Chemical reactions

Understanding the general types of chemical reactions will help you to write and balance chemical equations.

 

Physical states of matter and symbols

All physical states are given at standard temperature and pressure for each chemical species.

(aq) = aqueous solution (dissolved in water, from aqua or water).

(l) = liquid

(s) = insoluble solid or precipitate.

(g) = gas

 

Synthesis reactions

General form: A + B → AB

Description: In a synthesis reaction two chemical species combine to produce a single compound.

 

Examples of Synthesis reactions.

  1. Hydrogen + Oxygen → Water
  2. 2H2(g) + O2(g) → 2H2O(l)

  3. Sodium + Chlorine → Sodium chloride
  4. 2Na(s) + Cl2(g) → 2NaCl(s)

  5. Magnesium + Oxygen → Magnesium oxide
  6. 2Mg(s) + O2(g) → 2MgO(s)

  7. Carbon monoxide + Oxygen → Carbon dioxide
  8. 2CO(g) + O2(g) → 2CO2(g)

  9. Sulfur dioxide + Oxygen → Sulfur trioixde
  10. 2SO2(g) + O2(g) → 2SO3(g)

 

Decomposition reactions

General form: AB → A + B

Description: In a decomposition reaction a single compound decomposes to produce two or more chemical species

 

Examples of Decomposition reactions.

  1. Water → Hydrogen + Oxygen
  2. 2H2O(l) → 2H2(g) + O2(g)

  3. Hydrogen peroxide → Water + Oxygen
  4. 2H2O2(aq) → 2H2O(l) + O2(g)

  5. Copper carbonate → Copper oxide + carbon dioxide
  6. CuCO3(s) → CuO(s) + CO2(g)

  7. Ammonia → Nitrogen + Hydrogen
  8. 2NH3(g) → N2(g) + 3H2(g)

  9. Nitrogen triiodie → Nitrogen + Iodine
  10. 2NI3(s)  → N2(g) + 3I2(s)

 

Neutralization reactions

General form: Acid + Base → Salt + Water

Description: In a neutralisation an acid reacts with a base to produce salt and water. Sometimes the general form is given as

Acid + Alkali → Salt + Water

An alkali is a soluble base. The alkali metals all produce alkali solutions. eg. lithium hydroxide, sodium hydroxide and potassium hydroxide.

 

Examples of Neutralization reactions.

  1. Hydrochloric acid + Sodium hydroxide → Sodium chloride + Water
  2. HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)

  3. Sulfuric acid + Magnesium hydroxide → Magnesium sulfate + Water
  4. H2SO4(aq) + Mg(OH)2(aq) → MgSO4(aq) + 2H2O(l)

  5. Nitric acid + Potassium hydroxide → Potassium nitrate + Water
  6. HNO3(aq) + KOH(aq) → KNO3(aq) + H2O(l)

  7. Acetic acid + Sodium hydroxide → Sodium acetate + Water
  8. CH3COOH(aq) + NaOH(aq) → CH3COONa(aq) + H2O(l)

  9. Hydrochloric acid + Potassium hydroxide → Potassium chloride + Water
  10. HCl(aq) + KOH(aq) → KCl(aq) + H2O(l)

 

Acids and metal carbonates

General form: Acid + Metal carbonate → Salt + Water + Carbon dioxide

Description: Metal carbonates react with acids to produce salt, water and carbon dioxide gas. The chemical formula of the carbonate group is CO3.

 

Examples of reactions involving metal carbonates and acids.

  1. Hydrochloric acid + Sodium carbonate → Sodium chloride + Water + Carbon dioxide
  2. 2HCl(aq) + Na2CO3(aq) → 2NaCl(aq) + H2O(l) + CO2(g)

  3. Sulfuric acid + Magnesium carbonate → Magnesium sulfate + Water + Carbon dioxide
  4. H2SO4(aq) + MgCO3(s) → MgSO4(aq) + H2O(l) + CO2(g)

  5. Nitric acid + Potassium carbonate → Potassium nitrate + Water + Carbon dioxide
  6. 2HNO3(aq) + K2CO3(aq) → 2KNO3(aq) + H2O(l) + CO2(g)

  7. Acetic acid + Sodium hydrogen carbonate → Sodium acetate + Water + Carbon dioxide
  8. CH3COOH(aq) + NaHCO3(aq) → CH3COONa(aq) + H2O(l) + CO2(g)

  9. Hydrochloric acid + Potassium carbonate → Potassium chloride + Water + Carbon dioxide
  10. 2HCl(aq) + K2CO3(aq) → 2KCl(aq) + H2O(l) + CO2(g)

 

Acids and active metals

General form: Acid + Active metal → Salt + Hydrogen gas

Description: Acids reacts with active metals to produce a salt and hydrogen gas.

