Types of Chemical Reactions

Size: px

Start display at page:

Download "Types of Chemical Reactions"

Lewis Stephens
6 years ago
Views:

1 Types of Chemical Reactions There are five types of chemical reactions: 1. Formation (combination) 2. Decomposition 3. Single Displacement 4. Double Displacement 5. Combustion 1

2 Formation (Combination) Reactions A formation reaction or combination reaction is a reaction in which two or more reactants combine to form a single product. reactant A + reactant B product C The phrase simple combination reaction is used to describe reactions in which the reactants are elements. Remember: metal + non-metal ionic compound non-metal + non-metal molecular compound The reaction of sodium metal with chlorine gas: General formula: element + element compound Word equation: sodium + chlorine sodium chloride Chemical equation: Na (s) + Cl 2 (g) NaCl (s) Balanced Chemical Equation: 2 Na (s) + Cl 2 (g) 2 NaCl (s) 2

3 The reaction of hydrogen gas with chlorine gas: General formula: element + element compound Word equation: Chemical equation: H 2 (g) + Cl 2 (g) HCl (g) Balanced Chemical Equation: Carbon disulfide is produced by the reaction of carbon with sulfur: General formula: element + element compound Word equation: Chemical equation: C (s) + S 8 (s) CS 2 (g) Balanced Chemical Equation: 3

4 Decomposition reactions A compound differs from an element because a compound can be chemically separated into simpler substances. A chemical reaction that involves separating a compound into simpler substances is classified as a decomposition reaction. Combination reactions and decomposition reactions are opposites. reactant A product B + product C +... When a compound is decomposed into its elements, the reaction is termed simple decomposition. Compound element + element 4

5 Water is decomposed into its elements: General formula: Compound element + element Word equation: water hydrogen + oxygen Chemical equation: H 2 O (l) H 2 (g) + O 2 (g) Balanced Chemical Equation: 2 H 2 O (l) 2 H 2 (g) + O 2 (g) The decomposition of nitrogen trichloride into its elements: General formula: Compound element + element Word equation: Chemical equation: NCl 3 (s) N 2 (g) + Cl 2 (g) Balanced Chemical Equation: 5

6 Iron(III) oxide is broken down into its elements: General formula: Compound element + element Word equation: Chemical equation: Fe 2 O 3 (s) Fe (s) + O 2 (g) Balanced Chemical Equation: Write a word equation and a chemical equation for the problems: Be sure to: include states of matter and balance the final equation Elements - consult periodic table metals - all solid except Hg non-metals - may be s, l, or g Compounds ionic - all pure ionic compounds are solid at room temp. molecular - varies, may be s, l, or g (use prior knowledge to make best guess) 6

7 Formation (Combination) Reactions Write the word equation and a balanced chemical equation for each statement. 1. magnesium + oxygen 2. hydrogen + oxygen 3. nitrogen reacts with another element to produce ammonia 4. aluminum reacts with oxygen 5. sulfur (S8 (s) ) reacts with air to produce sulfur dioxide Decomposition reactions 6. Chlorine for the chlorination of water is produced by the decomposition of sodium chloride. 7. Chromium (III) oxide is decomposed into its elements 8. Nitrogen is produced from the breakdown of ammonia 9. Mercury (II) sulfide breaks down into its elements 10. Sodium hydroxide is decomposed into its elements 7

8 Single displacement reaction A single displacement reaction (also known as a single replacement reaction) occurs when an element and a compound react to produce different element and different compound. element A + compound BC element B + compound AC In the general form of the reaction, element B is replaced by element A In order to determine which elements switch we can look at their charges. All we need to keep in mind that opposite charges attract and like charges repel. Consider the reaction of zinc with copper (II) sulphate: In this case: Zn (s) + CuSO 4 (aq)? +?? zinc will form Zn 2+ copper will form Cu 2+ sulphate is the complex ion SO 4 2- The positive ions will repel each other so there is no way that Zn and Cu will combine. Zn (s) + CuSO 4 (aq) Cu (s) + ZnSO 4(aq) Zinc + copper (II) sulfate copper + zinc sulfate 8

