Presentation on theme: "Honors Chemistry All chemical reactions have two parts: Reactants - the substances you start with Products- the substances you end up with The reactants."— Presentation transcript:
All chemical reactions have two parts: Reactants - the substances you start with Products- the substances you end up with The reactants turn into the products. Reactants Products
In a chemical reaction The way atoms are joined is changed Atoms arent created of destroyed. Can be described several ways: 1. In a sentence Copper reacts with chlorine to form copper (II) chloride. 2. In a word equation Copper + chlorine copper (II) chloride
Symbols in equations the arrow separates the reactants from the products Read reacts to form The plus sign = and (s) after the formula = solid (g) after the formula = gas (l) after the formula = liquid
Symbols used in equations (aq) after the formula - dissolved in water, an aqueous solution. used after a product indicates a gas (same as (g)) used after a product indicates a solid (same as (s))
Symbols used in equations indicates a reversible reaction shows that heat is supplied to the reaction is used to indicate a catalyst is supplied, in this case, platinum.
What is a catalyst? A substance that speeds up a reaction, without being changed or used up by the reaction. Enzymes are biological or protein catalysts.
Skeleton Equation Uses formulas and symbols to describe a reaction doesnt indicate how many. All chemical equations are sentences that describe reactions.
Convert these to equations Solid iron (III) sulfide reacts with gaseous hydrogen chloride to form iron (III) chloride and hydrogen sulfide gas. Nitric acid dissolved in water reacts with solid sodium carbonate to form liquid water and carbon dioxide gas and sodium nitrate dissolved in water.
Now, read these: Fe(s) + O 2 (g) Fe 2 O 3 (s) Cu(s) + AgNO 3 (aq) Ag(s) + Cu(NO 3 ) 2 (aq) NO 2 (g) N 2 (g) + O 2 (g)
Balanced Equation Atoms cant be created or destroyed All the atoms we start with we must end up with A balanced equation has the same number of each element on both sides of the equation.
Rules for balancing: Assemble, write the correct formulas for all the reactants and products Count the number of atoms of each type appearing on both sides Balance the elements one at a time by adding coefficients (the numbers in front) - save H and O until LAST! Check to make sure it is balanced.
Never change a subscript to balance an equation. If you change the formula you are describing a different reaction. H 2 O is a different compound than H 2 O 2 Never put a coefficient in the middle of a formula 2 NaCl is okay, Na2Cl is not.
Example H 2 +H2OH2OO2O2 Need twice as much O in the product RP H O
Example H 2 +H2OH2OO2O2 Changes the O RP H O
Example H 2 +H2OH2OO2O2 Also changes the H RP H O
Example H 2 +H2OH2OO2O2 Need twice as much H in the reactant RP H O
Example H 2 +H2OH2OO2O2 Recount RP H O
Example H 2 +H2OH2OO2O2 The equation is balanced, has the same number of each kind of atom on both sides RP H O
Example H 2 +H2OH2OO2O2 This is the answer RP H O Not this
Balancing Examples 2AgNO 3 + Cu Cu(NO 3 ) 2 + 2Ag 3Mg +N 2 Mg 3 N 2 4P + 5O 2 P 4 O 10 2Na + 2H 2 O H 2 + 2NaOH CH 4 + 2O 2 CO 2 + 2H 2 O
Types of Reactions There are millions of reactions. Cant remember them all Fall into several categories. We will learn 5 major types. Will be able to predict the products. For some, we will be able to predict whether they will happen at all. Will recognize them by the reactants
COMBINATION REACTION A reaction in which two or more substances combine to form a single product. A +B + C ABC CaO(s) + SO 2 (g) CaSO 3 (s)
Write and balance Ca + Cl 2 Fe + O 2 Al + O 2 Remember that the first step is to write the correct formulas Then balance by using coefficients only
DECOMPOSITION REACTION A reaction in which a single compound reacts to give two or more substances, usually requiring a raise in temperature. ABC A + B + C 2KClO 3 (s) 2KCl(s) + 3O 2 (g)
#2 - Decomposition Reactions decompose = fall apart one reactant falls apart into two or more elements or compounds. NaCl Na + Cl 2 CaCO 3 CaO + CO 2 Note that energy is usually required to decompose
#2 - Decomposition Reactions Can predict the products if it is a binary compound Made up of only two elements Falls apart into its elements H 2 O HgO
Fig. 8-13, p H 2 O (l) Can predict the products if it is a binary compound Made up of only two elements Falls apart into its elements
#2 - Decomposition Reactions If the compound has more than two elements you must be familiar with page 10 of your packet NiCO 3 KClO 3 (aq)
pp. 218, 220 Single Displacement (or Replacement) Reactions
Fig. 8-15, p. 218
Single Displacement (or Replacement) Reactions PREDICT THE PRODUCT 1. Ca + HCl 2. ZnBr 2 + I 2 3. Cu + AgNO 3 Answers are on the next slide.
