In only first-order reactions, the half-life is independent of the initial concentration.
The units of R are in joules, while activation energy is often reported in kilojoules. Be sure to do this conversion.
Dynamic equilibrium may take a significant amount of time to reach in an experiment. Be patient.
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.