9 Consider the reaction of Chlorine with sodium bromide In this case: Cl 2(s) + NaBr (aq)? +?? chlorine will form Cl - sodium will form Na + and bromide is Br - This time the negative ions will repel each other so there is no way that Cl - and Br - will combine! Cl 2(s) + NaBr (aq)? +?? Balance Chlorine + sodium bromide bromine + sodium chloride In reactions involving water, the water dissociates into H+ and OH -. So we usually like to write water as HOH. Consider the reaction of calcium with water. In this case: Ca (s) + HOH (l)? +?? calcium will form Ca 2+ water will form H + and hydroxide OH - This time the positive ions will repel each other so there is no way that Ca 2+ and H + will combine! Ca (s) + HOH (l) Ca(OH) 2(s) + H 2(g) Balance Calcium + water calcium hydroxide + water 9

How do you know if the new ionic substance formed will be (s) or (aq)? When one of the reactants is a solution (aq), the (aq) means water is present as a solvent.

10 How do you know if the new ionic substance formed will be (s) or (aq)? When one of the reactants is a solution (aq), the (aq) means water is present as a solvent. Since water is present we have to decide if any of the new substances will dissolve in water. In order to determine this we use the solubility table normally found on the reverse of a periodic table. Double Displacement Reactions In chemistry, double displacement reactions (also known as double replacement reactions) involve the replacement of a cation in one compound by the cation in another compound and vice versa. In other words, there is an exchange of cations. These reactions tend to involve one or more aqueous ionic compounds. General Form: compound AB + compound CD compound AD + compound CB 10

11 where A and C are cations (+), and B and D are anions (-). How do you know which ones switch? In order to determine which elements switch once again we can look at their charges. Keep in mind that opposite charges attract and like charges repel. Consider the reaction of a solution of silver nitrate with a solution of sodium chloride: In this case: sodium will form Na + chlorine will form Cl - silver will form Ag + nitrate is the complex ion NO 3 - The positive ions will repel each other so there is no way that Na + and Ag + will combine! So the Na + will react with the NO 3- and the Ag + will react with the Cl - We need to balance it and decide on the states of matter for the products. Since water is present in the reactants (aq) we have to consult the solubility tables! 11

12 Write a balanced chemical equation for the double replacement reaction involving aqueous calcium chloride and aqueous sodium carbonate. In this case: sodium will form Na + chlorine will form Cl - silver will form Ag + and nitrate is the complex ion NO - 3 Single Displacement: Double Displacement: 1. magnesium + hydrochloric acid 2. Copper + silver nitrate 3. sodium + water 4. hydrogen sulfide + silver 1. Hydrochloric acid is neutralized by a sodium hydroxide solution 2. Aluminum hydroxide solid is reacted with hydrochloric acid 3. A solution of Cadmium Nitrate reacts with a solution of ammonium sulfide. 4. Solutions of Barium Chloride and silver nitrate are reacted. 5. A solution of potassium phosphate reacts with cobalt (III) chloride. 12

13 Combustion Reactions Combustion reactions typically require oxygen gas as a reactant. Energy in the form of heat and light is usually released The examples of combustion that you are probably most familiar with are the ones that involve hydrocarbons - substances like diesel, gasoline, and propane. Hydrocarbons - consist of hydrogen and carbon atoms. Propane - C 3 H 8 Octane - C 8 H 18 Candle wax - C 25 H 52 13

14 Exothermic and Endothermic Reactions: Exothermic Endothermic Any reaction which releases energy is said to be exothermic. The energy released by an exothermic, combustion reaction can be used to heat a home, or drive a car. "Heat Packs" often used in winter contain chemicals that release heat to the body. The reactants have more energy than the products because energy has been released. Any reaction in which energy is absorbed is said to be endothermic. "Cold Packs" used by athletes contain chemicals which absorb heat from the body. The energy of the products is higher than the energy of the reactants because energy has been absorbed. General Equation for Combustion: hydrocarbon + oxygen oxide of carbon + water There are two possible oxides of carbon produced by hydrocarbon combustion: Carbon dioxide is produced when the combustion reaction is complete. The evidence for complete combustion is a blue flame. hydrocarbon + oxygen carbon dioxide + water Carbon monoxide and carbon in the form of soot are produced when combustion is incomplete resulting in an orange, smoky flame. hydrocarbon + oxygen carbon monoxide + carbon + water 14

