Chapter 9 Chemical Vocabulary Ch. 9.1 Chemical reaction Reactant Product Word Equation Skeleton Equation Chemical equation Coefficient 1 2 Objectives Write chemical equations to describe chemical reactions Classify and identify chemical reactions Write ionic equations for reactions that occur in water 3 Kick Off Activity This can be put in your lab notebook. It is not due until the 4 th marking period. Answer the questions as we cover the subjects and hold onto it. (-5 points each time you ask for a new one.) This simple reaction that you will do will summarize most of the things you will learn over the next few months. 4 Interpreting Formulas Remember: Formulas represents a formula unit of an ionic compound or the number of atoms connected in a molecule. How do you represent more than one formula unit or molecule. Add a coefficient (number) before the formula. Example: 5 NaCl means 5 units of NaCl Interpreting Formulas A formula unit summarizes how much of each atom is in a compound. Multiply the subscript of the element by the coefficient to get the total number of each. Example: 3 NaCl Means there are three sodium and three chloride 5 6 1
Interpreting Formulas Practice Formula of compound 2Na 2 O 4H 2 SO 4 5CaSO 4 2H 2 O Number of each atom Writing Chemical In order to understand a chemical reaction, you have to describe the changes that take place. Part of the description is stating what is reacting (changing) and what forms. Reactants the substances that undergo a reaction Products The new substances that form 7 8 Writing Chemical HC 2 H 3 O 2 + NaHCO 3 CO 2 + H 2 O + NaC 2 H 3 O 2 Make description complete by indicating the state of the substance. Here are the symbols: (s) = Solid (l) = Liquid (g) = Gas (aq) = Aqueous (substance dissolved in water) 9 Writing Chemical Summary Here s a complete chemical formula description of the reaction we have witnessed: HC 2 H 3 O 2 (aq) + NaHCO 3 (s) CO 2 (g) + NaC 2 H 3 O 2 (aq) + H 2 O (l) Reaction Description Aqueous acetic acid and solid sodium hydrogen carbonate react to form carbon dioxide gas, aqueous sodium acetate, and water. 10 Balancing Chemical Balancing chemical equations is the application of the conservation of atoms law. If the number of atoms on the reactants (left) side is equal the number of atoms on the products (right) side, the equation is balanced. Balancing Chemical Left side of equation HC 2 H 3 O 2 + NaHCO 3 Right side of equation CO 2 + NaC 2 H 3 O 2 + H 2 O # Atoms (reactants) = #Atoms (Products) 11 12 2
Word Equation Acetic acid (aq) + sodium hydrogen carbonate (s) carbon dioxide (g) + sodium acetate (aq) + water(l) Skeleton Equation describes the reaction with balanced chemical formalas HC 2 H 3 O 2 (aq) + NaHCO 3 (s) CO 2 (g) + NaC 2 H 3 O 2 (aq) + H 2 O(l) Chemical Equation - describes the chemical formulas of the reactants and products along with their relative amounts in a chemical reaction 13 14 Balanced Chemical Equation HC 2 H 3 O 2 (aq) + NaHCO 3 (s) CO 2 (g) + NaC 2 H 3 O 2 (aq) + H 2 O(l) Reactants Side Products Side 5 Hydrogens 5 Hydrogens 3 Carbons 3 Carbons 5 Oxygens 5 Oxygens 1 Sodium 1 Sodium Steps for Balancing 1. Write the skeleton equation. All reactants and products have their correct balanced formulas. 