Chemical Reactions and Equations
Explore the fundamental concepts of Chemical Reactions and Equations with our comprehensive guide. Understand the types, examples, and balancing of chemical equations to master this essential topic in chemistry.
Introduction to Chemical Reactions
Chemical Reaction: The transformation of chemical substances into new substances with different properties.
Examples: Rusting of iron, setting of milk into curd, digestion of food, respiration.
Characteristics: In a chemical reaction, a new substance is formed which has properties different from the original substances.
Key Terminologies
Reactants: Substances that participate in a chemical reaction.
Example: In the reaction 2Mg + O2 → 2MgO, magnesium (Mg) and oxygen (O2) are reactants.
Products: New substances formed as a result of a chemical reaction.
Example: In the reaction 2Mg + O2 → 2MgO, magnesium oxide (MgO) is the product.
Characteristics of Chemical Reactions
- Evolution of Gas: Some reactions produce a gas.
Example: Reaction between zinc and dilute sulfuric acid produces hydrogen gas.
Zn + H2SO4 → ZnSO4 + H2
- Change in Color: Some reactions result in a color change.
Example: Reaction between citric acid and potassium permanganate changes color from purple to colorless.
- Change in State: Some reactions change the state of substances.
Example: Combustion of candle wax changes it from solid to liquid and gas.
- Change in Temperature: Some reactions release or absorb heat.
Example: Reaction between quick lime and water releases heat.
CaO + H2O → Ca(OH)2
- Formation of Precipitate: Some reactions form an insoluble solid.
Example: Reaction between sulfuric acid and barium chloride forms a white precipitate of barium sulfate.
BaCl2 + H2SO4 → BaSO4 + 2HCl
Chemical Equations
Chemical Equation: Represents a chemical reaction using symbols and formulas.
Example: H2 + O2 → H2O
Balanced Chemical Equation: Number of atoms of each element is equal on both sides.
Example: Zn + H2SO4 → ZnSO4 + H2
Unbalanced Chemical Equation: Number of atoms of each element is not equal on both sides.
Example: Fe + H2O → Fe3O4 + H2
Balancing Chemical Equations
To balance a chemical equation, follow these steps:
- Write the unbalanced equation.
- Count the number of atoms of each element on both sides.
- Use coefficients to balance the atoms for each element.
- Ensure that the number of atoms for each element is equal on both sides.
Example: Balancing the equation Fe + H2O → Fe3O4 + H2
Unbalanced Equation: Fe + H2O → Fe3O4 + H2
- Count the atoms of each element:
- Reactants: Fe = 1, H = 2, O = 1
- Products: Fe = 3, H = 2, O = 4
- Balance oxygen atoms by multiplying H2O by 4:
Fe + 4H2O → Fe3O4 + H2
- Balance hydrogen atoms by multiplying H2 by 4:
Fe + 4H2O → Fe3O4 + 4H2
- Balance iron atoms by multiplying Fe by 3:
3Fe + 4H2O → Fe3O4 + 4H2
Types of Chemical Reactions
- Combination Reactions: Two or more reactants combine to form one product.
Example: 2Mg + O2 → 2MgO
- Decomposition Reactions: One compound decomposes into two or more products.
- Thermal Decomposition: Decomposition due to heat.
Example: CaCO3 → CaO + CO2
- Electrolytic Decomposition: Decomposition due to electricity.
Example: 2H2O → 2H2 + O2
- Photolytic Decomposition: Decomposition due to light.
Example: 2AgCl → 2Ag + Cl2
- Thermal Decomposition: Decomposition due to heat.
- Displacement Reactions: A more reactive element displaces a less reactive element from its compound.
Example: Zn + CuSO4 → ZnSO4 + Cu
- Double Displacement Reactions: Exchange of ions between two reactants to form new compounds.
Example: Na2SO4 + BaCl2 → BaSO4 + 2NaCl
- Redox Reactions: Involve oxidation and reduction processes.
Example: CuO + H2 → Cu + H2O
- Exothermic Reactions: Reactions that release heat.
Example: Combustion of methane.
CH4 + 2O2 → CO2 + 2H2O + heat
- Endothermic Reactions: Reactions that absorb heat.
Example: Decomposition of calcium carbonate.
CaCO3 + heat → CaO + CO2
Effects of Oxidation Reactions in Everyday Life
- Corrosion: The slow conversion of metals into undesirable compounds by reaction with elements in the environment, such as oxygen and moisture.
Example: Rusting of iron.
4Fe + 3O2 + 6H2O → 4Fe(OH)3
Prevention: Painting, galvanizing, applying oil or grease, using rust-resistant alloys.
- Rancidity: The spoilage of food containing fats and oils due to oxidation.
Example: Oils and fats become rancid when exposed to air, causing unpleasant taste and smell.
Prevention: Adding antioxidants, vacuum packing, storing in airtight containers, flushing with nitrogen, refrigeration.
