Chemistry January Mock Exam Revision

Kinetic Theory and diffusion (1-5)

• In solids, particles are: closely, regularly packed, only movement is slight vibration.
• In liquids, the particles are: mainly touching, with some gaps, less dense than solids due to this, force of attraction between the particles is less than in solids, particles can move
• In gas, the particles are: further apart, almost no force of attraction, big space between the particles.
• Ice floats on water, because solid water (ice) is less dense than liquid water, this is very unusual, thus less dense thing floats because it is lighter.
• Changing State:
• When heating a solid, the thermal energy will make the solids particles vibrate faster and faster, until they virbrate fast enough, that the force of attraction between the particles is no longer strong enough to hold them together. The solid melts to a liquid. The temperature required to melt the solids is its MELTING POINT.
• From Solid to a liquid = Melting. From Liquid to a solid = Freezing, From liquid to a gas = Boilding/(evaporating). From Gas to a liquid = Condensing. and from a solid to a gas or gas to solid = sublimation.
• Particles diffuse down a concentration gradient, from an area of high concentration to an area of low concentration. = Diffusion (in gases and for particles dissolved in solutions)
• Diffusion in liquids is very slow as the gaps between the particles is not very big.

Slide 2

• To show that particles in diffrent gases, travel at different speeds:
• For example the reaction between ammonia and hydrogen chloride gases, to give white solid ammonium chloride
• HCl(g) + NH3(g) = NH4Cl(s)
• The white solid ammonium chloride ring will form closer to the hydrochloric acid (hydrogen chloride gas), thus suggesting the ammonium gas travelled faster.
• This is due to the ammonia particles being lighter than the hydrogen chloride particles.
• Lighter particles travel faster than heavier particles.