3. Determine the sign of both q and w for the following phase change at 25 °C and 1.0 atm:
H2O(l) → H2O(g)
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if heat is ADDED to the system then q is +.
If work is done by the system on the surroundings then W is -.
To determine the sign of both q (heat) and w (work) for the phase change of water from liquid to gas at 25 °C and 1.0 atm, we need to consider the direction of energy flow.
In this case, water is transitioning from the liquid phase to the gas phase, which corresponds to an endothermic process. Endothermic processes absorb heat from the surroundings, resulting in a positive value for q.
Since heat is being absorbed, the surroundings are doing work on the system to provide the necessary energy for the phase change. Therefore, work is also positive (w > 0) for this process.
In summary:
- q (heat) is positive (+q) since the process is endothermic.
- w (work) is positive (+w) since the surroundings are doing work on the system.
Please note that the signs of q and w can vary based on the conditions and the direction of the phase change. This explanation specifically applies to the given phase change of water vaporization at 25 °C and 1.0 atm.