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chemistry igcse acapprinted 7 · PDF 7
145 pagesrevision 46934
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Easily compressible due to lots of space between particles
State Changes in terms of Kinetic Theory
When Substances are heated, they absorb it (thermal energy) and convert it into kinetic energy
For example, heating a solid causes it to vibrate more. As you increase the temperature, the particles
vibrate so much that the structure breaks and the solid melts, turning into a liquid
When the particles gain enough energy to overcome the intermolecular forces of attraction, the
structure breaks and the state of the substance changes
When a liquid is heated, the particles with the highest energy gain some more to overcome the
intermolecular forces of attraction and evaporate .
When the substance reaches boiling point, all the particles have enough energy to overcome the
forces of attraction and escape, called boiling
A heating curve shows the increase in temperature with respect to time and changing of state of
the substance
A cooling curve shows the decrease in temperature with respect to time and the state change of the
substance
Important : when a substance is changing state, the temperature does NOT increase because :
For a heating curve, the particles are absorbing all that energy to overcome the forces of attraction
For a cooling curve, particles are releasing energy as the temperature decreases to maintain it
Heating curve