Types of Chemical Reactions: Recognize the Pattern

Types of Chemical Reactions A chemical reaction is a process in which one or more substances (reactants) are converted into new substances (products) with different properties. 1. Combination Reaction Two or more substances combine to form a single product. General form: \[ A+B\rightarrow AB \] Example: \[ 2Mg+O_2\rightarrow2MgO \] Magnesium combines with oxygen to form magnesium oxide. Another example: \[ CaO+H_2O\rightarrow Ca(OH)_2 \] --- 2. Decomposition Reaction A single compound breaks down into two or more simpler substances. General form: \[ AB\rightarrow A+B \] Example: \[ CaCO_3\xrightarrow{\Delta}CaO+CO_2 \] Calcium carbonate decomposes on heating. Types of decomposition a) Thermal decomposition — by heat \[ 2KClO_3\xrightarrow{\Delta}2KCl+3O_2 \] b) Electrolytic decomposition — by electricity \[ 2H_2O\xrightarrow{electricity}2H_2+O_2 \] c) Photochemical decomposition — by light \[ 2AgCl\xrightarrow{sunlight}2Ag+Cl_2 \] --- 3. Displacement Reaction A more reactive element displaces a less reactive element from its compound. General form: \[ A+BC\rightarrow AC+B \] Example: \[ Zn+CuSO_4\rightarrow ZnSO_4+Cu \] Zinc is more reactive than copper, so zinc displaces copper. Another example: \[ Fe+CuSO_4\rightarrow FeSO_4+Cu \] --- 4. Double Displacement Reaction Two compounds exchange their ions to form two new compounds. General form: \[ AB+CD\rightarrow AD+CB \] Example: \[ AgNO_3+NaCl\rightarrow AgCl\downarrow+NaNO_3 \] Here, AgCl is an insoluble precipitate. Therefore, this is also called a precipitation reaction. Another example: \[ HCl+NaOH\rightarrow NaCl+H_2O \] This is a neutralisation reaction because an acid reacts with a base. --- 5. Combustion Reaction A substance reacts rapidly with oxygen, usually producing heat and light. Example: \[ CH_4+2O_2\rightarrow CO_2+2H_2O+\text{heat} \] Methane undergoes combustion in oxygen. Example of metal combustion: \[ 2Mg+O_2\rightarrow2MgO+\text{heat} \] --- 6. Neutralisation Reaction An acid reacts with a base to produce salt and water. General form: \[ Acid+Base\rightarrow Salt+Water \] Example: \[ HCl+NaOH\rightarrow NaCl+H_2O \] Another example: \[ H_2SO_4+2NaOH\rightarrow Na_2SO_4+2H_2O \] --- 7. Redox Reaction A reaction in which oxidation and reduction occur simultaneously. Example: \[ Zn+CuSO_4\rightarrow ZnSO_4+Cu \] Zn → Zn²⁺ : oxidation Cu²⁺ → Cu : reduction So, this is a redox reaction. Quick Identification Table Reaction type Key feature Example Combination Many reactants → one product \(CaO+H_2O\rightarrow Ca(OH)_2\) Decomposition One reactant → many products \(CaCO_3\rightarrow CaO+CO_2\) Displacement One element replaces another \(Zn+CuSO_4\rightarrow ZnSO_4+Cu\) Double displacement Exchange of ions \(AgNO_3+NaCl\rightarrow AgCl+NaNO_3\) Combustion Reaction with O₂ + heat \(CH_4+2O_2\rightarrow CO_2+2H_2O\) Neutralisation Acid + base → salt + water \(HCl+NaOH\rightarrow NaCl+H_2O\) Redox Oxidation + reduction together \(Zn+Cu^{2+}\rightarrow Zn^{2+}+Cu\) Easy Memory Trick C-D-D-D-C-N-R Combination → Decomposition → Displacement → Double displacement → Combustion → Neutralisation → Redox.