Do Now CHEMICAL REACTIONS What are some signs that a chemical change may have taken place? Where are the reactants and products in a reaction? What do they represent? Describe the law of conservation of mass. Chemical Reaction A process in which one or more substances are converted into new substances with different chemical and physical properties. Chemical Reaction In chemical reactions, existing bonds are broken, atoms are rearranged, and new bonds are formed. Reactant: substances that enter the reaction (start) Product: substances that come out of reaction (end) Evidence How do we know that a reaction has taken place? Production or absorption of energy (heat and light) Production of a gas Formation of a precipitate (a solid that forms as a result of mixing 2 solutions). Color change Chemical Equations Represent reactions with symbols and formulas, tells us the identities and relative amounts of reactants and products in a chemical reaction. 1
Word Equations Give names of reactants and products + = reacts with, add, or added to = yields or produces Describe the following as a word equation: Calcium + Oxygen Calcium Oxide Formula Equations Give symbols or formulas of reactants and products When going from word to formula, be careful to use the correct formulas. (Remember the diatomic molecules Br 2, I 2, N 2, Cl 2, H 2, O 2, F 2 ) Write the formula for the previous word equation: Ca + O 2 CaO Additional symbols in equations: (s) or = Solid (l) = Liquid Write the word equation for the reaction that occurs when solid sodium oxide is added to water and forms sodium hydroxide (dissolved in water). (g) or = Gas (aq) = Aqueous (dissolved in water) Na 2 O (s) + H 2 O NaOH (aq) Names of Acids Write the word equation and formula for methane reacting with oxygen to produce carbon dioxide and water. Chemistry Reference Table K lists the common acids you need to use Methane + oxygen carbon dioxide + water CH 4 + O 2 CO 2 + H 2 O 2
LAW OF CONSERVATION OF MATTER (MASS) Formula equations must be written in accordance with the LAW OF CONSERVATION OF MATTER (MASS) = atoms cannot be created or destroyed in a chemical reaction. They can only be rearranged! Law of Conservation of Mass Antoine Lavoisier Mass is neither created nor destroyed during chemical or physical reactions. Total mass of reactants = Total mass of products Formula equations must be written in accordance with the LAW OF CONSERVATION OF MATTER (MASS) Law of Conservation of Mass The same number and kind of atoms must appear on both sides of the arrow!!! COEFFICIENTS= small whole numbers that appear in front of a formula in a chemical equation. The coefficient multiplies the number of atoms of each element in the formula that follows. Ex: 2 H 2 O = 4 H and 2 O Trial and Error is the best way to balance equations. Steps to Writing Balanced Equations: 1. Read the word equation that describes a reaction: zinc + hydrochloric acid zinc chloride + hydrogen 2. Replace the words with symbols. Zn +HCl ZnCl 2 + H 2 3. Count the number of atoms on each side of the arrow. (Keep polyatomic ions that exist on both sides of the equation as one!) Zn +HCl ZnCl 2 + H 2 1 Zn 1 Zn 1 H 2 H 1 Cl 2 Cl 4. Balance using trial and error. Zn +2HCl ZnCl 2 + H 2 5. Check 1 Zn 1 Zn 2 H 2 H 2 Cl 2 Cl 3
Practice Na + H 2 O NaOH + H 2 1 Na 1 Na 2 H 3 H 1 O 1 O 2Na + 2H 2 O 2NaOH + H 2 2 Na 2 Na 4 H 4 H 2 O 2 O Practice Iron (III) oxide and hydrogen are the reactants. Iron and Water are the products. Find the balanced equation. Fe 2 O 3 +H 2 Fe + H 2 O 2 Fe 1 Fe 3 O 1 O 2 H 2 H Practice Fe 2 O 3 + H 2 Fe + H 2 O 2 Fe 1 Fe 3 O 1 O 2 H 2 H Fe 2 O 3 + 3H 2 2Fe + 3H 2 O 2 Fe 2 Fe 3 O 3 O 6 H 6 H Review What do you notice about the arrangement of elements in the reactants and products? 2Al + Fe 2 O 3 2Fe + Al 2 O 3 HCl + NaOH H 2 O + NaCl TYPES OF CHEMICAL REACTIONS Thousands of chemical reactions occur in nature. Reactions can be classified into one of several categories. Classification is important for predicting products of reactions. 1. SYNTHESIS REACTIONS 2. DECOMPOSITION REACTIONS 3. COMBUSTION 4. SINGLE REPLACEMENT REACTIONS 5. DOUBLE REPLACEMENT REACTIONS SYNTHESIS DECOMPOSITION SINGLE REPLACEMENT DOUBLE REPLACEMENT COMBUSTION 4
1. SYNTHESIS REACTIONS Two or more substances combine to form a new compound (composition or direct combination). Examples: A + X AX 2 Mg +O 2 2 MgO 2 CO + O 2 2 CO 2 (car exhaust) CO 2 + H 2 O H 2 CO 3 (carbonic acid) 2. DECOMPOSITION REACTIONS A single compound undergoes a reaction that produces two or more simpler substances (breakdown). Examples: AX A + X 2 H 2 O 2(l) 2 H 2 O (l) +O 2(g) 2 H 2 O (l) 2 H 2(g) +O 2(g) Electrolysis- the decomposition of a substance by applying an electric current. Electrolysis of Water 3. COMBUSTION REACTIONS A substance combines with oxygen (O 2 ) to release large amounts of energy in the form of light and heat. CH 4 +O 2 CO 2 +2H 2 O http://www.chem.uiuc.edu/clcwebsite/meth.html Writing Chemical Reactions From Particle Diagrams Chemical formulas can be written from diagrams as well Just like word problems, you must look at your reactants and products as well as balance the equation Write the chemical reaction for the following diagram: Reactants Key: = Atom of element X = Atom of element C Products 5
