Physical and Chemical Properties — Revision Notes

⚡ 30-Second Revision

Physical Property: — Observed without changing chemical identity (e.g., color, $ho$, MP, BP).
Chemical Property: — Describes reactivity, leads to new substances (e.g., flammability, reactivity with acids).
Intensive Property: — Independent of amount (e.g., $ho$, MP, BP, T).
Extensive Property: — Depends on amount (e.g., mass, volume, energy).
Physical Change: — No change in chemical identity (e.g., melting, boiling, dissolving).
Chemical Change: — New substances formed (e.g., burning, rusting, cooking).
Indicators of Chemical Change: — Gas evolution, precipitate, color change, heat/light, odor change.

2-Minute Revision

Quickly recall the core distinctions for NEET. Physical properties are characteristics you can observe or measure without altering the substance's chemical makeup, like its color, density, melting point, or electrical conductivity.

These are further divided into intensive properties, which don't depend on the amount of substance (e.g., density, temperature), and extensive properties, which do (e.g., mass, volume). A physical change is when a substance changes its form or state but remains chemically the same, such as ice melting into water.

In contrast, chemical properties describe how a substance reacts to form new substances, like its flammability or reactivity with acids. A chemical change (or reaction) is when new substances are formed, often indicated by gas production, precipitate formation, color change, or heat/light release.

Always remember: if the chemical identity changes, it's chemical; if not, it's physical.

5-Minute Revision

For a comprehensive revision, let's solidify the concepts. Every substance has both physical and chemical properties. Physical properties are observable traits that don't involve a change in chemical composition.

Think of water: its colorless liquid state, its density of $1,\text{g/mL}$, its boiling point of $100^circ C$, and its ability to conduct electricity (when impure) are all physical properties. These are crucial for identification and separation.

Remember the sub-classification: intensive properties (like density, boiling point, temperature) are independent of the sample size, while extensive properties (like mass, volume, total energy) depend on the amount.

A simple test for extensive is to imagine cutting the sample in half; if the property value also halves, it's extensive.

Physical changes are transformations where the substance's chemical identity is preserved. Examples include phase changes (melting, freezing, boiling, condensation, sublimation, deposition), dissolving (e.g., sugar in water), or simply changing shape (cutting, bending). The original substance can usually be recovered by reversing the physical process.

Chemical properties, on the other hand, describe a substance's potential to undergo a chemical reaction, leading to the formation of entirely new substances. For instance, the flammability of wood, the reactivity of sodium with water, or the corrosiveness of an acid are chemical properties.

These are only observed when the substance undergoes a chemical change (a chemical reaction). Key indicators of a chemical change include: the evolution of gas (bubbles), formation of a precipitate (a solid forming in a liquid), a distinct color change, a significant temperature change (heat released or absorbed), or a change in odor.

For NEET, practice identifying these indicators in various scenarios and confidently classifying processes as either physical or chemical changes.

Prelims Revision Notes

Physical and Chemical Properties: NEET Quick Recall

1. Physical Properties:

Definition: — Characteristics observed/measured WITHOUT changing chemical identity.
Examples: — Color, odor, taste, state of matter (solid, liquid, gas), melting point (MP), boiling point (BP), density ($ho$), hardness, solubility, electrical conductivity, thermal conductivity, malleability, ductility, viscosity, refractive index.
Types of Physical Properties:

* Intensive Properties: Independent of amount of matter. Useful for identification. * Examples: $ho$, MP, BP, temperature, specific heat capacity, concentration, pressure, color, refractive index. * Extensive Properties: Depend on amount of matter. Additive. * Examples: Mass, volume, length, total energy, heat capacity, number of moles.

2. Chemical Properties:

Definition: — Describe a substance's ability to undergo a chemical reaction, forming NEW substances.
Observation: — Only observed DURING a chemical change.
Examples: — Flammability/combustibility, reactivity with acids/bases/water/oxygen, oxidation potential, reduction potential, corrosiveness, toxicity, stability/decomposition.

3. Physical Change:

Definition: — Alters form/state, but chemical composition remains SAME.
Key Feature: — NO new substances formed.
Examples: — Melting ice ($H_2O(s) \rightarrow H_2O(l)$), boiling water ($H_2O(l) \rightarrow H_2O(g)$), freezing water, condensation, sublimation, dissolving sugar in water, cutting paper, bending metal, crushing a solid.
Reversibility: — Often easily reversible by physical means.

4. Chemical Change (Chemical Reaction):

Definition: — Results in formation of NEW substances with different chemical compositions.
Key Feature: — Chemical bonds broken and formed.
Examples: — Burning wood, rusting iron, cooking an egg, photosynthesis, digestion, electrolysis of water, acid-base neutralization, explosion.
Indicators (Signs):

* Change in color. * Evolution of gas (bubbles/fizzing). * Formation of a precipitate (solid). * Significant temperature change (heat released/absorbed). * Emission of light. * Change in odor.

Reversibility: — Generally difficult to reverse; requires another chemical reaction.

NEET Focus: Be able to classify given examples as physical/chemical property or physical/chemical change. Understand the intensive/extensive distinction.

Vyyuha Quick Recall

To remember the difference between physical and chemical changes, think: 'Physical is Permanent (identity-wise), Chemical Creates Completely Changed Compounds.'

For Intensive vs. Extensive: 'Intensive is Independent of Input (amount). Extensive is Everything Else (depends on amount).'