2. By inspection, find an element or polyatomic group that does not have equal amounts on both sides. 3. Add coefficients to make the number of atoms or groups equal on both sides of equation. 15 16 Steps for Balancing 4. Repeat steps 2 and 3 until all atoms and groups are balanced. 5. Generally, it is better to balance oxygen and single elements as late as possible. 6. Write coefficients in their lowest possible whole-number ratios. Example Word Equation: sodium hydroxide(aq) + carbon dioxide(g) sodium carbonate(aq) + water Skeleton: NaOH(aq) + CO 2 (g) Na 2 CO 3 (aq) + H 2 O(l) What is the first atom that looks out of balance? 17 18 3
Start on this one by balancing sodium on both sides of the equation. How would we do that? Skeleton: NaOH(aq) + CO 2 (g) Na 2 CO 3 (aq) + H 2 O(l) Put a 2 in front of the NaOH: 2NaOH(aq) + CO 2 (g) Na 2 CO 3 (aq)+ H 2 O(l) Balancing Chemical Coefficients A number written in front of a reactant or product that states how many units of something are reacting or being formed. Don t change subscripts in a formula after you make the skeleton equation!! That would change the identity of the substance!! Don t put coefficients in the middle of a compound! 19 20 2NaOH(aq) + CO 2 (g) Na 2 CO 3 (aq) + H 2 O(l) So what did that coefficient do? Let s count the atoms: Reactants Products Na 2 2 O 4 4 H 2 2 C 1 1 Generally, balance Oxygen and single element-atoms last. 21 Diatomic Elements Diatomic Molecules Seven non metal elements are found naturally as molecular elements of two identical atoms H-H NΞN O=O F-F Cl-Cl Br-Br I -I They are: H 2, N 2, O 2, F 2, Cl 2, Br 2, and I 2 All are gases except Br 2 (liquid) and I 2 (Solid) 22 Example: Word Equation: Hydrogen(g) + Chlorine(g) Hydrogen chloride(g) Skeleton Equation: H 2 (g) + Cl 2 (g) HCl(g) Skeleton Equation: H 2 (g) + Cl 2 (g) HCl(g) Both H and C are out of balance. Put a 2 in front of HCl to give two of each on both sides of equation: H 2 (g) + Cl 2 (g) 2HCl(g) 23 24 4
H 2 (g) + Cl 2 (g) 2HCl(g) Here s what happened pictorally: H-H + Cl-Cl H-Cl and H-Cl Another example: magnesium(s) + hydrochloric acid(aq) magnesium chloride (aq) + hydrogen (g) These bonds were broken. These bonds were formed in making a new substance. 25 Skeleton: Mg(s) + 2HCl(aq) MgCl 2 (aq) + H 2 (g) What do we need to do to balance? Add a 2 in front of HCl. 26 Harder example: Iron(III) chloride(aq) + sodium hydroxide (aq) iron(iii) hydroxide(s) + sodium chloride(aq) Skeleton & Balanced: Balancing Chemical - Practice Word : 1) magnesium chloride (aq) + silver nitrate (aq) magnesium nitrate(aq) + silver chloride(s) 2) calcium(s) + water(l) calcium hydroxide (s) + hydrogen(g) 3) lithium phosphate(aq) + magnesium sulfate(aq) lithium sulfate(aq) + magnesium phosphate(s) 27 28 Balancing Chemical - Practice 1) magnesium chloride (aq) + silver nitrate (aq) magnesium nitrate(aq) + silver chloride(s) Step 1: Change to a skeleton equation Balancing Chemical - Practice 2) calcium(s) + water(l) calcium hydroxide (s) + hydrogen(g) Step 1: Skeleton Equation Step 2: Balance with coefficients Step 2: Balance with coefficients 29 30 5
