Chapter 16 Section 1 Kinetic Theory
Kinetic Theory • An explanation of the behavior of molecules in matter • 3 basic assumptions • All matter is composed of small particles (atoms, molecules, and ions) • These particles are in constant, random motion • These particles are colliding with each other and the walls of their container
Thermal Energy • The total energy of a material’s particles • Kinetic energy + potential energy • AVERAGE KINETIC ENERGY=TEMPERATURE • Faster moving particles = higher temp. • Slower moving particles =lower temp. • Absolute zero = -273.15 C (particle motion is so slow that no additional thermal energy can be removed)
Solid State • Has a definite shape and volume • Particles are closely packed together and vibrating in place • Particles have a geometric arrangement
Liquid State • Has a definite volume, but no definite shape • Particles slip out of their ordered arrangement and are able to move past each other • Still some attractive forces
Liquid State • Melting point – The temp. at which a solid begins to liquify • Heat of fusion – The amount of energy required to change a substance from the solid phase to the liquid phase at its melting point
Gas State • No definite shape or volume • Particles have enough kinetic energy to overcome the attractive forces between them • Particles bounce and collide, filling their container
Gas State • Boiling point – the temperature at which the pressure of the vapor in the liquid is equal to the external pressure acting on the surface of the liquid • Heat of vaporization – the amount of energy required for the liquid at its boiling point to become a gas
Gas State Evaporation Boiling • Occurs at the surface of a liquid • Can occur at temperatures below the boiling point • Must have enough kinetic energy to escape the attractive forces of the liquid • Occurs throughout a liquid • Occurs at a specific temp.
Diffusion • Spreading of particles throughout a given volume until they are uniformly distributed • Occurs in solids and liquids, but most rapidly in gases • From high concentration to low concentration
Heating Curves • Shows temp. change as thermal energy (heat) is added • Temp. remains constant during melting and while boiling • All energy is used to overcome attractive forces
Thermal Expansion • An increase in the size of a substance when the temp. is increased • Solids (gaps in sidewalks) • Liquids (thermometers) • Gases (hot air balloons)
The Strange Behavior of Water • Water molecules have highly positive and negative areas • As they cool, molecules align themselves by charge, so empty spaces occur in the structure • Water expands as it goes from liquid to solid • Ice is less dense than water (that’s why it floats!)
Plasma State • Matter consisting of positively and negatively charged particles (neural charge overall) • Very high energy hard collisions of molecules electrons stripped off • Ex - stars, lightning bolts, neon tubes, etc.
Amorphous Solids • Not all solids have a definite melting point • Some merely soften and turn into liquid over a range of temps. • They lack the ordered structures of crystals • Ex - glass and plastic (long, chainlike molecules)
Liquid Crystals • Start to flow during the melting phase similar to a liquid, but they do not lose their ordered arrangement completely • Highly responsive to temperature change and electric fields • Ex - LCD displays of watches, clocks, and calculators
Changes in Thermal Energy Experiment • Create a time/temperature table • Fill your beaker halfway with ice and cold water • Use your thermometer to measure the temperature of the water (DO NOT TOUCH THE THERMOMETER TO THE SIDES OR BOTTOM OF THE BEAKER) Record this temp. as time zero • Place your beaker on a hot plate over medium heat • Measure the temperature every minute and record it in your table • Create a graph using your data. • Write a paragraph describing what is happening in your graph.