Ch 05 - Changes Around Us: Physical and Chemical7th Science
Physical Change
What defines a 'Physical Change' regarding the chemical identity of a substance?
What defines a 'Physical Change' regarding the chemical identity of a substance?
A Physical Change is a transformation where only the physical properties (such as shape, size, state of matter, or colour) of a substance change.
Key Criteria:
- No new chemical substance is formed.
- The molecular composition of the substance remains exactly the same.
- Examples: Melting ice into water, tearing a sheet of paper, or crushing chalk.
Prism Memory Hook
Physical equals Phony change (looks different outside, same inside).
Irreversible Physical Changes
Are all physical changes reversible? Provide two examples to support your answer.
Are all physical changes reversible? Provide two examples to support your answer.
No. While many physical changes (like melting ice) are reversible, not all of them can be reversed.
Examples of Irreversible Physical Changes:
- Cutting Wood or Paper: The shape and size change (a physical property), but you cannot put the pieces back together to form the original continuous structure.
- Breaking Glass: The chemical composition remains entirely glass, but its physical macro-structure is permanently altered.
Prism Memory Hook
Humpty Dumpty breaking is an irreversible physical change.
Chemical Change
What is the defining characteristic of a 'Chemical Change' (also known as a Chemical Reaction)?
What is the defining characteristic of a 'Chemical Change' (also known as a Chemical Reaction)?
A Chemical Change is a process in which one or more entirely new substances are formed.
Characteristics:
- The molecular bonds of the original substance(s) are broken and rearranged.
- The newly formed substances have completely different physical and chemical properties from the original reactants.
- These changes are generally irreversible under normal conditions.
- Examples: Rusting of iron, burning of wood, digestion of food.
Prism Memory Hook
Chemical equals Create New.
Also in this chapter
30 more cards to study in Prism
- 4Burning of Magnesium
- 5Indicators of Chemical Change
- 6Magnesium Oxide in Water
- 7Vinegar and Baking Soda
- 8Lime Water Test Reaction
- 9Rusting of Iron
- 10Standard Test for Carbon Dioxide
- 11Displacement: Iron in Blue Vitriol
- 12Testing for Hydrogen Gas
- 13Crystallisation
- 14Sulphur Dioxide and Water
- 15Real-World Crystallisation: Mishri
- 16Rusting Challenges in Marine Environments
- 17Galvanisation
- 18Simple Rust Prevention Techniques
- 19Composition of Stainless Steel
- 20The Three Requirements for Combustion
- 21Ignition Temperature
- 22Emergency: Extinguishing a Clothing Fire
- 23The Burning Candle: A Dual Process
- 24Transformations of LPG (Cooking Gas)
- 25The Chemistry of Fireworks
- 26Weathering of Rocks
- 27The Ozone Layer's Protective Mechanism
- 28Biological Chemical Changes
- 29Decomposition: Food Spoilage & Composting
- 30Bioluminescence in Nature
- 31Chameleon Colour Adaptation
- 32Faraday and the Candle
- 33Endothermic vs. Exothermic Processes
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