The First Law of Thermodynamics can be summarized by simply saying that all thermodynamic processes follow the principle of the conservation of energy. It can also be captured in a simple equation.
First Law of Thermodynamics
ΔU=Q−W
... where U is the internal energy of the system, Q is the heat transferred to or from the system and W is the work done on or by the system.
Use the definition and equation representation of The First Law of Thermodynamics to answer these questions. Be careful, a negative work means you are subtracting a negative!
A total of 123 J of work is done on a gaseous refrigerant while it undergoes compression. If 13 J of heat is released during this process, what is the total change in internal energy of the system?
ΔU=Q−W
ΔU=−13 J+123 J
ΔU=110 J
ΔU=−13 J+123 J
ΔU=110 J
A gas expands when 778 J of heat is added to it. The expanding gas does 498 J of work on its environment. What is the change in internal energy of the gas?
ΔU=Q−W
ΔU=778 J−498 J
ΔU=280 J
ΔU=778 J−498 J
ΔU=280 J
A system's internal energy is 47 J before heat is added to the system. If the final internal energy is 68 J and the system does 29 J of work, how much heat is added to the system?
ΔU=Q−W
(68 J−47 J))=Q−29 J
21 J=Q−29 J
Q=50 J
(68 J−47 J))=Q−29 J
21 J=Q−29 J
Q=50 J
| A total of 123 J of work is done on a gaseous refrigerant while it undergoes compression. If 13 J of heat is released during this process, what is the total change in internal energy of the system? |
| ΔU=Q−W ΔU=−13 J+123 J ΔU=110 J |
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