Unit 4: Chemical Reactions and Stoichiometry

Unit 4: Chemical Reactions and Stoichiometry

Listed below are the learning objectives that you will be taught. At the conclusion of each lesson, check one of the four boxes to indicate your level of understanding for each individual objective.

AP/IB Chemistry Study Guide

Overview of Chemical Reactions

1. A chemical reaction is defined as a chemical transformation or change that occurs when substances interact and/or chemical bonds are broken to produce a new substance(s) with new properties. Chemical reactions are symbolically represented by a chemical equation.

Coefficients

The physical states of the reactants and products

(g) ? gas (l) ? liquid (s) ? solid (aq) ? aqueous (dissolved in water)

2H2(g) + O2(g) 2H2O(l )

Reactant(s) are the starting materials used to start a chemical reaction. The chemical bonds of the reactant(s) are broken.

Product(s) are the new materials made during the chemical reaction. After chemical bonds have been broken, the "free" atoms rearrange themselves into new chemical structures by creating new bonds.

2. Evidence that a chemical reaction has taken place:

1) The formation of a gas 2) The formation of a solid (Precipitate) 3) Color change 4) The production of heat and light

3. Law of conservation of matter (mass)

The Law of conservation of mass states that during a chemical reaction mass (matter) is not created nor is it destroyed. Atoms are simple rearranged.

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AP/IB Chemistry Study Guide

Molecular, Ionic, Net Ionic Equations

1. How to represent molecular, ionic and net ionic equations Molecular Equation:

Na2CO3(aq) + Ca(NO3)2(aq)

2NaNO3(aq) + CaCO3(s)

Ionic Equation: 2Na+(aq) + CO32-(aq) + Ca2+(aq) + 2NO3-(aq)

2Na+(aq) + 2NO3-(aq) + CaCO3(s)

Net Ionic Equation:

Ca2+(aq) + CO32-(aq)

CaCO3(s)

2. Practice 1) AgNO3(aq) + KCl(aq)

AgCl(s) + KNO3(aq)

2) Mg(NO3)2(aq) + Na2CO3(aq)

MgCO3(s) + NaNO3(aq)

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AP/IB Chemistry Study Guide

Balancing Equations

1. The same numbers of atoms of each element much occur on the reactant and product sides of equation to satisfy the law of conservation of mass. Formulas cannot be changed! Coefficients are placed in front of compounds to change number of specific elements.

2. Steps:

1) List elements in same order on each side 2) Inventory atoms on both sides 3) Decide on coefficients 4) Re-inventory 3. Strategies:

1) If polyatomic ions are intact on each side, list them in the inventory 2) Do elements that are un combined last 3) Even up elements that are diatomic 4) In redox reactions decide who is being oxidized, who is being reduced and then balance the half reactions

4. Practice 1) ____ Na3PO4 + ____ KOH ____ NaOH + ____ K3PO4 2) ____ MgF2 + ____ Li2CO3 ____ MgCO3 + ____ LiF 3) ____ P4 + ____ O2 ____ P2O3 4) ____ RbNO3 + ____ BeF2 ____ Be(NO3)2 + ____ RbF 5) ____ AgNO3 + ____ Cu ____ Cu(NO3)2 + ____ Ag 6) ____ CF4 + ____ Br2 ____ CBr4 + ____ F2 7) ____ HCN + ____ CuSO4 ____ H2SO4 + ____ Cu(CN)2 8) ____ GaF3 + ____ Cs ____ CsF + ____ Ga 9) ____ BaS + ____ PtF2 ____ BaF2 + ____ PtS 10) ____ N2 + ____ H2 ____ NH3 11) ____ NaF + ____ Br2 ____ NaBr + ____ F2 12) ____ Pb(OH)2 + ____ HCl ____ H2O + ____ PbCl2

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AP/IB Chemistry Study Guide

Classifying chemical Reactions

1. Combination or Synthesis Reactions

In this type of reaction, two or more substances combine to produce a single, more-complex substance. The reactants are molecular substances that may be elements, compounds, or both.

Element or Compound + Element or Compound yields compound

A

+

B

AB

a. The burning of hydrogen to form water

2H2(g) + O2(g)

2H2O(l)

b. The burning of carbon monoxide to form carbon dioxide

2CO(g) + O2(g)

2CO2(g)

c. The reaction of calcium oxide and water to form calcium

CaO(s) + H2O(l)

Ca(OH)2(s)

2. Decomposition or Analysis Reactions

In this type of reaction, a single substance is broken down into two or more simpler substances. These simpler substances may be either elements or compounds. Most decomposition reactions are endothermic.

Compound yields two or more elements or compounds

AB

A + B

a. Decomposition of water by an electric current (electrolysis of water).

2H2O(l)

2H2(g) + O2(g)

b. Mercury (II) oxide decomposed by heat

2HgO(s)

2Hg(l) + O2(g)

c. Decomposition of melted ionic solids by electrolysis

2NaCl (l)

2Na(l) + Cl2(g)

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