Balancing Chemical - Practice 3) lithium phosphate(aq) + magnesium sulfate(aq) lithium sulfate(aq) + magnesium phosphate(s) Step 1: Write Skeleton equation: Step 2: Balance equation with coefficients 31 Ch. 9.2 - Types of There are five types of chemical reactions we will talk about: 1. Synthesis reactions 2. Combustion reactions 3. Decomposition reactions 4. Single replacement reactions 5. Double replacement reactions You need to be able to identify the type of reaction and predict the product(s) 32 Steps to Writing Some steps for doing reactions 1. Identify the type of reaction 2. Predict the product(s) using the type of reaction as a model 3. Balance it Don t forget about the diatomic elements! There are seven diatomic elements They form a 7 on periodic chart and point toward the 7 th (H 2 ) 1. Synthesis reactions Synthesis reactions occur when two substances (generally elements) combine and form a compound. (Sometimes these are called combination, formation or addition reactions.) reactant + reactant 1 product Basically: A + B AB Example: 2H 2 + O 2 2H 2 O Example: 2Mg + O 2 2MgO Example: CaO(s) + H 2 O(l) Ca(OH) 2 (s) 33 34 Synthesis Here is another example of a synthesis reaction Practice Predict the products. Write and balance the following synthesis reactions. 1. sodium(s) + chlorine(g) 2. magnesium(s) + Iodine(s) 3. aluminum(s) + fluorine(g) 35 36 6
2. Combustion Combustion reactions occur when oxygen combines with another substance and releases energy as heat and light. Example: Mg(s) + O 2 (g) MgO(s) Combustion Combustion is also called burning!!! In order to burn something you need the 3 things in the fire triangle : 1) A Fuel (hydrocarbon) 2) Oxygen to burn it with 3) Something to ignite the reaction (spark) 37 38 Combustion In general: C x H y + O 2 CO 2 + H 2 O Hydrocarbon combustion ALWAYS produces carbon dioxide and water. (Oxide of carbon and oxide of hydrogen) Combustion is used to heat homes and run automobiles (octane, as in gasoline, is C 8 H 18 ) Combustion Example C 5 H 12 + 8O 2 5 CO 2 + 6 H 2 O Write the products and balance the following combustion reaction: C 9 H 20 + O 2 39 40 Classifying Chemical - Combustion Where can we find examples of a combustion reaction? Combust CH 4 to heat homes Combust gasoline for transportation Another example: Ethanol (l) + oxygen(g) carbon dioxide(g) + water(g) C 2 H 5 OH (l) + O 2 (g) CO 2(g) + H 2 O (g) C 2 H 5 OH (l) + 3O 2(g) 2CO 2(g) + 3H 2 O (g) What evidence do you have that reaction occurred? 41 3. Decomposition Decomposition reactions occur when a compound breaks up into the elements or in a few to simpler compounds 1 Reactant Product + Product In general: AB A + B Example: 2 H 2 O 2H 2 + O 2 Example: 2 HgO 2Hg + O 2 42 7
Decomposition Another view of a decomposition reaction: 43 Decomposition Exceptions Carbonates and chlorates are special case decomposition reactions that do not go to the elements. Carbonates (CO 3 2- ) decompose to carbon dioxide and a metal oxide Example: CaCO 3 CO 2 + CaO Chlorates (ClO 3- ) decompose to oxygen gas and a metal chloride Example: 2 Al(ClO 3 ) 3 2 AlCl 3 + 9 O 2 There are other special cases, but we will not explore those in Chemistry I 44 Practice Predict the products. Then, write and balance the following decomposition reaction equations: Solid Lead (IV) oxide decomposes PbO 2 (s) Aluminum