Reverse fusion

Moderators: Chem_Mod, Chem_Admin

305174946
Posts: 61
Joined: Fri Sep 28, 2018 12:17 am

Reverse fusion

Postby 305174946 » Fri Jan 25, 2019 11:43 am

Can someone please explain how the reversr rxn for fusion is exothermic please.

Dimitri Speron 1C
Posts: 60
Joined: Fri Sep 28, 2018 12:17 am
Been upvoted: 1 time

Re: Reverse fusion

Postby Dimitri Speron 1C » Fri Jan 25, 2019 1:48 pm

Fusion is an endothermic process because you put in heat to the system to change the phase, but the temp of the substance does not change. Solidification, or the reverse reaction, is exothermic because the heat that was input to liquify the substance (the enthalpy of fusion) is being released in order to shed energy and allow the bonds that make the substance solid to reform.

004932366
Posts: 31
Joined: Wed Nov 22, 2017 3:00 am

Re: Reverse fusion

Postby 004932366 » Sat Jan 26, 2019 6:43 pm

Fusion happens when solids are heated to such a point that bonds holding molecules together break apart and the solid becomes a liquid. An easy way to put it is to say that fusion means melting. The input of heat makes the change in enthalpy positive, and the reaction endothermic.

When you reverse fusion, when you freeze, the molecules release the heat to cool down . The change in enthalpy is negative.

It gets confusing when one starts factoring in entropy and exothermic reactions, but focusing strictly on heat helps.

Laura Gong 3H
Posts: 89
Joined: Fri Sep 28, 2018 12:26 am
Been upvoted: 1 time

Re: Reverse fusion

Postby Laura Gong 3H » Mon Jan 28, 2019 2:41 pm

Fusion (melting) occurs when a solid becomes liquid. In order to make that transition, intermolecular bonds between the substance need to be broken. Breaking bonds is an endothermic process that takes in heat, so enthalpy is positive.

Freezing occurs when a liquid becomes a solid. In order to make that transition, intermolecular bonds between the substance need to be formed. Forming bonds is an exothermic process that releases heat, so enthalpy is negative.


Return to “Phase Changes & Related Calculations”

Who is online

Users browsing this forum: No registered users and 2 guests