conduction + evaporation

Seite 1

Evaporation

-molecules in a liquid have a range of speeds

-occurs at the surface

-molecules with the most energy escaping from the surface - evaporation

-Average ke (kinetic energy) of molecules remaining decreases and hence the temperature decreases

-evaporation causes cooling

Factors that affect the rate of evaporation

The rate of evaporation increases if you:

-increase the temperature

-increase the surface area

-use a fan to blow air across the surface

Conduction

-occurs in solids

-generally, metals are good conductors and non-metals are good insulators

-air is a very good insulator and is often used to stop conduction, eg. fleece traps air making a very good insulating layer.

-other examples include sleeping bags, duvets

Conduction in non-metals

-When the end is heated, the atoms vibrate with greater amplitude (vibrate more)

-They collide with neighbouring atoms and pass on some of the kinetic energy

-heat is slowly transferred along the bar

-same amount of electrons as atoms