Question

what phase changes will take place when water is subjected to increasing pressure at a constant temperature of 0.0 °c?
options:

• deposition and condensation
• freezing and deposition
• boiling and freezing
• deposition and melting

Explanation:

1. First, analyze the phase diagram of water. At 0.0 °C (constant temperature), when pressure increases:

• For water vapor (gas) at low pressure, increasing pressure can cause deposition (gas to solid, ice) if pressure crosses the solid - gas boundary.
• For ice (solid), increasing pressure can cause melting (solid to liquid, water) because the solid - liquid boundary of water has a negative slope (unlike most substances), meaning increasing pressure at constant temperature (0 °C) can convert ice to liquid water.
• Now check the options:
• "deposition and condensation": Condensation is gas to liquid, but at 0 °C, with increasing pressure, gas (water vapor) would deposit to solid (ice) not condense to liquid (since 0 °C is freezing point, and the phase boundary for gas - liquid at 0 °C is not the path here). Eliminate.
• "freezing and deposition": Freezing is liquid to solid, but we start with either gas or solid. At 0 °C, increasing pressure on liquid water would not cause freezing (it would stay liquid or freeze only at lower pressure for water? No, water's solid - liquid line has negative slope, so higher pressure at 0 °C melts ice, not freezes liquid. Eliminate.
• "boiling and freezing": Boiling is liquid to gas, opposite of what happens with increasing pressure. Eliminate.
• "deposition and melting": Deposition (gas→solid) when pressure increases on water vapor (gas) at 0 °C (crossing solid - gas boundary), and melting (solid→liquid) when pressure increases on ice (solid) at 0 °C (crossing solid - liquid boundary). This matches.

Answer:

deposition and melting