Breaking one mole of CH₄(g) into atoms takes 1665 kJ.
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Breaking one mole of into atoms takes . Breaking one mole of ethane, , into atoms takes . Find the mean C-H bond enthalpy from methane, rounded to a whole number. Then use it to find the C-C bond enthalpy in ethane.
Need a reminder? The key ideaShow
Hess's law: the enthalpy change of a reaction is the sum of the enthalpy changes of any set of steps that lead from the same start to the same end. Equations add like algebra: reverse one and its changes sign, multiply one and its is multiplied. For gases, , using mean bond enthalpies.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. C-H. , to the nearest whole number.
Step 2. Ethane's C-H bonds. .
Step 3. C-C. .
Answer: C-H ; C-C . The table value, , differs a little because it is an average over many compounds.
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