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06/13/001 Types of Chemical Reactions And Balancing Chemical Equations.

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Presentation on theme: "06/13/001 Types of Chemical Reactions And Balancing Chemical Equations."— Presentation transcript:

1 06/13/001 Types of Chemical Reactions And Balancing Chemical Equations

2 06/13/002 IN A CHEMICAL REACTION, THE SUBSTANCES INVOLVED IN THE REACTION GO THROUGH A CHEMICAL CHANGE. Ex. 2H 2 (g) + O 2 (g) > 2H 2 O (l) CHEMICAL REACTIONS

3 06/13/003 2H 2 (g) + O 2 (g) > 2H 2 O (l) 2H 2 (g) + O 2 (g) > 2H 2 O (l) u This reaction is interpreted as follows: u 2 moles (or molecules) of hydrogen gas react with 1 mole (or molecule) of oxygen gas to form 2 moles (or molecules) of liquid water.

4 06/13/004 A chemical reaction consists of the following symbols: u Reactants are on the left side of the arrow. u Products are on the right side of the arrow. u The arrow means “yields” much like the equal sign means “equals”. u (g), (s), (l), (aq) ; these represent the physical state of each substance. Gas, solid, liquid, or aqueous, respectively.

5 06/13/005 reaction symbols continued: u A down arrow represents a precipitate formed in the products. u An up arrow represents a gas evolved in the products.  A  means that energy or heat was added to the reaction.

6 06/13/006 Balancing Chemical Equations u The Law of Conservation of Matter states that the mass of the products coming out of a reaction must equal the mass of the reactants going into the reaction. u Simply stated, the number of moles of a substance on the left of the arrow must equal the number of moles of that substance on the right of the arrow.

7 06/13/007 Balancing continued.... u Coefficients are placed in front of elements or compounds in the equation to balance numbers of moles (or molecules) of the substance. u Never use subscripts to balance an equation. Subscripts are ONLY used to write correct chemical formulas. u Balancing is achieved by trial and error.

8 06/13/008 Ex. BiCl 3 + H 2 S > Bi 2 S 3 + HCl u Notice that there is one Bi on the left and two Bi on the right. There are 3 Cl on the left and one Cl on the right. There are 2 H on the left and one H on the right. There is one S on the left and 3 S on the right. u continued.....

9 06/13/009 Balancing continued BiCl 3 + H 2 S > Bi 2 S 3 + HCl u If a coefficient of 2 is placed in front of BiCl 3, the Bi is then balanced but now there are 6 Cl on the left (2BiCl 3 ) because the coefficient is multiplied by all elements in the compound. u Fix this by placing a 6 in front of the HCl on the right. Now we have 6 H on the right. u Place a 3 in front of H 2 S on the left. Fini !

10 06/13/0010 The balanced chemical equation.. u 2 BiCl H 2 S --->Bi 2 S 3 +6 HCl 2Bi, 6 Cl, 6 H, 3S ---> 2Bi, 6Cl, 6H, 3S Reactants =Products

11 06/13/0011 Ex.2 Al + F > AlF 3 u Hint ; when you see two different subscripts on the same element, find the least common multiple. F has a 2 on the left and a 3 on the right. 2 and 3 both fit into 6 so.... u 2Al + 3F > 2AlF 3 u 2Al, 6 F, ----> 2Al, 6 F Reactants = Products

12 06/13/0012 Ex.3 Ca(OH) 2 + HC 2 H 3 O 2 ---> Ca(C 2 H 3 O 2 ) 2 + H 2 O u The polyatomic ions in this equation are hydroxide (2 on the left and one on the right) and acetate (one on the left and 2 on the right). u Hint ; treat polyatomic ions as units that do not separate. This makes them easier to balance. Note that H 2 O is the same as HOH u Ca(OH) 2 + 2HC 2 H 3 O 2 ---> Ca(C 2 H 3 O 2 ) 2 +2HOH

13 06/13/0013 Types of Chemical Reactions u Combination Reaction (also know as a synthesis reaction)- two or more elements and/or compounds combine to form one product. u Decomposition Reaction - A compound decomposes into two or more of its substituent elements and/or compounds. u continued...

14 06/13/0014 Types of Chemical Reactions continued.. u Double Replacement Reactions - Where the positive ions in two compounds exchange places. There are several types of double replacement reactions. u Single Replacement Reactions (oxidation / reduction reactions)- An element and a compound react. In so doing, either the metals or the non metals exchange places.

15 06/13/0015 Reaction Types continued... u Combustion Reactions - The reaction of a substance with Oxygen. u Acid / Base Reactions - An acid reacts with a base to form a salt and water. This is a type of double replacement reaction.

16 06/13/0016 Ex.1 Combination Reaction u In this reaction, solid potassium combines with chlorine gas to form solid potassium chloride. 2K (s) + Cl 2(g) ---> 2KCl (s)

17 06/13/0017 Ex.2 Decomposition Reaction u 2 KClO >2 KCl + 3 O 2 u In this reaction, potassium chlorate decomposes into potassium chloride and oxygen gas.

