DiffusionCambridge IGCSE Chemistry: Flashcards

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What is diffusion?

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What is diffusion?: The net movement of particles from a region of higher concentration to a region of lower concentration, caused by random particle motion, until evenly spread out.
Why does diffusion happen without stirring?: Because particles are in constant, random motion (kinetic particle theory) — this motion alone spreads them out over time.
In which state of matter is diffusion fastest, and why?: Gases — particles are far apart, move freely and quickly in all directions, so they spread out fastest.
Does diffusion occur in solids? Why or why not?: No — particles in a solid are fixed in a regular pattern and can only vibrate in place, so they cannot move from place to place.
How does relative molecular mass affect the rate of diffusion of a gas?: Gases with a lower relative molecular mass diffuse faster than gases with a higher relative molecular mass, at the same temperature.
Do all gas particles move at the same speed at a given temperature?: No — they have the same average kinetic energy, but lighter particles move faster on average than heavier particles.
In the ammonia/hydrogen chloride diffusion tube experiment, where does the white ring form and why?: Closer to the hydrochloric acid (HCl) end, because ammonia (NH3, lower Mr) diffuses faster than HCl (higher Mr) and travels further in the same time.
What happens to gas particles when temperature increases?: They gain kinetic energy and move faster, colliding with the container walls more often and with more force.
What happens to the volume of a gas if temperature increases and it is free to expand?: The volume increases, because faster-moving particles need more space to keep the same collision frequency/pressure.
What happens to the volume of a gas if pressure increases at constant temperature?: The volume decreases, because the same number of particles are forced into a smaller space.
Why do gas particles diffuse faster than liquid particles?: Gas particles are much further apart and move faster and more freely in all directions than liquid particles, which are still close together.
What is meant by a concentration gradient?: The difference in concentration of particles between two regions, which drives the net movement of particles during diffusion.