A solid changing directly into a gas without becoming a liquid.

What is the difference between boiling and evaporation?

Boiling happens throughout the liquid at the boiling point. Evaporation happens only at the surface at any temperature below the boiling point.

Give an example of a substance that sublimes.

Dry ice (solid carbon dioxide) or iodine.

Why are changes of state physical changes?

No new substance is made. Only the energy and arrangement of the particles change.

What does the flat part of a heating curve show?

The substance is changing state, so the temperature stays constant.

What happens to the particles when a liquid is cooled to its freezing point?

They lose energy, slow down and attractions pull them into fixed positions.

Why does temperature stay constant while a solid melts?

The energy supplied is used to overcome the forces between particles, not to increase their kinetic energy.

Why does temperature stay constant while a liquid freezes?

Energy is released as new attractions form, and this balances the energy lost to the surroundings.

Changes of stateIB MYP Chemistry: Flashcards

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What is sublimation?

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What is sublimation?: A solid changing directly into a gas without becoming a liquid.
What is the name of the change from gas to liquid?: Condensation.
What is the name of the change from liquid to solid?: Freezing.
What is the difference between boiling and evaporation?: Boiling happens throughout the liquid at the boiling point. Evaporation happens only at the surface at any temperature below the boiling point.
Give an example of a substance that sublimes.: Dry ice (solid carbon dioxide) or iodine.
Why are changes of state physical changes?: No new substance is made. Only the energy and arrangement of the particles change.
What does the flat part of a heating curve show?: The substance is changing state, so the temperature stays constant.
At what temperature does pure water boil?: 100 °C.
What happens to the particles when a liquid is cooled to its freezing point?: They lose energy, slow down and attractions pull them into fixed positions.
Why does temperature stay constant while a solid melts?: The energy supplied is used to overcome the forces between particles, not to increase their kinetic energy.
Why does temperature stay constant while a liquid freezes?: Energy is released as new attractions form, and this balances the energy lost to the surroundings.
What is the relationship between melting point and freezing point of a pure substance?: They are the same temperature.

Exam questions on Changes of state

A student in Reykjavik heats a beaker of crushed pure ice at −10 °C with a gentle flame, stirring and recording the temperature every minute. The temperature rises, then stays constant for several minutes while the ice melts, even though heating continues. It then rises again until the water boils.
Explain why the temperature stays constant while the ice is melting, even though the flame is still heating the beaker.2 marks
A delivery company in Dubai packs ice cream in insulated boxes with blocks of dry ice (solid carbon dioxide). The dry ice changes straight from a solid to a gas, leaving no liquid behind. When a box is taken out into the warm, humid air, droplets of water form on the cold outside of the box.
Describe, in terms of particles, what happens when dry ice sublimes.2 marks
Students in Accra heat solid stearic acid in a test tube in a hot water bath until it is completely liquid at 80 °C. They then stand the test tube in a beaker of cool water and record its temperature every minute for 13 minutes. The temperature falls from 80 °C to 69 °C by minute 3, stays at 69 °C until minute 8 while the liquid turns into a solid, and then falls to 55 °C by minute 13.
Describe the pattern in the temperature results.3 marks

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Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).