- A combination reaction is a reaction where two or more substances combine to form a single product.
Example: CaO + H₂O → Ca(OH)₂ - Combination reactions are often exothermic, meaning they release heat.
Example: Reaction of quick lime with water. - Respiration is an exothermic reaction where glucose combines with oxygen to release energy.
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy - One product is formed in combination reactions, regardless of the number of reactants (usually 2 or more).
Definitions [16]
Definition: Combination Reaction
A reaction in which a single product is formed from two or more reactants is known as a combination reaction.
OR
When two or more reactants combine in a reaction to form a single product, it is a combination reaction.
Define the term – double decomposition – neutralization reaction.
When an acid reacts with a base salt and water are formed and this is called Neutralisation.
Double-decomposition – Neutralisation reaction :
“Is the chemical reaction between two compounds (acid and base) to interchange radicals and produce salt and water.”
Definition: Thermal Decomposition
When a decomposition reaction is carried out by heating, it is called thermal decomposition.
Definition: Decomposition Reaction
A single reactant breaks down to give simpler products. This is a decomposition reaction.
OR
The chemical reaction in which two or more products are formed from a single reactant is a decomposition reaction.
Definition: Single Displacement Reaction
The reaction in which the place of the ion of a less reactive element in a compound is taken by another more reactive element by formation of its own ions, is called displacement reaction.
Definition: Double Displacement Reaction
Reactions in which there is an exchange of ions between the reactants are called double displacement reactions.
OR
The reaction in which the ions in the reactants are exchanged to form a precipitate is a double displacement reaction.
Define the following in terms of gain or loss of hydrogen with one example:
Oxidation
The loss of hydrogen from a substance is also called oxidation.
When hydrogen sulphide reacts with chlorine, then sulphur and hydrogen chloride are formed.
\[\ce{\underset{Hydrogen sulphide}{H2S} + \underset{Chlorine}{Cl2} -> \underset{Sulphur}{S} + \underset{Hydrogen chloride}{2HCl}}\]
Define the following in terms of gain or loss of hydrogen with one example:
Reduction
The gain of hydrogen to a substance is called reduction.
When nitrogen reacts with hydrogen to form ammonia (NH3).
\[\ce{N2 + 3H2 -> 2NH3}\]
Definition: Oxidation Reaction
The chemical reaction in which a reactant combines with oxygen or loses hydrogen to form the product is called oxidation reaction.
Definition: Oxidants or Oxidising Agents
Chemical substances which bring about an oxidation reaction by making oxygen available are called oxidants or oxidizing agents.
OR
Substances that can give oxygen to other substances are called oxidants or oxidizing agents.
Define redox reaction.
Redox reactions are those in which reduction and oxidation both takes place simultaneously i.e. one substance is reduced while the other gets oxidised.
Define oxidation number.
The oxidation number of an element is defined as the formal charge that an atom of that element appears to have when electrons are counted.
Define an oxidation reaction.
The chemical reaction in which reactants gain oxygen to form the corresponding oxide. Also, A chemical reaction in which reactants lose hydrogen to form a product is called oxidation.
Example: \[\ce{H2S + Cl -> 2HCl + S}\]
Define reduction.
Those reactions in which hydrogen combines with a substance or oxygen is removed from a substance, are known as reduction reactions.
Example: \[\ce{2HgO->[heat]2Hg +O2}\]
Define corrosion.
When a metal is attacked by substances around it, such as moisture, acids, etc., it is said to corrode, and this process is called corrosion.
Corrosion is an electrochemical process in which a metal is oxidised to a metal oxide or another salt of the metal by losing electrons to oxygen or another electronegative element, forming a coating on the metal surface.
Define neutralization.
Neutralization: A chemical reaction in which a base or an alkali reacts, with an acid to produce salt and water only.
\[\ce{\underset{\text{sodium hydroxide}}{NaOH(aq)} +\underset{\text{hydro chloride acid}}{HCl(aq)}->\underset{\text{sodium cholride}}{NaCl(aq)}+\underset{\text{water}}{H2O}}\]
Chemica Equations [1]
Chemical Equations: Combination Reaction
- C + O₂ → CO₂
- 2H₂ + O₂ → 2H₂O
- 2Mg + O₂ → 2MgO
Key Points
Key Points: Combination Reaction
Key Points: Decomposition Reaction
- Thermal decomposition involves heating a compound to break it into simpler substances, e.g.,
2Pb(NO₃)₂ ⟶ 2PbO + 4NO₂ + O₂ (brown fumes of NO₂ observed). - Electrolytic decomposition uses electricity to decompose compounds, e.g.,
2H₂O ⟶ 2H₂ + O₂ (Electrolysis of water gives hydrogen and oxygen gases). - Photodecomposition occurs when light energy breaks down a compound, e.g.,
2AgCl ⟶ 2Ag + Cl₂ (white silver chloride turns grey in sunlight). - Thermal decomposition of calcium carbonate produces lime (CaO) and CO₂ gas, which turns lime water milky.
