A 100g sample of water at 25 °C and 1 atm. of pressure. Then, 100g of water that has recently heated to 100 °C from 0 °C and then cooled to 25 °C at 1 atm. of pressure.
Correct answer: C. Has the same internal energy
- A. Has more internal energy
- B. Has less internal energy
- C. Has the same internal energy
- D. None of these
Explanation
The internal energy of a substance is dependent on its temperature, pressure, and phase, not on the path taken to reach that state. Both 100 g samples of water are at 25 °C and 1 atm pressure, meaning they have the same internal energy. The history of how they reached that temperature (whether they were heated then cooled or started at that temperature) does not affect the internal energy in the final state. Therefore, option C is correct. Options A and B are incorrect because they suggest a difference in internal energy that does not exist based on temperature alone. Option D is incorrect because option C is a valid and correct choice.
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About Thermochemistry and Energetics of Chemical Reactions
Thermochemistry measures energy changes in chemical reactions and distinguishes exothermic from endothermic processes. Work covers systems, surroundings and state functions, internal energy, the first law of thermodynamics, enthalpy and Hess's law, including the sign conventions used when heat enters or leaves a system.
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