Chapter 6 Notes Science 10 Name:

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1 6.1 Types of Chemical Reactions a) Synthesis (A + B AB) Synthesis reactions are also known as reactions. When this occurs two or more reactants (usually elements) join to form a. A + B AB, where A and B represent elements The elements may form compounds, like the following: Sodium metal and chlorine gas combine to form sodium chloride. 2Na + Cl 2 2NaCl Magnesium metal reacts with oxygen gas to form magnesium oxide. 2Mg + O 2 2MgO Or the elements may form compounds, like the following: Nitrogen gas and oxygen gas join to form dinitrogen monoxide. 2N 2 + O 2 2N 2 O 1. Complete and balance the following synthesis (combination) reactions. Remember to consider the chemical formulas of the products carefully before you begin to balance. (a) Mg + N2 (b) Al + F2 (c) K + O2 (d) Cd + I2 (e) Cs + P4 1

2 2. Identify whether or not each of the following chemical equations is a synthesis (combination) reaction. (a) 2H2 + O2 2H2O (d) S8 + 12O2 8SO3 (b) 2Al + 3CuCl2 2AlCl3 + 3Cu (e) 2Ti + 3 Cl2 2TiCl3 (c) 2KClO3 2KCl + 3O2 b) Decomposition (AB A + B) Decomposition reactions are the of synthesis reactions. A compound down into two or more products (often elements). AB A + B where A and B represent elements Ionic compounds may to produce elements, like the following: Table salt, sodium chloride, can be broken down into sodium metal and chlorine gas by salt at 800ºC and running through it. 2NaCl 2Na + Cl 2 Or covalent compounds may decompose into elements, like the following: By running through water, the water molecules into hydrogen and oxygen gases. 2H 2 O 2H 2 + O 2 2

3 1. Complete and balance the following decomposition reactions. Remember to check for diatomic elements as you write the formulas of the products. (a) AuCl3 (b) K2O (c) MgF2 (d) Ca3N2 (e) CsI 2. Identify each reaction as synthesis, decomposition, or neither. (a) CO2 C + O2 (b) 2AgCl + Cu CuCl2 + 2Ag (c) 2Cr + 3F2 2CrF3 (d) CaI2 + Na2CO3 2NaCl + CaCO3 (e) 2NaClO3 2NaCl + 3O2 c) Single Replacement Single replacement reactions replace one element from a compound with a separate element added as a reactant. A compound and an element react, and the element switches places with part of the original compound. A + BC B + AC where A is a, or A + BC C + BA where A is a -metal 3

4 When A is a metal: Aluminum foil in a solution of copper(ii) chloride produces solid copper and aluminum chloride. 2Al + 3CuCl 2 3Cu + 2AlCl 3 When A is a non-metal: When fluorine is bubbled through a sodium iodide solution, iodine and sodium fluoride are produced. F 2 + 2NaI I 2 + 2NaF 1. Complete and balance the following single replacement reactions. (a) PbCl 4 + Al (b) Na + Cu 2 O (c) CuF 2 + Mg (d) Cl 2 + CsBr (e) Be + Fe(NO 3 ) 2 2. Classify each reaction as synthesis, decomposition, or single replacement. (a) 2N2O 2N2 + O2 (b) Au(NO3)3 + 3Ag Au + 3AgNO3 (c) CH4 C + 2H2 (d) 2NH4Br + Cl2 2NH4Cl + Br2 (e) Br2 + I2 2IBr 4

5 d) Double Replacement (AB + CD AD + CB) Double replacement reactions elements between two compounds reacting together to form two new compounds. Two compounds react, with elements places between the original compounds. Two solutions react to form a (ppt, solid) and another solution Ionic solution + ionic solution ionic solution + ionic AB + CD AD + CB When potassium chromate and silver nitrate react, they form a red, silver chromate, in a of potassium nitrate. K 2 CrO 4 + 2AgNO 3 Ag 2 CrO 4 + 2KNO 3 1. Complete and balance the following double replacement reactions. You do not need to decide which product(s) form a precipitate or to show states in the balanced equation. (a) CaS + NaOH (b) K 3 PO 4 + MgI 2 (c) SrCl 2 + Pb(NO 3 ) 2 (d) AlCl 3 + CuNO 3 5

6 (e) AgNO 3 + Na 2 CrO 4 2. Classify each reaction as synthesis, decomposition, single replacement, or double replacement. (a) 2FeBr 3 + 3Zn 3ZnBr 2 + 2Fe (b) FeBr 2 + ZnSO 4 ZnBr 2 + FeSO 4 (c) 2Al + Fe 2 O 3 2Fe + Al 2 O 3 (d) 2Fe + O 2 2FeO (e) 2FeBr 3 2Fe + 3Br 2 e) Neutralization (Acid-Base Reactions) Neutralization reactions occur when an acid (most compounds starting with H) and a (most compounds ending in OH, or beginning with NH 4 ) react to form a salt and. Acid + base salt + water HX + MOH MX + H 2 O where X and M are elements Sulfuric acid is used to neutralize calcium : H 2 SO 4 + Ca(OH) 2 CaSO 4 + 2H 2 O Phosphoric acid helps to neutralize the compounds that cause rust, such as iron(ii). H 3 PO 4 + 3Fe(OH) 2 Fe 3 (PO 4 ) 2 + 6H 2 O 1. Complete and balance the following neutralization (acid-base) reactions. (a) HBr + NaOH (b) H 3 PO 4 + Mg(OH) 2 (c) HCl + Pb(OH) 2 (d) Al(OH) 3 + HClO 4 6

