As water is heated, several important changes occur at the molecular level:
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Increased Kinetic Energy: As heat energy is supplied to the water, the kinetic energy of the water molecules increases. This means that the molecules move faster and more vigorously.
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Breaking of Hydrogen Bonds: Water molecules are held together by hydrogen bonds, which are relatively weak interactions between the partially positive hydrogen atoms of one water molecule and the partially negative oxygen atoms of another. As the temperature rises and the kinetic energy increases, some of these hydrogen bonds begin to break, allowing the molecules to move more freely.
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Phase Changes: As heating continues, water may undergo phase changes:
- At 0°C (32°F), water can exist as ice (solid) or liquid water. As it is heated, ice melts into liquid water.
- At 100°C (212°F) under standard atmospheric pressure, liquid water can transition to steam (gas). This process is called evaporation when it occurs at the surface, and boiling when it happens throughout the liquid.
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Increased Vapor Pressure: With increasing temperature, the vapor pressure of the water also increases. This is the pressure exerted by the water vapor in equilibrium with its liquid phase. When the vapor pressure reaches atmospheric pressure, the water begins to boil.
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Expansion: As water is heated, it begins to expand. This is due to the increased movement of the molecules, which creates more space between them.
Overall, heating water increases the energy and motion of its molecules, leading to changes in physical state and behavior.