Multiple Choice
A system receives 575 J of heat and does 425 J of work on the surroundings. Calculate the change in the internal energy, ΔE, of the system.
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8. Thermochemistry
First Law of Thermodynamics
Multiple Choice
Which of the following statements regarding the First Law of Thermodynamics is false?
A
The First Law of Thermodynamics allows for the perpetual motion of machines.
B
The First Law of Thermodynamics states that energy cannot be created or destroyed, only transformed.
C
The change in internal energy of a system is equal to the heat added to the system minus the work done by the system.
D
The internal energy of a system increases if heat is added to the system and work is done on the system.
Verified step by step guidance1
Recall the First Law of Thermodynamics, which is a statement of the conservation of energy. It can be mathematically expressed as: \(\Delta U = Q - W\), where \(\Delta U\) is the change in internal energy of the system, \(Q\) is the heat added to the system, and \(W\) is the work done by the system.
Analyze each statement in the problem by comparing it to the First Law:
- The First Law states energy cannot be created or destroyed, only transformed, which is true.
- The change in internal energy equals heat added minus work done by the system, which matches the equation and is true.
- The internal energy increases if heat is added and work is done on the system. Since work done on the system means work is done on it (not by it), this would increase internal energy, so this is true.
Consider the statement about perpetual motion machines. The First Law forbids the creation of energy from nothing, so a machine that produces continuous energy without input (perpetual motion) violates this law and is impossible.
Identify the false statement as the one claiming the First Law allows perpetual motion machines, because this contradicts the principle of energy conservation.
Summarize that the First Law ensures energy conservation and transformation but does not permit energy creation or perpetual motion, making the statement about perpetual motion machines false.
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