INTRODUCTION TO PHYSICAL CHEMISTRY

• It is the quantitative and theoretical study of the properties and structure of matter, and their relation to the interaction of matter and energy.

• Can be regarded as the study of the physical principles underlying chemistry – we wanted to know how and why materials behave as they do.

• The ultimate goal of physical chemistry is to provide a model (mathematical) for all chemistry.

What is Physical Chemistry?

The study of physical chemistry includes several disciplines:• Thermodynamics: relationship between energy interconversion by

materials, and the molecular properties.• Kinetics: rates of chemical processes• Quantum Mechanics: phenomena at the molecular level• Statistical Mechanics: relationships between individual molecules and the

bulk properties of matter• Spectroscopy: non-destructive interaction of light (energy) and matter, in

order to study chemical structure• Photochemistry – interaction of light and matter with the intent of

coherently altering molecular structure.

What is Physical Chemistry?

WHAT IS PHYSICAL CHEMISTRY?

variables , relationships, and laws

VARIABLES: an experimental parameter we can change or tweak

RELATIONSHIPS: existence of effects between variables

LAWS: an observation or generalization that is universal

PHYSICAL CHEMISTRY : Cause and Effect

Why do we feel cold when we enter an air-conditioned room?

- heat travels from our body into cold air surrounding us- causing our own energy content to lower - we feel more comfortableA transfer of energy occurs therefore a change. Without

the cause, the effect of feeling warmer could have not followed.

PHYSICAL CHEMISTRY : Physicochemical relationsips

Why does water get hot in a pot?- Water remains cold until we turn on the stove.

electrical energy – heat energy – absorbed by the waterThe temperature of the water does not increase much if

small amount of energy is consumedMathematical relationship: T = f (energy)

PHYSICAL CHEMISTRY : Quantitative and qualitative measurements

Will the bitterness in my coffee disappear if I add cream on it?

In any investigation, we look at first at qualitative relationships.

If I change variable x is there a response in variable y? (qualitative relationships)

How much of the response is caused? (quantitative relationships)

PHYSICAL CHEMISTRY: Observed and controlled variables

Does my TV get louder if I vary the volume control?- We vary the volume control, and as a response, our

ears experience increase in the sound level.- The magnitude of the noise and the position of the

volume knob are both variables, they represent different types:

Volume control: controlled variableAmount of noise: observed variable

PHYSICAL CHEMISTRY: Relationships and graphs

Physical Chemists often depict relationships between variables by drawing graphs:

RELATIONSHIP BETWEEN VARIABLES

h = constant x p

LAWS and the -1th Law of Thermodynamics

Why does a radiator feel hot to touch when it is “on” and cold when it is “off”?

ON – heat travels from radiator to our body

OFF – heat from our body travels to radiator

-1th law of thermodynamics: Heat always travels from hot to cold

The zeroth law of thermodynamics:How does a thermometer work?

ZEROth Law: If A and B are in thermal equilibrium, and B and C are also in thermal equilibrium, then A and C will be in thermal equilibrium.

UNITS OF MEASURE

DERIVED UNITS:

FORCE:

• unit of force in SI system is the newton (N)

• force required to give a mass of 1 kg an acceleration of 1 m/s2

ENERGY:

• SI unit of energy is the joule (J) (1 J = 1 N m)

• a non-SI unit of energy some chemist still use is the calorie

1 cal = 4.184 J

DERIVED UNITS:

PRESSURE:

• defined as force per unit area (p = F/A)

• SI unit of measure is the Pascal (Pa) 1Pa = 1 N/m2

1 bar = 100 kPa

1 atm = 101.325 kPa

1 atm = 1.01325 bar

1 atm = 760 torr

Atomic Mass, Molecular Mass, the Mole

1 amu is defined as equal to exactly 1/12 of the mass of 1 C-12 atom.

1 mole of any substance is the mass of that substance that contains as many atoms molecules, ions or any other entities as there are atoms in exactly 12 g of C-12.

1 mole of C-12 contains 6.0221367 X 1023 atoms (Avogadro’s number)

The molar mass of a substance is the mass in grams of 1 mole of the substance.