writea symbolic representation of a chemical reaction and identify ithe reactant and products
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A chemical equation is the symbolic representation of a chemical reaction in the form of symbols and formulae, wherein the reactant entities are given on the left-hand side and the product entities on the right-hand side.
A chemical equation is a symbolic representation of all of the substances involved in a chemical reaction. We use the chemical formulas of substance to represent each chemical specie involved in the reaction. We also use the notation (g), (l), (s), or (aq) following the chemical formula to identify the phase of the substances in the equation.
As an example of a chemical reaction we watched the reaction between iron, Fe(s), and sulfur, S8(s), on video. There are some additional reactions on our Web site that you can review. We noted the physical properties of both iron and sulfur before the reaction and the physical property of the product of the reaction. The magnetic property of iron, present when iron was in its elemental form, was absent in the product. The yellow color of the sulfur, present in the elemental form as a reactant was absent in the product. Yet both iron and sulfur are in the product. Since the properties changed the product is a new substance.
How do we tell if a chemical reaction occurs? The best evidence is a difference in the physical and chemical properties of the reactants and the products. This can be obvious as in the case of the reaction between iron and sulfur.
The form of a chemical equation involves writing the formulas of the reactants (the substances that are mixed together) on the left, using '+' when more than one substance is involved and the formula(s) of the product(s) on the right. The reactants and the products are separated by an arrow '--->'. Sometimes additional information about the reaction is placed above or below the arrow which separates the reactants and products.
Well, how about writing the equation for the reaction between iron and sulfur? To do that we have to know the formula for both elements and their phases;
Fe(s) + S8(s) --heat-->
(Note: I can not use a delta symbol on the WEB easily). Now we have to know what the products are. This is a little more difficult but in this case is it easy. We are reacting a metal with a nonmetal so we know the product is an ionic compound. Since there are only two elements reacting the product has to be binary. So we need the formula for a binary ionic compound. You know how to do that. Metals form cations and the nonmetal forms an anion and we need to use the principle of electroneutrality to balance the charges. Our only other problem is that iron is a transition metal and as such it can have several different charges. For our purposes we limit the possibilities to 2+ or 3+. If we use 2+ for iron and we know sulfur is always 2-, the formula of the product would have to be, FeS(s). We know it is a solid because we saw on the video it was solid, but also ALL ionic compounds are solids!
So the reaction is,
Fe(s) + S8(s) --heat--> FeS(s)
Another reaction (side reaction) which occurred as the above reaction occurred was between sulfur and oxygen in the air. This side reaction was evident because of the bluish flame that appeared as the sulfur melted. At one point in the video as we looked the crucible, containing the reaction, from the side the blue flame was erupting from the crucible. The reaction was surpressed when the hand placed the crucible lid onto the crucible. But what was the reaction?
S8(s) + O2(g) --heat-->
This is a harder question because we are combining two nonmetals. The product of this reaction we know will be a binary covalent compound. But we do not know what the formula of the product might be because we have not discussed any rules for determining formulas of covalent compounds. So what do we do? Well, unfortunately, we have to know some formulas of binary compounds containing sulfur and oxygen. You know sulfate, SO42-, and sulfite, SO32- are either of these likely? No! And the reason is the charged nature of those species. We will not form a charged substance in this particular case. What else you ask? How about SO? Is that possible? Well, know it is not. If we try to find such a compound in the Merck Index or the CRC we will not. So how about SO2? In this case you would be right on! That is the correct formula. Sulfur dioxide is an evil smelling, colorless, gas. So the reaction is;