# Explain why ammonia gas diffuses faster than bromine vapour at the same temperature.

> Cambridge International IGCSE Chemistry (0620) — 1.2 Diffusion · Explain · 4 marks

> Ammonia (NH₃) has a relative molecular mass of 17. Bromine vapour (Br₂) has a relative molecular mass of 160.

## Mark scheme (4 marks)

1. Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration
2. Ammonia has a lower relative molecular mass than bromine vapour
3. At the same temperature, particles of both gases have the same average kinetic energy
4. Because ammonia molecules are lighter but have the same kinetic energy, they move at a greater speed / faster, so diffuse faster

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