L24 - Thermodynamics

Using the bond enthalpy to determine the heat of reactions Extension to fuel combustion

Exothermic Process

A process where heat exits the system, resulting in products with lower energy than reactants.

Endothermic Process

A process where heat enters the system, resulting in products with higher energy than reactants.

Enthalpy

The amount of heat flow can always be quantified by the difference in enthalpy of the reactants and products.

State Function

The heat flow during a chemical reaction is independent of the reaction path.

Enthalpy Change

The difference in enthalpy between reactants and products is always equal to the heat flow into or out of the system.

Hess's Law

The enthalpy change is independent of the path taken.

Enthalpy of Formation

The enthalpy change when elements in their standard states go to products.

Standard Conditions

One atmosphere pressure and 25 degrees Celsius

Gas Phase Atoms Pathway

Breaking all the bonds to produce neutral atoms; alternate path due to Hess's law.

Bond Dissociation Enthalpies

The energy required to break a bond between two atoms.

Average Bond Dissociation Enthalpies

Bond strength is not the same in every molecule

Lewis Structures

Need to draw the Lewis structures of your reactants and products in order to figure out whether breaking single bonds or double bonds