Thermodynamics Phases (states) of Matter & Latent Heat States of Matter

Phases of Matter Although there are six phases of matter - solid, liquid, gas, plasma, nuclear matter and quark matter – we will only look at the main three: –Solid; –Liquid;& –Gas. What is matter? Anything that has mass and occupies space. Most matter in the Universe is in the form of PLASMA On Earth, the most common phases of matter are SOLID, LIQUID and GAS

The Solid State Particles are arranged in a fixed crystalline manner Have distinct shape Strong molecular bond between atoms Atoms have vibrational kinetic energy and the force of attraction between neighbouring particles give them potential energy

The Liquid State Particles still closely packed, though they are able to “slide over each other” and can flow. Molecular bonds are weaker, and are able to break and reform. This allows them to diffuse. Particles have vibrational, rotational and some translational kinetic energy. Potential energy is higher than that in a solid as the mean distance between atoms is greater.

The Gaseous State Virtually no molecular bonds. Particles free to flow and only interact if they have a random collision. Diffusion of gas to shape of container due to random motion of particles. Very compressible. Much higher speeds of particles due to the increased translational kinetic energy of the particles. Higher potential energy than even liquids as the mean distance between atoms is greater.

Phase change and Molecular Behaviour What is phase change? A phase change is when matter transforms from one of the states of matter to another, ie; solid to liquid (melting) or solid to gas (sublimation). Why change phase? A change of phase occurs when the kinetic energy of the substance increases so much that that the bonds holding the particles together are broken.

Latent Heat The amount of energy released (or absorbed) during a phase change is the latent heat. When a solid is melting the heat energy added is building up the potential energy of the molecules to break the electrical forces holding them together. Similarly, when liquids are turning to gases the heat energy increases the energy of the molecules so they get further apart and become gas molecules

Latent heat of fusion Latent heat of fusion is the amount of heat required to melt 1 kg of a substance without changing its temperature. The latent heat of fusion for water is 3.3 x 105 J/kg, which means that 3.3 x 105 J of energy are needed to change 1 kg of ice at 0°C into water at 0°C

Latent heat of vaporization is the amount of heat required to vaporize 1 kg of a substance without changing its temperature.

Latent Heat Formula Latent heat can be calculated using the following formula: Q l = energy released or absorbed (in J) m= mass (in kg) L=latent heat (Jkg -1 )