5 Steps to a 5 AP Chemistry

 123

Thermodynamics

IN THIS CHAPTER:

Summary:Thermodynamicsis the study of heat and its transformations.

Thermochemistryis the part of thermodynamics that deals with changes in

heat that take place during chemical processes. We will be describing energy

changes in this chapter. Energy can be of two types: kinetic or potential.

Kinetic energyis energy of motion, while potential energyis stored energy.

Energy can be converted from one form to another but, unless a nuclear reac-

tion occurs, energy cannot be created or destroyed (Law of Conservation of

Energy). We will discuss energy exchanges between a system and the surround-

ings. The systemis that part of the universe that we are studying. It may be a

beaker or it may be Earth. The surroundingsare the rest of the universe.

The most common units of energy used in the study of thermodynamics

are the joule and the calorie. The joule(J) is defined as:

1 J =1 kg m^2 /s^2

Thecaloriewas originally defined as the amount of energy needed to raise

the temperature of 1 g of water 1°C. Now it is defined in terms of its relation-

ship to the joule:

1 cal = 4.184 J

It is important to realize that this is not the same calorie that is commonly

associated with food and diets. That is the nutritional Calorie, Cal, which is

really a kilocalorie (1 Cal =1000 cal).

Keywords and Equations

S°=standard entropy H°=standard enthalpy

G°=standard free energy q=heat

c=specific heat capacity Cp=molar heat capacity at constant pressure

ΔS°=ΣS°products −ΣS°reactants

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KEY IDEA

KEY IDEA