States of Matter

Liquids

States of Matter Objectives

Describe the motion of particles in liquids and the properties of liquids according to the kinetic-molecular theory

Discuss the process by which liquids can change into a gas and define vaporization

Discuss the process by which liquids can change into a solid and define freezing

States of Matter Properties of Liquids and the Kinetic-Molecular Theory

A liquid can be described as a form of matter that has a definite volume and takes the shape of its container

The attractive forces between particles in a liquid are more effective than those between particles in a gas

This attraction between liquid particles is caused by the intermolecular forces:

dipole-dipole forces London dispersion forces hydrogen bonding

States of Matter Properties of Liquids and the Kinetic-Molecular Theory

The particles in a liquid are not bound together in fixed positions. Instead, they move about constantly

A fluid is a substance that can flow and therefore take the shape of its container

States of Matter Properties of Liquids and the Kinetic-Molecular Theory

Relatively High Density

At normal atmospheric pressure, most substances are hundreds of times denser in a liquid state than in a gaseous state

States of Matter Properties of Liquids and the Kinetic-Molecular Theory

Relative Incompressibility

Liquids are much less compressible than gases because liquid particles are more closely packed together

States of Matter Properties of Liquids and the Kinetic-Molecular Theory

Ability to Diffuse

Any liquid gradually diffuses throughout any other liquid in which it can dissolve

The constant, random motion of particles causes diffusion in liquids

Diffusion is much slower in liquids than in gases because liquid particles are closer together

The attractive forces between the particles of a liquid slow their movement

As the temperature of a liquid is increased, diffusion occurs more rapidly

States of Matter Properties of Liquids and the Kinetic-Molecular Theory

Surface Tension

A property common to all liquids is surface tension, a force that tends to pull adjacent parts of a liquid’s surface together, thereby decreasing surface area to the smallest possible size

The higher the force of attraction between the particles of a liquid, the higher the surface tension

The molecules at the surface of the water can form hydrogen bonds with the other water, but not with the molecules in the air above them

States of Matter Properties of Liquids and the Kinetic-Molecular Theory

Surface Tension

Capillary action is the attraction of the surface of a liquid to the surface of a solid

This attraction tends to pull the liquid molecules upward along the surface and against the pull of gravity

The same process is responsible for the concave liquid surface, called a meniscus, that forms in a test tube or graduated cylinder

States of Matter Properties of Liquids and the Kinetic-Molecular Theory

Evaporation and Boiling

The process by which a liquid or solid changes to a gas is vaporization

Evaporation is the process by which particles escape from the surface of a non-boiling liquid and enter the gas state

Boiling is the change of a liquid to bubbles of vapor that appear throughout the liquid

Evaporation occurs because the particles of a liquid have different kinetic energies

States of Matter Properties of Liquids and the Kinetic-Molecular Theory

Formation of Solids

When a liquid is cooled, the average energy of its particles decreases

The physical change of a liquid to a solid by removal of energy as heat is called freezing or solidification