M1 Energy & Enthalpy

M1 Energy & Enthalpy - S olomons Study Notes...

Info iconThis preview shows pages 1–6. Sign up to view the full content.

View Full Document Right Arrow Icon

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

View Full DocumentRight Arrow Icon

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

View Full DocumentRight Arrow Icon

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

View Full DocumentRight Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: S olomons Study Notes General Chemistry II Spring 2010 Thermodynamics Solomon Weiskop PhD [ Energy & Enthalpy ] Thermodynamics (1) Study Notes & Practice Problems are available to print out by registering at www.solomonlinetutor.com Solomon Weiskop PhD Copyright 2010 1 1. Thermodynamics Thermodynamics is the study of the energy changes that accompany chemical and physical processes. Our discussion of Thermodynamics begins with these Study Notes ( Energy & Enthalpy ) and concludes with the following Study Notes ( Entropy & Gibbs Free Energy ). Thermodynamics starts by splitting up the Universe into two parts: the System and the Surroundings. The System is that part of the Universe that we are interested in studying. The Surroundings is everything else. System + Surroundings = Universe In Chemistry, a typical System of interest might be some chemicals (i.e. atoms/molecules) contained in a beaker or flask and undergoing some kind of process (usually chemical but perhaps also physical). Any process, either chemical or physical, is generally accompanied by changes in energy. In Thermodynamics, we are interested in understanding such energy changes. 2 2. Energy (E) unit: Joule(J) or kJ/mole Energy comes in many different forms (mechanical energy, nuclear energy, radiant energy etc.). In this course, however, we will mostly be interested in chemical energy . Energy of a C hemical System i.e. a system consisting of atoms/molecules is mainly associated with: Making/Breaking of Chemical Bonds Making/Breaking of Intermolecular Forces (IF) T hermal Motion of Atoms/Molecules Lets brie fly discuss the role of Energy for each of these. Making/Breaking of Chemical Bonds : In breaking a bond, energy is always supplied to the system. The amount of energy needed to break a bond is called Bond Energy ( BE ). BE s differ, depending on the stre ngth of the bond. Stronger bonds need more energy to be broken, i.e. BE is larger. Weaker bonds need less energy to be broken, i.e. BE is smaller. A typical BE is about 400 kJ/mol. In making a bond, energy is always released by the system. When a bond forms, the system becomes more stable . This means that the energy of the system decreases . [Recall the Important Correlation between Energy & Stability introduced in Structure of Atoms .] That is, the system releases energy. The amount of energy released when a bond is formed is, again, BE . 3 Making/Breaking of IFs : In breaking an IF, energy is always supplied to the system. In making an IF, energy is always released by the system. The amount of energy involved in the making/breaking of IF s is considerably less than for actual chemical bonds (i.e. considerably smaller than a typical BE ). Here are the three most important IF s and typical energies needed to break them: Hydrogen Bonding ( HB ) 40 kJ/mol Dipole-Dipole ( DD ) 20 kJ/mol London Dispersion ( LD ) 5-10 kJ/mol Thermal Motion of Atoms/Molecules : According to the Kinetic Theory (introduced last semester), the kinetic...
View Full Document

Page1 / 56

M1 Energy & Enthalpy - S olomons Study Notes...

This preview shows document pages 1 - 6. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online