Understanding Water's Specific Volume Change from 0°C When we talk about the behavior of water when heated, especially starting from 0°C, a key concept is its *specific volume*. Specific volume ($v$) is defined as the volume occupied by a unit mass of a substance. It is the reciprocal of density ($\rho$), meaning $v = 1/\rho$. So, if the density of water increases, its specific volume decreases, and vice versa.

Water's Anomalous Expansion Behavior

Water is unique because it exhibits "anomalous expansion" between 0°C and 4°C. This means it doesn't behave like most other substances which simply expand (decrease in density, increase in specific volume) as they are heated.

• From 0°C to 4°C: As water is heated from 0°C, its density actually increases. This is due to the unique hydrogen bonding structure in water, which allows molecules to pack more closely together as the temperature rises towards 4°C. Because density increases in this range, the specific volume ($v = 1/\rho$) decreases.
• Above 4°C: Beyond 4°C, water starts to behave normally. As temperature increases further, the kinetic energy of the molecules overcomes the hydrogen bonding forces, causing the molecules to move farther apart. This leads to a decrease in density. Consequently, the specific volume ($v = 1/\rho$) begins to increase as the temperature rises above 4°C.

Summary of Specific Volume Changes

We can summarize the change in the specific volume of water when heated from 0°C:

Temperature Range (°C)	Density Change	Specific Volume Change
0°C to 4°C	Increases	Decreases
Above 4°C	Decreases	Increases

Therefore, when water at 0°C is heated under standard atmosphere, its specific volume first decreases (as it warms towards 4°C) and then increases (as it warms above 4°C). This corresponds to the option describing this specific behavior.