Diffusion in gases
4 marks · NormalSolid carbon dioxide (dry ice) turns directly into a gas at room temperature.
What name is given to this change of state?
A lump of dry ice is placed in a beaker at one end of a room. After some time, people at the other end can notice the effects of carbon dioxide.
Explain, using a particle model, why carbon dioxide gas is detected throughout the room.
Why is no liquid seen during this process?
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
(a) Sublimation
(b) Gas particles move randomly and spread by diffusion from where their concentration is high (near the beaker) to where it is low (rest of the room), until the gas is distributed everywhere.
(c) Carbon dioxide does not exist as a liquid at room temperature and pressure; it goes directly from solid to gas.
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Marking points
B1 (a) · 1 mark · Gives 'sublimation' as the correct term.
M1 (b) · 1 mark · Mentions diffusion/spreading out of gas particles.
M2 (b) · 1 mark · Refers to particles moving randomly from high to low concentration.
B2 (c) · 1 mark · States that carbon dioxide does not exist as a liquid at room temperature or goes straight from solid to gas.
Worked solution
(a) Sublimation.
(b) The solid carbon dioxide turns directly to gas. The gas particles move randomly and spread out by diffusion from where their concentration is high (near the beaker) to the rest of the room.
(c) Carbon dioxide does not exist as a liquid at room temperature; it changes straight from solid to gas.