Second principle Increase of the entropy: The entropy in the universe increases over time. The entropy is a measure of the disorder of a system. The second law of thermodynamics has several formulations but the most common is that a process is spontaneous if, without external influence (isolated system), it induces an increase of the […]
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Chapter 2 : Methods of separation – extraction
Methods of separation One job of a chemist is to analyse samples of chemicals. To determine the composition of the sample, a separation of the different elements is necessary to avoid interferences between the species. It can be of importance to determine which chemical elements are present, in which quantities and oxidation state. Several methods […]
Chapter 1 : Thermodynamics – First principle
The thermodynamics is the study of the transfer of energy and especially of heat. It is important to make the distinction between heat (q) and temperature (T). The temperature reflects the motion of particles and is connected to their kinetic energy, but the temperature is no energy. Heat is an energy that exist if there […]
Chapter 4f: solids – conductivity
Electric conduction Some solids are conducting the electricity and some are not. We will explain here from where the conductivity comes and the difference between a conductor and an insulator. The conductivity is explained by the band theory. We have seen in the section on molecular orbitals that liaisons are the combination of the atomic orbitals […]
Chapter 11 : specific features of meiosis
Meiosis has three unique features : The mechanism of cell division varies in important details in different organism. This is particularly true of chromosomal separation mechanism, which differ substantially in protists and fungi from the process in plants and animals that we will describe here. Meiosis in a diploid organism consists of two rounds of […]
Chapter 10 : meiosis
The sequence of events during meiosis involves two nuclear divisions ( meiosis I and meiosis II ). Prophase 1 In prophase 1 of meiosis, the DNA coils tighter, and individual chromosomes first become visible under the light microscope as a matrix of fine threads. Because the DNA has already replicated before the onset of meiosis, […]
Chapter 4e: Phase diagram
The state of compounds depends on the temperature and on the pressure. We map the states of the matter on the diagram of phases. The pressure is put as ordinate and the temperature as abscise. The states are separated by full lines, the curves of transition of phase. The curve between the liquid and the […]
Chapter 4d: Solids – lattice energy
In gases, the heat capacity was a resultant of translation, vibration and rotation. In a solid, there is no translation and no rotation. The atoms may vibe around their equilibrium position. The vibration involves a potential energy and a kinetic energy, each term participating for ½R. As a solid has 3 dimensions, Cv=3R However, this […]
Chapter 4c: Solids – crystallography
A characteristic of the solids is that they have their own shape. Liquids are taking the shape of their recipient and gases take all the available space. So solids have their own shape but some are malleable, can be cut, be creased or smashed or can be very rigid. As explained at the beginning of […]
Chapter 4b: Liquids
Liquids Liquids are a condensed state: the volume of a liquid does not change by much when a pressure is applied. A liquid is a fluid: it has not its own shape and molecules can move inside it. As said previously, liquids are characterised by a short range order and a long range disorder. Properties […]