Key Concepts in Thermochemistry and Reaction Dynamics

Collision theory

bonds are broken and/or formed when reactant particles collide with enough energy and with contact orientation

Activated complex

an unstable cluster of atoms that exists during the transition from reactants to products

System

as a part of the universe on which you focus your attention

Surroundings

everything else in the universe that is not focused on

Heat

energy that moves from one object to another due to a temperature difference

Internal energy

total energy contained in a system

Change in enthalpy

the heat absorbed or released by a reaction at a constant pressure

Bond enthalpy

the amount of energy needed to break the bonds of one mole of a substance

Enthalpy of reaction

average bond enthalpies to estimate the total change in energy for a reaction

Activation energy

the minimum amount of energy that colliding particles need to react.

Thermochemical equation

a way to represent an enthalpy change by writing it as part of a chemical reaction.

Hess's Law

if you add 2 or more thermochemical equations to give an overall equation. Also, by adding the enthalpies of reactions to get the overall enthalpy

Standard enthalpy of formation

change in enthalpy when one mole of a compound is formed from its elements with all substances at standard states

Standard state

stable form of a substance at a temperature of 25 °C and a pressure of 100 kPa, may be liquid, gas, or solid.