Types of Chemical Reactions

Types of Reactions

• Objectives: Study different reaction types, oxidation-reduction reactions, exothermic and endothermic reactions, and balancing equations.

What is a Chemical Reaction?

• A chemical reaction is a chemical change where atoms and molecules rearrange to form a new product.
• Substances that participate in a reaction are called reactants.
• Newly formed substances are called products.
• The arrow (→) indicates the products of the reaction ("yields" or "produces").

Parts of a Chemical Reaction

• Reactants: Substances involved in a reaction (bonds are broken).
• Products: Newly formed substances (new bonds are formed).

Other Symbols in Chemical Reactions

• (s) = solid; (l) = liquid; (g) = gas; ↑ = gas given off
• (aq) = aqueous solution (substance dissolved in water)
• Dil. = dilute (more water, less solute); Conc. = concentrated (less water, more solute)
• "+" separates reactants or products

Evidence for a Chemical Reaction

• Evolution of light or heat: A reaction that emits light or heat (e.g., a glowing stick).
• Temperature Change: A change in temperature of the surroundings. A reaction that releases heat increases the surrounding temperature; one that absorbs heat decreases the surrounding temperature.

Word Equations

• Statements that show reactants and products in a reaction.
• Example: Iron (s) + chlorine (g) → iron (III) chloride (s)

Oxidation and Reduction

• Oxidation: Gain of Oxygen, loss of Hydrogen, loss of electrons, or increase in oxidation state
• Reduction: Loss of Oxygen, gain of Hydrogen, gain of electrons, or decrease in oxidation state

Oxidizing and Reducing Agents

• Oxidizing agent: A substance that oxidizes another substance or accepts electrons.
• Reducing agent: A substance that can remove oxygen from a compound.

Examples of Oxidation and Reduction Reactions

• Oxidation examples include: Zinc + oxygen → zinc oxide Sodium + oxygen → sodium oxide Calcium + oxygen → calcium oxide Carbon + oxygen → carbon monoxide/carbon dioxide Nitrogen + oxygen → nitrogen monoxide/nitrogen dioxide
• Reduction examples include: Iron oxide + carbon → iron + carbon dioxide

What is Combustion?

• Combustion is a chemical process where a substance reacts with oxygen to generate heat.
• Example: Burning of magnesium ribbon.

Balanced Equation for Methane

• CH₄ + 2O₂ → CO₂ + 2H₂O (Methane reacts with oxygen to form carbon dioxide and water).
• The balanced equation ensures equal numbers of each atom on both sides of the equation.

Decomposition Reactions

• A decomposition reaction occurs when a compound breaks into simpler substances, either elements or simpler compounds.

Types of Decomposition Reactions

• Thermal: Decomposition by heat (e.g., calcium carbonate → calcium oxide + carbon dioxide; mercury oxide → mercury + oxygen)
• Photo: Decomposition by light (e.g., silver chloride → silver + chlorine; silver bromide → silver + bromine)
• Electric: Decomposition using electric current (e.g., water → oxygen + hydrogen; sodium chloride → sodium + chlorine)

Acid-Base Neutralization Reaction

• Reaction between an acid and a base to form salt and water
• Example: Hydrochloric acid + sodium hydroxide → sodium chloride + water

Precipitation Reaction

• A precipitation reaction is a chemical reaction where one of the products is an insoluble solid (precipitate) that forms in a solution.
• Precipitation is indicated by an arrow pointing downwards (↓).
• Example includes lead nitrate + potassium iodide → lead iodide + potassium nitrate Sodium sulphate + barium nitrate → sodium nitrate + barium sulphate

Displacement Reaction

• A displacement reaction is when one element replaces another element in a compound.
• Example includes, Chromium oxide + aluminum → chromium + aluminum oxide Copper sulphate + Iron → iron sulphate + copper

Conservation of Mass

• During a chemical reaction, no atoms are created or destroyed; the total mass of the reactants equals the total mass of the products.
• This is why chemical equations must be balanced.

Exothermic and Endothermic Reactions

• Exothermic reaction: Releases heat to the surroundings.
• Endothermic reaction: Absorbs heat from the surroundings.
• Examples include: Magnesium + hydrochoric acid (Exothermic), barium hydroxide + ammonium chloride (Endothermic)

Counting Atoms and Balancing Equations

• Balanced chemical equations show equal numbers of each atom on both sides.
• Coefficients multiply the entire formula to balance atoms.
• Subscripts indicate the number of atoms of an element in a compound (Cannot be changed to balance).
• Examples include, SnO2 + 2H2 → Sn + 2H2O

Rules for Balancing Chemical Equations

• Coefficients are changed to balance the number of atoms on both sides of the equation.
• Never change the subscripts of a chemical formula to balance.

Periodic Table (Partial)

• A table that organizes elements by properties and atomic structure. Different elements have different numbers of electrons (e.g., Hydrogen - 1; Lithium - 2.1; Beryllium - 2.2 etc.).

This quiz covers different types of chemical reactions, including oxidation-reduction, exothermic and endothermic reactions. You'll learn about reactants, products, and the symbols used to represent various states of matter and solutions. Test your understanding of balancing chemical equations and the evidence of chemical changes.