Chemistry, Third edition

154 10 · GASES, LIQUIDS AND SOLIDS

1. The higher the temperature of a collection of particles, the higher the average
   kinetic energy of those particles. On average, particles move fasterat higher tem-
   perature.


2. There is a stickiness (attractive force) between all particles.

The attractive forces between particles in a material pull the particles together,

whereas the movement of the particles (the kinetic energy of the particles) pushes them

apart. Changes of state occur when one of these factors dominate. For example, if we raise

the temperature of a solid, the particles will eventually possess enough energy to par-

tially break away from each other, and melting takes place producing a liquid state.

Further heating causes the particles to move so fast that the attractive forces in the

liquid are unable to hold them even loosely together and they become well separated

BOX 10.1

Temperature scales

The units of temperature are degrees Celsius

(C) or kelvin (K), (Fig. 10.1). The size of one

kelvin and one degree Celsius is the same,

and the two are interconverted using the

expression

T(K)T(°C)273.15

Although there is no theoretical limit to the

upper temperature of matter, the lowest

temperature that is permitted in nature is

273.15C (0 K): this temperature is known

asabsolute zero. The limitation is similar to

that found in mechanics, where no object may

travel faster than the speed of light. (NB

Absolute zero is often approximated to

273 °C.)

Even at 0 K all motion does not cease.

Particles in a solid at 0 K vibrate very slightly

and so matter still possesses some energy,

even at absolute zero. This energy is called

thezero point vibrational energy.

Fig. 10.1Temperature scales.

Fig. 10.2Gases, liquids and
solids.
(a) The bulk appearance of
the three states of matter.
(b) The molecular picture.