1412 Lecture 6 Ch 18

# 1412 Lecture 6 Ch 18 - Entropy Free Energy and Equilibrium...

This preview shows pages 1–13. Sign up to view the full content.

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: Entropy, Free Energy, and Equilibrium Chapter 18 Thermodynamics • Thermodynamics is the study of the relationship between heat and other forms of energy in a chemical or physical process. We have discussed the thermodynamic property of enthalpy, H . We noted that the change in enthalpy equals the heat of reaction at constant pressure . In this chapter we will define enthalpy more precisely, in terms of the energy of the system. Thermodynamics • Thermodynamics can be used to predict if a reaction will occur………. kinetics tell us how fast the reaction will occur. First Law of Thermodynamics • “energy can be converted from on form to another, but it cannot be created or destroyed” • One measure of these changes is the amount of heat given off or absorbed by a system during a constant pressure process, which chemists define as a change in enthalpy (∆H) Second Law of Thermodynamics • “The entropy (S) of the universe increases in a spontaneous process and remains unchanged in an equilibrium process.” • Helps explain why chemical reactions favor a particular direction. Third Law of Thermodynamics • An extension of the Second Law stating: “the entropy of a perfect crystalline substance is zero at absolute 0 K” • This allows us to determine the absolute entropies of substances. Spontaneous Processes and Entropy • A spontaneous process is a physical or chemical change that occurs by itself. Examples include: A rock at the top of a hill rolls down. Heat flows from a hot object to a cold one. An iron object rusts in moist air. These processes occur without requiring an outside force and continue until equilibrium is reached . Spontaneous Physical and Chemical Processes • A waterfall runs downhill • A lump of sugar dissolves in a cup of coffee • At 1 atm, water freezes below 0 C and ice melts above 0 C • Heat flows from a hotter object to a colder object • A gas expands in an evacuated bulb • Iron exposed to oxygen and water forms rust spontaneous nonspontaneous spontaneous nonspontaneous Does a decrease in enthalpy mean a reaction proceeds spontaneously? CH 4 ( g ) + 2O 2 ( g ) CO 2 ( g ) + 2H 2 O ( l ) ∆ H = -890.4 kJ H + ( aq ) + OH- ( aq ) H 2 O ( l ) ∆ H = -56.2 kJ H 2 O ( s ) H 2 O ( l ) ∆ H = 6.01 kJ NH 4 NO 3 ( s ) NH 4 + ( aq ) + NO 3- ( aq ) ∆ H = 25 kJ H 2 O Spontaneous reactions Does a decrease in enthalpy mean a reaction proceeds spontaneously? • We cannot decide whether or not a chemical reaction will occur spontaneously solely on the basis of energy changes in the system. • To make predictions of spontaneity we need another thermodynamic quantity; ENTROPY Entropy and the Second Law of Thermodynamics • The second law of thermodynamics addresses questions about spontaneity in terms of a quantity called entropy ....
View Full Document

{[ snackBarMessage ]}

### Page1 / 93

1412 Lecture 6 Ch 18 - Entropy Free Energy and Equilibrium...

This preview shows document pages 1 - 13. Sign up to view the full document.

View Full Document
Ask a homework question - tutors are online