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Chemical Equations

Chemical Equations. These interactions are called chemical reactions . A substance that undergoes a chemical reaction is called a reactant . A substance that is formed in a chemical reaction is called a product .

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Chemical Equations

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  1. Chemical Equations These interactions are called chemical reactions. A substance that undergoes a chemical reaction is called a reactant. A substance that is formed in a chemical reaction is called a product.

  2. The law of conservation of mass states that in any chemical reaction, the mass of the products is always equal to the mass of the reactants. • Thus we must balance the reactions.

  3. Balance metals, followed by non-metals, and then polyatomic ions if they are located on both sides. • Balance the hydrogens. • Finally balance the oxygens. • Verify all values.

  4. Synthesis Reactions • In a synthesis reaction, two or more elements or compounds combine to form a new substance. A + B → C

  5. Synthesis Reactions • 2 H2(g) + O2(g) → 2 H2O(g) • 2 Mg(s) + O2(g) → 2 MgO(s) • 2 K(s) + Cl2(g) → 2 KCl(s) • 4 Fe(s) + 3 O2(g) → 2 Fe2O3(s) Must look at charges to make compounds!

  6. Synthesis Reactions • When a non-metallic oxide reacts with water, the product is an acid. • SO3(g) + H2O(l) → H2SO4(aq) • Conversely, when a metallic oxide reacts with water, the product is a metal hydroxide. • CaO(s) + H2O(l) → Ca(OH)2(aq)

  7. Decomposition Reactions • In a decomposition reaction, a compound breaks down into elements or other compounds. Therefore, a decomposition reaction is the opposite of a synthesis reaction. C → A + B

  8. Decomposition Reactions • 2 H2O → 2 H2 + O2 • NH4NO3(s) → N2O(g) + 2 H2O(g) • Generally decompose into elemental form, but maybe some compounds.

  9. Decomposition Reactions • Carbonates decompose into carbon dioxide and a metal oxide: • MgCO3(s) CO2(g) + MgO(s) • Hydroxides decompose into water and a metal oxide: • Ca(OH)2(s) H2O(l) + CaO(s)

  10. Decomposition Reactions • Chlorates decompose into oxygen and a metal halide: • 2 KClO3(s) 3 O2(g) + 2 KCl(s)

  11. Combustion Reactions • A combustion reaction occurs when a compound reacts in the presence of oxygen to form oxides and energy. • S8(s) + 8 O2(g) → 8 SO2(g) • Complete combustion of a hydrocarbon occurs when the hydrocarbon reacts completely in the presence of sufficient oxygen. The complete combustion of a hydrocarbon produces only water vapour and carbon dioxide gas as products. • C3H8(g) + 5 O2(g) → 3 CO2(g) + 4 H2O(g)

  12. Incomplete combustion of a hydrocarbon occurs when there is not enough oxygen present for the hydrocarbon to react completely. The incomplete combustion of a hydrocarbon produces water, carbon dioxide, carbon monoxide, and solid carbon in varying amounts. • 2 C3H8(g) + 7 O2(g) → 2 CO2(g) + 8 H2O(g) + 2 CO(g) + 2 C(s)

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