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1 Chapter 7 Chemical Reactions. 2 All chemical reactions l have two parts l Reactants - the substances you start with l Products- the substances you end.

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Presentation on theme: "1 Chapter 7 Chemical Reactions. 2 All chemical reactions l have two parts l Reactants - the substances you start with l Products- the substances you end."— Presentation transcript:

1 1 Chapter 7 Chemical Reactions

2 2 All chemical reactions l have two parts l Reactants - the substances you start with l Products- the substances you end up with l The reactants turn into the products. Reactants Products

3 3 In a chemical reaction l The way atoms are joined is changed l Atoms arent created of destroyed. l Can be described several ways l In a sentence l Copper reacts with chlorine to form copper (II) chloride. l In a word equation Copper + chlorine copper (II) chloride

4 4 Symbols used in equations l the arrow separates the reactants from the products l Read reacts to form l The plus sign = and l (s) –solid, (g) –gas, (l) –liquid aq) after the formula l (aq)- dissolved in water, an aqueous solution.

5 5 Convert these to equations l Solid iron (III) sulfide reacts with gaseous hydrogen chloride to form iron (II) chloride and hydrogen sulfide gas. l Nitric acid dissolved in water reacts with solid sodium carbonate to form liquid water and carbon dioxide gas and sodium nitrate dissolved in water.

6 6 The other way Fe(g) + O 2 (g) Fe 2 O 3 (s) Cu(s) + AgNO 3 (aq) Ag(s) + Cu(NO 3 ) 2 (aq)

7 7 Balanced Equation l Atoms cant be created or destroyed l All the atoms we start with we must end up with l A balanced equation has the same number of each element on both sides of the equation.

8 8 C + O 2 CO 2 l This equation is already balanced l What if it isnt already? C + O O C O O

9 9 C + O 2 CO l We need one more oxygen in the products. l Cant change the formula, because it describes what is C + O C O O

10 10 l Must be used to make another CO l But where did the other C come from? C + O C O O O C

11 11 l Must have started with two C 2 C + O 2 2 CO C + O C O O O C C

12 12 Rules for balancing 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) Check to make sure it is balanced.

13 13 Never l Change a subscript to balance an equation. l If you change the formula you are describing a different reaction. l H 2 O is a different compound than H 2 O 2 l Never put a coefficient in the middle of a formula l 2 NaCl is okay, Na2Cl is not.

14 14 Example H 2 +H2OH2OO2O2 Make a table to keep track of where you are at

15 15 Example H 2 +H2OH2OO2O2 Need twice as much O in the product RP H O

16 16 Example H 2 +H2OH2OO2O2 Changes the O RP H O

17 17 Example H 2 +H2OH2OO2O2 Also changes the H RP H O

18 18 Example H 2 +H2OH2OO2O2 Need twice as much H in the reactant RP H O

19 19 Example H 2 +H2OH2OO2O2 Recount RP H O

20 20 Example H 2 +H2OH2OO2O2 The equation is balanced, has the same number of each kind of atom on both sides RP H O

21 21 Example H 2 +H2OH2OO2O2 This is the answer RP H O Not this

22 22 Examples CH 4 + O 2 CO 2 + H 2 O AgNO 3 + Cu Cu(NO 3 ) 2 + Ag Mg + N 2 Mg 3 N 2 P + O 2 P 4 O 10 Na + H 2 O H 2 + NaOH

23 23 Techniques l If an atom appears more than once on a side, balance it last. l If you fix everything except one element, and it is even on one side and odd on the other, double the first number, then move on from there. l C 4 H 10 + O 2 CO 2 + H 2 O

24 24 Types of Reactions l There are millions of reactions. l Cant remember them all l Fall into several categories. l We will learn 5 types. l Will be able to predict the products. l For some we will be able to predict whether they will happen at all. l Will recognize them by the reactants

25 25 #1 Combination Reactions l Combine - put together l 2 elements, or compounds combine to make one compound. Ca +O 2 CaO SO 3 + H 2 O H 2 SO 4 l We can predict the products if they are two elements. Mg + N 2

26 26 Write and balance Ca + Cl 2 Fe + O 2 iron (II) oxide Al + O 2 l Remember that the first step is to write the formula l Then balance

27 27 #2 Decomposition Reactions l decompose = fall apart l one reactant falls apart into two or more elements or compounds. l NaCl Na + Cl 2 l CaCO 3 CaO + CO 2

28 28 #2 Decomposition Reactions l Can predict the products if it is a binary compound l Made up of only two elements l Falls apart into its elements lH2OlH2O l HgO

29 29 #2 Decomposition Reactions l If the compound has more than two elements you must be given one of the products l The other product will be from the missing pieces l NiCO 3 H 2 CO 3 (aq)

30 30 #3 Single Replacement l One element replaces another l Reactants must be an element and a compound. l Products will be a different element and a different compound. Na + KCl K + NaCl F 2 + LiCl LiF + Cl 2

31 31 #3 Single Replacement l Exceptions weve missed along the way l Zinc, Zn, always forms a +2 ion doesnt need parenthesis l ZnCl 2 is zinc chloride l Silver, Ag, always forms a +1 ion l AgCl is silver chloride

32 32 #3 Single Replacement l Metals replace metals (and hydrogen) K + AlN Zn + HCl l Think of water as HOH l Metals replace one of the H, combine with hydroxide. Na + HOH

33 33 #3 Single Replacement l We can tell whether a reaction will happen l Some are more active than other l More active replaces less active l There is a list on page 155 l Higher on the list replaces lower. l If the element by itself is higher, it happens, in lower it doesnt

34 34 #3 Single Replacement l Note the * l H can be replaced in acids by everything higher l Only the first 5 (Li - Na) react with water. Fe + CuSO 4 Pb + KCl Al + HCl

35 35 #3 Single Replacement l What does it mean that Au And Ag are on the bottom of the list? l Nonmetals can replace other nonmetals l Limited to F 2, Cl 2, Br 2, I 2 l The order of activity is that on the table. l Higher replaces lower. F 2 + HCl Br 2 + KCl

36 36 #4 Double Replacement l Two things replace each other. l Reactants must be two ionic compounds or acids. l Usually in aqueous solution NaOH + FeCl 3 l The positive ions change place. NaOH + FeCl 3 Fe +3 OH - + Na +1 Cl -1 NaOH + FeCl 3 Fe(OH) 3 + NaCl

37 37 #4 Double Replacement l Will only happen if one of the products –doesnt dissolve in water and forms a solid –or is a gas that bubbles out. –or is a covalent compound usually water.

38 38 How to recognize which type l Look at the reactants l E + E Combination l CDecomposition l E + CSingle replacement l C + CDouble replacement

39 39 Last Type l Combustion l A compound composed of only C H and maybe O is reacted with oxygen l If the combustion is complete, the products will be CO 2 and H 2 O. l If the combustion is incomplete, the products will be CO and H 2 O.

40 40 An equation l Describes a reaction l Must be balanced because to follow Law of Conservation of Energy l Can only be balanced by changing the coefficients. l Has special symbols to indicate state, and if catalyst or energy is required.

41 41 Reactions l Come in 5 types. l Can tell what type they are by the reactants. l Single Replacement happens based on the activity series using activity series. l Double Replacement happens if the product is a solid, water, or a gas.

42 42 The Process l Determine the type by looking at the reactants. l Put the pieces next to each other l Use charges to write the formulas l Use coefficients to balance the equation. Homework

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