Question #538c9

1 Answer
Feb 2, 2017

Answer:

#"Bond formation is exothermic".............#

Explanation:

#"And bond breaking (fission) is endotherimic........."#

When we combust a hydrocarbon to get energy (to warm the house for instance), we have to break strong #C-H#, #C-C#, and #O=O# bonds; such a process requires energy.

Upon complete combustion, we MAKE STRONGER #C=O# and #O-H# bonds in the combustion products, #CO_2# and #H_2O#; such a process RELEASES energy, which we can use to heat our homes, or drive a motor. And the enthalpy or energy change of a reaction can be precisely measured:

#CH_4(g) + 2O_2(g) rarr CO_2(g) + 2H_2O(l) + Delta#

In the given reaction, we have to break STRONG #C-H# and #O=O# bonds. Such a process requires energy. But we make STRONGER #C=O# and #O-H# bonds. The balance, the energy difference is the enthalpy of reaction represented as #Delta# (and quoted as a NEGATIVE value if heat is released!).