delta U = q + w

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Jasmine W 1K
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Joined: Sat Sep 07, 2019 12:18 am

delta U = q + w

Postby Jasmine W 1K » Mon Feb 10, 2020 11:38 pm

In this equation: delta U = q + w, how would you know whether or not q would be positive or negative?

Abigail Sanders 1E
Posts: 112
Joined: Wed Sep 11, 2019 12:16 am

Re: delta U = q + w

Postby Abigail Sanders 1E » Tue Feb 11, 2020 12:15 am

Q is positive or negative depending on if heat is added or removed from the reaction. If heat is added to the system that you are finding the internal energy for then it will be positive, if it is removed, Q will be negative.

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Re: delta U = q + w

Postby anjali41 » Tue Feb 11, 2020 12:38 am

Another way to think about it is in terms of exothermic and endothermic reactions. If the reaction is exothermic and is releasing heat, then the q will be negative. If the reaction is endothermic and absorbing energy, the q will be positive.

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Re: delta U = q + w

Postby alex_4l » Tue Feb 11, 2020 1:20 am

An easy way to look at it is:

Q is positive when heat is transferred INTO a system (endothermic)
Q is negative when heat is transferred OUT of a system (exothermic)

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