Intro to Reactions/ Balancing Equations

Transcription

1 Intro to Reactions/ Balancing Equations

2 Chemical Reactions Chemical reactions involve change. Evidence of a chemical reaction could include the following Evolution of heat, light, and/or sound Production of a gas Formation of a precipitate Color change

3 Chemical Reactions Chemical Equation: a representation of a chemical reaction using the symbols for the reactants and products Skeleton Equation: a chemical equation that does not indicate the relative amounts of the reactants and products

4 Chemical Reactions Reactants: Starting substances in a chemical reaction Products: Substances produced by a chemical reaction Coefficient Subscript Reactants Product

5 + Symbols in Chemical Equations used to separate two reactants or products yields separates reactants from products used in place of single arrow for reversible reactions (s) (l) solid liquid

6 (g) (aq) Δ Symbols in Chemical Equations gas aqueous substance dissolved in water heat is supplied to the reaction heat Pt indicates use of the element as a catalyst

7 Chemical Reactions Catalyst: substance that speeds up the rate of a reaction but is not used up by the reaction Catalysts speed up a reaction by lowering the activation energy (energy required for a reaction to start).

8 Chemical Reactions In addition to aqueous or (aq), soluble or in solution also indicate that a substance is dissolved in water. Precipitate: a solid product that forms in an aqueous solution reaction

9 Chemical Equations Write the following equation into symbols. Aqueous lead (II) nitrate and aqueous potassium iodide will produce solid lead (II) iodide and aqueous potassium nitrate. Pb(NO 3 ) 2(aq ) + KI (aq) PbI 2(s) + KNO 3(aq)

10 Chemical Equations Write the following equation into words. Aqueous calcium acetate and aqueous strontium chloride will produce aqueous strontium acetate and a calcium chloride precipitate. Ca(C 2 H 3 O 2 ) 2(aq) + SrCl 2(aq) Sr(C 2 H 3 O 2 ) 2(aq) + CaCl 2(s)

11 Chemical Equations In a reaction, atoms are rearranged, but mass, charge, and energy are all conserved. The Law of Conservation of Mass Mass cannot be created or destroyed, it can only be rearranged. Total Mass of Reactants = Total Mass of Products

12 Balancing Chemical Equations Balanced equation: There should be equal number of atoms of each element on each side of the equation. Coefficients are used to balance equations.

13 Balancing Chemical Equations H 2(g) + O 2(g) H 2 O (l) H O 2H 2(g) + O 2(g) 2H 2 O (l)

14 Balancing Chemical Equations Pb(NO 3 ) 2(aq) + KI (aq) PbI 2(s) + KNO 3(aq) Pb NO 3 K I Pb(NO 3 ) 2(aq) + 2 KI (aq) PbI 2(s) + 2 KNO 3(aq)

15 Types of Chemical Reactions

16 Synthesis Reactions A reaction that forms one compound General Form A + B Binary Compound AB Two elements react to form one compound. Examples H 2 + Cl 2 HCl sodium and chlorine will yield sodium chloride.

17 Synthesis Reactions Ternary Acid A nonmetallic oxide and water react to form a ternary acid Examples P 2 O 5 + H 2 O H 3 PO 4 Sulfur trioxide and water will produce sulfuric acid.

18 Synthesis Reactions Base A metallic oxide and water react to form a base. Examples MgO + H 2 O Mg(OH) 2 Sodium oxide and water will produce sodium hydroxide.

19 Synthesis Reactions Metallic Salt A metallic oxide and a nonmetallic oxide react to form a metallic salt Examples Na 2 O + SO 2 Na 2 SO 3 Barium oxide and dinitrogen trioxide react to form barium nitrite.

20 Decomposition Reactions reaction that breaks down one compound into two or more substances General Form AB A + B

21 Decomposition Reactions Binary Compound A binary compound decomposes into two elements. Examples HBr H 2 + Br 2 Strontium chloride will produce strontium and chlorine.

22 Decomposition Reactions Ternary Acid A ternary acid will decompose into a nonmetallic oxide and water. Examples H 2 SO 4 SO 3 + H 2 O Nitric acid plus heat will produce dinitrogen pentoxide and water.

23 Decomposition Reactions Base A base will decompose into a metallic oxide and water. Examples RbOH Rb 2 O + H 2 O Aluminum hydroxide plus heat will produce aluminum oxide and water.

