Why does water boil stop boiling and then again when instant coffee is added to microwaved water?

This is a great question! It's not that the water stops boiling and then starts again, but rather a change in the apparent boiling activity. Here's what's happening:

* Boiling Point: When water reaches its boiling point (100°C or 212°F), it turns into steam. This process requires energy, and if you continue adding heat, the water will keep boiling as long as there's enough energy to sustain the transition from liquid to gas.

* Microwave Heating: Microwaves heat food by exciting water molecules. The molecules vibrate faster, which generates heat. When the water reaches its boiling point, the microwave oven continues to add energy, causing the water to boil vigorously.

* Adding Instant Coffee: When you add instant coffee, a few things happen:

* Heat Absorption: The instant coffee absorbs some of the heat from the water. This can cause the water to cool down slightly, which might make the boiling appear to slow down or stop.

* Surface Tension: The coffee particles can change the surface tension of the water, making it more difficult for bubbles to form and rise to the surface. This can also create the illusion that the water is not boiling as actively.

* Convection: The coffee particles can also disrupt the convection currents within the water, which are essential for maintaining a consistent boiling process.

In essence, the instant coffee does not make the water stop boiling and then start again. It's more about a change in how the boiling appears due to the heat absorption, surface tension changes, and convection disruption.

Here's a way to think about it:

* Imagine a pot of boiling water on the stove. If you remove the pot from the heat, the water will stop boiling.

* Adding instant coffee to the microwaved water is like momentarily removing the heat source. The water may briefly cool down, but the microwave continues to supply energy.

The water doesn't really stop boiling, just the rate of boiling changes as a result of adding the coffee.