nitride decomposes AlN(s) Classifying Chemical - Decomposition What happens when things decompose? They break down into simpler structures Take for example, NaHCO 3 Can you name this compound? NaHCO 3 (s) Na 2 CO 3 (s) + CO 2 (g) + H 2 O(g) 2NaHCO 3 (s) Na 2 CO 3 (s) + CO 2 (g)+ H 2 O(g) 45 46 Practice Identify the type of reaction (synthesis, combustion or decomposition) and balance the equation: 1. Al 2 O 3 (s) Al(s) + O 2 (g) 2. C 3 H 8 (g)+ O 2 (g) CO 2 (g)+ H 2 O(g) 3. Co(s)+ S(s) Co 2 S 3 (s) 4. BaCO 3 (s) BaO(s) + CO 2 (g) 47 4. Single Replacement Single Replacement occur when one element replaces another in a compound. A metal can replace a metal ion (+) OR a nonmetal can replace a nonmetal ion (-). element + compound product + product A + BC AC + B (if A is a metal) OR A + BC BA + C (if A is a nonmetal) (remember the cation always goes first!) 48 8
Single Replacement Another view: Single Replacement - Example Write and balance the following single replacement reaction equation: Zinc(s) + hydrochloric acid(aq) zinc chloride(s) + hydrogen(g). Zn(s) + 2HCl(aq) ZnCl 2 (s) + H 2 (g) Note: Zinc replaces the hydrogen ion in the reaction 49 50 Single Replacement Reaction: Single Replacement (Redox) In reality, Single replacement reaction is a simplified term for a REDOX reaction Stands for: Oxidation: Loss of electrons Example: Zn(s) Zn 2+ (aq) + 2e - Reduction: Gain of electrons Example: 2H + (aq)+ 2e - H 2 (g) 51 52 Single Replacement (Redox) Oxidation Number is the charge on an atom (zero) or ion. So in our previous example: Zn(s) Zn 2+ (aq) + 2e - The Oxidation number of Zn(s) metal is zero. The Oxidation number of the Zn 2+ ion is +2. Oxidation number increases (more positive) for an oxidized substance. 53 Single Replacement (Redox)- Practice Sodium chloride(s) + fluorine(g) sodium fluoride(s) + chlorine(g). 2NaCl(s) + F 2 (g) 2NaF(s) + Cl 2 (g) Note that fluorine replaces chlorine in the compound Aluminum(s) + copper (II) nitrate(aq) aluminum nitrate(aq) + copper(s) 2Al(s)+ 3Cu(NO 3 ) 2 (aq) 2Al(NO 3 ) 3 (aq) + 3Cu(s) 54 9
Examples of Activity AgNO 3 (ag) + Cu(s) Cu(NO 3 ) 2 (aq) + Ag(s) Copper metal is more active than silver ion so it replaces silver ion in solution. Ag(s) + CuSO 4 (aq) No Reaction Why? Because copper ion is more active than silver metal and will remain as an ion. Note that activity for metals means it is more likely to be oxidized. 55 Practice Predict the products, if any, note oxidation # s, and balance the reaction: 1. Fe(s) + CuSO 4 (aq) FeSO 4 (aq) + Cu(s) 2. Br 2 (l) + MgCl 2 (aq) No Reaction 3. Fe(s) + Na 3 PO 4 (aq) No Reaction 4. Al(s) + _3CuCl(aq) 56 AlCl 3 (aq) + 3_Cu(s) Chapter 7 Review Name Sodium chloride Potassium carbonate Molybdenum(VI) chloride Formula 5. Double Replacement Double Replacement occur when a metal ion replaces a metal ion in a compound and a nonmetal ion replaces a nonmetal ion in a compound. Compound + compound product + product AB + CD AD + CB Iron(III) oxalate 57 58 Classifying Chemical Double Replacement Example: CaCl 2 (aq) + K 2 CO 3 (aq) CaCO 3 (s)+ 2KCl(aq) Double Replacement Think about it like foil ing in algebra, first and last ions go together + inside ions go together Example: AgNO 3(aq) + NaCl (aq) AgCl (s) + NaNO 3(aq) Another example: K 2 SO 4(aq) + Ba(NO 3 ) 2(aq) 2 KNO 3(aq) + BaSO 4(s 59 60 10
