- #1
RobNik
- 1
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Hello,
I'm trying to understand the concepts of the change in internal energy (U) or enthalpy (H) of a reaction, given the laws and equations of basic thermodynamics, but I'm getting confused with the following thought experiment. I'm looking at U, since I find it easier to imagine, even though H is used more often. (Sorry but this latex entry thing seems busted, so I'll write out "delta U".) Imagine a reaction:
A + B --> C + D
has delta U = -500 kJ. Say they are all gases, and I put them in a constant volume, insulated container, so the process is adiabatic, and no work is done. (The reaction could be started with a tiny trigger, like a spark).
q = 0 [adiabatic, insulated container]
w = 0 [constant volume]
delta U = w + q = 0 + 0 = 0
Obviously the reaction is exothermic, and the temperature of this container would rise, but what exactly is the "system" for which the delta U = -500 kJ. The box as a whole has 0 delta U, right?
thanks,
Rob
I'm trying to understand the concepts of the change in internal energy (U) or enthalpy (H) of a reaction, given the laws and equations of basic thermodynamics, but I'm getting confused with the following thought experiment. I'm looking at U, since I find it easier to imagine, even though H is used more often. (Sorry but this latex entry thing seems busted, so I'll write out "delta U".) Imagine a reaction:
A + B --> C + D
has delta U = -500 kJ. Say they are all gases, and I put them in a constant volume, insulated container, so the process is adiabatic, and no work is done. (The reaction could be started with a tiny trigger, like a spark).
q = 0 [adiabatic, insulated container]
w = 0 [constant volume]
delta U = w + q = 0 + 0 = 0
Obviously the reaction is exothermic, and the temperature of this container would rise, but what exactly is the "system" for which the delta U = -500 kJ. The box as a whole has 0 delta U, right?
thanks,
Rob