particulate nature of matter

• when a solid changes directly to gas • this happens only to a few solids such as iodine or solid carbon dioxide • the reverse reaction is also called sublimation • occurs at a specifc temperature which is unique for a pure substance

• brownian motion/random motion of suspended particles in fluid • this is because the suspended particles are constantly being hit by the unseen particles of the fluid whcih are also in a state of random, continous motion • smoke particles in air • pollen grains in water under a microscope

spreading or mixing of particles froma region of high concentration to a region of lower concentration caused by bollisions due to the random movement of the particles

• no energy input required and spread is even • higher temperature leads to higher rate of diffusion because of more collisions between particles • lower the molecular mass of a substance, the faster it moves and thus a higher rate of diffusion

gaseous particles are in a state of continous random motion. An increase in temperature causes an increase in the partilces’ kinetic energy which helps them move faster. As they move faster they collide with the walls of the container more often and with greater magnitude and thus the pressure of the gas increases