## Endothermic vs Exothermic

Brandon Valafar
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### Endothermic vs Exothermic

How can I tell whether a reaction is exothermic or endothermic?

805394719
Posts: 104
Joined: Wed Sep 11, 2019 12:16 am

### Re: Endothermic vs Exothermic

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.

haileyramsey-1c
Posts: 105
Joined: Thu Jul 25, 2019 12:18 am

### Re: Endothermic vs Exothermic

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.

Sue Bin Park 2I
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Joined: Mon Jun 17, 2019 7:24 am

### Re: Endothermic vs Exothermic

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.

EMurphy_2L
Posts: 128
Joined: Sat Sep 07, 2019 12:16 am

### Re: Endothermic vs Exothermic

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

Lauren Tanaka 1A
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Joined: Sat Aug 17, 2019 12:18 am

### Re: Endothermic vs Exothermic

If the ∆H is given a negative value means that the reaction is exothermic and a positive value means that the reaction is endothermic.

505306205
Posts: 97
Joined: Thu Jul 25, 2019 12:15 am

### Re: Endothermic vs Exothermic

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.

Joowon Seo 3A
Posts: 100
Joined: Sat Aug 24, 2019 12:17 am

### Re: Endothermic vs Exothermic

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.