To determine the state of water at [tex]$0^{\circ}C$[/tex] and 1 atm, let's analyze the scenario using the phase diagram for water, [tex]\( H_2O \)[/tex].
A phase diagram displays the states of matter (solid, liquid, and gas) at various temperatures and pressures. The key areas to consider for water are the melting point line (solid-liquid boundary) and the boiling point line (liquid-gas boundary).
1. Temperature and Pressure Conditions:
- Temperature: [tex]\(0^{\circ}C\)[/tex]
- Pressure: 1 atm
2. Identify the Important Points on the Phase Diagram:
- The melting point of water at 1 atm is [tex]\(0^{\circ}C\)[/tex]. This is the temperature at which water transitions between solid (ice) and liquid.
- The boiling point of water at 1 atm is [tex]\(100^{\circ}C\)[/tex]. This is the temperature at which water transitions between liquid and gas (steam).
3. Analyzing the Conditions:
- At [tex]\(0^{\circ}C\)[/tex] and 1 atm, we are exactly at the melting/freezing point of water.
- This means water exists in a phase equilibrium between ice (solid) and liquid water. This is the point where ice can start melting to form liquid water, or liquid water can start freezing to form ice, depending on the direction of energy change (heat addition or removal).
4. Conclusion:
- Since the conditions describe the melting point where water transitions from solid to liquid, this is not the boiling point, and it is not a gas. At this specific point, water can exist as either ice or liquid water in equilibrium, but the key description is that it is at the melting/freezing point.
Therefore, the correct description of water at [tex]\(0^{\circ}C\)[/tex] and 1 atm is:
C. At the melting point
