Geometric isomers exist in alkenes due to the rigidity of their double bonds, allowing for cis and trans configurations, while alkanes lack double bonds, preventing such isomerism. The rate of a chemical reaction can be increased by methods such as increasing surface area, concentration, temperature, and using catalysts, which lower activation energy. Catalysts do not speed up reactions directly but facilitate them at lower energy states. Understanding these concepts is crucial for grasping the dynamics of chemical reactions. Overall, activation energy plays a significant role in determining reaction rates.