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1 Jan 2026

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4 pages

Understanding Phase Changes: Chemistry Notes Chapter 2

Karen

@karen_kysr

Matter exists in three distinct states and can undergo various... Show more

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Chapter 2 Notes

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States of Matter and Properties

You encounter solids, liquids, and gases every day without realising how differently their particles behave. Solids maintain both definite volume and shape because particles are tightly packed and can't move about. Liquids keep their volume but take the shape of their container since particles can flow past each other whilst staying close together.

Gases are the rebels of the matter world - they expand to fill any container completely because their particles are spread far apart and easily compressed. Think of how air fills a balloon or how steam spreads throughout a kitchen.

Physical properties can be observed without changing what the substance actually is. These split into extensive properties (like mass and volume that depend on how much you have) and intensive properties (like melting point and density that stay the same regardless of sample size). A physical change alters appearance but keeps the same chemical composition - ice melting into water is still H₂O.

Quick Tip: Remember that physical changes are often reversible, whilst chemical changes create entirely new substances with different properties.

Chemical Changes and Pure Substances

Chemical changes are far more dramatic than physical ones - they actually create new substances with completely different compositions. Watch for telltale signs: energy transfers (heat or light), gas production, solid formation from mixing liquids, or colour changes.

The Law of Conservation of Mass is chemistry's golden rule: mass never disappears during reactions. What goes in must equal what comes out, just rearranged differently.

Elements are chemistry's building blocks - the simplest forms of matter that can't be broken down further. Compounds form when two or more elements chemically bond in fixed proportions, creating substances with entirely different properties than their original elements. Sodium (explosive metal) plus chlorine (poisonous gas) equals table salt!

Chemical symbols represent elements with one or two letters (first capitalised, second lowercase), whilst chemical formulas show compound compositions. The Law of Definite Proportions ensures compounds always contain the same element ratios regardless of sample size.

Key Point: Compounds can only be separated into elements through chemical means, not physical methods like filtering or heating.

Laws and Calculations

The percent by mass calculation helps determine how much of each element exists in a compound using the formula: (mass of element ÷ mass of compound) × 100. This becomes crucial for identifying unknown substances and checking compound purity.

The Law of Multiple Proportions explains why the same elements can form different compounds. When examining compounds like NO and NO₂, the oxygen masses that combine with the same nitrogen mass always form simple whole number ratios.

Mixtures are physical blends where substances keep their individual properties. Heterogeneous mixtures show obvious differences (like Chex mix or oil and water), whilst homogeneous mixtures appear uniform throughout (like properly mixed salt water).

Separating mixtures exploits differences in physical properties: filtration uses size differences, chromatography relies on retention factors, distillation separates by boiling points, sublimation works when only one solid can change directly to gas, and crystallisation forms pure solid particles from solutions.

Study Hack: Practice identifying mixture types around you - your lunch tray probably contains both heterogeneous and homogeneous examples!

Advanced Separation Techniques

Crystallisation represents one of the most elegant separation methods, forming pure solid particles directly from solutions. This technique proves essential in both laboratory work and industrial processes for obtaining high-purity substances.

Understanding these separation principles helps you tackle practical chemistry problems and explains how scientists isolate specific compounds from complex mixtures in real-world applications.

Real-World Connection: These separation techniques are used everywhere from water treatment plants to pharmaceutical manufacturing - mastering them opens doors to understanding countless industrial processes.

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Chemistry

•

1 Jan 2026

•

4 pages

Understanding Phase Changes: Chemistry Notes Chapter 2

Karen

@karen_kysr

Matter exists in three distinct states and can undergo various changes whilst following specific laws. Understanding the differences between physical and chemical properties, elements and compounds, and how to separate mixtures forms the foundation of chemistry.

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States of Matter and Properties

Quick Tip: Remember that physical changes are often reversible, whilst chemical changes create entirely new substances with different properties.

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Chemical Changes and Pure Substances

The Law of Conservation of Mass is chemistry's golden rule: mass never disappears during reactions. What goes in must equal what comes out, just rearranged differently.

Key Point: Compounds can only be separated into elements through chemical means, not physical methods like filtering or heating.

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Laws and Calculations

Study Hack: Practice identifying mixture types around you - your lunch tray probably contains both heterogeneous and homogeneous examples!

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Advanced Separation Techniques

Understanding these separation principles helps you tackle practical chemistry problems and explains how scientists isolate specific compounds from complex mixtures in real-world applications.

Real-World Connection: These separation techniques are used everywhere from water treatment plants to pharmaceutical manufacturing - mastering them opens doors to understanding countless industrial processes.