THERMAL STABILITY OF THE GROUP 2 CARBONATES AND NITRATES Go to the main page. 2) Thermal stability of Group II nitrates increases down the Group. Thermal decomposition of Group 2 Nitrates Group 2 nitrates decompose on heating to produce group 2 oxides, oxygen and nitrogen dioxide gas. Start studying Thermal stability of Group II nitrates, carbonates and hydroxides. 2Ca(NO 3) (s) 2CaO (s) + 4 NO 2(g) + O 2(g) As we move down group 1 and group 2, the thermal stability … This is a rather more complicated version of the bonding you might have come across in benzene or in ions like ethanoate. You have to supply increasing amounts of heat energy to make them decompose. Unfortunately, in real carbonate ions all the bonds are identical, and the charges are spread out over the whole ion - although concentrated on the oxygen atoms. if you constructed a cycle like that further up the page, the same arguments would apply. Don't waste your time looking at it. Therefore they are 2 2 One of the products of lithium nitrate's decomposition would turn limewater cloudy; When sodium decomposes, it does so in the same way as lithium; Group 2 nitrates and carbonates behave in the same way as lithium (in terms of thermal decomposition) Beryllium carbonate produces oxygen on its decomposition Explaining the trend in terms of the energetics of the process. If the attractions are large, then a lot of energy will have to be used to separate the ions – the lattice enthalpy will be large. This is because the cation size increases down the Group, this reduces the charge density and polarising power of cation. For reasons we will look at shortly, the lattice enthalpies of both the oxides and carbonates fall as you go down the Group. The rates at which the two lattice energies fall as you go down the Group depends on the percentage change as you go from one compound to the next. It describes and explains how the thermal stability of the compounds changes as you go down the Group. 2LiNO3 +Heat -> Li 2 O +2NO 2 +O 2 2Ca (NO 3) 2 +Heat -> 2CaO +4NO 2 +O 2 Thermal stabilities of nitrates of group-1 and group-2 metals increase on moving down the group from top to bottom. Remember that the reaction we are talking about is: You can see that the reactions become more endothermic as you go down the Group. The nitrates are white solids, and the oxides produced are also white solids. In order to make the argument mathematically simpler, during the rest of this page I am going to use the less common version (as far as UK A-level syllabuses are concerned): Lattice enthalpy is the heat needed to split one mole of crystal in its standard state into its separate gaseous ions. Group 2 nitrates also become more thermally stable down the group. If you aren't familiar with Hess's Law cycles (or with Born-Haber cycles) and with lattice enthalpies (lattice energies), you aren't going to understand the next bit. The next diagram shows the delocalised electrons. Exactly the same arguments apply to the nitrates. You wouldn't be expected to attempt to draw this in an exam. The rates at which the two lattice energies fall as you go down the Group depends on the percentage change as you go from one compound to the next. The lattice enthalpies of both carbonates and oxides fall as you go down the Group because the positive ions are getting bigger. Forces of attraction are greatest if the distances between the ions are small. 2. In other words, as you go down the Group, the carbonates become more thermally stable. If you calculate the enthalpy changes for the decomposition of the various carbonates, you find that all the changes are quite strongly endothermic. In order to make the argument mathematically simpler, during the rest of this page I am going to use the less common version (as far as UK A level syllabuses are concerned): Lattice enthalpy is the heat needed to split one mole of crystal in its standard state into its separate gaseous ions. The oxide lattice enthalpy falls faster than the carbonate one. Similar to lithium nitrate, alkaline earth metal nitrates also decompose to give oxides. Observed reduction temperatures ( T r ) for nitrates of the base metals and the noble metals are lower than their T d , i.e., T r < T d . The calculated enthalpy changes (in kJ mol-1) are given in the table. Also, does thermal stability increase or decrease as you go down group … You wouldn't be expected to attempt to draw this in an exam. The ones lower down have to be heated more strongly than those at the top before they will decompose. This decreases the charge density and the ability of the cation to polarize the anion. If you worked out the structure of a carbonate ion using "dots-and-crosses" or some similar method, you would probably come up with: This shows two single carbon-oxygen bonds and one double one, with two of the oxygens each carrying a negative charge. The peroxy nitrates shown in Table II are observed to fall into two classes of thermal stability. Beryllium nitrate Beryllium has a smaller ionic radius than strontium, since there is The enthalpy changes (in kJ mol-1) which I calculated from enthalpy changes of formation are given in the table. The small positive ions at the top of the Group polarise the nitrate ions more than the larger positive ions at the bottom. 