Question Video: Converting an Energy in Joules to Electron Volts | Nagwa Question Video: Converting an Energy in Joules to Electron Volts | Nagwa

# Question Video: Converting an Energy in Joules to Electron Volts Chemistry • First Year of Secondary School

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The energy needed to ionize a valence electron from an atom of zinc is 1.50 × 10⁻¹⁸ J. What is this value in electron volts (eV)? Give your answer to 2 decimal places.

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### Video Transcript

The energy needed to ionize a valence electron from an atom of zinc is 1.50 times 10 to the negative 18th joules. What is this value in electron volts, eV? Give your answer to two decimal places.

In this question, we have been given the amount of energy required to ionize a valence electron from an atom of zinc. This amount of energy is the ionization energy, most likely the first ionization energy, which is the amount of energy required to remove the most loosely bound electron completely from an isolated gaseous atom.

We’ve been given the ionization energy measured in the unit joules. The joule is the SI unit for energy. One joule is the quantity of energy needed to raise the temperature of one gram of water by one divided by 4.184 degrees Celsius. A joule is a rather small amount of energy. For example, the energy contained in a single slice of bread is approximately 250000 joules. But we can see from the question that the amount of energy needed to ionize a valence electron from an atom of zinc is many times smaller than a single joule. So the unit joule is not always the most practical when working with energy on an atomic scale.

When working with energy on an atomic scale, scientists often use the unit electron volts. One electron volt is the energy gained by an electron when it is accelerated through a potential difference of one volt. One electron volt is equal to 1.602 times 10 to the negative 19th joules. We can use this relationship to convert the energy in joules into electron volts.

To do this, we need to multiply 1.50 times 10 to the negative 18th joules by the conversion factor written as a fraction. We’ll need to write the conversion factor with one electron volt in the numerator and 1.602 times 10 to the negative 19th joules in the denominator. This will cancel out the joule units, leaving us with electron volts. Performing the calculation gives us an answer of 9.363 electron volts.

But the question asks us to give our final answer to two decimal places. Rounding to two decimal places, we have determined that 1.50 times 10 to the negative 18th joules is equivalent to 9.36 electron volts.

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