States and state change Chapter 11 sec 1 States and state change

States of Matter The fundamental difference between states of matter is the distance between particles.

States of Matter Gases – fill container, random rapid motion, never coming to rest or clumping together Motion is mainly translational Liquids – fixed volume, flow and assume shape of container, only slightly compressible, stronger forces hold molecules together Motion is mainly translational EOS Solids – fixed volume, definite shape, generally less compressible than liquids, forces hold particles in a fixed shape Motion is mainly vibrational

Solid particles have fixed position Crystalline form: they can be very hard and brittle or they can be very soft.

Liquid particles can move easily past one another Liquid flow to take the shape of the lower part of a container. A meniscus is the interface between a liquid and the air above it EOS Capillary action results from intermolecular interactions

Surface Tension Surface tension (g) is the amount of work required to extend a liquid surface and is usually expressed in unit of J m–2 Adhesive forces are intermolecular forces between unlike molecules Cohesive forces are intermolecular forces between like molecules EOS

Vaporization and Condensation Vaporization is the conversion of a liquid to a gas. EOS Condensation is the change of a gas to a liquid. The boiling point of a liquid is the temperature at which its vapor pressure becomes equal to the external pressure

Phase Changes Involving Solids The conversion of a solid to a liquid is called melting, or fusion, and the temperature at which a solid melts is its melting point Sublimation is the process of a molecule’s passing directly from the solid to the vapor state

Phase Diagrams A phase diagram is a graphical representation of the temperature and pressure conditions under which a substance exists as a solid, liquid, gas, or some combination of these in equilibrium EOS critical point fusion curve vapor pressure curve sublimation curve triple point

Practice A sample of water has a fixed volume and shape. What state is it in? What property of a liquid enable you to pour a liquid into a cup until the top of the liquid is slightly higher than the top of the cup? During what process does a liquid change to solid? solid Surface tension freezing