Science 1206 Unit 2: Chemistry

Chemical Reactions Unit 2: Chemistry

Chemical Reactions Chemical reactions are a part of our everyday life. Brushing our teeth, getting a ride to school in the family car, digesting food, and many others are all examples of chemical reactions. The reactions may be very complex, as in the creation of explosives, or they may be very simple, as in the reaction of a bathroom cleaner and a stain. The basic structure of a chemical reaction is the creation of some new substance(product) from the reaction of one, two, or more, initial substances(reactants).

Reactants—> Products 2 Na + CaO —> Na 2 O + Ca Sodium reacts with calcium oxide to produce sodium oxide and calcium

Types of Reactions There are five basic types of chemical reactions. These include. 1. Synthesis / Simple Composition Reactions 2. Decomposition / Simple Decomposition Reactions 3. Double Replacement/Double Displacement 4. Single Replacement/Single Displacement 5. Combustion Reactions 6. Other

The Law of Conservation of Mass In a chemical reaction, the total mass of the reactants is always equal to the total mass of products. Mass(reactants)=Mass(products) Example 1: NaCl+CaO—>Na 2 O+CaCl 2 12g20g—>15g17g Mass(reactants)=12g + 20g = 32g Mass(products)=15g + 17g =32g

Example 2: NaCl+CaO—>Na 2 O+CaCl 2 18g40g—> 30g?g Mass(reactants)=18g + 40g = 58g Mass(products)=20g + ?g =58g

Types of Chemical Equations: There are three basic representations of reaction equations. These are; Word Equations a way of writing chemical reactions in which the left side of the equation lists the names of all the reactants and the right side of the equation lists the names of all of the products. Let’s look at the chemical reaction where iron reacts with oxygen to produce iron(III) oxide(rust) Example: Iron + Oxygen —> Iron (III) oxide

Skeleton Equation a representation of a chemical reaction in which formulas of the reactants are connected to the formulas of the products by an arrow. Example: Fe + O 2 —> Fe 2 O 3

Balanced Equation an equation in which the reactants and products contain equal number of each type of atoms. Example: 4 Fe + 3 O 2 —> 2 Fe 2 O 3 Four formula units of iron react with three molecules of oxygen to produce two formula units of iron(III) oxide. Example: CH 4 + 2O 2 —> CO H 2 O One molecule of methane reacts with two molecules of oxygen to produce one molecule of carbon dioxide and two molecules of water.

In a chemical reaction it is very important that the numbers of individual atoms on one side of the equation is equal to the number of individual atoms on the other side of the reaction. In the above reaction equation, for example, you will notice that there are four iron atoms on both the reactant and product sides of the equation.

Type 1:Synthesis / Simple Composition Reactions to synthesize is to ‘create’ when elements or compounds combine to form a new substance a synthesis reaction occurs can be compared to the formation of a new ‘couple’ from two individuals Model: A + B —> AB element + element —> compound simple compound + simple compound —> complex compound

Example1: Hydrogen and oxygen react to produce water word equation: hydrogen + oxygen —> water skeleton equation: H 2 + O 2 —> H 2 O balanced equation: 2 H 2 + O 2 —> 2 H 2 O

Example 2: Hydrochloric acid and ammonia react to produce ammonium chloride word equation: Hydrochloric acid + ammonia —> ammonium chloride skeleton equation: HCl + NH 3 —> NH 4 Cl balanced equation: HCl + NH 3 —> NH 4 Cl same as skeleton equation

Example 3: Write word, skeleton and balanced chemical equations for the synthesis of aluminum chloride word equation: skeleton equation: balanced equation:

Type 2:Decomposition / Simple Decomposition Reactions to decompose is to ‘break down’ when compounds break down into two or more elements or compounds a decomposition reaction occurs. can be compared to the ‘break-up’ of a couple

Model: AB —> A + B compound —> element + element complex compound —> simple compound + simple compound

Example 1: Nitrogen triodide decomposes to its individual elements word equation: Nitrogen triodide —> nitrogen + iodine skeleton equation: NI 3 —> N 2 + I 2 balanced equation 2 NI 3 —> N I 2

Example 2: Sodium chloride decomposes to its individual elements word equation: Sodium chloride —> sodium + chlorine skeleton equation: NaCl —> Na + Cl 2 balanced equation: 2 NaCl —> 2 Na + Cl 2

Example 3: Write a word, skeleton and balanced chemical equation for the decomposition of gallium sulfide. word equation: skeleton equation: balanced equation:

Type 3: Single Replacement/Single Displacement when an element replaces another element in a compound to form a new substance a single replacement reaction occurs think of this kind of reaction as a person ‘cutting in’ on a couple dancing Model: AC + B —> A + BC compound + element —> compound + element

Example1: Sodium reacts with calcium oxide to produce word equation: sodium + calcium oxide —> sodium oxide + calcium skeleton equation: Na + CaO —> Na 2 O + Ca balanced equation: 2Na + CaO —> Na 2 O + Ca

Example 2: Calcium iodide reacts with chlorine to produce calcium chloride and iodine word equation: calcium iodide + chlorine —> calcium chloride + iodine balanced equation: CaI 2 + Cl 2 —> I 2 + CaCl 2