#3 Single Replacement Metals replace other metals (and hydrogen) K + AlN Zn + HCl Think of water as HOH Metals replace one of the H, combine with hydroxide. Na + HOH
We can tell whether a reaction will happen Some chemicals are moreactive than others More active replaces less active There is a list on page 11 - called the Activity Series of Metals Higher on the list replaces lower.
#3 Single Replacement Note the * concerning Hydrogen H can be replaced in acids by everything higher Li, K, Ba, Ca, & Na replace H from acids and water Fe + CuSO 4 Pb + KCl Al + HCl
#3 - Single Replacement What does it mean that Hg and Ag are on the bottom of the list? Nonmetals can replace other nonmetals Limited to F 2, Cl 2, Br 2, I 2 (halogens) Higher replaces lower. F 2 + HCl Br 2 + KCl
pp. 220, 223 Double Displacement (or Replacement) Reactions
PREDICT THE PRODUCT & BALANCE 1. MgSO 4 + LiOH ___________ 2. Pb(NO 3 ) 2 + Na 2 CO 3 ____________ 3. HNO 3 + Ba(OH) 2 ___________ Answers are on the next slide.
Double Displacement (or Replacement) Reactions ANSWERS 1. MgSO LiOH Mg(OH) 2 + Li 2 SO 4 2. Pb(NO 3 ) 2 + Na 2 CO 3 PbCO NaNO HNO 3 + Ba(OH) 2 Ba(NO 3 ) H 2 O Exchange cations
Double Replacement Two things replace each other. Reactants must be two ionic compounds or acids. Usually in aqueous solution NaOH + FeCl 3 The positive ions change place. NaOH + FeCl 3 Fe +3 OH - + Na +1 Cl -1 NaOH + FeCl 3 Fe(OH) 3 + NaCl
Double Replacement Has certain driving forces Will only happen if one of the products: doesnt dissolve in water and forms a solid (a precipitate), or is a gas that bubbles out, or is a covalent compound (usually water).
Oxidation and Reduction Reactions Early chemists saw oxidation as the combination of a material with oxygen Today, many of these reactions may not even involve oxygen Redox currently says that electrons are transferred between reactants Always occur simultaneously. Called redox reactions.
Oxidation and Reduction Reactions Oxidation – refers to a loss of electrons, or gain of oxygen Reduction – refers to a gain of electrons, or loss of oxygen Oxidizing agent – the substance being reduced Reducing agent – the substance being oxidized
Oxidation and Reduction Reactions Loss of Electrons is Oxidation Gain of Electrons is Reduction LEO SAYS GER
Rules For Assigning Oxidation States Oxidation numbers are used to keep track of how many electrons are lost or gained by each atom
Balancing Redox Reactions If the oxidation number changes, that element has undergone oxidation or reduction Reaction as a whole must be redox Half-reaction – equation showing just the oxidation or just the reduction
Balancing Redox Reactions (in an acid) SO 2 + MnO 4 - SO Mn 2+ Divide the equation into half-reactions. SO 2 SO 4 2- MnO 4 - Mn 2+ Oxidation Reduction Balance all atoms except O and H
Balancing Redox Equations Balance O by adding H 2 O. 2H 2 O + SO 2 SO 4 2- MnO 4 - Mn H 2 O Balance H by adding H +. 2H 2 O + SO 2 SO H + 8H + + MnO 4 - Mn H 2 O
Balance net charge by adding e -. 2H 2 O + SO 2 SO H + + 2e - 5e - + 8H + + MnO 4 - Mn H 2 O Step 6. Make e - gain equal e - loss; then add half- reactions. 5(2H 2 O + SO 2 SO H + + 2e - ) 2(5e - + 8H + + MnO 4 - Mn H 2 O) ______________________________________ 10H 2 O + 5SO e H + + 2MnO 4 - 2Mn H 2 O + 5SO H e -
