The conversion of joules (j) to moles (mol) commonly is calculated when measuring the energy changes during chemical reactions. A joule is a measure of energy; a mole is a measure of mass. If a chemical reaction produces a certain amount of energy, you can figure out how many moles of chemicals were used to create the reaction. You will need to know the joules per mole (j/mol) produced by that specific type of reaction.
Calculate the number of joules per mole that a specific chemical reaction should produce. For example, if you dissolve sodium hydroxide in water, the reaction will produce 55,200 joules per mole.
Determine the number of joules of energy that were released in the reaction.
Divide the number of joules released in the reaction by the known joules per mole constant for that type of reaction. For example, if a reaction between sodium hydroxide and water releases 30,000 joules of energy, divide 30,000 by 55,200 to get .54 moles.