Chapter 11: Chemical Reactions chemical reaction: the process by which one or more substances are changed into one or more different substances. in a reaction: REACTANTS PRODUCTS Exothermic Heat/Light Indications of a Chemical Reaction Evolution of heat and light Production of a gas Formation of a precipitate (insoluble solid) Gas Produced Precipitate Word and Formula Equations rewrite formulas into an equation showing reactants and products. sodium oxide and water yields sodium hydroxide

Na2O + H2O  NaOH Lead(II)chloride added to sodium chromate produces lead(II)chromate and sodium chloride PbCl2 + Na2CrO4  PbCrO4 + NaCl Beware of diatomic molecules!!!!! H2 O2 F2 Br2 I2 N2 Cl2 Additional notations to consider: Solid  (s) liquid  (l) gas  (g) aqueous  (aq)

5 different types of reactions Combination/ Synthesis Decomposition Single replacement/ displacement Double replacement/ displacement Combustion

Types of reactions A combination reaction is a chemical change in which two or more substances react to form a single new substance. A decomposition reaction is a chemical change in which a single compound breaks down into two or more simpler products A single-replacement reaction is one in which one element replaces a second element in a compound

Types of Reactions(continued) This is an example of a double-replacement reaction, which is a chemical change involving an exchange of positive ions between two compounds A combustion reaction is a chemical change in which an element or a compound reacts with oxygen, often producing energy in the form of heat and light.

Combination/ Synthesis Magnesium metal and oxygen gas combine to form the compound magnesium oxide. 2Mg(s) + O2 → 2 MgO(s)

2HgO(s) ___________> 2Hg(l) + O2(g) Decomposition When mercury(II) oxide is heated, it decomposes or breaks down into two simpler substances. 2HgO(s) ___________> 2Hg(l) + O2(g)

Single Replacement Reaction Dropping a small piece of potassium into a beaker of water creates the vigorous reaction. 2K(s) + 2H2O(l) → 2KOH(aq) + H2

Double Replacement Reaction 2KI(aq) + Pb(NO3)2(aq) → PbI2 + 2KNO3(aq) 2KI(aq) + Pb(NO3)2(aq) → PbI2 + 2KNO3(aq)

Combustion reaction The complete combustion of a hydrocarbon produces carbon dioxide and water. But if the supply of oxygen is limited during a reaction, the combustion will not be complete. It forms carbon monoxide instead of carbon dioxide.

Combustion Reactions The complete combustion of a hydrocarbon releases a large amount of energy as heat That’s why hydrocarbons such as methane (CH4), propane (C3H8), and butane (C4H10) are important fuels. CH4(g) + 2O2(g) → CO2(g) + 2H2O(g) 2C8H18(l) + 25O2(g) → 16CO2(g) + 18H2O(g)

Activity series and single replacement reactions activity series: a list of elements in order of decreasing activity; the activity series of halogens is Fl, Cl, Br, I Higher the position of the element in the series, higher is its activity. Aluminum can displace copper from its solution but copper cannot displace zinc from its solution.

Activity Series of the Elements Activity of metals Activity of halogen nonmetals F2 Cl2 Br2 I2 Li Rb K Ba Sr Ca Na React with cold water and acids, replacing hydrogen. React with oxygen, forming oxides. Mg Al Mn Zn Cr Fe Cd React with steam (but Not cold water) and acids, Replacing hydrogen. React with oxygen forming oxides.