7 2. Classify each reaction as synthesis, decomposition, single replacement, double replacement, or neutralization. (a) 2HCl + Zn ZnCl 2 + H 2 (b) 2HCl H 2 + Cl 2 (c) 2HCl + Sr(OH) 2 SrCl 2 + 2H 2 O (d) 2HCl + Pb(NO 2 ) 2 2HNO 2 + PbCl 2 f) Combustion Combustion reactions occur when a compound or element reacts with to release and produce an. Also sometimes referred to as combustion. C X H Y + O 2 CO 2 + H 2 O where X and Y represent integers Natural gas ( ) is burned in furnaces to heat homes. CH 4 + O 2 CO 2 + 2H 2 O An acetylene torch is used to metals together. 2C 2 H 2 + 5O 2 4CO 2 + 2H 2 O Carbohydrates like glucose combine with oxygen in our body to release energy. C 6 H 12 O 6 + 6O 2 6CO 2 + 6H 2 O 1. Complete and balance the following combustion reactions. (a) C 3 H 8 + O 2 (b) C 4 H 10 + O 2 (c) C 2 H 4 + O 2 7

8 (d) C 6 H 12 O 6 + O 2 (e) C 12 H 22 O 11 + O 2 2. Classify each reaction as synthesis, decomposition, single replacement, double replacement, neutralization, or combustion. (a) 3Ca(NO3)2 + 2Na3PO4 6NaNO3 + Ca3(PO4)2 (b) Ca(OH)2 + H2SO4 2H2O + CaSO4 (c) 2C6H6 + 15O2 12CO2 + 6H2O (d) 6Mg + P4 2Mg3P2 (e) C2H6O + 3O2 2CO2 + 3H2O Summary of Types of Chemical Reactions 8

9 For each of the following reactions, classify the reaction type and then predict what the products will be. Then write the skeleton equation and balance it. 1. Fe 2 O 3 2. Al + NiBr 3 3. Cl 2 + NiBr 2 4. HCl + Mg(OH) 2 5. C 18 H 38 + O 2 6. Li + N 2 7. AgNO 3 + Na 2 CrO Factors Affecting the Rate of Chemical Reactions Often, controlling the rate of a chemical reaction is as important as having the reaction occur in the first place. Altering certain factors can determine the at which a chemical reaction occurs. To make a reaction happen quickly: Increase the where the reaction occurs. Increase the of reactants. Increase the amount of area that reacts. Add a or remove an. To make a reaction happen slowly: the temperature where the reaction occurs. the concentration of reactants. the amount of surface area that reacts. a catalyst or an inhibitor. 9

10 a) Temperature Temperature is the energy of molecules. The more energy molecules have, the higher the temperature. When molecules have more energy, they around more, into other molecules more, and therefore react. The rate of reaction changes with the temperature. Higher temperature = reaction rate, and vice versa. Sometimes we want slower reactions (we use a to prevent spoilage). Sometimes we want faster reactions (we food to speed up the production of new molecules). Learning Check (p ) 1. Heating a light stick can make it glow brighter. Why? The brighter light of a hot glow stick is due to a faster reaction rate caused by heating. 2. What happens to the rate of a chemical reaction when the temperature is raised? Raising the temperature of a chemical reaction increases the reaction rate. 3. What does cooling do to the frequency at which particles of reactants can collide? Cooling decreases the frequency at which particles of reactants can collide. 4. How does cooling affect the energy of the collisions between particles? Cooling lowers the energy of the collisions between reactant particles. b) Concentration Concentration refers to how many molecules of a substance exist in a certain. Concentration is how much is dissolved in. Concentration is measured in mass per unit volume (g/l). 10

11 Usually, the higher the concentration of reactants, the faster the reaction occurs. c) Surface Area Since there are molecules per unit volume in high concentrations, there are more for molecules to collide and react. A splint of wood glows brighter in highly oxygen than in normal with a lower concentration of oxygen. Chemical reactions occur when and where atoms and compounds collide. Therefore, the more atoms and molecules there are to collide, the higher the reaction rate. Increasing surface area the rate of reaction. Surface area can be increased by creating pieces. A substance has far more surface area than one large. The increase in surface area must also be exposed for reaction; a powder only reacts more quickly if it is in contact with the other reactant(s). Reading Check (p. p ) 1. How does increasing concentration result in an increase in reaction rate? 2. Can the concentration of a substance change if it is a gas? 3. Can the concentration of a solution change if it is an aqueous solution? 11

12 4. How does increasing the surface area of a reactant increase reaction rate? d) Catalysts Sometimes, increasing the temperature or concentration is not a desirable method to increase reaction rate. Changing these two variables may be impractical or dangerous. An alternate technique is to use a catalyst. A catalyst is a chemical that allows a reaction to occur more without actually participating in the reaction itself. The catalyst speeds up the reaction rate but does not get up as a reactant. Catalysts often the amount of energy necessary to break the bonds in the reactants. are an example of biological catalysts. Saliva has enzymes that help speed the breakdown of when they enter the mouth. A catalytic converter is a device installed in cars to. Car exhaust passes through the catalytic converter before leaving the car. Catalysts found in the honeycomb-shaped filters in the converter help to change many of the pollutants into substances. carbon monoxide is changed into CO 2. Hydrocarbons are converted into CO 2 and. Nitrogen oxides are changed into and. Non-metal oxide 2N 2 O 3 2N 2 + 3O 2 12