## Endo vs Exo [ENDORSED]

AlexNguyen15
Posts: 66
Joined: Fri Sep 25, 2015 3:00 am

### Endo vs Exo

Is there a way to tell if a reaction is endothermic or exothermic by looking at the reaction? One of the past final exams had a question where this was asked of a reaction, so I just want to be prepared.

DevinSandoval_1D
Posts: 24
Joined: Fri Sep 25, 2015 3:00 am

### Re: Endo vs Exo

In a chemical reaction, chemical bonds are either formed or broken. Typically, when chemical bonds are broken, this requires energy in the form of heat to be put into the system. This would be considered endothermic. On the other hand, when chemical bonds are formed, energy is instead released from the system and is thus exothermic.

Examples:

Endothermic- $2K+Cl_{2}\rightarrow 2KCl$

Exothermic- $MgCl_{2}\rightarrow Mg+Cl_{2}$

Sophia Galluccio
Posts: 20
Joined: Fri Sep 25, 2015 3:00 am

### Re: Endo vs Exo

I would also like to add that during an exothermic reaction the equilibrium of the reaction will shift left and during endothermic reactions the equilibrium will shift towards the right. This is in the case when you use Le Chatliers principle! Hope this helps as well!

Mahlet Dis 2D
Posts: 13
Joined: Fri Sep 25, 2015 3:00 am

### Re: Endo vs Exo

Endothermic reactions need activation energy to proceed. Therefore, heat energy is needed for an endothermic reaction to occur. whereas, an exothermic reaction releases heat energy. whenever you come across to that kind of question and change in H is not given, ask yourself if whether the rxn needs energy to proceed or release energy. usually synthesis rxns( A+B=C) are endothermic and decomposition rxns( C=A+B) are exothermic.

Chiemeka Ezechukwu 3K
Posts: 22
Joined: Wed Nov 18, 2015 3:00 am

### Re: Endo vs Exo

How are you able to tell if a reaction is going to be forward or reverse based on if the change is negative or positive ?

Chem_Mod
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### Re: Endo vs Exo  [ENDORSED]

Chiemeka Ezechukwu wrote:How are you able to tell if a reaction is going to be forward or reverse based on if the change is negative or positive?

The sign of $\Delta H$ does not predict reaction direction.