Nota Terkini

Thursday, March 26, 2009

[Chemistry Form 4] The Enthalpy Of Change

If the amount of thermal energy needed to change one mole of substance from a solid to a liquid or vice versa is called the enthalpy change of fusion, define, then, the enthalpy change of vapourisation.

It take energy to change a substance from a solid to a liquid, and then to a gas.

As energy transferred to a solid, particles in the solid vibrate more until they break out of their fixed lattice positions. This is when solid melts.

There is no change in temperature during this time, because all the energy transferred goes into overcoming the forces that hold the particles in the lattice.

When the solid melted, a rise in temperature is needed so that particles in the liquid have more energy to move faster.

At boiling point, the liquid begins to change into a gas, and the temperature again stays constant, since all the energy taken in by the liquid is used to overcome the forces that hold the particles in the liquid state.

When the liquid has boiled to form a gas, the temperature is raised again to enable the particles to move faster.

The process that involves changes in the state of a substance is a physical process because no chemical bonds are broken.

Did you know?

Solid carbon dioxide as dry ice, changes directly into a gaseous state at room temperature.

This is why it is often used to create 'fog' on stage and movie sets.

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