Particle Model of Matter

Temperature θ 27 °C

Volume V 60 cm³

Extra detail · compared with 27 °C and 60 cm³ How often particles hit each cm² of wall×1.00 How hard each hit is×1.00

Not to scale. The particles are drawn millions of times larger than real atoms and molecules, and they move tens of thousands of times more slowly (air molecules at room temperature move at about 500 m/s). Real gas particles are about ten of their own diameters apart; here they are drawn closer. To keep the picture simple, the gas particles here do not collide with each other. A real smoke particle is hundreds to thousands of times wider than an air molecule; here it is about eight times wider. The orange flashes on the smoke particle are a simplified picture: in reality a huge number of molecules hit it every second.

How to write it in the exam

Solid: the particles are very close together in a regular pattern. They vibrate about fixed positions.
Liquid: the particles are close together but not in a regular pattern. They move around and slide past each other.
Gas: the particles are far apart and randomly arranged. They move quickly in random directions.
When the temperature rises, the particles move faster. At absolute zero, −273 °C (0 K), the particles have the least kinetic energy. T (in K) = θ (in °C) + 273.
Gas particles collide with the walls of the container and exert a force on them. The pressure is the force per unit area.
Heating a gas at constant volume: the particles move faster, so they hit the walls more often and with more force. The pressure increases.
Reducing the volume at constant temperature: the particles move at the same speed but hit the walls more often. The pressure increases. For a fixed mass of gas at constant temperature, pV = constant.
Brownian motion: the air molecules move fast and randomly and collide with the smoke particles. The collisions on different sides are unequal, so each smoke particle moves in a random, zig-zag way.