Chem

Kinetic Molecular Theory (KMT) Model explaining gas behavior based on particle motion and energy

Assumption of KMT: particle size Gas particles are extremely small compared to the space between them

Assumption of KMT: empty space There is mostly empty space between gas particles

Assumption of KMT: no intermolecular forces Gas particles have no attractive or repulsive forces between them

Assumption of KMT: constant motion Gas particles move in constant random straight-line motion until collisions occur

Assumption of KMT: elastic collisions Collisions between gas particles do not lose kinetic energy

Assumption of KMT: kinetic energy relationship Average kinetic energy of gas particles depends on temperature

Gas pressure The force exerted by gas particles colliding with container walls per unit area

Elastic collision A collision in which no kinetic energy is lost

Density formula D = m/V

Why gases have low density Gas particles are far apart and there is mostly empty space

Compression (gases) Gases can be compressed because empty space between particles can be reduced

Expansion (gases) Gases expand to fill the entire container

Effect of temperature on gas particles Increasing temperature increases particle speed

Diffusion The movement of particles from an area of high concentration to low concentration

Effusion The movement of gas particles through a tiny opening without collisions

Graham’s Law Lighter gases diffuse faster than heavier gases

Graham’s Law relationship Diffusion rate is inversely related to the square root of molar mass

Example of Graham’s Law NH₃ diffuses faster than HCl because NH₃ has lower molar mass

Barometer Instrument used to measure atmospheric pressure

Standard atmospheric pressure 1 atm = 760 torr

Atmospheric pressure at higher altitude Pressure decreases because there are fewer air molecules above you

Dalton’s Law of Partial Pressures Total pressure of a gas mixture equals the sum of individual gas pressures

Partial pressure The pressure exerted by one gas in a mixture of gases

Solid state of matter Has definite shape and definite volume

Particle motion in solids Particles vibrate in place only

Particle arrangement in solids Particles are tightly packed together

Density of solids Usually high because particles are closely packed

Compressibility of solids Solids are not easily compressed because there is little empty space

Expansion of solids Solids expand when heated as particles move faster

Liquid state of matter Has definite volume but no definite shape

Particle arrangement in liquids Particles are loosely packed compared to solids

Particle motion in liquids Particles slide past each other

Density of liquids Medium density compared to solids and gases

Exception to density rule Ice is less dense than liquid water due to hydrogen bonding

Hydrogen bonding A strong intermolecular force between hydrogen and electronegative atoms like oxygen

Viscosity The resistance of a liquid to flow

High viscosity liquids Flow slowly because of strong intermolecular forces

Low viscosity liquids Flow quickly because of weaker intermolecular forces

Effect of temperature on viscosity Increasing temperature lowers viscosity

Surface tension The energy required to increase the surface area of a liquid

Cause of surface tension Strong cohesive forces between liquid molecules

Example of surface tension Insects can walk on water due to strong surface tension

Cohesion Attraction between molecules of the same substance

Adhesion Attraction between molecules of different substances

Capillary action The movement of liquid through a narrow tube due to adhesion and cohesion

Cause of capillary action in water Adhesion between water and glass is stronger than cohesion between water molecules

Meniscus The curved surface of a liquid in a container

Concave meniscus Forms when adhesion is stronger than cohesion (example: water in glass)

Convex meniscus Forms when cohesion is stronger than adhesion (example: mercury in glass)