When you add hot water to cold water, the overall temperature of the cold water increases because heat transfers from the hot water to the cold water until they reach a common temperature. This process is governed by the principle of heat transfer known as conduction.
Here's what happens at a molecular level:
- Molecules in hot water have more kinetic energy (they are moving faster) than molecules in cold water.
- When the hot water is mixed with the cold water, the fast-moving molecules of hot water collide with and transfer some of their kinetic energy to the slower-moving molecules of cold water.
- As a result of these collisions, the average kinetic energy (temperature) of the molecules in the cold water increases, causing the cold water to heat up.
- This process continues until the two bodies of water reach a thermal equilibrium, where their temperatures are the same, and there is no net transfer of heat between them.
In summary, hot water transfers heat to cold water through molecular collisions, causing the cold water to heat up until both reach the same temperature. This is a fundamental principle of thermodynamics known as the law of conservation of energy, which states that energy (in this case, thermal energy or heat) is transferred from hotter objects to colder objects until they reach equilibrium.