Which statement best describes water's heat capacity?

• A. Water is a poor conductor of heat
• B. Water has a low heat capacity
• C. Water has a moderate heat capacity
• D. Water has a high heat capacity

Answer: (D)

Heat capacity refers to how much energy a substance can store as its temperature changes. Water stores a lot of energy for a given rise in temperature, so its temperature changes slowly when heat is added or removed. This large energy storage comes from hydrogen bonding between water molecules; those bonds can absorb heat as they continuously form and break, which buffers temperature changes. In numbers, water’s specific heat capacity is about 4.18 J/g°C, much higher than most substances, which explains why oceans help moderate climate and why body temperature stays steadier.

Describing water as a poor conductor speaks to how quickly heat moves through it, not to how much heat it can store, so that option isn’t as accurate. Saying it has a low or moderate heat capacity would understate its ability to absorb heat. Therefore, a high heat capacity is the best description.