A chemical change: any change in which a new substance is formed.

Transcription

1 Chemical Reactions

2 A chemical change: any change in which a new substance is formed. Evidence of a Chemical Change: Release of energy as heat Release of energy as light Change in color Formation of a gas Change in odor

3 Types of Reactions There are SIX types of chemical reactions we will talk about (FOCUS ON THE first 5!) 1. Synthesis reactions (S) 2. Decomposition reactions (D) 3. Single replacement/ displacement reactions (SR) 4. Double replacement/displacement reactions (DR) 5. Combustion reactions (C ) 6. Neutralization (Acid base) You need to be able to identify the type of reaction and predict the product(s)

4 1. Synthesis: A + B AB 2. Decomposition: AB A + B 3. Single Replacement/displacement: A + BC AC + B 4. Double Replacement/ displacement: AB + CD AD + CB 5. Combustion: AB + oxygen CO 2 + H 2 O 6. Neutralization: Acid(H) + Base(OH) salt + H(OH)

5 Steps to Writing Reactions 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! (BrINClHOF) For example, Oxygen is O 2 (NOTE: oxygen is not an element anymore, it s a compound!)

6 The law of conservation of mass French chemist Antoine Lavoisier In 1774 found that if nothing is allowed to enter or leave a reaction vessel, the total mass is the same after as it was before Atoms are not created or destroyed in chemical equations they are simply rearranged so equations must balance!

7 Balanced chemical equations 1) Tell us the reactants and products in a reaction, and the relative amounts involved. 2) Equation is balanced using coefficients so that there are equal numbers of each type of atom on both sides the arrow. CH 4 (g) + 2O 2 (g) CO 2 (g) + 2H 2 0 (l) State symbols State (phase) symbols are included in chemical equations to show the physical state of the reactants and products (g) Gas (l)liquid (s)solid (aq) aqueous solution

8 Steps for balancing equations The reaction between solid Ca and H 2 0 produces calcium hydroxide in solutions and hydrogen gas. STEP 1 Determine what the reactants (starting substances) and products (resulting substances)are: calcium(s) + water(l) calcium hydroxide(aq) + hydrogen(g) STEP 2 Write formulas for the substances and state symbols Ca (s) + H 2 0 (l) Ca (OH) 2 (aq) + H 2 (g) STEP 3 Use coefficients to balance the equation so there are the same number of each kind of atom on both sides of the arrow Ca (s) + 2H 2 0 (l) Ca (OH) 2 (aq) + H 2 (g) Equations can only be balanced by putting numbers (coefficients) in front of the formulas. You cannot balance them by altering the formulas themselves because you would then create different substances.

9 Tips for balancing: Start by balancing the substance with the largest number of elements. If O 2 (or any BrINClHOF) is in the equation, save it for last. If a polyatomic ion stays the same on both sides of the arrow, count it as a unit when counting atoms. When finished, make sure you have the smallest whole number ratio of coefficients.

10 Make a RIP chart C 6 H (aq) + 6 O 2 (g) 6 CO 2 (g) + 6 H 2 O (l) 6 C 12 H 18 O R (reactants) I P (Products) 6 C 12 H 18 O (You will Rest In Peace in chemistry if you do this!)

11 Make a RIP chart Pb(NO 3 ) 2 (aq) + KI (aq) KNO 3 (aq) +PbI 2 R (reactants) I P (Products) (You will Rest In Peace in chemistry if you do this!)

12 1. Synthesis reactions Synthesis reactions occur when two substances (generally elements) combine and form a compound. (Sometimes these are called combination or addition reactions.) reactant + reactant 1 product Basically: A + B AB Example: 2H 2 + O 2 2H 2 O Example: C + O 2 CO 2

13 2. Decomposition Reactions 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

14 3. Single Replacement Reactions Single Replacement Reactions occur when one element replaces another in a compound. A metal can replace a metal (+) OR a nonmetal can replace a nonmetal (-). element + compound element + compound 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!) NOTE: When H 2 O splits into ions, it splits into H + and OH - (not H+ and O -2!!)

15 1. When A is a metal: aluminum foil in a solution of copper(ii) chloride produces solid copper and aluminum chloride. Al + CuCl 2 Cu + AlCl 3 BALANCE: 2Al + 3CuCl 2 3Cu + 2AlCl 3 2. When A is a non-metal: When fluorine is bubbled through a sodium iodide solution, iodine and sodium fluoride are produced. F 2 + NaI I 2 + NaF BALANCE: F 2 + 2NaI I 2 + 2NaF

16 4. Double Replacement Reactions Double Replacement Reactions occur when a metal replaces a metal in a compound and a nonmetal replaces a nonmetal in a compound Compound + compound compound+ compound AB + CD AD + CB

17 Types: Double displacement Example: MgO + CaS Mg + Ca Mg + Ca O S S O General: AB + CD AD + CB

18 5. Combustion Reactions Combustion reactions occur when a hydrocarbon reacts with oxygen gas. This 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)

