When it is cooled down If we cool a gas why does it become a liquid?

Solids, liquid and gases

Solids ArrangementParticles:- Are very close together Have regular arrangement MotionParticles do not have free movement, but can vibrate about a fixed point PropertiesFixed shape and volume Not compressible Effect of increasing temperature An increase in temperature will give the particles more energy. The amplitude of vibration increases and, therefore, the solid expands

Liquids ArrangementParticles:- Are close together but further apart than in a solid, due to weaker forces between them. Have random arrangement MotionForces are present between particles, but weaker than in solid so particles can move throughout the bulk of the liquid. Properties Take shape of container e.g. jelly mould Definite volume Not compressible Effect of increasing temperature Increasing temperature gives the particles more kinetic energy so they move more quickly. One result is decreasing viscosity with increasing temperature.

Gases ArrangementIntermolecular forces are small but do exist. Particles:- Move in a random fashion. Are far apart Move quickly in all directions MotionMove quickly in all directions Properties Do not stay in an open container; spread out to fill available space. Volume depends on volume of container Particles are very far apart, so gases are easy to compress

Heating Curve for Water

Gases