Practice Balance the following equations. 1. HCl(aq) + AgNO 3 (aq) AgCl(s) + HNO 3 (aq) 2. 3CaCl 2 (aq) + 2Na 3 PO 4 (aq) Ca 3 (PO 4 ) 2 (s) + 6NaCl(aq) 3. FeCl 3 (aq) + 3NaOH(aq) Fe(OH) 3 (s) + 3NaCl(aq) Harder Practice Predict products, then balance the following equations. 1. Pb(NO 3 ) 2 + BaCl 2 PbCl 2 + Ba(NO 3 ) 2 2. H 2 SO 4 + 2NaOH 2HOH + Na 2 SO 4 3. 2KOH + CuSO 4 K 2 SO 4 + Cu(OH) 2 62 61 in Aqueous Solutions Ch. 9.3 Solute is dissolved in water ions are separated from each other (eg CaCl 2 is a solute) Solvent is what it is dissolved in (eg water is the solvent) These form an aqueous solution (aq) The solute particles dissociate, they separate in the solution. 63 Complete Ionic What really happened in our famous experiment? Solutes CaCl 2 and K 2 CO 3 are soluble in water, so The reactants CaCl 2 (aq) and K 2 CO 3 (aq) dissociated to make ions Ca +2 (aq) and 2Cl - (aq) and 2 K + (aq) and CO 3 (aq) Then what happened? 64 Complete Ionic Ca +2 (aq) and CO 3 (aq) got together to form a solid CaCO 3 (s) leaving 2K + (aq) and 2Cl - (aq) still dissolved in solution. How do we know CaCO 3 forms a solid? See solubility table. Describing Ionic Equation for CaCO 3 Reaction Complete ionic equation shows all particles as they exist in solution. Ca +2 (aq) + 2Cl - (aq) + 2K + (aq) + CO 3 (aq) CaCO 3 (s) + 2 K + (aq) + 2Cl - (aq) Note that Cl - and K + don t change! They are spectator ions. Net ionic equation shows only the particles that take part in the reaction. 65 Ca +2 (aq) + CO 3 (aq) CaCO 3 (s) 66 11
Net Ionic Cancel out ions that appear on BOTH sides of the reaction in the complete ionic equation to get the net ionic equation. Complete Ionic Equation: 2 K + (aq) + CrO 4 (aq) + Pb +2 (aq) + 2 NO 3- (aq) PbCrO 4 (s) + 2 K + (aq) + 2 NO 3- (aq) Net Ionic Equation: CrO 4 (aq) + Pb +2 (aq) PbCrO 4 (s) Net Ionic Practice From the full chemical equation write the complete ionic and net ionic equations for this reaction. Chemical: 2AgNO 3 (aq) + K 2 Cr 2 O 7 (aq) Ag 2 Cr 2 O 7 (s) + 2KNO 3 (aq) Complete Ionic: Net Ionic: 67 68 More Net Ionic Practice Given this Full Chemical Equation: K 2 CrO 4 + Pb(NO 3 ) 2 PbCrO 4 (s) + 2 KNO 3 Soluble Soluble Insoluble Soluble Write the Complete Ionic Equation: And the Net Ionic Equation: in Aqueous Solutions If all solutes are soluble and don t react to produce a solid or a gas then no reaction occurs. Example are solutes KCl and Zn(NO 3 ) 2 : K + (aq) + Cl - (aq) + Zn +2 (aq) + 2NO 3- (aq) K + (aq) + Cl - (aq) + Zn +2 (aq) + 2NO 3- (aq) Which really means: K + (aq) + Cl - (aq) + Zn +2 (aq) + 2NO 3- (aq) NR 69 70 Water formed in Reaction When a solid is one of the products, it is called a precipitate. We ve had numerous examples CaCO 3, PbCrO 4 and AgCl Can also make water if have H + and OH - in solution (acid/base) H + (aq) + NO 3- (aq) + Na + (aq) + OH - (aq) Na + (aq) + NO 3- (aq) + H 2 0(l) Gases formed in Ionic Reaction Sulfuric acid (H 2 SO 4 ) reacts with 2NaCN: Complete Ionic Equation: 2H + (aq) + SO 4 (aq) + 2Na + (aq) + 2CN - (aq) 2HCN(g)+ SO 4 (aq) + 2Na + (aq) Net ionic equation: H + (aq) + CN - (aq) HCN(g) Or H + (aq) + OH - (aq) H 2 O(l) 71 72 12