## The sign of q

Abigail Urbina 1K
Posts: 102
Joined: Thu Jul 27, 2017 3:01 am

### The sign of q

For questions involving heat transfers between a system and its surroundings, I'm a little bit confused on how you determine where the negative sign goes (which q is going to take the negative sign).

If q is negative, doesn't it mean that the temperature is going down, meaning it is losing heat?
And if q is positive, doesn't it mean that the temperature is increasing, meaning that it is gaining heat?

In the example Dr. Lavelle provided us during lecture 4 where 1.0 M HCl and 1.0 M NaOH are mixed in a calorimeter and we are asked to find how much heat is released, I'm a little bit confused as to why he set it up as qsys=-qsurroundings. Shouldn't qsys be negative since the system is losing heat? He was saying that the surroundings gain the heat that the system gives off, so I'm a bit confused...

Kelly Kiremidjian 1C
Posts: 62
Joined: Fri Sep 29, 2017 7:04 am

### Re: The sign of q

q is postitive is heat is added to the system and q is negative is heat is removed from the system.

Kayla Danesh 1F
Posts: 38
Joined: Thu Jul 13, 2017 3:00 am

### Re: The sign of q

Yes, you are correct that this is an exothermic reaction and the system is releasing energy. The statement "qsys=-qsurroundings" is just to help us solve for the missing variable. This statement though is the equivalent of saying that "-qsys=qsurroundings." What one gains is what the other loses.

Michael Lee 2I
Posts: 51
Joined: Fri Sep 29, 2017 7:05 am

### Re: The sign of q

qsys + qsurr = 0 is a "perfect system" with no extra released/absorbed.

Jimmy Zhang Dis 1K
Posts: 30
Joined: Fri Sep 29, 2017 7:05 am

### Re: The sign of q

I think the system should be thought of as the calorimeter which is gaining heat and thus the q is considered positive

Justin Bui 2L
Posts: 51
Joined: Fri Sep 29, 2017 7:06 am

### Re: The sign of q

Yeah, since the equation of q in the system is closed, the sign's position really just depends on whether the reaction is exo or endothermic.