What happens to the density of water as it is heated?

• A. The density decreases.
• B. The density first increases, then decreases.
• C. The density increases.
• D. The density remains unchanged.

Answer: (A)

Verified step by step guidance

1. Recall that density (\(\rho\)) is defined as mass divided by volume: \(\rho = \frac{m}{V}\). For water, the mass remains constant as temperature changes, so changes in density are due to changes in volume.
2. Understand that when water is heated, it generally expands, meaning its volume increases. Since mass is constant and volume increases, density decreases according to the formula.
3. However, water has a unique behavior near 4°C where it reaches its maximum density. Below 4°C, as water warms up to 4°C, its density actually increases because the volume decreases slightly.
4. Above 4°C, as water continues to heat, it expands more significantly, causing the volume to increase and the density to decrease.
5. Therefore, the overall behavior is that the density of water first increases as it warms from 0°C to 4°C, then decreases as temperature rises beyond 4°C.