Reactions of Iron with Sulfur, Zinc with Sulfur
When heated with a red-hot metal rod, mixtures of iron and sulfur and of zinc and sulfur react vigorously. The reaction with zinc produces flame and a near explosion.
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Keywords
combination reaction, descriptive chemistry, enthalpy/heat, evidence of chemical reaction, exothermic process, iron, metals, reactivity - kinetic/thermodynamic stability, redox reaction, sulfur/sulfur oxides/sulfuric acid
Multimedia
Iron
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(QuickTime 3.0 Sorenson, duration 32 seconds, size 2.2 MB)
Iron powder and sulfur are mixed. A heated metal rod initiates an exothermic reaction. The reaction product, iron sulfide, is fused to the rod.
 Iron powder and sulfur are mixed. |
 A metal rod is heated. |
 The heat initiates an exothermic reaction. |
 Iron sulfide is fused to the rod. |
Additional still images for this movie
Zinc
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(QuickTime 3.0 Sorenson, duration 19 seconds, size 1.3 MB)
Zinc powder and sulfur are mixed. A heated metal rod causes the mixture to react vigorously. Here is another view of the reaction.
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Additional still images for this movie
Discussion
Iron(II) sulfide and zinc sulfide are quite stable compounds and their formation from the metal and sulfur is highly exothermic. However, iron and sulfur and zinc and sulfur can be mixed at room temperature and no reaction takes place. Only when heated to the temperature of a red-hot metal rod do they react rapidly-in the case of zinc, almost explosively.
Equations for the principal reaction in each case are
8 Fe(s ) + S8(s ) --> 8 FeS(s )
8 Zn(s ) + S8(s ) --> 8 ZnS(s )
In addition to ZnS(s ) some ZnO(s ) and some SO2(g ) are produced by the high temperature of the second reaction.
Demonstration Notes, Warnings, Safety Information, etc.
Exam and Quiz Questions
1. What observable evidence indicates that a chemical reaction is taking place?
2. Are the reactions shown exothermic or endothermic? Cite observations that justify your choice.
3. What kinds of experimental work would you need to do to determine that the empirical formula for the product of the reaction of iron (zinc) with sulfur is FeS (ZnS)?
4. How could you demonstrate that the iron and sulfur before reaction constituted a mixture, but after the reaction a compound had been made?