Energy Exchange in N2 + H2 Reaction: Examining the Bond Changes

[Erin_Sharpe]

When N2 and H2 are reacted in a bomb calorimeter to form NH3 the temperature of the bomb calorimeter and the water it contains increases.
Is the energy required to break the bonds in the reactants greater or less than the energy released during the formation of the bonds of the prouducts.

I said it was less...but I don't think that's right. Can someone help?

Thanks,
Erin

 

[maverick280857]

You have to reason based on experimental evidence but generally nitrogen is considered to have a high bond dissociation enthalpy so you need to invest quite a large amount of energy per mole to break nitrogen-nitrogen bonds in N2 gas. At the same time if you are told that heat is released all that you can say is that delta(H) < 0 or equivalently

$$\Delta H_{product} < \Delta H_{reactants}$$

Cheers
Vivek