Question

What is the potential energy change of the molecules when a 1.00-gram sample of H₂O (l) undergoes a phase transition to H₂O (g) at 100.°C?

Answer 1

The potential energy of the molecules increases when water undergoes a phase transition from liquid to gas. The energy required for this phase change is called the heat of vaporization. By calculating the moles of water in the sample and multiplying it by the heat of vaporization, we can determine the potential energy change of the molecules.

Step-by-step explanation:

When a 1.00-gram sample of H₂O (l) undergoes a phase transition to H₂O (g) at 100.°C, the potential energy of the molecules increases. This is because in the gas phase, the molecules have greater freedom of motion and higher kinetic energy compared to the liquid phase.

The energy required for a phase change from liquid to gas is called the heat of vaporization. For water, the heat of vaporization is 40.7 kJ/mol. To calculate the potential energy change, we need to convert the mass of water to moles and multiply it by the heat of vaporization.

Using the molar mass of water (18.015 g/mol), the moles of water in a 1.00-gram sample can be calculated as follows:

1. Mass of water (g) = 1.00 g
2. Molar mass of water (g/mol) = 18.015 g/mol
3. Moles of water = Mass of water (g) / Molar mass of water (g/mol)

After calculating the moles of water, we can multiply it by the heat of vaporization to find the potential energy change:

1. Moles of water = [calculated value]
2. Heat of vaporization (J/mol) = 40.7 kJ/mol × 1000 J/1 kJ
3. Potential energy change (J) = Moles of water × Heat of vaporization (J/mol)

So, by using the given heat of vaporization and the mass of the water, we can calculate the potential energy change of the molecules.