15 The factor that determines whether a combustion reaction is complete or incomplete is the amount of oxygen available for the reaction. If there is insufficient oxygen, deadly carbon monoxide is produced. A great method to use when balancing combustion reactions is The Method of C H O. That is: balance C balance H balance O last. Write a balanced chemical equation for the complete combustion of propane gas - C3H8 (g). hydrocarbon + oxygen carbon dioxide + water C 3 H 8 (g) + O 2 (g) CO 2 (g) + H 2 O (g) 1. Balance C first: 3 C on the left -- multiply CO 2 by 3 to get 3 C on the right C 3 H 8 (g) + O 2 (g) 3 CO 2 (g) + H 2 O (g) 2. Balance H second: 8 H on the left -- multiply H 2 O by 4 to get 8 H on the right C 3 H 8 (g) + O 2 (g) 3 CO 2 (g) + 4 H 2 O(g) 3. Balance O last: We have two sources of O on the right: 3 x CO 2 = 6 O 4 x H 2 O = 4 O Thus we have 10 O on the right -- multiply O 2 by 5 to get 10 O on the left. C 3 H 8 (g) + 5 O 2 (g) 3 CO 2 (g) + 4 H 2 O (g) 15

16 Write a balanced chemical equation for the complete combustion of butane gas C 4 H 10 (g) 1. Balance C first: 4 C on the left -- multiply CO 2 by 4 to get 4 C on the right C 4 H 10 (g) + O 2 (g) 4 CO 2 (g) + H 2 O (g) 2. Balance H second: 10 H on the left -- multiply H2O by 5 to get 10 H on the right C 3 H 10 (g) + O 2 (g) 4 CO 2 (g) + 5 H 2 O (g) 3. Balance O last: We have two sources of O on the right:4 x CO 2 = 8 O 5 x H 2 O = 5 O We have 13 O on the right -- multiply O 2 by 6 1/2 to get 13 O on the left. C 4 H 10 (g) + 6 1/2 O 2 (g) 4 CO 2 (g) + 5 H 2 O (g) To remove the fraction we multiply the whole equation by 2. 2 C 4 H 10 (g) + 13 O 2 (g) 8 CO 2 (g) + 10 H 2 O (g) Here are some of the key points: 1. Always make sure you have written the chemical formulas correctly 2. Never balance an equation by changing the numerical subscripts in chemical formulas 3. Whenever possible, treat polyatomic ions as units 4. Balance the most numerous species first (unless the reaction is a combustion reaction) 5. If you place a coefficient in front of a formula to balance one of its atoms or ions, then check to see if you have changed the number of other atoms or ions in the formula 6. If you are having trouble balancing an equation, check the chemical formulas to make sure they are correct. 7. Incorrect chemical formulas are the number one cause of incorrectly balanced equations. 8. When a species occurs in two or more formulas on the same side of an equation, balance it last. (E.G. O2 in combustion reactions) 16

17 Try: 1. Methane completely combusts in air. 2. Pentane C 5 H 12 (g) is completely combusted in the presence of oxygen. 3. Candle wax C 25 H 52 (s) is burned in excess oxygen. 4. In a high efficiency engine octane, C 8 H 18 (l) is completely combusted. 5. A propane fireplace malfunctions and burns its gas incompletely to produce deadly carbon monoxide gas. 17

Science 1206 Chemistry Unit #11

Science 1206 Chemistry Unit #11 Types of Chemical Reactions Types of Chemical Reactions Five types of chemical reactions: Formation (synthesis) Decomposition Single Displacement Double Displacement Combustion