18 06/13/0018 Ex.3 Double Replacement Reaction u In this reaction aqueous silver nitrate reacts with hydrogen sulfide gas to produce a precipitate of solid silver sulfide and aqueous nitric acid. 2AgNO 3 + H 2 S ---->Ag 2 S (s) + 2HNO 3

19 06/13/0019 Double Replacement continued... u An insoluble product must form (that is, a precipitate) u A neutral, molecular product must form (like water) In order for a double replacement reaction to occur, one of the following must be true:

20 06/13/0020 Solubility Rules SolubleExceptions Ammonium salts Group IA some Li + compounds salts Nitrates Halides Ag +, Hg +2, Pb +2 noneAcetatesAg +, Al +3 Sulfates Ba +2, Sr +2, Ca +2, Pb +2, Ag +, Hg +2, Hg +2 none

21 06/13/0021 Ex.4 Single Replacement Reaction (REDOX) u In this reaction, solid zinc replaces aqueous lead in the lead nitrate, to form aqueous zinc nitrate. Solid lead is displaced. Zn must be more reactive than Pb in order to replace it. continued... Zn (s) + Pb(NO 3 ) > Zn(NO 3 ) 2 + Pb (s)

22 06/13/0022 continued... In order for one substance to replace another in a single replacement reaction, that substance must be more reactive than the one that it will replace. We use a table called the activity series to determine if one substance is more active than another. Ag, Cu, H, Pb, Ni, Zn, Al, Mg, Na, Ca, Ba, K, Li increasing activity >

23 06/13/0023 Single Replacement / Redox continued... Zn (s) + Pb(NO 3 ) > Zn(NO 3 ) 2 + Pb (s) An important feature of this type of reaction is that the charges (oxidation states ) on some of the elements change. Zn went from having a zero charge to having a +2 charge. Lead went from having a +2 charge to having a zero charge. The number of electrons lost by one substance must equal the number of electrons gained by the other substance.

24 06/13/0024 Single Replacement /Redox continued.... Electrical current is defined as the flow of electrons. In an oxidation /reduction reaction, (Redox), electrons are exchanged from one substance to another, thus a flow of electrons is produced. The substance that gains the electrons is said to be reduced. The substance that loses electrons is said to be oxidized. continued...

25 06/13/0025 continued... Ex. Li (s) + AlCl 3(aq) ----> LiCl (aq) + Al (s) In this reaction: Li is more active than Al so it replaces Al. Li goes from having a zero charge to +1, therefore it is oxidized. (It got more Positive) Al went from a +3 to a zero therefore it was reduced. (It got more negative, gained electrons)

26 06/13/0026 COMBUSTION REACTIONS C 3 H O > 3 CO H 2 O In this reaction a hydrocarbon (that is a compound composed only of carbon and hydrogen) reacts with oxygen to form carbon dioxide and water. When a hydrocarbon is burned in oxygen (that is combustion) the products are always carbon dioxide and water.

27 06/13/0027 Acid / Base Reactions Acid / Base reactions are a special type of double replacement reactions. We must first be able to recognize an acid and a base. We will start with a simple Bronstedt definition for now. An acid gives up a hydrogen in the reaction and the base accepts that hydrogen. A hydrogen is referred to as a proton because it lost its electron and has a +1 charge. continued....

28 06/13/0028 Acid / Base continued... So, we can say that an acid is a proton donar and a base is a proton acceptor. Lets look at an example.... The products of this type of reaction are always a salt (which is simply an ionic compound) and water.

29 06/13/0029 H 3 PO NaOH ----> Na 3 PO 4 + 3HOH continued... Notice that the Na replaced the Hydrogens on the H 3 PO 4. The H 3 PO 4 gave up its hydrogens therefore it is the acid. Also note that the new product was not H 3 OH but instead 3 HOH (or 3 H 2 O). This is because the OH has a -1 charge and a hydrogen without its electron (a proton) has a +1 charge. The correct formula is H +1 OH -1 (written HOH or H 2 O). continued....

30 06/13/0030 H 3 PO 4 + 3NaOH ---> Na 3 PO 4 + 3HOH For now, a simple way to recognize an acid is that it is a compound that has hydrogen as the first atom. A base is a compound composed of a metal hydroxide. continued...

31 06/13/0031 Acids and Bases continued... examples of acids: HCl, H 3 PO 4, H 2 SO 4,H 2 CO 3, HNO 3, HC 2 H 3 O 2 examples of bases: NaOH, Ca(OH) 2, KOH, LiOH,Mg(OH) 2 Al(OH) 3

32 06/13/0032 u balance a chemical equation u define and use the symbols in a chemical equation u Identify and give examples of the different types of chemical reactions u Identify and give examples of acids and bases You should be able to.....


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