Week 3/4 Hw #6

[Jada Dawson]

Hi,
Question 6 asks to identify another quantity that is equal to deltah of the reaction. One of the options is -4 x bond energy of C-H. Is the bond energy negative because that's the reverse reaction or is it negative because the system requires more energy to break bonds in the products than in the reactants? thanks

[Sharlene Duong 3E]

For CH4(g)⟶C(g)+4H(g), the standard enthalpy of reaction is equivalent to 4×bond energy of C−H because 4 C—H bonds are being broken and it takes energy to break bonds, so the reaction is endothermic and the standard enthalpy of reaction is positive. For C(g)+4H(g)⟶CH4(g) I believe that the bond energy is negative in -4xbond energy of C—H because when the C—H bonds are formed in the products, they release energy, making it negative since it is an exothermic reaction. This reaction is also the reverse reaction of the first reaction, so the sign changed to negative. Hope this helps!