Final answer:
When the internal energy of a piece of iron and a cup of water doubles when heated, the redistribution of energy differs between the substances. The iron's temperature increases due to its higher specific heat capacity, while the water undergoes a phase change from liquid to vapor due to its high latent heat of vaporization.
Step-by-step explanation:
When a piece of iron and a cup of water have the same temperature and their internal energy doubles when heated, the energy is redistributed differently in each substance.
In the iron, the increase in internal energy causes the temperature to rise. This is because iron has a higher specific heat capacity compared to water, which means it requires more energy to raise its temperature.
In the water, the increase in internal energy leads to a phase change - from liquid to vapor. This is because water has a high latent heat of vaporization, which means it requires a significant amount of energy to change its phase.