## Enthalpy

Marsenne Cabral 1A
Posts: 59
Joined: Fri Sep 28, 2018 12:19 am

### Enthalpy

Why is the enthalpy of bonds (delta H b) always greater than zero and endothermic?

Posts: 77
Joined: Fri Sep 28, 2018 12:28 am
Been upvoted: 1 time

### Re: Enthalpy

They're just given as positive values, but if you're forming the bond then you would write them as negative because it is an exothermic process

Toru Fiberesima 1L
Posts: 63
Joined: Fri Apr 06, 2018 11:02 am

### Re: Enthalpy

Bond breaking is an endothermic process ie a process that requires energy. For endothermic reactions, the products of the reaction have a greater enthalpy than the reactants, and heat is absorbed by the system from its surroundings. Therefore, the delta H b must be positive because the energy is being added to the system.

Bruce Chen 2H
Posts: 60
Joined: Fri Sep 28, 2018 12:26 am

### Re: Enthalpy

Endothermic is using heat, so delta H would be positive, whereas exothermic reactions lose heat so it'll be a negative delta H.

Lopez_Melissa-Dis4E
Posts: 66
Joined: Fri Sep 28, 2018 12:20 am

### Re: Enthalpy

Endothermic requires heat, therefore delta H is positive.
Exothermic releases heat, therefore delta H is negative.
Whether you are forming bonds (endothermic), or breaking bonds (exothermic) you would refer to your positive/negative value of delta H.

Xinyi Zeng 4C
Posts: 63
Joined: Fri Sep 28, 2018 12:18 am

### Re: Enthalpy

Just to add on, "enthalpy of bond" has a more formal name as "Bond Energy" and its definition is the amount of energy required to break that particular bond. Breaking of bond requires energy and hence is endothermic.

Charles Gu 1D
Posts: 60
Joined: Fri Sep 28, 2018 12:16 am

### Re: Enthalpy

In order to break bonds, you need a input of heat so thats why delta h is positive (endothermic)