Cancel anything that's the same on both sides. 2H 2 O + 5SO 2 +2MnO 4 - 2Mn SO H +
Balancing Redox Reactions (in a base) Follow steps 1 – 7 then: 8. Identify the number of proton (H + ) in the acidic answer. Add the same number of OH + ions to BOTH sides of the equation. 9. If H + and OH + appear on the same side of the equation, they will react in a 1:1 ratio to form H 2 O. 10. Cancel out water molecules that appear on both sides of the equation. 11. Check that all is balanced
PRECIPITATION REACTION A reaction where an insoluble solid is formed during a reaction between two aqueous solutions. (aq) + (aq) (aq) + (s) 2KI (aq) + Pb(NO 3 ) 2 (aq) 2KNO 3 (aq) + PbI 2 (s) Exchange cations
Ionic Equations Many reactions occur in water- that is, in aqueous solution Many ionic compounds dissociate, or separate, into cations and anions when dissolved in water AgNO 3 + NaCl AgCl + NaNO 3 1. this is the full equation 2. Write it as an ionic equation 3. Eliminating ions not directly involved (spectator ions) = net ionic equation
Molecular, Ionic, Net Ionic Equations
How Do We Predict Solubility?
NEUTRALIZATION REACTION A reaction between an acid and a base which results in the production of a salt and water. HA + BOH (metal/nonmetal) + H 2 O HNO 3 (aq) + KOH(aq) KNO 3 (aq) + H 2 O(l)
COMBUSTION REACTION Means add oxygen A compound composed of only C, H, and maybe O is reacted with oxygen If the combustion is complete, the products will be CO 2 and H 2 O. If the combustion is incomplete, the products will be CO (possibly just C) and H 2 O. A reaction of a substance with oxygen, usually the rapid release of heat produces a flame. CH + O 2 CO 2 + H 2 O 2C 4 H 10 (g) + 13O 2 (g) 8CO 2 (g) + 10H 2 O (g)
Combustion Many times in a combustion reaction, heat energy is given off. In chemical terms this is called an exothermic reaction. Thermochemistry is field of chemistry which studies the transfer of heat in a reaction. The thermodynamic equation representing this exothermic reaction is: 2C 4 H 10 (g) + 13O 2 (g) 8CO 2 (g) + 10H 2 O(g) + heat (in Joules)
Examples C 4 H 10 + O 2 (assume complete) C 4 H 10 + O 2 (incomplete) C 6 H 12 O 6 + O 2 (complete) C 8 H 8 +O 2 (incomplete)
GAS FORMATION REACTIONS A reaction that produces a gas from reactants not in the gaseous state. 2 HCl (aq) + ZnS (s) ZnCl 2 (aq) + H 2 S (g) Zn (s) + 2 HCl (aq) ZnCl 2 (aq) + H 2 (g) Many gas formation reactions involve two steps, first the double displacement reaction then the decomposition reaction of an unstable substance. Na 2 CO 3 + 2HCl 2 NaCl + H 2 CO 3 H 2 CO 3 CO 2 + H 2 O Besides carbonic acid (H 2 CO 3 ), sulfurous acid (H 2 SO 3 ) also decomposes into SO 2 and water.
COMMON GAS FORMATION REACTIONS YOU SHOULD REMEMBER NH 4 OH NH 3 (g) + H 2 O (l) H 2 CO 3 CO 2 (g) + H 2 O (l) H 2 SO 3 SO 2 (g) + H 2 O (l)
Remember an equation... Describes a reaction Must be balanced in order to follow the Law of Conservation of Mass Can only be balanced by changing the coefficients. Has special symbols to indicate physical state, and if a catalyst or energy is required.
Table 8-3, p. 223
Examples H 2 + O 2 H 2 O Zn + H 2 SO 4 HgO KBr +Cl 2 AgNO 3 + NaCl Mg(OH) 2 + H 2 SO 3