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).
