This document discusses chemical reactions and equations. It defines chemical reactions and how to identify when one has occurred. It explains the three types of chemical equations - word, skeleton, and chemical - and how to balance chemical equations. The five types of chemical reactions are described: synthesis, combustion, decomposition, single replacement, and double replacement. Aqueous solutions and writing ionic equations are also covered, including the difference between complete ionic and net ionic equations.

1. Chapter 10 Chemical Reactions

2. Reactions and Equations 10.1 A chemical reaction is when the atoms of one or more substances are rearranged to form different substances How to tell if a chemical reaction has taken place Is there evidence? (Temperature change, color change, odor, gas bubbles, general appearance) Equations are used to represent chemical reactions Show reactants: the starting substances Show Products: resulting or ending substances Do not show numerical values so arrow is used instead of an equals sign

3. Types of Equations Three types of equations Word Skeleton Chemical Word equations Used to indicate the reactants and products of chemical reactions Uses the actual names of the substances involved Setup: Reactant 1 + Reactant 2  Product 1 Ex: Iron(s) + Chlorine(g)  Iron(III) Chloride(s)

4. Skeleton Equations Uses chemical formulas to represent the substances unlike the word equation Chemical formulas take the place of the words Iron(s) + Chlorine(g)  Iron(III) Chloride(s) would become: Fe(s) + Cl2(g)  Fe Cl3(S) Chemical Equations Uses chemical formulas like the skeleton equation Shows matter is conserved during a reaction (Law of Conservation of Mass) Chemical eqation: Uses identities and relative amounts of the substances involved in a chemical reaction Everything is balanced in a chemical equation Balancing Chemical Equations Finding the correct coefficients for chemical formulas in the skeleton equation is very important Coefficient is usually a whole number and 1 is understood

5. Steps to Balance a Chemical Equation Write the skeleton equation Count the atoms of elements in the reactants Count the atoms of elements in the products Place or change the coefficients to make both sides of the equation equal (DO NOT CHANGE SUBSCRIPTS) Write the coefficient(s) in the lowest ratio possible Check your work Ex: H2(g) + O2(g)  H2O(g) Balanced: 2H2 + O2(g)  2H2O(g) Practice website www.chem.vt.edu/RVGS/ACT/notes/scripts/bal_eq1.html

6. Examples Hydrogen gas and bromine gas form gaseous hydrogen bromide H2 + Br2  HBr Balanced: H2 + Br2  2HBr Balancing hints: When odd numbers of oxygen needed use a fraction, then multiply by two Al + O2  Al2O3 2Al + O2  Al2O3 need three oxygens (odd number) 2Al + 1.5O2  Al2O3 fractions/ decimals cannot be left as coefficients 4Al + 3O2  2Al2O3 Whole equation multiplied by two to get rid of decimals or fractions Try the following: C2H6 + O2 CO2 + H2O

7. Examples/ hints cont. When balancing with polyatomic ions found both in the reactants and products, replace the ions by a variable. Fe2O3 + H2SO4  Fe2 (SO4)3+ H2O Fe2O3 + H2X Fe2 (X)3+ H2O Fe2O3 + 3H2X Fe2 (X)3+ 3H2O Fe2O3 + 3H2SO4  Fe2 (SO4)3+ 3H2O Balancing with elements that appear more than twice in different formulas (leave for last!) CO2 + H2  CH4 + H2O hydrogen appears more than twice CO2 + H2  CH4 + 2H2O balance C and O CO2 + 4H2  CH4 + 2H2O

8. Classifying Chemical Reactions 10.2 There are five types of chemical reactions. Synthesis Combustion Decomposition Single-Replacement Double-Replacement Synthesis Reaction Chemical reaction in which two or more substances combine to form one single product. A + B  AB Ex: 2Na(s) + Cl2(g)  2NaCl(s) 4Fe(s) + 3O2(g)  2Fe2O3 (s)

9. Combustion Reaction Oxygen combined with a substance releasing energy in the form of light and heat Many combustion reactions are also synthesis reactions Ex: 2H2(g) + O2  2H2O(g) Decomposition reactions Only one compound Breaks down into 2 or more compounds or elements Setup: AB A + B Often requires an energy source (i.e. heat, light, electricity) Ex: NH4NO3(s)  N2O(g) + 2H2O(g) The above reaction occurs when the reactant is heated Replacement Reactions Unlike the other reactions, replacement reactions involve the replacement of an element in a a compound 2 kinds of replacement reactions: Single Double

10. Single Replacement reactions When atoms of one element replace the atoms of another element in a compound Setup: A+ BX  AX + B Whether or not a metal will replace another metal or any other substance depends on the reactivity it has Double Replacement reactions Invovles the exchange of ions between 2 compounds Setup: AX + BY  AY + BX If a solid is produced during the reaction it is called a precipitate

11. Practice – Classify the following equations Cl2 + 2KBr  KCl + Br2 2Ag2O  4Ag + O2 2Na + Cl2  2NaCl PbCl2 + Li2SO4  PbSO4 + 2LiCl

13. Solvent- The water in the solution

14. Solute- The compound dissolved in the water

15. Precipitate- Solid formed in a chemical reaction

16. Spectator ion- Ions that do not participate

17. Complete ionic equation- Shows all particles as they really exist

19. Writing Ionic Equations Ionic and chemical equations differ in that substances that are ions in the solution are written as ions in the equation. To write an ionic equation you must show the reactants and the product as ions. A complete ionic equation shows all of the particles in the solution as they realistically exist. A net ionic equation is a simplified version of the complete ionic equation. It only shows particles that participate in the reaction. To write a net ionic equation from a complete ionic equation cross out all spectators.

20. Ionic equations AgNO3(aq) + NaCl(aq)  AgCl(s) + NaNO3(aq) What type of reaction is this? A complete ionic equation shows dissolved ionic compounds as their free ions. Ag+(aq) + NO3-(aq) + Na+(aq) + Cl-(aq)  AgCl(s) + Na+(aq) + NO3-(aq)

21. Ionic Equations Ag+(aq) + NO3-(aq) + Na+(aq) + Cl-(aq)  AgCl(s) + Na+(aq) + NO3-(aq) Ions that are not directly involved in a reaction are called spectator ions. Rewriting the equation, leaving out the spectator ions, gives us the net ionic equation… Ag+(aq) + Cl-(aq)  AgCl(s)

22. Ionic Equations You also have to make sure that the net charge is balanced. For example… Pb(s) + 2Cl-(aq) PbCl2(s)

23. Examples HCl(aq) + ZnS(aq)  H2S(g) + ZnCl2(aq) Cl2(g) + NaBr(aq)  Br2(l) + NaCl(aq)