Science, Tech, Math › Science Joule to Electron Volt Conversion Example Problem Worked Chemistry Problems Share Flipboard Email Print The Joule and electron volt are units of energy. LAWRENCE LAWRY / Getty Images Science Chemistry Basics Chemical Laws Molecules Periodic Table Projects & Experiments Scientific Method Biochemistry Physical Chemistry Medical Chemistry Chemistry In Everyday Life Famous Chemists Activities for Kids Abbreviations & Acronyms Biology Physics Geology Astronomy Weather & Climate By Todd Helmenstine Todd Helmenstine is a science writer and illustrator who has taught physics and math at the college level. He holds bachelor's degrees in both physics and mathematics. our editorial process Todd Helmenstine Updated February 07, 2019 Joules (J) and electron volts (eV) are two common units of energy. This example problem demonstrates how to convert joules to electron volts.When working with energy values typical for the atomic scale, the joule is too large of a unit to be effective. The electron volt is a unit of energy suited to energies involved in atomic studies. The electron volt is defined as the total amount of kinetic energy gained by an unbound electron as it is accelerated through a potential difference of one volt.The conversion factor is 1 electron volt (eV) = 1.602 x 10-19 JProblem:The ionization energy of a hydrogen atom is 2.195 x 10-18 J. What is this energy in electron volts?Solution:x eV = 2.195 x 10-18 J x 1 ev/1.602 x 10-19 J x eV = 13.7 eV Answer:The ionization energy of a hydrogen atom is 13.7 eV.