[Folypeelarks]

Hi,

I am preparing for a SAT subject test in chemistry and I met some problems with the understanding of heat of formation, I can't find where I am mistaking with my logic, so I'll be very thankful if someone help.

Ok, When we are having a synthesis (A + B --> AB) and highly exotermic reaction (low, negative ΔH), the synthesis would undergo easily in contrast to when We are having such, but highly endotermic reaction (high positive ΔH).

What confuses me is that When we are talking about analysis (decomposition AB ---> A + B) it's the reversed.Highly exotermic (low, negative ΔH) decomposition would undergo harder than highly endotermic (high positive ΔH) which determs a compound that decomposes easily.
And I can't find out how a reaction as the endotermic decomposition, which needs a source of this heat and influence, would be much easier for acomplishing in contrast to a decomposition where no source of heat/energy is needed (exotermic decomposition).Sounds strange to me.I suppose that maybe the difference is in the nature of the 2 types of reactions - decomposition and synthesis but I have no idea where.

I hope that this is not a dumb wondering,
Thanks.

[UVN]

Hi,

Can you please explain what you are trying to say, more clearly? I don't really understand what you are trying to ask.

Thanks

[Folypeelarks]

I was studying the prediction of chemical reactions according to their heat of formation.It says that an endotermic synthesis (A + B  AB - Q) would be realized hardily, but an endotermic decomposition (AB  A + B - Q) would be realized easily (AB is unstable).

Why is there such a difference since in both of the cases heat must be absorbed?