Question

On a heating/cooling curve, at what temperatures in degrees Celsius do the two plateaus occur?

A) 0°C and 100°C

B) 100°C and 200°C

C) 0°C and 200°C

D) 100°C and 300°C

Answer 1

The two plateaus on a heating/cooling curve for water occur at 0°C and 100°C, which are the temperatures for water’s freezing/melting point and boiling/condensation point, respectively.

Step-by-step explanation:

On a heating/cooling curve for water, there are typically two plateaus that reflect the temperatures at which phase changes occur. The correct answer to the question about the temperatures at which the two plateaus occur is A) 0°C and 100°C.

At 0°C, water transitions between solid (ice) and liquid phases, which is known as the melting or freezing point of water. At 100°C, water transitions between liquid and gas phases, which is the boiling or condensation point at standard atmospheric pressure. During these phase changes, despite heat being added or removed, the temperature remains constant as the energy is used to change the phase rather than to change the temperature.

These phase changes can be seen on both heating and cooling curves. The heating curve would show a plateau when a substance is changing from a solid to a liquid, and from a liquid to a gas. Conversely, the cooling curve would show a plateau when a substance is changing from a gas to a liquid, and from a liquid to a solid.