Synthesis Reaction
A synthesis reaction (also called a combination reaction) is a type of chemical reaction in which two or more reactants combine to form a single, more complex product, following the general pattern A + B → AB. Synthesis reactions are fundamental in both nature and industry — for example, the formation of water from hydrogen and oxygen, or the industrial synthesis of ammonia by the Haber process. They are the opposite of decomposition reactions and often release energy in the form of heat or light.
Key Formula
A + B → AB (two or more reactants combine to form one product)
LaTeX: A + B \rightarrow AB
| Symbol | Meaning | Unit |
|---|---|---|
| A | First reactant (element or compound) | dimensionless |
| B | Second reactant (element or compound) | dimensionless |
| AB | Single product formed by combination | dimensionless |
Worked Example
Problem
Write the balanced equation for the synthesis of water from hydrogen and oxygen gases.
Solution
Step 1: Identify the reactants — hydrogen gas (H₂) and oxygen gas (O₂). Step 2: Identify the product — water (H₂O). Step 3: Write the unbalanced equation: H₂ + O₂ → H₂O Step 4: Count atoms: H: 2=2 ✓; O: 2≠1 ✗ Step 5: Balance oxygen by placing a coefficient of 2 in front of H₂O: H₂ + O₂ → 2 H₂O Step 6: Recount H: 2≠4 ✗; place coefficient 2 in front of H₂: 2 H₂ + O₂ → 2 H₂O Step 7: Verify — H: 4=4 ✓; O: 2=2 ✓
Answer
2 H₂ + O₂ → 2 H₂O (balanced synthesis reaction)
Common Examples of Synthesis Reactions
| Reactants | Product | Equation | Application |
|---|---|---|---|
| Hydrogen + Oxygen | Water | 2 H₂ + O₂ → 2 H₂O | Fuel cells, rocket engines |
| Nitrogen + Hydrogen | Ammonia | N₂ + 3 H₂ → 2 NH₃ | Fertiliser production (Haber process) |
| Sodium + Chlorine | Sodium chloride | 2 Na + Cl₂ → 2 NaCl | Common table salt |
| Carbon + Oxygen | Carbon dioxide | C + O₂ → CO₂ | Combustion processes |
| Calcium + Oxygen | Calcium oxide | 2 Ca + O₂ → 2 CaO | Cement and construction |
Interactive Tools
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Related Terms
Decomposition Reaction
A decomposition reaction is a type of chemical reaction in which a single compound breaks down into two or more simpler substances, following the general pattern AB → A + B. Decomposition reactions are the reverse of synthesis reactions and typically require an input of energy such as heat (thermal decomposition), light (photodecomposition), or electricity (electrolysis) to break the chemical bonds of the original compound. They play vital roles in industrial chemistry, such as the decomposition of limestone to produce quicklime, and in biological systems, such as the breakdown of hydrogen peroxide by the enzyme catalase.
Chemical Reaction
A chemical reaction is a process in which one or more substances (reactants) are transformed into one or more different substances (products) through the breaking and forming of chemical bonds. Chemical reactions involve changes in the arrangement of atoms, resulting in new materials with different properties from the original substances. They are fundamental to all biological, industrial, and environmental processes, from cellular respiration to the manufacture of medicines.
Balancing Chemical Equations
Balancing chemical equations is the process of adjusting the stoichiometric coefficients in front of each formula in a chemical equation so that the number of atoms of each element is equal on both the reactant and product sides, satisfying the Law of Conservation of Mass. Only coefficients (not subscripts) may be changed during balancing, because altering subscripts would change the identity of the compounds. Balanced equations are essential for calculating the exact quantities of reactants and products in stoichiometric calculations used in laboratories and industry.
From Greek "synthesis" meaning "a putting together", derived from "syn-" (together) and "tithenai" (to place). The term has been used in chemistry since the early 19th century to describe reactions that build larger molecules from smaller ones.