24 Decomposition Reactions Metallic Carbonate or Metallic Sulfite A metallic carbonate will decompose into a metallic oxide and carbon dioxide. A metallic sulfite will decompose into a metallic oxide and sulfur dioxide. Examples CaCO 3 CaO + CO 2 Lithium sulfite plus heat will produce lithium oxide and sulfur dioxide.

25 Decomposition Reactions Metallic Bicarbonate or Metallic Bisulfite A metallic bicarbonate will decompose into a metallic carbonate, carbon dioxide, and water. A metallic bisulfite will decompose into a metallic sulfite, sulfur dioxide, and water. Examples NaHCO 3 Na 2 CO 3 + CO 2 + H 2 O Barium bisulfite plus heat yields barium sulfite, sulfur dioxide, and water.

26 Decomposition Reactions Group I nitrate A group I nitrate will decompose into a group I nitrite and oxygen. Examples KNO 3 KNO 2 + O 2 Lithium nitrate plus heat will produce lithium nitrite and oxygen.

27 Decomposition Reactions All other metallic nitrates A metallic nitrate will decompose into a metallic oxide, nitrogen dioxide, and oxygen. Examples Ba(NO 3 ) 2 BaO + NO 2 + O 2 Iron (III) nitrate plus heat will produce iron (III) oxide, nitrogen dioxide, and oxygen.

28 Decomposition Reactions Metallic chlorate A metallic chlorate will decompose into a metallic chloride and oxygen. Examples CsClO 3 CsCl + O 2 Magnesium chlorate plus heat will yield magnesium chloride and oxygen.

29 Single Replacement Reactions reaction of an element with a compound to produce a different element and different compound General Form AX + B BX + A

30 Single Replacement Reactions Active metal + water (alkali or alkaline earth metal) An active metal reacts with water to produce a base and hydrogen. Examples Cs + H 2 O CsOH + H 2 Calcium reacts with water to produce calcium hydroxide and hydrogen

31 Single Replacement Reactions Element reacts with a compound An element reacts with a compound to produce a different element and a different compound. Check the Activity Series (on STAAR chart) to determine if the reaction will occur. Single element must be higher on list than element to replace within the compound. (If not, then no reaction will occur.)

32 Single Replacement Reactions Element reacts with a compound (cont.) Examples Cu + AgNO 3 CuNO 3 + Ag Au + NaCl No Reaction Calcium reacts with lead (II) carbonate to produce calcium carbonate and lead.

33 Double Replacement Reactions General Form AB + CD AD + CB Two compounds will produce two different compounds. Examples Ca(NO 3 ) 2 + Na 2 C 2 O 4 CaC 2 O 4 + NaNO 3 Lead (II) oxide and silver sulfide will produce lead (II) sulfide and silver oxide.

34 Combustion Reactions Hydrocarbons burn in oxygen to produce carbon dioxide and water. General Form Examples C x H y + O 2 CO 2 + H 2 O CH 4 + O 2 CO 2 + H 2 O Octane (C 8 H 18 ) and oxygen will produce carbon dioxide and water.

35 Predicting Products

36 Reactions in Solution Net Ionic Equations

37 Reactions in Solutions Many important reactions take place in aqueous solution. When describing these reactions, it is often desirable to write the equation in ionic form. Ionic form describes the ionic species that exist in solution.

38 Ionic Equations AgNO 3(aq) + NaCl (aq) AgCl (s) + NaNO 3(aq) This is the standard form of a chemical equation, but it is important to understand that most ionic compounds dissociate (separate into ions) when they dissolve in water.

39 Dissociation of Ions Ex. NaCl (aq) Na + (aq) + Cl - (aq)

40 Ionic Equations AgNO 3(aq) + NaCl (aq) AgCl (s) + NaNO 3(aq) Ionic equations show aqueous ionic compounds as their free ions. Solids (precipitates), gases, and water are left together. Ag + (aq) + NO 3 - (aq) + Na + (aq) + Cl - (aq) AgCl (s) + Na + (aq) + NO 3 - (aq)

41 Net Ionic Equations Simplify the equation by eliminating ions that do not participate in the reaction. These ions are called spectator ions. Ag + (aq) + NO 3 - (aq) + Na + (aq) + Cl - (aq) AgCl (s) + Na + (aq) + NO 3 - (aq)

42 Net Ionic Equations Net Ionic Equation shows only ions that participate in a chemical reaction Ag + (aq) + Cl - (aq) AgCl (s) Of the reaction types we have discussed, single and double replacement reactions can usually be written in net ionic form.