Single Replacement Reaction
A single replacement reaction (also called a single displacement reaction) is a type of chemical reaction in which one element displaces another element from a compound, following the general pattern A + BC → AC + B. The reaction occurs when the displacing element is more reactive (higher on the activity series) than the element it replaces; if the displacing element is less reactive, no reaction occurs. Single replacement reactions are widely used in metallurgy and electrochemistry — for example, extracting metals from their ores or in galvanic cells.
Key Formula
A + BC → AC + B (element A displaces element B from compound BC)
LaTeX: A + BC \rightarrow AC + B
| Symbol | Meaning | Unit |
|---|---|---|
| A | More reactive element (the displacing element) | dimensionless |
| BC | Compound containing the element to be displaced | dimensionless |
| AC | New compound formed | dimensionless |
| B | Displaced element, released as free element | dimensionless |
Worked Example
Problem
Will zinc metal react with copper sulphate solution? If so, write the balanced equation.
Solution
Step 1: Check the activity series — Zinc (Zn) is above Copper (Cu), so zinc is more reactive. Step 2: Since Zn is more reactive than Cu, Zn will displace Cu from CuSO₄. Step 3: Write the unbalanced equation: Zn + CuSO₄ → ZnSO₄ + Cu Step 4: Count atoms: Left: 1 Zn, 1 Cu, 1 S, 4 O Right: 1 Zn, 1 S, 4 O, 1 Cu Step 5: All atoms balance — no coefficients needed.
Answer
Zn + CuSO₄ → ZnSO₄ + Cu (reaction proceeds; blue solution becomes colourless and copper deposits form)
Activity Series of Common Metals (Reactivity Decreasing Downward)
| Metal | Symbol | Relative Reactivity | Displaces |
|---|---|---|---|
| Potassium | K | Very high | All metals below it |
| Zinc | Zn | Moderate | Fe, Ni, Cu, Ag, Au |
| Iron | Fe | Moderate | Ni, Cu, Ag, Au |
| Copper | Cu | Low | Ag, Au only |
| Silver | Ag | Very low | Au only |
| Gold | Au | Least reactive | None (noble metal) |
Interactive Tools
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Related Terms
Double Replacement Reaction
A double replacement reaction (also called a double displacement or metathesis reaction) is a type of chemical reaction in which the cations and anions of two ionic compounds exchange partners, following the general pattern AB + CD → AD + CB. These reactions typically occur in aqueous solution and are driven by the formation of a precipitate, a gas, or a weakly ionised product (such as water). Double replacement reactions underlie many important processes, including precipitation reactions used in water treatment, neutralisation reactions in acid-base chemistry, and qualitative analysis in analytical chemistry.
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.
Oxidation-Reduction Reaction
An oxidation-reduction reaction (redox reaction) is a chemical reaction involving the simultaneous transfer of electrons between two species: the substance that loses electrons is oxidised (its oxidation state increases), and the substance that gains electrons is reduced (its oxidation state decreases). Redox reactions are among the most important in chemistry and biology — they underpin cellular respiration, photosynthesis, corrosion, electroplating, and the operation of batteries and fuel cells. The key mnemonic "OIL RIG" (Oxidation Is Loss, Reduction Is Gain) helps students remember the direction of electron transfer.
From Latin "displacere" (to displace) combined with "single" to indicate that only one element is exchanged. The concept was formalised as chemists developed the activity (reactivity) series of metals in the 19th century.