states of matter

Of course. Here are your ultimate, remade Cambridge IGCSE hybrid notes for States of Matter and Diffusion, incorporating the cooling curve and designed to be the markscheme.

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### ULTIMATE CAMBRIDGE IGCSE CHEMISTRY NOTES - STATES OF MATTER & DIFFUSION

#### 1. Properties & Particle Theory

| :--- | :--- | :--- | :--- |

| Compressibility? | No | No | Yes |

How to draw the Particle Diagram:

* Solid: Draw particles (○) in neat, touching rows.

* Liquid: Draw particles randomly, but still close and touching.

* Gas: Draw very few particles far apart with arrows (→) showing random movement.

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#### 2. Changes of State

* Melting: Solid → Liquid (at melting point)

* Freezing: Liquid → Solid (at freezing point)

* Boiling: Liquid → Gas. Occurs throughout liquid at a fixed temperature (B.P.).

* Evaporation: Liquid → Gas. Occurs only at the surface, at any temperature.

* Condensation: Gas → Liquid

* Sublimation: Solid → Gas (directly) e.g., Iodine, Dry Ice.

Exam Tip: For 2 marks on "difference between boiling and evaporation":

1. Boiling occurs throughout the liquid, evaporation only at the surface.

2. Boiling occurs at a fixed temperature (B.P.), evaporation at any temperature.

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#### 3. Heating & Cooling Curves (Kinetic Particle Theory)

Heating Curve:

How to draw it: A line with two flat plateaus.

* Sloping Up: Temperature ↑. Particles gain kinetic energy.

* **First Plateau (Melting):** Temperature constant. Energy is used to break intermolecular forces (solid → liquid).

* **Second Plateau (Boiling):** Temperature constant. Energy is used to break intermolecular forces (liquid → gas).

Cooling Curve:

How to draw it: A line falling from left to right with two flat plateaus.

* Sloping Down: Temperature ↓. Particles lose kinetic energy.

* **First Plateau (Condensing):** Temperature constant. Energy is released as intermolecular forces form (gas → liquid).

* **Second Plateau (Freezing):** Temperature constant. Energy is released as intermolecular forces form (liquid → solid).

Key Explanation for ALL Plateaus:

"The temperature remains constant because the energy being added/removed is used to break/form intermolecular forces between the particles, not to change the kinetic energy (temperature)."

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#### 4. Gas Pressure & Temperature

* Increasing Temperature (in a sealed container):

Particles gain *kinetic energy**.

Move *faster** and collide with walls more frequently and with greater force.

* Result: Pressure increases.

* Increasing Pressure (on a movable piston):

Particles are forced *closer together**.

* Result: Volume decreases. (The gas is compressed).

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#### 5. Diffusion

* Definition: The net movement of particles from a region of higher concentration to a region of lower concentration down a concentration gradient.

* Cause: The random motion of particles.

* **States it occurs in:** Gases (fast) and Liquids (slow). Not in solids (particles are fixed).

* Effect of Relative Molecular Mass (RMM):

* Lighter gas (lower RMM) diffuses faster.

* Heavier gas (higher RMM) diffuses slower.

* Explanation: At the same temperature, all particles have the same average kinetic energy. Kinetic energy = ½ x m x v².

Therefore, a particle with a *smaller mass (m)** must have a higher velocity (v).

* Faster-moving particles (lighter ones) will travel further and mix more quickly.

Diffusion Experiment Diagram:

How to draw it: A long tube. Cotton wool with NH₃ (Mr=17) on the left, HCl (Mr=36.5) on the right. A white ring forms closer to the HCl end.

**Why the ring forms closer to the HCl end:** Ammonia particles are lighter (lower RMM) and have a higher speed at the same temperature, so they diffuse faster than the heavier hydrogen chloride particles.