Change of State
Matter normally exists in three states: solid, liquid, and gas. A transition from one of these states to another is called a change of state.
Two common changes of states are solid to liquid and liquid to gas (and vice versa). These changes can occur when the exchange of heat takes place between the substance and its surroundings.
The change of state from solid to liquid is called `text(melting)` and from liquid to solid is called `text(fusion)`.
It is observed that the temperature remains constant until the entire amount of the solid substance melts. That is, both the solid and liquid states of the substance coexist in thermal equilibrium during the change of states from solid to liquid.
The temperature at which the solid and the liquid states of the substance in thermal equilibrium with each other is called its `text(melting point)`.
Melting point is characteristic of the substance. It also depends on pressure. The melting point of a substance at standard atmospheric pressure is called its normal melting point.
Let us do the following activity to understand the process of melting of ice.
Take a slab of ice. Take a metallic wire and fix two blocks, say 5 kg each, at its ends. Put the wire over the slab as shown in Fig. You will observe that the wire passes through the ice slab. This happens due to the fact that just below the wire, ice melts at lower temperature due to increase in pressure. When the wire has passed, water above the wire freezes again. Thus the wire passes through the slab and the slab does not split. This phenomenon of refreezing is called `text(regelation)`.
Skating is possible on snow due to the formation of water below the skates. Water is formed due to the increase of pressure and it acts as a lubricant.
The change of state from liquid to vapor (or gas) is called `text(vaporization)`.
The temperature at which the liquid and the vapor states of the substance coexist is called its `text(boiling point)`.
The change from solid state to vapor state without passing through the liquid state is called `text(sublimation)`.
During the sublimation process both the solid and vapor states of a substance coexist in thermal equilibrium.
Two common changes of states are solid to liquid and liquid to gas (and vice versa). These changes can occur when the exchange of heat takes place between the substance and its surroundings.
The change of state from solid to liquid is called `text(melting)` and from liquid to solid is called `text(fusion)`.
It is observed that the temperature remains constant until the entire amount of the solid substance melts. That is, both the solid and liquid states of the substance coexist in thermal equilibrium during the change of states from solid to liquid.
The temperature at which the solid and the liquid states of the substance in thermal equilibrium with each other is called its `text(melting point)`.
Melting point is characteristic of the substance. It also depends on pressure. The melting point of a substance at standard atmospheric pressure is called its normal melting point.
Let us do the following activity to understand the process of melting of ice.
Take a slab of ice. Take a metallic wire and fix two blocks, say 5 kg each, at its ends. Put the wire over the slab as shown in Fig. You will observe that the wire passes through the ice slab. This happens due to the fact that just below the wire, ice melts at lower temperature due to increase in pressure. When the wire has passed, water above the wire freezes again. Thus the wire passes through the slab and the slab does not split. This phenomenon of refreezing is called `text(regelation)`.
Skating is possible on snow due to the formation of water below the skates. Water is formed due to the increase of pressure and it acts as a lubricant.
The change of state from liquid to vapor (or gas) is called `text(vaporization)`.
The temperature at which the liquid and the vapor states of the substance coexist is called its `text(boiling point)`.
The change from solid state to vapor state without passing through the liquid state is called `text(sublimation)`.
During the sublimation process both the solid and vapor states of a substance coexist in thermal equilibrium.