Question

A tea kettle is warmed on an electric stove. After a while, water vapor builds inside the kettle and causes a whistle in the lid to make a sound. How does this demonstrates the first law of thermodynamics?

Answer 1

Electrical energy in the stove is transformed into heat. The heat flows to the water in the kettle, increasing the internal energy of the water. As the energy in the water increases, the water molecules move faster until the liquid water becomes water vapor. The water vapor does work on the whistle, causing it to make a sound. Energy is neither created nor destroyed, it has simply changed form in the process.

Answer 2

The first law of thermodynamics states that energy can neither be created nor destroyed, but it can be converted from one form to another form.
The electric stove is supplying heat to the kettle, this makes the water particles in the kettle to gain more kinetic energy and to increase their motion until they gather enough energy to turn to vapor. The energy gained by the water particles is used to carry out the work of whistling of the kettle.