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Chemistry - States of Matter

Grade 10IGCSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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The Kinetic Particle Theory states that all matter is composed of tiny particles in constant, random motion. The average kinetic energy (EkE_k) of these particles is directly proportional to the absolute temperature in Kelvin (KK).

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In a solid, particles are packed in a regular lattice arrangement, vibrating about fixed positions. They have the least energy and strongest intermolecular forces.

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In a liquid, particles are close together but can move past each other. They have more energy than solids and take the shape of the container's base.

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In a gas, particles are far apart and move rapidly in all directions. Intermolecular forces are negligible. The pressure (PP) of a gas is caused by the collisions of particles against the walls of the container.

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Changes of state: Melting (s→ls \to l), Freezing (l→sl \to s), Boiling/Evaporation (l→gl \to g), Condensation (g→lg \to l), and Sublimation (s→gs \to g).

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During a change of state, the temperature remains constant. This is because the energy supplied is used to overcome the forces of attraction between particles rather than increasing their kinetic energy.

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Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration. The rate of diffusion is faster in gases than in liquids and is affected by temperature and molecular mass (MrM_r).

📐Formulae

T(K)=T(∘C)+273T(K) = T(^{\circ}C) + 273

P1V1=P2V2P_1V_1 = P_2V_2

Rate∝1MrRate \propto \frac{1}{\sqrt{M_r}}

P=FAP = \frac{F}{A}

💡Examples

Problem 1:

In an experiment to demonstrate diffusion, a glass tube is set up with a cotton wool soaked in concentrated ammonia (NH3NH_3) at one end and a cotton wool soaked in concentrated hydrochloric acid (HClHCl) at the other. Where will the white smoke of ammonium chloride (NH4ClNH_4Cl) form?

Solution:

The white smoke of NH4Cl(s)NH_4Cl(s) will form closer to the HClHCl end of the tube.

Explanation:

The relative molecular mass of NH3NH_3 is 14+(3×1)=1714 + (3 \times 1) = 17, while the relative molecular mass of HClHCl is 1+35.5=36.51 + 35.5 = 36.5. According to kinetic theory, lighter particles travel faster than heavier particles at the same temperature. Since NH3NH_3 has a lower MrM_r, it diffuses faster and covers a greater distance than HClHCl in the same amount of time.

Problem 2:

A sample of gas occupies a volume of 2.0 dm32.0\text{ dm}^3 at a pressure of 100 kPa100\text{ kPa}. If the temperature is kept constant, calculate the new pressure if the volume is compressed to 0.5 dm30.5\text{ dm}^3.

Solution:

P2=P1V1V2=100 kPa×2.0 dm30.5 dm3=400 kPaP_2 = \frac{P_1V_1}{V_2} = \frac{100\text{ kPa} \times 2.0\text{ dm}^3}{0.5\text{ dm}^3} = 400\text{ kPa}

Explanation:

Boyle's Law states that for a fixed mass of gas at constant temperature, pressure is inversely proportional to volume (P∝1VP \propto \frac{1}{V}). When the volume decreases by a factor of 4, the pressure must increase by a factor of 4.

States of Matter - Revision Notes & Key Formulas | IGCSE Grade 10 Science