Answer :
To explain why energy must be given to a liquid for it to change to a gas in terms of particles, we need to consider the concept of intermolecular forces. When a liquid transitions to a gas, it undergoes a process called vaporization or evaporation.
1. In a liquid, the particles are relatively close together and have enough kinetic energy to move around but are still attracted to each other due to intermolecular forces like Van der Waals forces or hydrogen bonding.
2. When energy is added to the system, such as heat, the particles in the liquid gain more kinetic energy, causing them to move faster and overcome the attractive forces holding them together.
3. As the particles gain enough energy to break free from the liquid's surface, they escape into the gas phase. This process requires energy to overcome the intermolecular forces that keep the liquid particles together.
4. The energy input needed for this transition is called the latent heat of vaporization. It is the amount of energy required to change a substance from a liquid to a gas at its boiling point without changing its temperature.
In summary, when a liquid changes to a gas, energy must be supplied to break the intermolecular forces holding the liquid particles together, allowing them to escape into the gas phase. This energy input is essential for the phase transition to occur.
