IMG_2524.jpeg

# Chemical Change vs. Physical Change - **New substances** formed from reaction: usually irreversible - **No new substances** formed from reaction: usually reversible ## Clues of chemical change: - Effervescence (gas produced) - Precipitate (solid) formed - Light or heat given off ## Representat...

# Chemical Change vs. Physical Change - **New substances** formed from reaction: usually irreversible - **No new substances** formed from reaction: usually reversible ## Clues of chemical change: - Effervescence (gas produced) - Precipitate (solid) formed - Light or heat given off ## Representation of chemical change: **(i) Word Equation** *Reactant(s) Condition, Product(s)* eg. Carbon dioxide + water → glucose + oxygen *Light* * **Mass is conserved** in chemical changes (Rearrangement of atoms) **(ii) Balance Chemical Equations (Account for ALL atoms)** 1. Mg(OH)₂ + 2HCl → MgCl₂ + 2H₂O *Balance H, O last* eg * C₂H₆ + O₂ → CO₂ + H₂O * Al + O₂ → * Fe₂O₃ + CO → ## Types of Chemical Changes ### **Thermal Decomposition** * Single substance breaks down into simpler substances when heated. * Metal Carbonate → Metal Oxide + Carbon Dioxide ### **Oxidation (reacts with oxygen)** **A. Rusting** * Hydrated iron (II) oxide * Conditions: Water and Oxygen * Salts (sodium chloride) speed up rusting **B. Combustion (burn in oxygen)** * Releases a lot of heat. * Petrol + Oxygen → Carbon Dioxide + Water * Limited/insufficient incomplete combustion: releases toxic carbon monoxide **C. Respiration** * Glucose + Oxygen → Carbon Dioxide + Water * *Light* ### Reactions with Light #### **Photosynthesis** * Carbon Dioxide + Water → Glucose + Oxygen * *Light* ### Reactions with Electricity **A. Electrolysis:** * Chemical decomposition of substances using electricity * eg. Copper Chloride → Copper + Chlorine **B. Electroplating** * Substance is coated with another metal using electricity ## Acid + Alkali (Neutralisation) * No gas is produced * Acid + Alkali → Salt + Water ### Examples: * Hydrochloric acid + Sodium Hydroxide → Sodium Chloride + Water * Sulfuric Acid + Potassium Hydroxide → ## Acid + Metal * No effervescence * Acid + Metal → Salt + Hydrogen gas * Extinguishes lighted splint with a *pop* * **Except Copper, Silver, Gold** ### Examples: * Nitric Acid + Magnesium → Magnesium Nitrate + Hydrogen gas * Hydrochloric acid + Calcium → Calcium Chloride + Hydrogen gas ## Acid + Metal Carbonate * Acid + Metal Carbonate → Salt + Water + Carbon Dioxide * Gives white precipitate in limewater ### Examples: * Sulphuric acid + Zinc Carbonate → Zinc Sulfate + Water + Carbon Dioxide * Hydrochloric acid + Copper Carbonate → Copper Chloride + Water + Carbon Dioxide ## Neutralisation Reaction * Reaction between acid and alkali * Produces a salt and water * Produces a neutral pH ## PH * Acid: Taste sour, pH value < 7 * Alkali: Taste bitter, pH value > 7 * PH level: 0-14 * PH 7: Neutral ### Examples: * Hydrochloric acid * Sulphuric acid * Nitric acid * Sodium Hydroxide * Potassium Hydroxide * Aqueous Ammonia