PHASE CHANGES

Kinetic Theory Kinetic = motion Particles in a gas are considered to be hard, small spheres with an insignificant volume. The motion of particles in a gas is rapid, constant, and random.

All collisions between particles in a gas are perfectly elastic. Particles in a gas only interact when they collide.

Temperature (in kelvins, K) is directly proportional to the average kinetic energy of the particles of a substance. Objects expand when heated because of increased vibrational motion.

Gas pressure is caused by the collisions of particles with an object (wall).

Atmospheric pressure results from the weight of air above an object. Higher altitudes have less atmospheric pressure.

Standard atmospheric pressure is: 1 atm = 101.3 kPa = 760 mm Hg A barometer measures atmospheric pressure.

Liquids Condensed states of matter – solids and liquids In liquids KE is high enough for molecules to flow and take the shape of their container.

Intermolecular attractions give liquids a definite volume.

Evaporation – changing from liquid to vapor at the surface - cooling process

Condensation – warming process

Vapor pressure – pressure in a bubble

Boiling point – temperature at which the vapor pressure equals external pressure on the liquid

Gas Stoichiometry 1 mol of a gas at standard temperature and pressure (STP) = 22.4 L

Volume – Volume Problems 2NO + O2  2NO2 How many liters of nitrogen dioxide are produced when 34 L of O2 react?

What cancels?

Volume – Moles Problems 2NO + O2  2NO2 How many moles of nitrogen dioxide are produced when 34 L of O2 react?

Solids Phase Changes The general properties of solids reflect the orderly arrangement and fixed locations of their particles. Crystal - regular geometric arrangement

Allotropes - (diamond, graphite) 2 or more different molecular forms of the same element in the same physical state

Amorphous - no geometric pattern

Phase changes Sublimation - solid to vapor Vaporization - liquid to vapor (evaporation or boiling) Solidification - liquid to solid Melting - solid to liquid

A) 0.016C, 0.61 kPa B) S, L, V C) 100C; 0C

Ch 13 Review Notes Atmospheric pressure affects the boiling point of a liquid.

STP – standard temperature and pressure - 0C and 1 atm 1 atm = 760 mm Hg so…

Absolute zero = 0 K is the temperature the motion of particles theoretically ceases.

Triple point – conditions ( temperature & pressure) at which solid, liquid, and vapor (gas) can exist in equilibrium.

Solids are more dense than liquids and gases. Sublimation can occur because solids have a vapor pressure.