1. Two factors are involved in dissolving: 1. The carbonates become more stable to heat as you go down the Group. THERMAL STABILITY OF THE GROUP 2 CARBONATES AND NITRATES This page looks at the effect of heat on the carbonates and nitrates of the Group 2 elements - beryllium, magnesium, calcium, strontium and barium. Brown nitrogen dioxide gas is given off together with oxygen. You need to find out which of these your examiners are likely to expect from you so that you don't get involved in more difficult things than you actually need. The nitrates also become more stable to heat as you go down the Group. b) lower c) A white solid producing a … Exactly the same arguments apply to the nitrates. Although the inter-ionic distance will increase by the same amount as you go from magnesium carbonate to calcium carbonate, as a percentage of the total distance the increase will be much less. The effect of heat on the Group 2 nitrates. A smaller 2+ ion has more charge packed into a smaller volume than a larger 2+ ion (greater charge density).. Thermal Stability of Group 1/2 Nitrates (4:38) Flame tests (9:14) Uses of Group 2 Compounds AS: GROUP 7 (4B) GROUP 7 OVERVIEW Group 7 Properties & Trends (6:55) Testing for Halide Ions Reactions of Group … The positive ion attracts the delocalised electrons in the carbonate ion towards itself. All the carbonates in this Group undergo thermal decomposition to give the metal oxide and carbon dioxide gas. Eight resources on the thermal decomposition of the group 1 and 2 nitrates and carbonates. All the nitrates in this Group undergo thermal decomposition to give the metal oxide, nitrogen dioxide and oxygen. If this is heated, the carbon dioxide breaks free to leave the metal oxide. The inter-ionic distances in the two cases we are talking about would increase from 0.365 nm to 0.399 nm – an increase of only about 9%. A bigger 2+ ion has the same charge spread over a larger volume of space. Going down group II, the ionic radii of cations increases. GROUP 2: THERMAL STABILITY OF THE CARBONATES AND NITRATES 1. a) Both barium carbonate and barium oxide (the product) are white. Remember that the reaction we are talking about is: You can see that the reactions become more endothermic as you go down the Group. The first resource is a differentiated worksheet with the questions designed around the style of AQA, Edexcel and OCR exam papers and test students on every aspect of the topic including the reactions, observations, trends, theory of charge density/polarisation and finishes with a few questions … The 2 If "X" represents any one of the elements: As you go down the Group, the carbonates have to be heated more strongly before they will decompose. Learn vocabulary, terms, and more with flashcards, games, and other study tools. The small positive ions at the top of the Group polarise the nitrate ions more than the larger positive ions at the bottom. 2. The explanation for change in thermal stability is the same as for carbonates Magnesium nitrate decomposes the easiest because the Mg 2+ ion is smallest and has the greater charge density. Drawing diagrams to show this happening is much more difficult because the process has interactions involving more than one nitrate ion. This means that the enthalpy change from the carbonate to the oxide becomes more negative so more heat is needed to decompose it. Strontium Nitrate Strontium has a greater ionic radius than beryllium since it is affected by more electrostatic forces of attraction due to more protons in its nucleus and more electron shells. Nitrates of alkaline-earth metals and LiNO3 decompose on heating to form oxides, nitrogen to form oxides, nitrogen dioxide and oxygen. Thermolysis of 2-methyl-2-butanol nitrate in diethyl ether over a Magnesium and calcium nitrates normally have water of crystallisation, and the solid may dissolve in its own water of crystallisation to make a colourless solution before it starts to decompose. All other group 1 carbonates are stable in Bunsen flame. All the nitrates in this Group undergo thermal decomposition to give the metal oxide, nitrogen dioxide and oxygen. All of these carbonates are white solids, and the oxides that are produced are also white solids. Here's where things start to get difficult! I can't find a value for the radius of a carbonate ion, and so can't use real figures. Confusingly, there are two ways of defining lattice enthalpy. If this is the first set of questions you have done, please read the introductory page before you start. Explaining the trend in terms of the polarising ability of the positive ion. This page looks at the effect of heat on the carbonates and nitrates of the Group 2 elements – beryllium, magnesium, calcium, strontium and barium. The effect of heat on the Group 2 nitrates. All the nitrates in this Group undergo thermal decomposition to give the metal oxide, nitrogen dioxide and oxygen. The thermal stability of hydroxide-nitrate systems has, however, been discussed in few papers. Note: If you are interested, you could follow these links to benzene or to organic acids. The Thermal Stability of the Nitrates and Carbonates This page examines at the effect of heat on the carbonates and nitrates of the Group 2 elements (beryllium, magnesium, calcium, strontium and barium). The oxide lattice enthalpy falls faster than the carbonate one. The thermal stability of the nitrates follows the same trend as that of the carbonates, with thermal stability increasing with proton number. A small 2+ ion has a lot of charge packed into a small volume of space. 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