🎓 Prepared by students from Boğaziçi University

What are Synthesis Reactions?

Synthesis reactions occur when two or more substances combine to form a single, new product. They follow the pattern A + B → AB and are fundamental to understanding chemical change and bonding.

Short answer

A synthesis reaction combines two or more reactants into one product: A + B → AB. Common examples include burning hydrogen (2H₂ + O₂ → 2H₂O) and reacting sodium with chlorine (2Na + Cl₂ → 2NaCl).

Synthesis Reaction: A + B → AB

1
Reactant A
First substance
↓
2
Reactant B
Second substance
↓
3
Combine
Chemical reaction occurs
↓
4
Product AB
Single new compound forms

Step-by-step worked examples

Sodium (Na) reacts with chlorine gas (Cl₂) to form sodium chloride. Write and balance the equation.

Unbalanced: Na + Cl₂ → NaCl
Balance Cl: need 2 NaCl on right
Balance Na: need 2 Na on left
Balanced: 2Na + Cl₂ → 2NaCl

Hydrogen gas (H₂) burns in oxygen (O₂) to form water (H₂O). Balance this synthesis reaction.

Unbalanced: H₂ + O₂ → H₂O
Balance O: need 2 H₂O on right
Balance H: need 2 H₂ on left
Balanced: 2H₂ + O₂ → 2H₂O

Carbon (C) burns completely in oxygen to form carbon dioxide. Write the balanced synthesis equation.

Unbalanced: C + O₂ → CO₂
Carbon: 1 on left, 1 on right ✓
Oxygen: 2 on left, 2 on right ✓
Balanced: C + O₂ → CO₂

Flashcards

Quick quiz

Q1.Which equation is a synthesis reaction?

Correct answer: B. 2Na + Cl₂ → 2NaCl combines two reactants into one product.

Q2.What is the general form of synthesis?

Correct answer: B. Synthesis: A + B → AB (two or more combine into one).

Q3.Is 2H₂ + O₂ → 2H₂O synthesis?

Correct answer: B. Two substances (hydrogen and oxygen) combine to form one product (water).

Q4.When iron (Fe) burns in oxygen, it forms Fe₃O₄. This is synthesis because…

Correct answer: B. Fe and O₂ (two reactants) combine to form Fe₃O₄ (one product).

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Common mistakes

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Synthesis always involves elements only. — Correct: Synthesis can involve elements, compounds, or both. For example, 2Al + 3Cl₂ → 2AlCl₃ combines an element and a compound.

✗

Burning something is not synthesis. — Correct: Combustion is a type of synthesis reaction. Hydrogen burning: 2H₂ + O₂ → 2H₂O.

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Synthesis has many products. — Correct: Synthesis defines having one single product from multiple reactants.

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A + B → A + B + C is synthesis. — Correct: That is not synthesis — synthesis requires all reactants to form ONE product: A + B → AB.

FAQ

What does synthesis mean in chemistry?

Synthesis means combining two or more substances into one new product (A + B → AB).

Is combustion a synthesis reaction?

Yes. Burning is a synthesis reaction. Example: 2H₂ + O₂ → 2H₂O (hydrogen + oxygen → water).

What is an example of synthesis?

Sodium + chlorine gas → sodium chloride: 2Na + Cl₂ → 2NaCl. Two substances combine into salt.

How do I identify synthesis?

Look for the pattern: two or more reactants (left) forming one product (right). Count substances: many in → one out.