Forward vs Reverse Reaction (both endo/exo thermic)

[ldv1452]

Can both the forward and reverse reaction be endothermic or exothermic? Or must they ALWAYS be inverse one another?

Thanks

 

[Borek]

What about energy conservation?

 

[horsecandy911]

They cannot both be exothermic or endothermic. Enthalpy (H) is a state function. This means that the enthalpy of a system is completely independent of how one arrived at that system. It's like mass. It follows from this that the enthalpy change in any process is expressed by:

H_{final}-H_{initial} = \Delta\ H

for all processes. So if the forward process has a negative change in enthalpy (exothermic), the reverse process will have a positive change in enthalpy of equal magnitude. For a reverse reaction, you just switch the "final" and "initial" states, which amounts to multiplying the left by negative one. So this equation relates forward and reverse processes:

H_{for}= -H_{rev}

EDIT:
Sorry I can't get LaTex to work right, I'm new to this.

 

[ldv1452]

They cannot both be exothermic or endothermic. Enthalpy (H) is a state function. This means that the enthalpy of a system is completely independent of how one arrived at that system. It's like mass. It follows from this that the enthalpy change in any process is expressed by:

H_{final}-H_{initial} = \Delta\ H

for all processes. So if the forward process has a negative change in enthalpy (exothermic), the reverse process will have a positive change in enthalpy of equal magnitude. For a reverse reaction, you just switch the "final" and "initial" states, which amounts to multiplying the left by negative one. So this equation relates forward and reverse processes:

H_{for}= -H_{rev}

Good answer on this. I appreciate it. Thanks!