Example 3: Demo Copper reacts with silver nitrate to produce word equation:Copper + silver nitrate —> balanced equation:Cu + AgNO 3 —>

Example 4: Demo Magnesium reacts with silver nitrate to produce word equation:magnesium + silver nitrate —> balanced equation:Mg + AgNO 3 —>

Type 4:Double Replacement/Double Displacement when an element in one compound replaces an element in a another compound to form two new substances a double replacement reaction occurs think of this type of reaction as two couples dancing and part ways through the dance they switch partners

Model: AC + BD —> AD + BC compound + compound —> compound + compound

Example 1: Sodium chloride reacts with calcium oxide to produce word equation: sodium chloride + calcium oxide —> sodium oxide + calcium chloride skeleton equation: NaCl + CaO —> Na 2 O + CaCl 2 balanced equation: 2 NaCl + CaO —> Na 2 O + CaCl 2

Example 2: Magnesium sulfide reacts with aluminum oxide to produce..... word equation: magnesium sulfide + aluminum oxide —> balanced equation: MgS + Al 2 O 3 —>

Example 3: Gallium sulfate reacts with iron III nitrate to produce... word equation: Gallium sulfate + iron III nitrate —> balanced equation: Ga 2 (SO 4 ) 3 + Fe(NO 3 ) 3 —>

Example 4: Demo Calcium carbonate reacts with hydrochloric acid to produce calcium chloride, carbon dioxide and hydrogen gas word equation: Calcium carbonate + hydrochloric acid —> calcium chloride + carbon dioxide + hydrogen balanced equation CaCO 3 + HCl (aq) —> CaCl 2 + CO 2 + H 2

Neutralization A neutralization reaction is a special case of a double replacement reaction that involves the reaction of an acid substance with a base substance to produce a salt and water. Model: Acid + base —> salt + water

Example 5: Hydrochloric acid reacts with sodium hydroxide to produce... word equation: hydrochloric acid + sodium hydroxide —> balanced equation: HCl + NaOH —>

Type 5:Hydrocarbon Combustion Reactions rapid reaction of a substance with oxygen to produce an oxide fuel + oxygen —> oxides + energy One of the most important current fuel sources on this planet is hydrocarbons (Carbon and Hydrogen) Model: hydrocarbon + oxygen —> carbon dioxide + water vapour

Example 1: Write a word and reaction equation for the complete combustion of butane. word equation: butane + oxygen —> carbon dioxide + water vapour skeleton equation: C 4 H 10 + O 2 —> CO 2 + H 2 O reaction equation: 2 C 4 H O 2 —> 8 CO H 2 O

Example 2: Write a word and reaction equation for the complete combustion of methane. word equation: methane + oxygen —> carbon dioxide + water vapour reaction equation: CH O 2 —> CO H 2 O

Example 3: Write a word and reaction equation for the complete combustion of gasoline(C 8 H 18 ). word equation: gasoline + oxygen —> carbon dioxide + water vapour reaction equation: C 8 H O 2 —> 8CO 2 + 9H 2 O 2 C 8 H O 2 —> 16 CO H 2 O

Example 4: Write a word and reaction equation for the complete combustion of propane(C 3 H 8 ). word equation: gasoline + oxygen —> carbon dioxide + water vapour reaction equation: C 3 H O 2 —> 3 CO H 2 O

Example 5: Write a word and reaction equation for the complete combustion of cyclopropane(C 3 H 6 ). word equation: cyclopropane + oxygen —> carbon dioxide + water vapour reaction equation: 2 C 3 H O 2 —> 6 CO H 2 O

Incomplete Combustion When materials burn and the conditions are not perfect the combustion is incomplete. The materials do not completely change and four products are produced instead of two.

Model: hydrocarbon + oxygen —> carbon monoxide + carbon + carbon dioxide + water vapour 2 C 4 H O 2 —> 8 CO + 10 C + 8 CO H 2 O Other All reactions that do not fit into the categories above.

Evidence of Chemical Reactions 1.Precipitate forms: New substance forms which has a lower solubility than the original substance 2.Gas forms: A new substance is formed which is a gas in the lab conditions of temperature and pressure 3.Colour change: A new substance is formed which has a different colour than the original substance 4.Energy Change: Heat produced or used. Energy is released or absorbed to obey the Law of Conservation of Energy o Releases energy -Exothermic o Absorbs Energy - Endothermic

Phase of compounds and elements at room Temperature Denoted in subscripts at the end of an element or compound name (s) solid (l) liquid (g) gas (aq) aqueous - soluble in water

Determining Phase - in chemical equations Elements - use periodic table Molecular compounds - personal experience - see table below

Ionic Compounds all ionic compounds not in water are solids when ionic compounds are placed in water some completely dissociate, or completely dissolve (are soluble), while other ionic compounds do not Solubility of Ionic Compounds the solubility table on your periodic table is required to determine the phase of ionic compounds in water. When one of the reactants has an (aq) there is water present and therefore you need to determine the phase of the products.

to use the table find the anion (the negative part of the compound) example BaSO 4 - look up the SO 4 in the table. Most are highly soluble but not Ba 2+. So we would write BaSO 4 (s) example CuSO 4 - look up the SO 4 in the table. Most are highly soluble and Cu 2+ is not in the list of those that have low solubility. So we would write CuSO 4(aq)