Question

Ou cool a 100.0 g slug of red-hot iron (temperature 745 ∘C) by dropping it into an insulated cup of negligible mass containing 85.0 g of water at 20.0 ∘C. Assume no heat exchange with the surroundings.

What is the final mass of the iron and the remaining water?

Answer 1

The final mass of iron remains at 100.0 g and the final mass of the remaining water stays at 85.0 g, as mass is conserved in the heat exchange in an isolated system without phase change involving mass transfer.

Step-by-step explanation:

The student's question involves the calculation of the final mass of iron and water after the iron is dropped into the water and both reach a final equilibrium temperature. To solve this problem, we would normally use the principle of conservation of energy, which states that the heat lost by the iron must be equal to the heat gained by the water. However, since this is a conceptual question asking about the final mass, and not the final temperature or the amount of heat transferred, the answer is straightforward.

The mass of substances does not change during a heat exchange in an isolated system assuming no phase change releases or absorbs mass (such as evaporation or condensation). As no heat is lost to the surroundings and no mention is made of water boiling or ice melting, the final mass of the system will be the sum of the masses of the constituents. Therefore, the final mass of the iron will remain at 100.0 g and the final mass of the remaining water will stay at 85.0 g.