Question Video: Calculating the Molar Bond Energy for C–H Bonds Given the Amount of Energy Required to Break All C–H Bonds in Methane | Nagwa Question Video: Calculating the Molar Bond Energy for C–H Bonds Given the Amount of Energy Required to Break All C–H Bonds in Methane | Nagwa

Question Video: Calculating the Molar Bond Energy for C–H Bonds Given the Amount of Energy Required to Break All C–H Bonds in Methane Chemistry • First Year of Secondary School

It takes approximately 2.757 × 10⁻¹⁸ J of energy to break all the bonds in a single molecule of methane, CH₄. What is the average molar bond energy for C–H bonds? Give your answer to the nearest whole number.

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Video Transcript

It takes approximately 2.757 times 10 to the negative 18 joules of energy to break all the bonds in a single molecule of methane, CH4. What is the average molar bond energy for CH bonds? Give your answer to the nearest whole number.

In this question, we are given the amount of energy required to break all the bonds in a molecule of methane. The units of this measurement are joules per molecule. Our goal in this question is to find the average molar bond energy for carbon-to-hydrogen single bonds.

Molar bond energy is also known more simply as bond energy and is defined as the average amount of energy required to break a particular bond in one mole of gaseous particles. Therefore, the units of our answer will be kilojoules per one mole of carbon-to-hydrogen single bonds.

In one molecule of methane, there are four carbon-to-hydrogen single bonds. In other words, we must convert the energy needed to break four CH bonds to the energy needed to break one mole of CH bonds. Our answer will be much larger. Therefore, chemists often use kilojoules to express this amount.

Let’s begin by converting the energy in joules per one methane molecule to joules per one mole of methane molecules. We will need to multiply 2.757 times 10 to the negative 18 joules per CH4 molecule by 6.022 times 10 to the 23rd CH4 molecules per one mole. The conversion factor we are using here is Avogadro’s constant, which is the number of entities per mole of substance. When multiplying, the units CH4 molecules cancel.

Now, let’s convert our answer to joules per one mole of CH bonds. Because one molecule of methane contains four CH bonds, then one mole of methane contains four moles of CH bonds. When multiplying, the units moles of CH4 cancel.

Finally, we’re ready to convert our answer from joules per mole to kilojoules per mole. All we need to do is multiply our answer by the conversion factor one kilojoule per 1000 joules. When multiplying, the units joules cancel.

Finally, after rounding to the nearest whole number, the average molar bond energy for CH bonds is 415 kilojoules per mole.

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