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### Endothermic vs Exothermic

Posted: Mon Jan 20, 2020 10:52 am
How can I tell whether a reaction is exothermic or endothermic?

### Re: Endothermic vs Exothermic

Posted: Mon Jan 20, 2020 10:55 am
I think you can tell by looking at the hear input of output if it is given, or you could look at whether there is bond formation or the breakage of bonds which would indicate whether energy is needed or released. By looking at the energy of the products and the reactants you can determine that the reaction is endothermic if the products have more energy than the reactants and exothermic if the products have less energy than the reactants.

### Re: Endothermic vs Exothermic

Posted: Mon Jan 20, 2020 5:18 pm
A reaction is exothermic if the ΔH is negative (as it is thermodynamically favorable) which means it is releasing heat in the process. A reaction is endothermic if the ΔH is positive which means heat/energy is required to have the reaction proceed.

### Re: Endothermic vs Exothermic

Posted: Mon Jan 20, 2020 5:36 pm
An exothermic reaction will result in products which are more thermodynamically stable than its reactants; lower energy bonds are more stable than high energy bonds, so if you have some knowledge of which side has the more "common" or "stable" species (e.g. O2 is much more common and stable than O3 in nature), you can make an educated assumption about if the rxn is exo/endothermic.

### Re: Endothermic vs Exothermic

Posted: Mon Jan 20, 2020 5:42 pm
there was one question which asked to label reactions as endo or exo thermic basically and two good examples are:

N2O4(g) <> 2NO2 where delta H= +57K
this is endothermic because heat is required

X2(g) <> 2X(g)
this is also endothermic because a bond is being broken to form two X molecules and breaking bonds requires energy

### Re: Endothermic vs Exothermic

Posted: Mon Jan 20, 2020 6:06 pm
If the ∆H is given a negative value means that the reaction is exothermic and a positive value means that the reaction is endothermic.

### Re: Endothermic vs Exothermic

Posted: Mon Jan 20, 2020 6:09 pm
An exothermic reaction will have a delta H value that is negative and an endothermic reaction will have a delta H value that is positive.

### Re: Endothermic vs Exothermic

Posted: Mon Jan 20, 2020 6:23 pm
A reaction is generally endothermic if involves the breaking of bonds which causes the absorption of heat. A reaction is generally exothermic when the product forms bonds.