Questions and Answers
Which process usually results in new substances being formed?
Mass is conserved in chemical changes.
True
Name one clue of a chemical change.
Effervescence, precipitate formation, light or heat given off
A reaction between acid and alkali produces a ___ and water.
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What is the word equation for photosynthesis?
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Which of these is an example of a thermal decomposition reaction?
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What is produced when an acid reacts with a metal carbonate?
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What are the pH values for acids and alkalis?
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What is a common characteristic of acids?
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What happens during combustion?
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Copper, Silver, and Gold ___ with acids.
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Study Notes
Chemical Change vs. Physical Change
- Chemical changes result in new substances and are typically irreversible.
- Physical changes do not create new substances and are generally reversible.
Clues of Chemical Change
- Effervescence: Gas production indicates a chemical reaction.
- Precipitate Formation: A solid that forms and separates from a liquid.
- Energy Release: Light or heat may be emitted during the reaction.
Representation of Chemical Change
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Word Equation Format: Reactant(s) + Condition → Product(s)
- Example: Carbon dioxide + water → glucose + oxygen (with light).
- Mass Conservation: During chemical changes, mass is conserved through atom rearrangement.
- Balancing Equations: Ensure all atoms are accounted for in reactions.
Types of Chemical Changes
Thermal Decomposition
- A single substance breaks down into simpler substances upon heating.
- Example: Metal Carbonate → Metal Oxide + Carbon Dioxide.
Oxidation
- Rusting: Iron reacts with water and oxygen to form hydrated iron(II) oxide.
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Combustion: A rapid reaction with oxygen producing heat.
- Example: Petrol + Oxygen → Carbon Dioxide + Water.
- Incomplete combustion produces toxic carbon monoxide.
- Respiration: Process of converting glucose and oxygen into carbon dioxide and water while releasing energy.
Reactions with Light
Photosynthesis
- Plants convert carbon dioxide and water into glucose and oxygen using light energy.
Reactions with Electricity
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Electrolysis: Uses electricity for the chemical decomposition of substances.
- Example: Copper Chloride → Copper + Chlorine.
- Electroplating: Coating a substance with another metal through electric current.
Neutralisation
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Acid + Alkali Reaction: Results in salt and water without gas production.
- Example: Hydrochloric acid + Sodium Hydroxide → Sodium Chloride + Water.
Acid + Metal Reactions
- Reaction produces salt and hydrogen gas without effervescence.
- Produces a 'pop' sound extinguishing a lit splint.
- Exceptions: Copper, Silver, and Gold do not react.
- Example: Nitric Acid + Magnesium → Magnesium Nitrate + Hydrogen gas.
Acid + Metal Carbonate Reactions
- Reaction produces salt, water, and carbon dioxide, often producing a white precipitate in limewater.
- Example: Sulphuric Acid + Zinc Carbonate → Zinc Sulfate + Water + Carbon Dioxide.
pH Scale
- Acidic substances taste sour with a pH < 7; examples include hydrochloric and sulfuric acids.
- Alkaline substances taste bitter with a pH > 7; examples include sodium and potassium hydroxide.
- Neutral pH is represented by a pH of 7.
Summary of Common Acids and Bases
- Common Acids: Hydrochloric acid, Sulfuric acid, Nitric acid.
- Common Bases: Sodium Hydroxide, Potassium Hydroxide, Aqueous Ammonia.
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Description
This quiz explores the differences between chemical and physical changes. Understand the key indicators of chemical reactions and how new substances are formed. Test your knowledge with various examples and representations of these changes.