SYNTHESIS DECOMPOSITION Single and Double Replacement Reactions SINGLE REPLACEMENT DOUBLE REPLACEMENT COMBUSTION 4. SINGLE REPLACEMENT REACTIONS One element replaces a similar element in a compound (displacement). A + BX B + AX Mg (s) + 2HCl (aq) MgCl 2(aq) + H 2 2Al (s) +3Pb(NO 3 ) 2(aq) 2Al(NO 3 ) 3(aq) +3Pb (s) This type of reaction occurs only under certain conditions! What does certain conditions mean? A + BX B + AX A (metal or nonmetal) B (metal) X (nonmetal) Metals can only switch with Metals Nonmetals can only switch with Nonmetals Using the Activity Series (Table J) Some elements are considered to be very reactive, some are considered unreactive. The ability of an element to react is called the element s activity activity. Higher metals are more reactive than lower metals. A metal will only replace another metal in a compound if it is HIGHER on Table J. 6
Using the Activity Series Metals: the higher the activity, the greater its tendency is to lose electrons and therefore more reactive. Nonmetals: the higher the reactivity, the greater its tendency to gain electrons and therefore more reactive. The activity series is used to predict whether or not a chemical reaction will occur (single replacement reactions). If it is lower no reaction (NR) will occur! Using the Activity Series Single Replacement reactions only occur when an element is more reactive (higher on table J) than the element being replaced. Identify METALS: Will a Singlereplacement reaction occur? If the single element is further up on the activity chart (Table J) the reaction will occur. For example: Al + CuCl 2 AlCl 3 + Cu In each of the following, circle which metal is more active: 1. Li or Al 2. Au or Mg 3. Na or Pb In each of the following, predict whether there will be a reaction, then balance the reactions: Mg + CuSO 4 Al + LiCl Identify NONMETALS: Will a Single-replacement reaction occur? If the single element is higher up on table J, then the reaction will occur! For example: F 2 + 2LiBr Br 2 + 2LiF Sn + Ba 3 PO 4 7
In each of the following, circle which nonmetal is more active: 4. F 2 or I 2 In each of the following, predict whether there will be a reaction, then balance the reactions: I 2 + NaF 5. Br 2 or Cl 2 F 2 + MgBr 2 6. Cl 2 or I 2 Cl 2 + BaI 2 Rules for completing and writing single replacement reactions. 1. Determine whether the reaction will occur or not Li + CuSO 4 Yes a reaction will occur (Lithium is higher up on the chart) 2. Determine the products of the reaction by switching the appropriate elements. Li +CuSO 4 LiSO 4 + Cu 3. Place the charges on the elements and balance each of the new compounds formed. Li + CuSO 4 Li 2 (SO 4 ) + Cu 4. Balance the entire equation. 2 Li + CuSO 4 Li 2 (SO 4 ) + Cu Practice Completing Single- Replacement Reactions 1. Cu + Ag(NO 3 ) 2. Fe + Cu(NO 3 ) 2 3. Ca + H 2 O 4. Zn + NaCl 5. DOUBLE REPLACEMENT REACTIONS The ions of 2 compounds exchange places in an AQUEOUS solution to form 2 new compounds. Examples: AB + CD AD + CB Pb(NO 3 ) 2(aq) +KI (aq) KNO 3(aq) + PbI 2(s) Double replacement reactions do not always occur. We use the term No Reaction (NR) when no significant change occurs in a reaction. Conditions when Double Replacement Reactions occur 1. If the product is insoluble. (A precipitate is formed) Insoluble: cannot be dissolved in water Precipitate: an insoluble product 8
Solubility Chart (Table F) Determine whether the compound is soluble or insoluble a. NH 4 OH b. PbCl 2 c. BaCO 3 d. Al(OH) 3 e. Na 2 S f. K 2 SO 4 g. CaSO 4 h. Mg 3 (PO 4 ) 2 i. Zn(OH) 2 Now complete each of the following double replacement equations. For each of the products use Table F to assign a notation of (s) or (aq) below each formula. 1. BaCl 2 (aq) + Na 2 CO 3 (aq) 3. CaI 2(aq) + Na 3 PO 4 (aq) 2. Zn(NO 3 ) 2 (aq) + KOH (aq) 4. CuSO 4(aq) + (NH 4 ) 2 CO 3(aq) Type of reaction Definition Example When will the reaction take place Synthesis Two or more substances combine to form a new compound. 2Mg + O 2 2MgO Decomposition A single compound undergoes a reaction that produces two or more simpler substances (breakdown). H 2O 2(l) 2H 2O (l) + O 2 (g) Single Replacement One element replaces a similar element in a compound. Mg (s) + HCl (aq) MgCl 2(aq)+ H 2(g) Single Replacement reactions only take occur when one element is more active than the element being replaced. Use Table J Activity Series Metals replace metals in a compound. Nonmetals replace nonmetals in a compound. Double Replacement The ions of 2 compounds exchange places in an AQUEOUS solution to form 2 new compounds. The metals in the compounds switch places. 2 Li + CuSO 4 Li 2(SO 4) + Cu 1. If the product is insoluble. (A precipitate is formed) 2. If water is a product 3. If the product decomposes into a gas. Combustion Reaction A substance combines with oxygen (O 2) to release large amounts of energy in the form of light and heat. CH 4 +O 2 CO 2 +2H 2O 9