Final answer:
In the reaction of potassium with water, work (w) is positive due to gas expansion, heat (q) is negative because the reaction releases heat, and both the change in internal energy (ΔU) and enthalpy (ΔH) are negative, indicating an exothermic process.
The correct option is B.
Step-by-step explanation:
When potassium metal reacts with water, the reaction is as follows: 2K (s) + 2H₂O (l) → 2KOH (aq) + H₂ (g). The final temperature is higher than the initial temperature, indicating that the reaction is exothermic, meaning it releases heat.
Now, considering thermodynamic quantities:
Work (w) is positive because gas is produced, leading to an expansion against atmospheric pressure.
Heat (q) is negative because heat is being released by the system to the surroundings.
The change in internal energy (ΔU) is the sum of q and w. Since heat is released (q is negative) and work is done by the system (w is positive), whether ΔU is positive or negative depends on the magnitude of q compared to w.
However, typically, in exothermic reactions like this one, the amount of heat released is so significant that ΔU is negative.
ΔH, or enthalpy change, is negative for exothermic reactions because the total heat content of the system decreases as heat is released.
Therefore, the correct option is:
b) w is positive, q is negative, ΔU is negative, ΔH is negative.
This is consistent with the law of conservation of energy and the definitions of thermodynamic quantities.
The correct option is B.