Unit 4: Chemical Reactions in AP Chemistry focuses on the processes that transform substances through the breaking and forming of chemical bonds. Students explore reaction types such as synthesis, decomposition, single replacement, double replacement, and combustion. Key concepts include balancing chemical equations, reaction stoichiometry, limiting reactants, and percent yield. The unit also introduces the use of net ionic equations and explores energy changes in reactions, providing a solid foundation for understanding the mechanisms and applications of chemical reactions.