Question Video: Converting between Energy per Molecule and Energy per Mole Units | Nagwa Question Video: Converting between Energy per Molecule and Energy per Mole Units | Nagwa

# Question Video: Converting between Energy per Molecule and Energy per Mole Units Chemistry • First Year of Secondary School

Which of the following quantities of bonds requires the most energy to break? [A] 1.7 mol O=O (494 kJ/mol) [B] 2.0 mol H-Cl (428 kJ/mol) [C] 1.0 mol C≡C (835 kJ/mol) [D] 2.0 mol H-H (436 kJ/mol) [E] 5.8 mol I-I (148 kJ/mol))

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### Video Transcript

Which of the following quantities of bonds requires the most energy to break? (A) 1.7-mole oxygen-to-oxygen double bond, 494 kilojoules per mole. (B) 2.0-mole hydrogen-to-chlorine single bond, 428 kilojoules per mole. (C) 1.0-mole carbon-to-carbon triple bond, 835 kilojoules per mole. (D) 2.0-mole hydrogen-to-hydrogen single bond, 436 kilojoules per mole. (E) 5.8-mole iodine-to-iodine single bond, 148 kilojoules per mole.

In this question, we are told that the answer choices provided each include a specific quantity of bonds. This quantity is expressed as the number of moles. For example, in answer choice (A), there are 1.7 moles of oxygen or O2. The value provided inside the parentheses is the molar bond energy, which is the amount of energy required to break a specific bond in one mole of a gas form of a substance. Let’s use this simplified cartoon of one mole of oxygen gas molecules.

If one mole of oxygen gas absorbs 494 kilojoules of energy from the surroundings, the double bonds in all of the O2 molecules would be broken, and we would be left with gaseous oxygen atoms. However, in answer choice (A), we have more than one mole of O2. So, we would expect that the amount of energy needed to break all of the bonds would be greater than 494 kilojoules.

Our job in this question is to determine the total amount of energy required to break bonds in a sample of a certain amount of moles. Let’s think about the process we can use to determine the total energy required to break the specific quantities of bonds listed in the answer choices. We’ll need to take the given amount of moles and multiply by the molar bond energy, which is the value given inside the parentheses. Let’s perform the calculation for answer choice (A).

We’ll need to multiply 1.7 moles by 494 kilojoules per mole. This gives us an answer of 839.8 kilojoules. This is the specific amount of energy needed to break all the oxygen-to-oxygen double bonds in 1.7 moles of O2. Now, let’s complete this process for all of the other answer choices, and then we can stop and compare our answers. For answer choice (B), we need to multiply 2.0 moles by 428 kilojoules per mole, which results in an answer of 856 kilojoules.

For answer choice (C), we’ll multiply 1.0 mole by 835 kilojoules per mole, giving us an answer of 835 kilojoules. For answer choice (D), we’ll multiply 2.0 moles by 436 kilojoules per mole, giving us an answer of 872 kilojoules. Finally, for answer choice (E), we’ll multiply 5.8 moles by 148 kilojoules per mole, which gives us an answer of 858.4 kilojoules.

When comparing these answers from our calculations, we see that our answer from choice (D) is the greatest. The energy required to break all of the hydrogen-to-hydrogen single bonds in 2.0 moles of H2 is the greatest. Therefore, the correct answer is answer choice (D).

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