Question

Will the KE and PE of water molecules increase if the water at 25 degree Celsius is heated to 50 degree Celsius? And what happens to KE and PE if they boil at 100 degree C and turn into steam?

Answer 1

When water is heated from 25 degrees Celsius to 50 degrees Celsius, both the kinetic energy (KE) and potential energy (PE) of the water molecules increase.

1. Increase in KE: Heating the water increases the average kinetic energy of the water molecules. As the temperature rises, the water molecules gain more thermal energy, causing them to move faster and have higher kinetic energy. The individual molecules will have a greater range of speeds, with some moving faster and some moving slower, but on average, the kinetic energy will increase.

2. Increase in PE: The potential energy of water molecules is primarily associated with their intermolecular interactions, such as hydrogen bonding. When water is heated, the increased kinetic energy of the molecules allows them to overcome the attractive forces between them to a greater extent. This results in an increase in the potential energy of the water molecules.

Now, if the water reaches its boiling point at 100 degrees Celsius and turns into steam (water vapor), the following changes occur:

1. Further increase in KE: As the water boils and turns into steam, the temperature remains constant at 100 degrees Celsius until all the liquid water has converted to vapor. During this phase change, the added heat energy is absorbed by the water molecules as latent heat of vaporization. This causes a further increase in the kinetic energy of the water molecules, even though the temperature remains constant.

2. No change in PE: During the phase change from liquid water to steam, there is no significant change in the intermolecular interactions or potential energy of the water molecules. The potential energy associated with the intermolecular forces remains relatively constant.

In summary, heating water from 25 to 50 degrees Celsius increases both the kinetic energy and potential energy of the water molecules. When the water boils at 100 degrees Celsius and turns into steam, the kinetic energy of the molecules increases further due to the absorption of latent heat of vaporization, while the potential energy remains relatively constant.