Daily Chemical Processes

Identifying Chemical Changes and Their Effects

Before judging an activity as "green" or "not green", we need to know what chemical process is happening. Burning waste, washing clothes, making compost, cooking, photosynthesis in plants, and rusting iron all involve substances changing or interacting.

Green chemistry evaluates how a chemical product or process is designed from the start. The design should reduce hazards, waste, excessive energy use, single-use materials, and accident risks. It also aims to reduce the use or generation of hazardous substances.

Checking a process means answering four questions, one for each part of the process.

Part of the process	Question
Starting substances	What substances enter the process?
Change	Are the substances only mixed, or do they become new substances?
Products	What substances form after the process runs?
Impact	Is there waste, excess heat, hazardous gas, or material that is hard to degrade?

How Atoms Form Elements and Molecules

The periodic table identifies each element symbol, but a symbol alone does not state the particle type. We must still distinguish an atom, an element, an elemental molecule, and a compound molecule.

An atom is the smallest particle that still characterizes a chemical element. A chemical element is a species of atoms with the same number of protons. A molecule is an electrically neutral entity made of more than one atom.

Atom and Molecule Model

Rotate the model to distinguish one atom, one element, an elemental molecule, and a compound molecule before reading reaction equations.

One particle in this diagram represents one atom.

What you are reading: One $\mathrm{C}$ atom.
How to read it: The symbol $\mathrm{C}$ identifies this atom as carbon.

The table below distinguishes four terms used in the reaction examples.

Term	Meaning	Example
Atom	One particle of an element.	a $\mathrm{C}$ atom or an $\mathrm{O}$ atom
Element	A type of atom with the same number of protons.	iron, carbon, oxygen
Elemental molecule	A molecule made from atoms of the same element.	$\mathrm{O_2}$ , $\mathrm{N_2}$ , $\mathrm{P_4}$ , $\mathrm{S_8}$
Compound molecule	A molecule made from atoms of different elements.	$\mathrm{H_2O}$ , $\mathrm{CO_2}$ , $\mathrm{C_6H_{12}O_6}$

Not every compound exists as separate molecules. Table salt, for example, forms a repeating ionic arrangement. The examples below use molecules to show how simple reaction equations are read.

Parts of a Reaction Equation

A chemical reaction equation records reactants, products, and their relative amounts. Substances on the left are reactants, substances on the right are products, the arrow means "yields", and numbers placed before formulas are called coefficients.

In a chemical equation, reactants are written on the left and products on the right. Plus signs separate substances, and coefficients show relative amounts.

The basic pattern is:

\text{reactants} \rightarrow \text{products}

State symbols are written after the formula.

Symbol	Meaning
$\mathrm{(s)}$	solid
$\mathrm{(l)}$	liquid
$\mathrm{(g)}$	gas
$\mathrm{(aq)}$	dissolved in water

Coefficients may be changed to balance a reaction. Subscripts inside formulas must not be changed casually, because subscripts define the substance. Writing $\mathrm{H_2O}$ is different from writing $\mathrm{H_2O_2}$ .

Balance the Photosynthesis Equation

Photosynthesis is often written as a summary reaction. The real process has many steps, but the summary equation records the atoms before and after the reaction. Photosynthesis uses carbon dioxide and water to produce sugar and oxygen.

An unbalanced equation can be written as:

\begin{aligned} &\mathrm{CO_2(g)} + \mathrm{H_2O(l)} \\ &\rightarrow \mathrm{C_6H_{12}O_6} + \mathrm{O_2(g)} \end{aligned}

If we count atoms, the two sides do not match.

Element	Left	Right
$\mathrm{C}$	$1$	$6$
$\mathrm{H}$	$2$	$12$
$\mathrm{O}$	$3$	$8$

The right coefficients make the atom count match:

\begin{aligned} &6\mathrm{CO_2(g)} + 6\mathrm{H_2O(l)} \\ &\xrightarrow{\text{light}} \mathrm{C_6H_{12}O_6} + 6\mathrm{O_2(g)} \end{aligned}

This formal summary covers the many steps of photosynthesis. The carbohydrate formula is therefore shown without a phase symbol.

The number of atoms of each element is now equal on both sides of the equation.

Element	Left	Right
$\mathrm{C}$	$6$	$6$
$\mathrm{H}$	$12$	$12$
$\mathrm{O}$	$18$	$18$

To balance the equation, keep each chemical formula unchanged, adjust only the coefficients, and confirm that both sides contain the same number of atoms of every element.

Evaluate the Process with Green Chemistry

After we can read a reaction, we can judge whether the process fits green chemistry principles. A process can be useful but still not green if it forms pollutants, uses unnecessary hazardous substances, or needs too much energy.

Everyday process	Chemical change	Green chemistry assessment
Burning plastic waste	Organic substances in the plastic react with oxygen and release heat. Smoke and gaseous products can form.	This disposal method creates additional pollutants and does not prevent waste at the source.
Using cleaner in the right amount	Cleaning agents help remove dirt without excessive use.	The correct dose avoids unnecessary consumption and residue, while the product's hazard instructions still apply.
Composting food scraps	Microorganisms break organic materials down step by step.	Proper composting can reduce organic waste. Moisture and airflow must be controlled to limit odor, leachate, and pests.
Randomly mixing household cleaners	Substances that are safe separately can react to form hazardous gas.	This raises accident risk. Mix cleaners only when the manufacturer explicitly instructs it.

Do not mix household bleach or disinfectants with other cleaners. The mixture can release vapors that are dangerous to breathe. Follow the product label and ventilation instructions.

A material's origin alone does not determine whether it is safe. We also need to examine its composition, dose, and use. Composting can help, but poor management can still create odor, leachate, or pests. A manufactured cleaner can be safer when its composition is known, the dose is correct, and less waste is produced.

Judging Processes from Substances and Impact

Imagine three ways to handle dry leaves in a yard.

Option	What happens	Judgment
Burn them	Leaves react with oxygen and produce smoke.	Not suitable for green chemistry because pollution forms.
Put them in mixed trash	The leaves add to the waste that must be handled.	Better than burning, although waste is still produced.
Compost them properly	Organic material slowly breaks down into compost.	This avoids burning and turns existing organic waste into material that can be added to suitable soil. Composting alone does not redesign a chemical product or process.

Composting is a waste-treatment method, and it counts as green chemistry only when a chemical product or process is deliberately redesigned to prevent harm at the source.

To analyze an everyday chemical process, identify the substances that enter, the changes that occur, the substances that leave, and the hazards that can be prevented at the source.