Due to rapid advances in kinetic modeling, elementary surface reactions are key to understand the complex chemistry of catalytic partial oxidations. There is a limited experimental knowledge of surface species and a large number of unknown thermochemical and rate parameters. The challenge lies in identifying important reaction intermediates and estimating parameters to build a detailed surface reaction mechanism. This book addresses these challenges by presenting computationally efficient methods for thermodynamically consistent temperature and coverage-dependent enthalpies of surface species and reactions. The book develops detailed surface reactions for industrially important silver- catalyzed ethylene epoxidation. This book is targeted for chemical reaction engineers and kinetic modelers in catalytic partial oxidations. Examples of silver-catalyzed ethylene epoxidation demonstrate the practical use of computational methods developed. Detailed reaction mechanism explains the yield and selectivity of ethylene to ethylene oxide. With 15 MMTPA of ethylene oxide produced worldwide, every percent yield increase saves 95,500 tonnes of ethylene worth $67 million.