Definition: Physical Chemistry is a branch of chemistry that deals with the properties, behavior, and reactions of chemical substances. It studies how physical and chemical properties change under various conditions including temperature, pressure, concentration, and solubility. The word "Physical Chem" means something physical or chemically based, which in this context refers to any substance that can be observed, measured, or manipulated. Examples include elements like hydrogen, carbon, nitrogen, oxygen, silicon, aluminum, iron, mercury, lithium, zinc, gold, platinum, and zirconium, as well as compounds. The word "Physical Chem" has a long history with the development of physical chemistry. It was first used in 1873 by Carl Ludwig Ehrenfest and his colleagues to describe chemical reactions that involve forces other than those present in atoms or molecules, such as magnetic fields and electric currents. In addition to its scientific name, Physical Chem is also a term used in everyday language to refer to physical chemistry. For example, when someone says "The weather is good today," they might say "It's been a beautiful day compared to the previous one", which translates to "Physical Chemistry". Similarly, when someone says "I'm feeling tired," they might say "I've been getting tired of this for a while now," which also translates to "Physical Chemistry".