as a liquid is heated and changed into a gas what happens to molecules
As a liquid is heated and changes into a gas, the molecules within the liquid gain energy. This increase in energy causes the molecules to move more rapidly and collide with each other more frequently. Eventually, some of the molecules near the surface of the liquid gain enough energy to overcome the forces of attraction between them and escape into the surrounding space as gas molecules.
To understand this process, you can consider the concept of kinetic energy. Kinetic energy is the energy an object possesses due to its motion. As heat is applied to a liquid, the average kinetic energy of its molecules increases. This leads to an increase in their movement and collisions, which eventually results in the transformation of the liquid into a gas.
The phase transition from liquid to gas is known as vaporization or evaporation. It occurs at the boiling point of the liquid, which is the temperature at which the vapor pressure of the liquid equals the atmospheric pressure. At temperatures below the boiling point, evaporation still takes place, but at a slower rate.
It's important to note that not all molecules within a liquid gain enough energy to escape as gas molecules during the process of vaporization. The remaining liquid molecules continue to exert attractive forces on each other, keeping them together as a liquid.