19 Combustion Reactions Edgar Allen Poe s drooping eyes and mouth are potential signs of CO poisoning.

20 Combustion reactions occur when a compound or element react with oxygen to release energy and produce an oxide. Also sometimes referred to as hydrocarbon combustion. C X H Y + O 2 CO 2 + H 2 O where X and Y represent integers See page 264 (c) McGraw Hill Ryerson 2007

21 Neutralization reactions occur when an acid (most compounds starting with H) and a base (most compounds ending in OH) react to form a salt and water. Neutralization reactions are a type of double replacement (DR). Acid + base salt + water HX + MOH MX + H 2 O where X and M are elements See page 263 (c) McGraw Hill Ryerson 2007

22 1. Sulfuric acid is used to neutralize calcium hydroxide H 2 SO 4 + Ca(OH) 2 CaSO 4 + 2H 2 O 2. Phosphoric acid helps to neutralize the compounds that cause rust, such as iron(ii) hydroxide 2H 3 PO 4 + 3Fe(OH) 2 Fe 3 (PO 4 ) 2 + 6H 2 O (c) McGraw Hill Ryerson 2007

23 Some 2 special products If H 2 CO 3 is formed, it immediately decomposes into H 2 O and CO 2 If H 2 SO 3 is formed, it immediately decomposes into H 2 O and SO 2

24 Class of reaction Reactants Possible products General equation Example Synthesis 2 or more substances one new compound A + B AB 2 Mg + O 2 2 MgO Decomposition One compound Two or more substance AB A + B 2 H 2 O 2 H 2 + O 2 Single Replacement An element and a compound A different element & compound A+BC B+AC or Zn + 2HCl ZnCl 2 + H 2 A+BC C+BA Double Replacement Two compounds (exchange parts) Two different compounds AB + CD AD + CB 2KI+Pb(NO 3 ) 2 PbI 2 + 2KNO 3 Combustion Substance (usually a fuel w/ C & H) + oxygen oxides, light, heat Fuel + O 2 CO 2 + H 2 O CH 3 OH + O 2 CO 2 + H 2 O Acid/Base or Neutralization (a type of Double Replacement) Acid and Base Salt and water HX + MOH salt + H 2 O HCl + NaOH NaCl + H 2 O

25 (c) McGraw Hill Ryerson 2007

26 Reactions in Aqueous Solutions Molecular Equations: shows complete formulas for reactants and products Does not show what happens on the molecular level Total (or Complete) Ionic Equations: All substances that are strong electrolytes (are soluble and dissociate) are written as their ions. Some ions participate in the reaction Some ions do NOT participate in the reaction-called spectator ions. Net Ionic Equations (NIE): show only the ions that participate in the reaction

27 Total Ionic Equations Once you write the molecular equation (synthesis, decomposition, etc.), you should check for reactants and products that are soluble or insoluble. We usually assume the reaction is in water We can use a solubility table to tell us what compounds dissolve in water. If the compound is soluble (does dissolve in water), then splits the compound into its component ions If the compound is insoluble (does NOT dissolve in water), then it remains as a compound

28 Use the solubility rules See periodic table!! Learn how to read and apply the rules based on your periodic table

29 Total Ionic Equations Molecular Equation: K 2 CrO 4(aq) + Pb(NO 3 ) 2(aq) PbCrO 4 (S) + 2KNO 3(aq) Soluble Soluble Insoluble Soluble Total Ionic Equation: 2 K + (aq)+ CrO 4 2- (aq) + Pb 2+ (aq)+ 2 NO 3 - (aq) PbCrO 4 (s) + 2 K + (aq)+ 2 NO 3 - (aq)

30 Net Ionic Equations These are the same as total ionic equations, but you should cancel out ions that appear on BOTH sides of the equation Total Ionic Equation: 2 K + (aq)+ CrO 4 2- (aq)+ Pb 2+ (aq)+ 2 NO 3 - (aq)+ PbCrO 4 (s) + 2 K + (aq)+ 2 NO 3 - (aq) (Spectator ions) Net Ionic Equation: CrO Pb +2 PbCrO 4 (s)

31 Net Ionic Equations Try this one! Write the molecular, total ionic, and net ionic equations for this reaction: silver nitrate reacts with lead (II) chloride in hot water. Molecular: Total Ionic: Net Ionic:

32 Net Ionic Equations Try this one! Write the molecular, total ionic, and net ionic equations for this reaction: silver nitrate reacts with lead (II) chloride in hot water. Molecular: AgNO 3 (aq)+ PbCl 2 (aq) 2 AgNO 3 (aq) + PbCl 2 (aq) 2 AgCl (s) + Pb(NO 3 ) 2 (aq) Total Ionic: 2 Ag NO Pb Cl - 2 AgCl (s) + Pb NO 3 - Net Ionic: Ag + (aq) + Cl - (aq) AgCl (s)