Melting, Boiling and Evaporation

2.2.3 Melting and Boiling Temperatures of Water

This section focuses on understanding the melting and boiling points of water under standard atmospheric pressure. These are crucial concepts in physics and chemistry.

Melting Point

The melting point is the temperature at which a solid substance changes into a liquid. For water, the melting point is defined as 0°C (or 273.15 K) at standard atmospheric pressure.

• At temperatures below 0°C, water exists as ice (solid).
• At 0°C, ice and water can coexist in equilibrium.
• When heat is added to ice at 0°C, it melts into water.

Boiling Point

The boiling point is the temperature at which a liquid substance changes into a gas (or vapor). For water, the boiling point is defined as 100°C (or 373.15 K) at standard atmospheric pressure.

• At temperatures below 100°C, water exists as a liquid.
• At 100°C, water and steam (water vapor) can coexist in equilibrium.
• When heat is added to water at 100°C, it boils into steam.

Standard Atmospheric Pressure

It's important to note that the melting and boiling points mentioned above are specific to standard atmospheric pressure. This is approximately 101.325 kPa (or 1 atm). Changes in atmospheric pressure will affect these temperatures.

Table of Melting and Boiling Points of Water

Property	Value	Units
Melting Point (Ice to Water)	0	°C
Melting Point (Ice to Water)	273.15	K
Boiling Point (Water to Steam)	100	°C
Boiling Point (Water to Steam)	373.15	K

Key Concepts

Understanding melting and boiling points is essential for comprehending phase changes and the properties of matter. These points are characteristic of a substance and can be used for identification and characterization.

Formulae

The relationship between heat and temperature during a phase change can be described using the following formula:

$$q = mc\Delta T$$

Where:

• q = heat energy transferred
• m = mass of the substance
• c = specific heat capacity of the substance
• ΔT = change in temperature