Thermo-chemistry - Report Example

Thermo-chemistry Chemical reactions releases energy either in form of heat, light or sound. Thermo-chemistry is a branch of chemistry that studies given out and absorbed heat during chemical reaction therefore, leading to two types of reaction mainly endothermic and exothermic reactions. Endothermic reaction do not occur spontaneously and they require input of energy in form of heat hence heat is absorbed. In contrast, exothermic reaction releases energy and therefore heat is lost to the environment. Thermo-chemistry focuses on calculation of heat of combustion, heat capacity, heat of formation, enthalpy changes, free energy and entropy. The energy given out or absorbed is measured in terms of joules using a calorimeter. Some chemical elements have important applications as either magnetic or laser materials. The amount of heat released or heat absorbed is determined by chemical property and composition of the elements. Some processes used in extraction of these elements are hazardous to environment. Lanthanides and group 3B Elements Lanthanide group has metallic elements that have atomic numbers ranging from 57 to 71 with Lanthanum as the first and Lutetium as the last. All the lanthanides are f-block elements with an exception of lutetium which is a member of the d-block. However, its chemical properties are similar to the f-blocks elements hence considered as a lanthanide. Lanthanides form trivalent cations whose chemical properties are determined by the ionic radius of the elements. The ionic radius of the lanthanides decreases down the group from lanthanum to lutetium. It should be notes that both lanthanum and lutetium are classified as group 3 elements since they posses a single valence electron in their d-shell of their structure. Melting point increases down the group from Lanthanum with 920oc to lutetium with 1622oc due to hybridisation at the 6s, 5d and 4f orbital of the elements. The hybridisation is assumed to be greatest at cerium that records the lowest melting point of about 795oc. Europium has the least density with 5.24g/cm3 while lutetium has the highest with 9.84 g/cm3. Lanthanides have high resistance that ranges from 29 to 144µOhm/cm. Moreover, the elements are paramagnetic in that they posses’ magnetic susceptibilities with exceptions of Lanthanum, Ytterbium and lutetium that lacks unpaired f electrons. For example, Gadolinium has its ferromagnetism staring at 16oc. As the metals become heavier in their densities, their ferromagnetism temperature is reached at lower temperatures. The lanthanides have an oxidation state of 3+ with a rare case of cerium losing its single f electron to form Ce4+. In addition, europium can gain a single electron to form Eu2+. Promethium can be man made and its isotopes are radioactive. Lanthanides reacts with water to form hydroxides, Ln(OH)3. In addition lanthanides have hexagonal structure with the exception of lutetium which has cubical structure. Lanthanides Element Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Atomic number 57 58 59 60 61 62 63 Element Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Atomic number 64 65 66 67 68 69 70 71 Occurrence and extraction of lanthanides Due to the lanthanide contraction feature, the lanthanides are divided as either light or heavy. Ytterbium and cerium are referred to as the rare earths. Most of the light lanthanides are present in the earths crust while the heavy ones are found in the earth’s mantle. Radioisotopes of lanthanum, samarium and lutetium have long half-lives hence used in dating rocks and minerals in the earth, meteorites and the moon. The main ores for the lanthanide are the monazite and basnasite ores. Monazite ores has all the lanthanide elements. On the other hand, heavy elements are not present in the bastnasite ores. Lanthanides are split into either heavy or light enriched minerals (Richards 26) Monazite sand Gray mud solution solution Ln3+ H2SO4 98% SiO2 andTiO2 residue Th- containing mud This method however led to loss of acid and a lot of phosphate from the ore, leading to a more recent method of extraction using sodium hydroxide. Hydrochloric acid is later used to yield chlorides from these hydroxides of lanthanides. (Richards 26) Cold water Monazite sand mud NaOH 73% Residue (Ln (OH) 3, ZrSiO4 ThO2 etc) HCl Solution (Ln3+, Cl, H+) Residue (ZrSiO4, ThO2, TiO2 etc.) Applications of lanthanides Much lanthanide is used in glass production as catalysts. They are too used as Super-conductors, electronic polishers, hybrid cars in batteries and magnets and magnesium alloys. Ions of the lanthanides are used luminescent materials for opto-electronics applications. Dopants of lanthanides together with phosphors are used widely in cathode ray tube in television sets technology. Moreover, lanthanide oxides are mixed with tungsten in welding whereby they improve the high temperature properties. Goggles used in the night to improve vision are also made from lanthanide elements. Europium and terbium are used in life science assays in discovery of drugs. Internet traffic carried through optic transmissions is made of lasers, a component of lanthanide elements. The table below is a summary of lanthanides applications in other industrial functions. (Cotton 56) Application Percentage usage Catalytic converters 47 Petroleum refining catalyst 23 Permanent magnets 14 metallurgical 6 Glass polishing and ceramics 6 phosphors 3 Other uses 1 Hazards of lanthanides extraction The elements are rare and sparsely distributed in the earths crust. Moreover, they have low solubility hence they are unavailable in the biosphere. In addition, they form no part of living molecules. Therefore they have low chances of pollution. However, the radio-isotopes forms (lanthanum, samarium and lutetium) may be potential radiant that can interfere with living cells leading to mutations. All mining activities create environmental risks and human health. The extent of these risks depends on the difference in mines and their exploitation operations. During mining lanthanides related hazards are radiological emissions. During crushing and grinding dust and other pollutants become hazardous to human health. For example, Lutetium is toxic when ingested by living organisms. Lanthanides are also toxic to neural signals hence interfering with nervous system. (Cotton 109) Conclusion Lanthanides are sometimes known as rare earth elements with the group containing 15 elements with most of them being members of f-bock with an exception of Lutetium which is a member the d-block. Their ionic radius decreases down the group while their melting points increase down the group. The elements have very important industrial uses as a catalysts and manufacture of other materials. Ion medicine, the elements especially europium and terbium are used in drug discoveries in life sciences. Work cited Cotton, Simon. Lanthanide and Actinide. New Jersey: John Wiley & Sons, 2013. Richard, Beatty. The lanthanides. Singapore: Marshall Cavendish, 2007. Read More