- Decomposition reactions are usually endothermic and require heat, light, or electricity to occur (e.g., the decomposition of ferrous sulphate, calcium carbonate, or sugar).
Key Points: Single Displacement Reactions
- A more reactive metal can replace a less reactive metal from its compound in solution.
- Zinc, iron, and lead can displace copper from copper sulphate or copper chloride solutions.
- During displacement, the displaced metal appears in elemental form, while the replacing metal forms its salt.
- In the reaction Fe + CuSO₄ → FeSO₄ + Cu, the iron nail turns brownish due to deposited copper, and the blue solution fades.
- Heat may be released during displacement reactions, indicating that the reaction is exothermic.
Key Points: Oxidation
- Combustion fully oxidises carbon compounds, breaking all chemical bonds and producing CO₂ and H₂O.
- Oxidising agents like potassium permanganate or potassium dichromate can convert alcohols to carboxylic acids.
- Air inlets in stoves ensure complete combustion; black soot indicates incomplete combustion and fuel wastage due to blocked air inlets.
Important Questions [31]
- The Reaction of Iron Nail with Copper Sulphate Solution is ......................... Reaction.
- Complete the following reaction: CA12HA22OA11→Heat ______ + ______.
- Taking into Consideration the Relationship in the First Pair, Complete the Second Pair 2h2 + O2 → 2h2o :Combination Reaction :: 2hgo → 2hg + O2
- Rewrite the Following Statement by Selecting the Correct Options: ________________ is a Decomposition Reaction.
- The chemical reaction in which two or more products are formed from a single reactant is called ______ reaction.
- Rewrite the Following Statements by Selecting the Correct Options: Ce{Caco3 ->Delta Cao + Co2 ^}Is a __________ Reaction.
- What is meant by a decomposition reaction?
- Write the molecular formula of calcium carbonate.
- Give a scientific reason. When the gas formed on heating limestone is passed through freshly prepared lime water, the lime water turns milky.
- Identify the type of chemical reaction given below: CuSOA4+Fe⟶FeSOA4+Cu
- CuSO4(aq) + Zn(s) → ZnSO4(aq) + Cu(s) is an example of a decomposition reaction.
- Complete the given chemical reaction:CuSOX4X(aq)+FeX(s)⟶ _______ + _______ Name the type of the reaction.
- The Reddish Brown Deposit Formed on Iron Nails Kept in a Solution of Copper Sulphate is
- Reaction of Iron Nails with Copper Sulphate Solution is an Example of
- When the substance ‘A’ is added to a solution of BaSO4, a yellow precipitate is formed.
- Complete the following reaction, balance it and write the name of the products CuO + HCI
- Study the following chemical reaction and answer the questions given below: \\ce{AgNO3_{(aq)} + NaCl_{(aq)} -> \underset{(Precipitate)}{AgCl_{(s)}}↓ + NaNO3_{(aq)}}\
- If Sodium Chloride is Added to Silver Nitrate Solution: A. Which Precipitate is Formed? B. Name the Type of Reaction. C. Write the Chemical Equation.
- Define an oxidation reaction.
- Define ‘Redox Reaction’. Give One Example.
- The Chemical Formula for Rust is
- Define corrosion.
- What is Meant by Rust?
- Write the Chemical Formula of Rust.
- Corrosion Can Be Prevented by Using Anti-rust Solution.
- Give scientific reason. It is reccommended to use air tight container for storing oil for long time.
- Distinguish between oxidation and reduction.
- Identify the type of chemical reaction given below: 2Mg+OA2⟶2MgO
- After You Have Dinner Tonight, Wash Your Own Plates with Soap/Detergent.
- Answer the Following Question : Grills of Doors and Windows Are Always Painted before They Are Used? Give Reason.
- Answer the Following: What is Corrosion? Do Gold Ornaments Corrode? Justify.
Concepts [6]
- Types of Chemical Reactions > Combination Reaction
- Types of Chemical Reactions > Decomposition Reaction
- Types of Chemical Reactions > Single Displacement Reaction
- Types of Chemical Reactions > Double Displacement Reaction
- Chemical Properties of Carbon Compounds > Oxidation
- Types of Double Displacement: Neutralization Reaction
