The energy involved in change of state
2 marks · EasyExplain why the temperature of a substance does not change during boiling, even though energy is still being supplied.
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Because all the supplied energy is used to break the forces between particles, not to increase kinetic energy.
Also accept: Energy is used to overcome the forces holding the liquid together; temperature only increases when kinetic energy of particles increases.; All the heat is used for the phase change, not for increasing temperature.
Common mistakes: States energy is used to raise temperature.
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Marking points
B1 · 1 mark · States energy is used to overcome forces between particles.
B2 · 1 mark · States no increase in kinetic energy/temperature during this phase.
Worked solution
At boiling point, energy supplied is used entirely to break intermolecular forces between particles, not to increase their speed. Therefore, temperature does not increase until the phase change is complete.