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