Anomalous expansion of water in basic thermodynamics: When liquid water is gently heated from 1°C up to 4°C (with no phase change and at approximately atmospheric pressure), what happens to its volume?

Introduction:
Water exhibits an unusual behavior near its density maximum. Unlike most liquids, which expand on heating, water between about 0°C and 4°C becomes denser as temperature increases. Appreciating this “anomalous expansion” is fundamental to thermodynamics and environmental engineering because it influences lake stratification, ice formation, and heat transfer calculations.

Given Data / Assumptions:

• Pure liquid water, atmospheric pressure, no impurities.
• Temperature range considered: 1°C to 4°C.
• No phase change; water remains liquid.

Concept / Approach:
Density ρ is inversely related to volume V for a fixed mass (ρ = m / V). Water has a well-known density maximum at approximately 4°C. Therefore, as temperature increases from 1°C to 4°C, its density increases and its specific volume decreases. For a fixed mass, decreasing specific volume means the bulk volume contracts.

Step-by-Step Solution:
Identify the unique property: water's maximum density occurs at around 4°C.Consider a fixed mass of water in the 1–4°C range.As temperature rises toward 4°C, density increases ⇒ volume must decrease.Hence, water contracts when heated from 1°C to 4°C.

Verification / Alternative check:
Reference density tables show ρ(1°C) < ρ(4°C). Because m is constant, V must be smaller at 4°C than at 1°C, confirming contraction.

Why Other Options Are Wrong:

• Expands/has same volume: Opposite to observed behavior within this interval.
• May contract or expand: Not ambiguous in this specific range; it contracts.
• “Becomes less dense but keeps the same mass”: Mass is constant, but density does not decrease here; it increases.

Common Pitfalls:
Assuming all liquids expand on heating at all temperatures. Water is an important exception near 0–4°C due to hydrogen-bond network rearrangements.

Final Answer:
contracts