Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
The kinetic particle theory states that all matter is made of tiny particles that are in constant, random motion. The energy of these particles is proportional to the temperature in Kelvin ().
In a solid, particles are packed closely in a regular lattice arrangement, vibrating about fixed positions. They have the least kinetic energy and strong intermolecular forces.
In a liquid, particles are close together but arranged irregularly. They can slide over each other, allowing liquids to flow and take the shape of their container.
In a gas, particles are far apart and move rapidly in random directions. Intermolecular forces are negligible, allowing gases to be highly compressible.
Changes of state involve energy transfers. Melting and boiling require energy to overcome attractive forces (endothermic), while freezing and condensation release energy (exothermic). During a change of state, the temperature remains constant.
Evaporation occurs at any temperature below the boiling point and only at the surface of a liquid. Boiling occurs at a specific temperature () throughout the liquid.
Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration, down a concentration gradient.
The rate of diffusion depends on temperature and molecular mass. Higher temperatures increase the kinetic energy () of particles, causing faster diffusion. Heavier molecules (those with higher ) diffuse more slowly than lighter molecules.
📐Formulae
💡Examples
Problem 1:
In an experiment, a cotton wool plug soaked in aqueous ammonia () and another soaked in hydrochloric acid () are placed at opposite ends of a long glass tube. A white ring of ammonium chloride () forms. Where will the ring form, and why?
Solution:
The white ring forms closer to the end of the tube.
Explanation:
Ammonia () has a relative molecular mass () of approximately (), while hydrogen chloride () has an of approximately (). Because is lighter, its particles move with a higher average velocity than the heavier particles at the same temperature. Therefore, diffuses further along the tube in the same amount of time, resulting in the reaction occurring closer to the source of the slower-moving gas.
Problem 2:
Explain what happens to the particles of a solid when it is heated until it melts.
Solution:
The particles gain kinetic energy and vibrate more vigorously until the forces of attraction are weakened enough for the particles to slide past each other.
Explanation:
Heating provides thermal energy, which is converted into kinetic energy (). At the melting point, the energy supplied is used to overcome the intermolecular forces holding the particles in the solid lattice rather than increasing the temperature. This process is represented by the flat plateau on a heating curve where remains constant until the phase change is complete.