A beaker of water at room temperature is left in a classroom; which explains the change in its temperature over time?

• A. Heat from the room causes the water to warm
• B. The water remains at the same temperature
• C. The water instantly freezes
• D. The water changes into steam immediately

Answer: (A)

Heat transfer between the water and its surroundings causes the temperature to change. The room acts as a heat source or sink, so if the air in the classroom is warmer than the water, energy flows into the water, warming it gradually until the water reaches the room’s temperature. This gradual warming happens because heat moves from regions of higher temperature to lower temperature until thermal equilibrium is reached. The water wouldn’t instantly freeze or turn into steam at room temperature, and it wouldn’t stay exactly the same temperature unless there were perfect insulation and no net heat flow.