Bond energy help!!!!

[reliefe123]

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i i know how to figure out the whole scheme of things when it comes to getting the answer...BUT...i always get stuck at the end witth the sign conventions...how can you tell if it will be a poistive or a negative...i know that you have to make it a positive sign for an endothermic and a neg for an exothermic but sometimes it just not work that way????

 

[peyman2002]

could you explain more!

 

[UCLAzy]

breaking a bond is endothermic, as it requires energy to be broken

forming a bond is exothermic (enerrgy is released)

endothermic processes have a positive sign and exothermic have negative sign

this should always work, or else you have proven that the first law of thermodynamics is faulty