Final answer:
Steam can be hotter than the boiling point of water once all the liquid has boiled away. The presence of air affects the boiling behavior in open containers, and phase diagrams show the relationship between pressure, temperature, and the state of matter.
Step-by-step explanation:
The temperature of steam can indeed be higher than the boiling point of water, contrary to what might be expected. At the boiling point, liquid water is transforming into steam, which is an endothermic process that consumes heat, meaning the temperature remains constant. However, once all the water has boiled away and turned to steam, additional heat will raise the temperature of the steam above the boiling point.
The presence of air or other gases affects the boiling process in open containers because it reduces the number of water molecules in the gas phase, allowing the liquid to boil away as not all molecules in the vapor phase are water.
A cup of water with ice stays at 0°C because the melting ice keeps absorbing heat without a change in temperature. This is due to the high heat of fusion of ice, the energy required to change ice at its melting point into liquid water without changing its temperature.
On a hot day, the heat entering the cup from the surrounding air is used to melt the ice, rather than raising the temperature of the water.
Boiling points vary with pressure because higher external pressures require water molecules to have more kinetic energy to escape as vapor.
Therefore, at pressures above 1 atm, water boils at temperatures above 100°C, while at lower pressures, such as higher altitudes, water boils at temperatures below 100°C. This is depicted in phase diagrams, which demonstrate the relationship between pressure, temperature, and phase states of a substance.