Video: Identifying the Name for the Heat Released per Mole of a Substance That Is Completely Reacted with Oxygen in a Set of Names

Which of the following is the heat released per mole of a substance that is completely reacted with oxygen? [A] Reduction potential [B] Ionization energy [C] Electronegativity [D] Heat of combustion [E] Activation Energy

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Video Transcript

Which of the following is the heat released per mole of a substance that is completely reacted with oxygen? A) reduction potential, B) ionization energy, C) electronegativity, D) heat of combustion, or E) activation energy.

In this question, we’re being asked to identify a property that have something to do with the substance being reacted with oxygen. A common example of this in chemistry is the combustion reaction, which occurs when a substance is burned in the presence of oxygen. A common example of a combustion reaction is when we burn fuel such as the fuel in our vehicles, which forms carbon dioxide and water vapor. A combustion reaction typically releases a lot of energy as a result of the reaction, which is why we can use this combustion reaction to power our vehicles. This question is asking us to identify the property that has to do with the heat or energy released as a result of this reaction. As the name suggests, the heat that’s released as a result of a combustion reaction is the heat of combustion.

So we’ve identified our correct answer choice. But let’s take a look at the other answer choices just so we know what they are. The reduction potential is the tendency of an element to be reduced. Reduction is what happens when a chemical species gains electrons. We most often see a reduction reaction in the context of an electrochemical cell, where a reduction reaction, where a chemical species is gaining electrons, is paired with an oxidation reaction, where chemical species is losing electrons. The ionization energy is the energy that’s required to remove an outer electron from an atom. For example, if we were to remove an electron from a sodium atom, which would give us a positively charged sodium ion, the ionization energy would be the energy that was required to remove that electron.

The electronegativity is the tendency of an atom to attract the electrons in bonds. A bond between a chemical species is formed because each of the atoms participating in the bond contribute one of their electrons. If we have a highly electronegative atom like fluorine bonded to another atom that’s not as electronegative like hydrogen, fluorine will attract the electrons and the bond more than the hydrogen will. So as a result, the electrons will be closer to the fluorine than the hydrogen.

Our last answer choice is the activation energy, which is the energy that’s required for a reaction to occur. We’ve probably seen one of these reaction coordinate diagrams before, which show us the difference in energy between the reactant state and the product state. I’ve labelled the activation energy on this diagram with the E with the subscript a. Unless this amount of energy is put in, the reactants won’t be able to overcome the hump in the diagram to form the products. But as we’ve discussed, we’re looking for the property that describes the heat released per mole of a substance that’s completely reacted with oxygen, which is the heat of combustion.

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