Chapter 10

States of Matter

The Kinetic-Molecular Theory

• Particles of Matter are in a continual state of motion

KM Theory and Gases

• Ideal Gas: a hypothetical gas that perfectly fits all assumptions of the km theory

• Five Assumptions:– Gases consist of large numbers of tiny particles that

are far apart relative to their size

– Collisions between gas particles and between particles and container walls are elastic collisions

• A collision in which there is no net loss of kinetic energy• KE transferred between two particles during collisions.

However the total ke of two particles remains same as long as temperature is a constant

Assumptions continued

– Gas particles are in continuous, rapid, random motion. They therefore possess kinetic energy, which is energy of motion

– There are no forces of attraction between particles

– The temperature of a gas depends on the average ke of the particles of the gas

KE= ½ mv2

KE theory and Nature of Gas

• KE theory only applies to ideal gas• If temp is not too low or pressure too high,

many gases act ideal• Theory accounts for physical properties

– Expansion – Fluidity– Low density– Compressibility– Diffusion and effusion

Deviations of Real Gas from Ideal

• A real gas is one that does not behave completely according to the assumptions of the KM theory

• At high pressure and low temperature, gas particles can not overcome forces of attraction

• Polar gases deviate from ideal more that nonpolar

Liquid and KM theory

• Particles in continual state of motion, however, are closer together that in gas

• Intermolecular forces cause for attractions (dipole-dipole, London Dispersion, and Hydrogen Bonding)

• Liquids have a lower fluidity than that of gases (most flow downhill due to gravity)

Physical Prop of Liquid

• Relatively high density (compared to gas)• Relative incompressibility• Ability to diffuse• Have surface tension

– Forces pull liquid surface together, decreasing surface area

– Capillary action caused by the surface of liquid to the surface of a solid---cause of meniscus

• Evaporation and boiling– Vaporization: change from liq to gas– Evaporation: process by which particles

escape the surface of liquid without boiling

• Formation of solids– Freezing: the physical change from liq to

solid by removal of thermal energy– Also called solidification

Solids and Kinetic Molecular theory

• Particles closely packed, intermolecular forces at the highest

• Forces hold particles in relatively fixed positions—defn. shape

• Two types of solids– Crystalline: consist of crystals (geometric

patterns)– Amorphous: one in which the particles are

arranged randomly

• Theory responsible for solid properties of– Definite shape and volume

– Definite melting point• Melting is the physical change of a solid to a liquid by the

addition of energy as heat• Supercooled: substances retain liq properties even at

temperatures at which they appear solid (glass and plastics are amorphous solids that have no defn. melting point)

– High density and incompressibility

– Low rate of diffusion

Energy Changes

• Every chemical change involves a loss or gain of energy

• Most usually energy in form of heat

• The amount of heat transfer is measured in calories (cal) or joules (j)

• 1 j = .239 cal or 1 cal = 4.184 j

• Temperature is the condition of a body which determines the transfer of heat to or from other bodies. It is an indication of the average kinetic energy of the particles of which that body is made.

• Heat energy applied to a body may produce one of two effects in the body– It may raise the temp– It may bring about a change of state of that body

• The amount of heat needed to change a substance from a solid to a liquid is called its heat of fusion

• The amount of heat needed to change a substance from liquid to gas is called heat of vaporization

• Heat absorbed or released during a chemical change is known as the heat of reaction. The heat of reaction is usually expressed in units of kcal/mol

Heat of fusion (Hf)• Most calc. are going to use

Q=m x Cp x ▲TQ= quantity of heatM=massCp= specific heat (The amount of heat, measured in calories,

required to raise the temperature of one gram of a substance by one Celsius degree. )

▲T=change in temperature

Hf= Q/mHf=heat of fusion usually in cal/g or j/gQ=quantity of heatM=mass

Heat of vaporization Hv

• Hv=Q/m Hv=heat of vaporization

Q=quantity of heat

M=mass

Example

• How much heat is released when 52.5 g of water cools from 67.5 to 23.3 Celsius? The specific heat of water is 1.00cal/Cg

Q=m x Cp x ▲T

Q=52.5g x 1.00 cal./Cg x (67.5-23.3)

Q=2330 cal or 2.33 Cal (kcal)

• What mass of aluminum can be melted by the addition of 250. cal of heat? The heat of fusion of aluminum is 94.5 cal/g

Q= Hf x m m= Q/Hf

M=250.cal/ 94.5 cal/g

M= 2.65 g