Plotting Kinetics Experiments

In only first-order reactions, the half-life is independent of the initial concentration.

Arrhenius Equation

The units of R are in joules, while activation energy is often reported in kilojoules. Be sure to do this conversion.

Dynamic Equilibrium

Dynamic equilibrium may take a significant amount of time to reach in an experiment. Be patient.

Le Chatelier's Principle

1. Make sure that you use gas pressures when working with K_p and molar concentrations when working with K_c.
2. Sometimes it is possible to simplify the equilibrium expression. If the value of x is much smaller than the concentrations in the initial concentrations, then it is possible to remove x from the equilibrium expression. Like anyone else, chemists like to avoid work whenever possible. See below for an example.

Thermodynamics

An exothermic reaction has a positive ΔH value while an endothermic reaction has a negative ΔH value, which sometimes seems counterintuitive.

Entropy for an element or compound is always greater than zero. However, the change in entropy (ΔS) can be negative. A common example: water freezing.