An active metal is a metal that displaces hydrogen from an acid. Examples of active metals include magnesium, zinc and iron.

This type of reaction is also called a single displacement reaction where the active metal 'displaces' the hydrogen from the acid.

 

Examples of reactions involving acids and active metals.

  1. Hydrochloric acid + Magnesium → Magnesium chloride + Hydrogen
  2. 2HCl(aq) + Mg(s) → MgCl2(aq) + H2(g)

  3. Sulfuric acid + Iron → Iron sulfate  + Hydrogen
  4. H2SO4(aq) + Fe(s) → FeSO4(aq) + H2(g)

  5. Nitric acid + Magnesium → Magnesium nitrate  + Hydrogen
  6. 2HNO3(aq) + Mg(s) → Mg(NO3)2(aq) + H2(g)

  7. Zinc + Hydrochloric acid → Zinc chloride  + Hydrogen
  8. Zn(s) + 2HCl(aq)  → ZnCl2(aq) + H2(g)

  9. Lead + Sulfuric acid → Lead sulfate  + Hydrogen
  10. Pb(s) + H2SO4(aq) → PbSO4(s) + H2(g)

 

Precipitation reactions

General form: Solution A + Solution B → Insoluble Solid C + Solution D.

Description: In a precipitation reaction two solutions are mixed together to produce an insoluble solid which is called the precipitate.

This type of reaction is also called a double displacement reaction

 

Examples of reactions involving acids and active metals.

  1. Lead nitrate(aq) + Potassium iodide(aq) → Lead iodide(s)  + potassium nitrate(aq)
  2. Pb(NO3)2(aq) + 2KI(aq) → PbI2(s) + KNO3(aq)

  3. Silver nitrate(aq) + sodium chloride(aq) →Silver chloride(s)  + sodium nirate(aq)
  4. AgNO3(aq) + NaCl(aq) → AgCl(s) + NaNO3(aq)

  5. Mercury(II) nitrate(aq) + Potassium iodide(aq) → Mercury iodide(s)  + Potassium nitrate
  6. Hg(NO3)2(aq) + 2KI(aq) → HgI2(s) + KNO3(aq)

  7. Barium chloride(aq) + Sodium sulfate(aq) → Barium sulfate(s)  + Sodium chloride(aq)
  8. BaCl2(aq) + Na2SO4(aq) → BaSO4(s) + NaCl(aq)

  9. Copper sulfate(aq) + Sodium hydroxide(aq) → Copper hydroxide(s)  + Sodium sulfate(aq)
  10. CuSO4(aq) + 2NaOH(aq) → Cu(OH)2(s) + Na2SO4(aq)

 

Complete Combustion of hydrocarbons

General form: Hydrocarbon +Oxygen → Carbon dioxide + Water

Description: The complete combustion of hydrocarbons in oxygen produces carbon dioxide and water as by products

A hydrocarbon is a compound that contains the elements hydrogen and carbon. Hydrocarbons are commonly obtained by the fractional distillation of crude oil which is a fossil fuel.

 

Rules for balancing chemical equations for the combustion of hydrocarbons.

Balance the carbon atoms first, then hydrogen atoms second and finally oxygen atoms.

 

Examples of complete combustion reactions involving hydrocarbons

  1. Methane  + Oxygen → Carbon dioxide + Water
  2. CH4(g) + 2O2(g) → CO2(g) + 2H2O(l)

  3. Octane + Oxygen → Carbon dioxide + Water
  4. 2C8H18(l) + 25O2(g) → 16CO2(g) + 18H2O(l)

  5. Propane + Oxygen → Carbon dioxide + Water
  6. C3H8(g) + 5O2(g) → 3CO2(g) + 4H2O(l)

  7. Ethanol + Oxygen → Carbon dioxide + Water
  8. CH3CH2OH(l) + 3O2(g) → 2CO2(g) + 3H2O(l)

  9. Butane + Oxygen → Carbon dioxide + Water
  10. 2C4H10(l) + 13O2(g) → 8CO2(g) + 10H2O(l)

 

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