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Both the joule (J) and the electronvolt (eV) are units of energy. To make the conversion from joules to electronvolts, the equivalences between both measures can be used. For example: 1 J = 6.241 507 649 ×10 18 and 1eV = 1.602 176 634 ×10 -19 .
What is joule (J)
The joule (J) is a very small unit used to measure energy, work, and heat. It has that name in honor of the English physicist James Prescott Joule, one of the most important references in thermodynamics.
It can be defined as the work that needs to be done to produce one watt or watt (W) of power for one second, or watt-second (W · s). The watt measures power and is equal to 1 joule per second (1 J/s). The watt is also defined by the formula kg⋅m²/s³ .
Other equivalences of joule are:
- 1 J = 6.2415 × 10 18 eV (electronvolt)
- 1 J = 1 C V (coulomb volt)
- 1 J = 1 N m (newton meter)
- 1 J = 0.238 cal (calorie)
Some multiples of joule are:
- 1 kJ (kilojoule) = 10 3 J
- 1 MJ (megajoule) = 10 6 J
- 1 GJ (gigajoule) = 10 9 J
- 1 TJ (terajoule) = 10 12 J
What is volt (V)
The volt (V), also called volt or voltage, is a measure used to measure electrical potential, electrical voltage, and electromotive force. It allows to measure the force or pressure with which electricity flows. It bears that name in honor of the Italian physicist and chemist Alessandro Volta, creator of the first voltaic battery.
The volt is defined as the potential difference across a conductive material when a current of one ampere (A) uses one watt (W) of power. This can be represented as follows: 1 V = 1 W/A . The ampere measures the intensity of an electric current. Watts or watts measure the electrical energy that is produced.
Some multiples of the volt are:
- 1 daV (decavolt) = 10 1 V
- 1 hV (hectovolt) = 10 2 V
- 1 kV (kilovolt) = 10 3 V
Some equivalences of the volt with other measurements are:
1 Volt = 1 Ampere 1 Ohm
What is the electronvolt (eV)
When it is necessary to make calculations with energy values on an atomic scale, the electronvolt is used as a reference, which is a smaller measurement than the joule. The electronvolt (eV) is a unit of energy that expresses the change in energy that exists when an electron moves from one point of potential to another, in case the potential difference of the electric field is 1 volt.
The electronvolt can also be defined as the total amount of kinetic energy an electron gains as it moves through a potential difference of one volt.
The electronvolt is equal to: 1.602 176 634 ×10 −19 J.
Some multiples of the electron volt are:
- 1 keV (kiloelectronvolt) = 10 3 eV
- 1 MeV (megaelectronvolt) = 10 3 keV = 10 6 eV
- 1 GeV (gigaelectronvolt) = 10 3 MeV = 10 9 eV
- 1 TeV (teraelectronvolt) = 10 3 GeV = 10 12 eV
joules to electronvolts conversion
To convert from joules to electronvolts we simply have to use the equivalence between the electronvolt and the joule as a conversion factor:
- 1 eV = 1.602 ×10 -19 J
- 1 J = 6.241 ×10 18 eV
Taking this into account, any problem where a conversion between joules and electronvolts has to be made can be solved.
One of the most common problems that require conversion from joules to electronvolts is calculating the ionization energy of an element. This is the minimum energy needed to capture an electron from a neutral atom, in a gaseous and fundamental state.
problem 1
If the ionization energy of a hydrogen (H) atom is 2.195 ×10 -18 J, how many electron volts is this energy equal to?
This problem can be solved in the following way:
X [eV] = 2.195 ×10 -18 J × 1 eV / 1.602 ×10 -19 J
X [eV] = 13.7 eV
Therefore, we obtain that the ionization energy of a hydrogen atom is 13.7 eV.
problem 2
If we know that the ionization energy of a mole of carbon (C) is 1086.5 kJ, to determine its equivalence in electronvolts we must do the following:
Convert from kilojoules (kJ) to joules (J):
X [J] = 1086.5 kJ ×10 3 J / 1 kJ = 1 086 500 J
X [eV] = 1 086 500 J × 1 eV / 1.602 × 10 -19 J
X [eV] = 6.782 ×10 24 eV
Therefore, the ionization energy of one mole of carbon (C) is 6.782 ×10 24 eV.
Bibliography
- Several authors. The Physics book. (2020). Spain. Akal.
- Barrero González, F. Electric power systems. (2004). Spain. Auditorium Editions.
- Sanchez, JL; Choren, E.; Arteaga, A. Introduction to the International System (SI) of Units. (2018, 3rd Edition. Kindle Edition). Venezuela. University of Zulia.
- Joule to electron volts conversion example problem . Today’s science. Available at https://cienciadehoy.com/problema-de-ejemplo-de-conversion-de-joule-a-electron-voltios/ .
