of every element is identical before and after the reaction.

This is the mathematical basis of balancing chemical equations: find the smallest whole-number coefficients that satisfy all of the atom-count constraints simultaneously.