Let’s fire things up 🔥—here comes your full Lesson 6: Chemical Reactions and Equations blog post!

⚗️ Lesson 6: Chemical Reactions and Equations

When atoms break up, rearrange, and form something brand new.

Pop quiz: What do fireworks, rust, digestion, and baking all have in common?

They’re all chemical reactions—processes where substances are transformed into new substances. Atoms don’t disappear; they just rearrange themselves. This is where chemistry gets explosive, colorful, bubbly, and beautifully balanced.

Let’s dig into how reactions work, the different types, and how to write them in the language of chemistry: equations.

🔄 What Is a Chemical Reaction?

A chemical reaction happens when substances (called reactants) interact and form products with different chemical identities.

💡 Think of it like cooking:

Reactants = ingredients

Reaction = the cooking process

Products = the final dish (can’t “uncook” a cake!)

🔥 Evidence of a Chemical Reaction

How do you know if something’s a chemical reaction and not just a physical change (like melting or breaking)? Look for these clues:

• 🔥 Temperature change (without heating it)
• 💨 Gas production (bubbles, fizz)
• 💧 Formation of a precipitate (a solid forms in a liquid)
• 🎨 Color change
• 🌟 Light or sound released

🧪 Types of Chemical Reactions

Chemistry has 5 “main families” of reactions—knowing them helps you predict how substances behave.

1. 

Synthesis (Combination)

• Two or more substances form one product.
• A + B → AB
• 🧠 Example: 2H₂ + O₂ → 2H₂O (hydrogen and oxygen make water)

2. 

Decomposition

• One substance breaks into two or more products.
• AB → A + B
• 🔥 Example: 2H₂O₂ → 2H₂O + O₂ (hydrogen peroxide breaks down)

3. 

Single Replacement

• One element replaces another in a compound.
• A + BC → B + AC
• 🧪 Example: Zn + CuSO₄ → Cu + ZnSO₄

4. 

Double Replacement

• Two compounds switch ions to form new compounds.
• AB + CD → AD + CB
• 🧫 Example: AgNO₃ + NaCl → AgCl + NaNO₃

5. 

Combustion

• A hydrocarbon reacts with oxygen to produce carbon dioxide and water.
• Fuel + O₂ → CO₂ + H₂O
• 🔥 Example: CH₄ + 2O₂ → CO₂ + 2H₂O
• Almost always exothermic (releases heat)

✍️ Writing Chemical Equations

Chemical equations show what’s reacting and what’s produced.

Basic format:

Reactants → Products

But there’s a rule: the Law of Conservation of Mass.

⚖️ The Law of Conservation of Mass

Matter cannot be created or destroyed. So in a reaction:

• The number of atoms of each element must stay the same before and after.
• That means: equations must be balanced.

🔢 How to Balance a Chemical Equation

Follow these steps:

Step 1: Write the unbalanced equation

Example:

H₂ + O₂ → H₂O

Step 2: Count atoms on each side

Left: H = 2, O = 2

Right: H = 2, O = 1 ❌ Not balanced

Step 3: Use coefficients to balance

Try: 2H₂ + O₂ → 2H₂O

Now:

Left: H = 4, O = 2

Right: H = 4, O = 2 ✅ Balanced!

Tip:

• Only change coefficients, never change subscripts (that changes the compound).
• Balance metals first, then nonmetals, and oxygen/hydrogen last (especially in combustion).

🧠 Recap Chart:

Concept	Explanation
Reactants → Products	Starting substances → New substances
Synthesis	A + B → AB
Decomposition	AB → A + B
Single Replacement	A + BC → B + AC
Double Replacement	AB + CD → AD + CB
Combustion	Fuel + O₂ → CO₂ + H₂O
Law of Conservation	Same number of atoms on both sides of the equation
Balanced Equation	Coefficients used to keep atom counts equal

🧨 Thought to Take With You:

“A reaction is just a change in relationships—atoms leaving old bonds and forming new ones. Chemistry is breakups and makeups, but with molecules.”