Heat & Temperature

Phases of Matter

● Depend on strength

of forces of attraction

between particles.

● Intermolecular

forces: H-bonding,

dipole-dipole, and

london dispersion

forces

Polar vs. Non-Polar

Solids

● Definite shape and volume.

● Most dense phase (Exception is water!)

● Difficult to compress.

● Particles vibrate in fixed positions

● Crystalline lattice structure.

● Most attraction between particles.

Note:

● Amorphous solids include glass,

plastic, wax, and silly putty

Definite volume

● No definite shape

● Hard to compress

● Particles slide past each

other

● Forces of attraction

between particles still high

Gases

● No definite shape or volume

● Expands to fill container

● Lowest density

● Little attraction between

particles

“Vapor” = a gaseous state of

something that is normally

liquid

● (Ex: water vapor)
Changes in Phase

Gas

Condensation Vaporization

(Boiling or Evaporating)

Liquid

Solidification Melting (fusion)

Solid

Removing Heat

- IMFs form

Adding Heat

- IMFs break

Sublimation

● Directly from the solid phase

to the gas phase.

● Happens with substances

with very weak

intermolecular forces of

attraction

They separate easily!

● Ex: CO2

(s) dry ice, Iodine

CO2

(s) → CO2

(g)

Deposition gas → solid

Heat and Enthalpy

Physical Change

Endothermic process:

Solid → Liquid or Liquid → Gas

● Energy is absorbed and

overcomes attractive forces

between particles

Exothermic process:

Gas → Liquid or Liquid → Solid

● As particles come closer

together energy is released

Chemical Change

Exothermic Reaction:

A + B → C + D + energy

● Energy is released or “ex”its

Endothermic Reaction:

A + B + energy → C + D

● Energy is absorbed or

“en”ters

Energy

Energy = capacity to do work or produce

heat. It can be anything that causes matter to

move or change direction.

● Many different types of energy

Ex: electrical, thermal, atomic, mechanical

“Thermal” energy is the kinetic energy the

atoms/molecules gain through heat

“Chemical” energy is the potential energy

stored in the bonds between atoms

Law of Conservation of Energy

● Energy can’t be

created or

destroyed, just

transferred from

one form to another

What does this

remind you of?

Fundamental Forms

of Energy

● Potential Energy stored

energy

● Energy can be stored in bonds

between atoms

● Kinetic Energy energy of

motion

● All atoms are moving and

vibrating unless at absolute zero

Heat Energy

Thermal energy: it makes particles move more as it is

added → measured in Joules (J) OR calories (cal)

Law of Thermodynamics: Heat transfers from a high

temperature object to a low temperature object until

they reach thermal equilibrium.

HOT & COLD do NOT exist in science!!

Heat Flow/Transfer

● Heat energy travels from

an object of higher temp.

to one of lower temp.

until both reach the same

temp.

3 Methods:

- Conduction

- Convection

- Radiation

READING

Temperature

Measure of the AVERAGE kinetic energy

(motion) of all the particles in a sample.

Not a form of energy!!!

But if you add heat energy or take it away, it causes particles

to move faster or slower and thus changes the temp.

Both at 25 ̊C

● Which one

contains more heat

energy?

● Which one has the

greater average

KE?

Temperature Scales in Chemistry

Celsius

● Fixed points of scale based

on the freezing point and

boiling point of water

0 °C = water freezes

100 °C = water boils

Kelvin

● Scale based on kinetic

energy. Lowest

temperature possible is:

0 K = absolute zero

Absolute Zero

● Temperature at which particles have

slowed down so much they no

longer possess any kinetic energy.

0 Kelvin

-273° Celsius