Chemical Changes and Reactions

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A chemical reaction is the process of breaking the chemical bonds of the reacting substances and making new bonds to form new substances. It changes reactants into products.

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A chemical bond is the force that holds the atoms of a molecule together, as in a compound. Bonds break in reactants and new bonds form in products.

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General combination reaction: A + B → AB. Two substances combine to form a single new product.

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Balanced equation: N2 + 3H2 ⇌ 2NH3. Iron acts as the catalyst and molybdenum acts as a promoter. The reaction is carried out at high pressure and about 450°C to 500°C.

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Balanced equation: 2KClO3(s) → 2KCl(s) + 3O2(g). Potassium chlorate normally decomposes at 700°C, but with manganese dioxide it decomposes at 300°C. MnO2 remains unaffected and acts as a positive cata…

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A positive catalyst speeds up a reaction. Manganese dioxide increases the rate of decomposition of potassium chlorate and hydrogen peroxide without being changed itself.

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Molybdenum is a promoter, not the main catalyst. It improves the efficiency of iron in the manufacture of ammonia.

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A negative catalyst is a substance that retards a reaction. Phosphoric acid retards the decomposition of hydrogen peroxide, and alcohol decreases the rate of oxidation of chloroform.