Chemistry Question

Chapter: Chemical Reactions and Equations

1. Chemical Reaction

A chemical reaction is a process in which one or more substances change into new substances.

Reactants = starting substances

Products = new substances formed

Example:

Magnesium + Oxygen Magnesium Oxide

What happens (diagram explanation in words):

A magnesium ribbon is burned in air. It burns with a bright white flame and forms a white powder called magnesium oxide.

2. Chemical Equations

A chemical equation shows a reaction using chemical formulas.

Example:

Mg + O MgO

Balanced Equation

The number of atoms on both sides must be equal.

Balanced form:

2Mg + O 2MgO

What happens (in diagram):

It shows equal numbers of magnesium and oxygen atoms on both sides.

3. Types of Chemical Reactions

1. Combination Reaction

Two or more substances combine to form one product.

Example:

CaO + HO Ca(OH)

What happens (in diagram):

Quicklime (CaO) reacts with water, producing slaked lime and releasing heat.

2. Decomposition Reaction

A single substance breaks down into simpler substances.

Example:

CaCO CaO + CO

What happens (in diagram):

Calcium carbonate is heated and breaks into calcium oxide and carbon dioxide gas.

3. Displacement Reaction

A more reactive element replaces a less reactive element.

Example:

Zn + CuSO ZnSO + Cu

What happens (in diagram):

A zinc strip is placed in blue copper sulphate solution. The solution becomes colorless and copper metal is deposited.

4. Double Displacement Reaction

Two compounds exchange ions.

Example:

NaSO + BaCl BaSO + 2NaCl

What happens (in diagram):

Two solutions are mixed, and a white solid (precipitate) is formed.

4. Oxidation and Reduction

Oxidation = Addition of oxygen / Loss of hydrogen

Reduction = Removal of oxygen / Gain of hydrogen

Example:

CuO + H Cu + HO

What happens (in diagram):

Black copper oxide reacts with hydrogen gas and turns into brown copper metal and water.

5. Effects of Oxidation

Corrosion

Slow damage of metals due to air and moisture

Example: Rusting of iron

What happens (in diagram):

Iron reacts with oxygen and water to form reddish-brown rust.

Rancidity

Spoilage of food due to oxidation

Example: Oil and fats become bad in smell and taste

What happens (in diagram):

Food is shown getting spoiled when exposed to air; sealed packets prevent this.

6. Important Points

Always balance chemical equations

Different reactions have different types

Oxidation and reduction occur together (redox reaction)

Corrosion and rancidity are common in daily life

7. Important Definitions

Chemical Reaction Formation of new substances

Reactants Substances that react

Products Substances formed

Balanced Equation Equal atoms on both sides

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