Signs for enthalpy

Moderators: Chem_Mod, Chem_Admin

Riya Sood 4G
Posts: 160
Joined: Sat Aug 24, 2019 12:18 am

Signs for enthalpy

Postby Riya Sood 4G » Sun Jan 26, 2020 11:31 pm

Are enthalpies always expressed as positive? Can they ever be negative?

Eesha Sohail 1D
Posts: 100
Joined: Sat Aug 17, 2019 12:16 am

Re: Signs for enthalpy

Postby Eesha Sohail 1D » Sun Jan 26, 2020 11:38 pm

Negative enthalpy would indicate that through a reaction, heat was lost. A reaction with negative enthalpy is the same as an exothermic reaction.

Alison Trinh 1E
Posts: 104
Joined: Thu Jul 25, 2019 12:16 am

Re: Signs for enthalpy

Postby Alison Trinh 1E » Sun Jan 26, 2020 11:48 pm

Positive enthalpies are equivalent to endothermic reactions that take up heat. Enthalpies can be expressed as negative when a reaction is exothermic and therefore releases heat and warms the surroundings.

Jacob Motawakel
Posts: 103
Joined: Wed Sep 18, 2019 12:20 am
Been upvoted: 1 time

Re: Signs for enthalpy

Postby Jacob Motawakel » Sun Jan 26, 2020 11:57 pm

Enthalpies can be negative, indicating an exothermic reaction.

Emily Burghart 1k
Posts: 50
Joined: Wed Sep 18, 2019 12:17 am

Re: Signs for enthalpy

Postby Emily Burghart 1k » Mon Jan 27, 2020 10:35 am

When a reaction has a negative enthalpy, it is considered ectothermic because it is releasing heat. You can think of how ecto sounds slightly like exit, and the negative sign as subtracting heat from a system and sending it into its surrounding environment. For endothermic, think of endo like enter. Endothermic enthalpies are positive because the heat must be entered, or added into a system. Heat is thus taken from its environment.

Hannah Romeo 1J
Posts: 58
Joined: Thu Jul 11, 2019 12:16 am

Re: Signs for enthalpy

Postby Hannah Romeo 1J » Mon Jan 27, 2020 12:11 pm

Enthalpy means the amount of heat transferred. In an exothermic reaction heat is released, therefore the enthalpy is negative. It is the reverse for an endothermic reaction.

sarahforman_Dis2I
Posts: 109
Joined: Sat Aug 17, 2019 12:18 am

Re: Signs for enthalpy

Postby sarahforman_Dis2I » Mon Jan 27, 2020 12:14 pm

Since enthalpy is a measure of the heat released or gained in chemical reactions, it can be negative. If a reaction has a negative enthalpy, that means it is losing enthalpy to the surroundings (releasing heat), meaning it is exothermic

805097738
Posts: 180
Joined: Wed Sep 18, 2019 12:20 am

Re: Signs for enthalpy

Postby 805097738 » Mon Jan 27, 2020 12:27 pm

the sign of enthalpy indicates if the reaction is endothermic (positive) or exothermic (negative)

pmokh14B
Posts: 107
Joined: Sat Aug 17, 2019 12:15 am

Re: Signs for enthalpy

Postby pmokh14B » Mon Jan 27, 2020 12:41 pm

Enthalpy is positive for endothermic reactions or indicates energy needs to be put in (i.e breaking bonds). negative enthalpy indicates exothermic reactions, or breaking bonds.


Return to “Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)”

Who is online

Users browsing this forum: No registered users and 2 guests