reversing signs

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Mallika Singh 1G
Posts: 99
Joined: Sat Aug 24, 2019 12:16 am

reversing signs

Postby Mallika Singh 1G » Mon Feb 03, 2020 2:25 pm

for calculating enthalpy change, when do you need to reverse the sign of delta H?

Bilal Pandit 1J
Posts: 98
Joined: Wed Sep 11, 2019 12:16 am

Re: reversing signs

Postby Bilal Pandit 1J » Mon Feb 03, 2020 2:26 pm

You only need to reverse the sign for the delta H if you are measuring the change in enthalpy in the surroundings, so the actual system will be the opposite of that.

Sam McNeill 1E
Posts: 110
Joined: Sat Aug 24, 2019 12:17 am

Re: reversing signs

Postby Sam McNeill 1E » Mon Feb 03, 2020 4:56 pm

If something is heating something, the q will be negative since it is releasing heat into its surroundings.

005162902
Posts: 102
Joined: Wed Sep 18, 2019 12:15 am

Re: reversing signs

Postby 005162902 » Mon Feb 03, 2020 5:59 pm

The sign of delta H depends on whether or not the reaction is exothermic or endothermic. If it is exothermic, delta H will be negative. If the reaction is endothermic delta H will be positive because heat will be added.

BCaballero_4F
Posts: 94
Joined: Wed Nov 14, 2018 12:22 am

Re: reversing signs

Postby BCaballero_4F » Mon Feb 03, 2020 9:15 pm

Whether or not delta H is positive or negative depends on the reaction (if it is endothermic or exothermic)

Kishan Shah 2G
Posts: 132
Joined: Thu Jul 11, 2019 12:15 am

Re: reversing signs

Postby Kishan Shah 2G » Mon Feb 03, 2020 10:43 pm

You can reverse the sign of enthalpy change when doing Hess's law and you are trying to determine the overall reaction by manipulating the equations.


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