Chapter 5: Thermochemistry

Energy

The ability to do work or transfer heat.

Change in Energy

\Delta E=E_{final}-E_{initial}

Thermodynamics

The study of energy and its transformations.

Thermochemistry

The study of chemical reactions and the energy changes involving heat.

First Law of Thermodynamics

Energy cannot be created or destroyed, only converted from one form to another.

Systems and Surroundings

The system is the portion of the universe under study, while the surroundings are everything else.

Types of Systems

Open System, Closed System, Isolated System.

Internal Energy

The sum of kinetic and potential energies of a system's components.

Changes in Internal Energy

Positive and negative changes indicate energy absorption or release.

\Delta E=q+w

Heat (q)

Energy exchanged between the system and surroundings.

Work (w)

Energy exchanged as work during a process.

Exchange of Heat Between System and Surroundings

Endothermic and exothermic processes.

State Functions

Internal energy is independent of the path taken to reach a state.

Work

Mechanical work associated with changes in gas volume.

Enthalpy

Internal energy plus the product of pressure and volume.

H=E+PV

Amount of Heat

q=mc\Delta T

Enthalpy of Reaction

Heat of reaction, dependent on reactants' and products' states.

Calorimetry

Measurement of heat flow.

Hess’s Law

Enthalpy change for an overall reaction equals the sum of changes for individual steps.

\Delta H=\sum n\Delta H_{f,products}-\sum m\Delta H_{f,reactan ts}^{°}

Enthalpies of Formation

Enthalpy change for forming a compound from its elements.

Bond Enthalpy

Energy required to break chemical bonds.

Bond Enthalpies and Enthalpy of Reaction

Predicting endothermic or exothermic reactions using bond energies.

\Delta H_{rxn}=\sum bonds\:broken-\sum bonds\:formed