1. Reactions Chapter 8

2. Chemical Reaction Equations A reaction equation must… A reaction equation must… Represent all known facts Represent all known facts Contain correct formulas for reactants and products Contain correct formulas for reactants and products Follow the law of conservation of mass. Follow the law of conservation of mass.

3. Reactants/Products Reactants are the substances present when the reaction starts. Reactants are the substances present when the reaction starts. Products are the substances formed after the reaction takes place. Products are the substances formed after the reaction takes place.

4. Writing Equations Given a word equation you can write a formula equation. Given a word equation you can write a formula equation. This is done by… This is done by… Determining the reactants and products Determining the reactants and products Writing the correct formula for them Writing the correct formula for them Balancing the reaction. Balancing the reaction.

5. Equation Symbols An arrow is used in a formula equation to represent the change from reactants to products. Arrows always point to the products. An arrow is used in a formula equation to represent the change from reactants to products. Arrows always point to the products. Any conditions under which the reaction takes place are written above the arrow. Any conditions under which the reaction takes place are written above the arrow. A reversible reaction that can proceed in both directions is shown using a double arrows. A reversible reaction that can proceed in both directions is shown using a double arrows. The phases of the products can be shown in parenthesis as a subscript after the substance. Common phases are (s) solid, (l) liquid, (g) gas, and (aq) aqueous. The phases of the products can be shown in parenthesis as a subscript after the substance. Common phases are (s) solid, (l) liquid, (g) gas, and (aq) aqueous.

6. Types of Reactions There are many ways to classify chemical reactions. There are many ways to classify chemical reactions. One way breaks the reactions down into five basic types: One way breaks the reactions down into five basic types: Synthesis Synthesis Decomposition Decomposition Single displacement Single displacement Double displacement Double displacement Combustion Combustion

7. Synthesis In a synthesis reaction, two or more substances combine to form a new compound. In a synthesis reaction, two or more substances combine to form a new compound. A + X  AX A + X  AX

8. Iron metal reacts with oxygen to form iron III oxide (rust). 4Fe + 3O 2 --> 2Fe 2 O 3 The copper Statue of Liberty reacting with oxygen to form the green copper oxide. 2Cu + O 2 --> 2CuO Sodium metal reacts with chlorine gas to form sodium chloride (table salt). 2Na + Cl 2 --> 2NaCl

9. Decomposition In a decomposition reaction, a single compound undergoes a reaction that produces two or more simpler substances. In a decomposition reaction, a single compound undergoes a reaction that produces two or more simpler substances. AX  A + X AX  A + X

10. Carbonic acid decomposes to form water and carbon dioxide. H 2 CO 3 --> H 2 O + CO 2

11. Single Displacement In a single displacement reaction, one lone cation replaces a cation within a compound. In a single displacement reaction, one lone cation replaces a cation within a compound. A + BX  B + AX A + BX  B + AX

12. Copper wire reacts with silver nitrate solution to form silver and copper nitrate solution Cu + 2AgNO 3 --> Cu(NO 3 ) 2 + 2Ag 2Na + 2HOH --> 2NaOH + H 2 *Can form precipitates

13. Activity Series Activity Series To determine whether a single cation has the ability to replace another in a compound depends on the activity series. To determine whether a single cation has the ability to replace another in a compound depends on the activity series. This shows the ease with which the elements undergo change in a reaction. This shows the ease with which the elements undergo change in a reaction. An element can replace any element that falls below it on the activity series. An element can replace any element that falls below it on the activity series. If the element it is trying to replace is above it on the chart, it will not be able to replace it and no reaction will occur. If the element it is trying to replace is above it on the chart, it will not be able to replace it and no reaction will occur.

14. Double Displacement In a double displacement reaction, the cations of two compounds exchange places to form two new compounds. In a double displacement reaction, the cations of two compounds exchange places to form two new compounds. AX + BY  AY + BX AX + BY  AY + BX

15. Magnesium carbonate (an antacid) reacts with hydrochloric acid (found in the stomach) to form magnesium chloride and carbonic acid MgCO 3 + 2HCl --> MgCl 2 + H 2 CO 3 *Can form precipitates

16. Combustion In a combustion reaction, a substance combines with oxygen gas to produce a large amount of energy in the form of heat and light. In a combustion reaction, a substance combines with oxygen gas to produce a large amount of energy in the form of heat and light. Hydrocarbons burn completely in oxygen Hydrocarbons burn completely in oxygen to produce carbon dioxide and water vapor.

17. Predicting Products Given the reactants and the type of reaction, the products of the reaction can be predicted. Given the reactants and the type of reaction, the products of the reaction can be predicted. To do so, the elements must rearrange in the appropriate way and the correct formulas for the new compounds must be written. To do so, the elements must rearrange in the appropriate way and the correct formulas for the new compounds must be written.

19. Balancing To balance you must begin by counting the number of atoms of each element present on the reactant side and product side. To balance you must begin by counting the number of atoms of each element present on the reactant side and product side. Coefficients must be added that balance the number of atoms of the element. Coefficients must be added that balance the number of atoms of the element. Coefficients not only change the one element by also any other element within the compound. Coefficients not only change the one element by also any other element within the compound.

21. Balancing Hints Write a list of the elements below the reaction with the number that exist. Write a list of the elements below the reaction with the number that exist. Cross out these numbers and change them accordingly as you go. Cross out these numbers and change them accordingly as you go. Start with the elements that only appear once on both sides of the equation. Start with the elements that only appear once on both sides of the equation. Polyatomic ions are balanced as single units, not as separate elements. Polyatomic ions are balanced as single units, not as separate elements. Save hydrogen and oxygen to be balanced last. Save hydrogen and oxygen to be balanced last. Count atoms one last time to ensure everything is equal. Count atoms one last time to ensure everything is equal.