Chemical Reactions Chapter 11 SC2 Students will relate how the Law of Conservation of Matter is used to determine chemical composition in compounds and chemical reactions. SC2.a. Identify and balance the following types of chemical equations: Synthesis, Decomposition, Single Replacement, Double Replacement, and Combustion SC2.b. Experimentally determine indicators of a chemical reaction specifically precipitation, gas evolution, water production, and changes in energy to the system. 1
Transcript
1
Chemical Reactions Chapter 11
SC2 Students will relate how the Law of Conservation of Matter is used to determine chemical composition in compounds and chemical reactions. SC2.a. Identify and balance the following types of chemical equations: Synthesis, Decomposition, Single Replacement, Double Replacement, and Combustion SC2.b. Experimentally determine indicators of a chemical reaction specifically precipitation, gas evolution, water production, and changes in energy to the system.
2
Writing chemical Equations
• In chemical reactions one or more reactants change into one or more products.
• Chemists use a chemical equations to convey a s much information as possible about what happens in a chemical reaction.
• The reactants are written on the left and the products on the right
• An arrow separates them, read the arrow as yields, gives, or reacts to produce. Reactants → products– example: iron + oxygen → iron (III) oxide
3
Writing chemical Equations
• To write word equations, write the names of the reactants to the left of the arrow separated by plus signs; write the names of the products to the right of the arrow, also separated by plus signs.– Example: hydrogen peroxide decomposes to form water and oxygen
gas– Hydrogen peroxide → water + oxygen
• Chemical equation is a representation of a chemical reaction• Skeleton equation is a chemical equation that does not
indicate the relative amounts of the reactants and products.• Write the formulas of the reactants to the left of the yields
sign (arrow) and the formulas of the products to the right.
4
Writing chemical Equations
• You can indicate the physical states of substances by putting a symbol after each formula: (s) = solid, (l) = liquid, (g) = gas, and (aq) = aqueous solution [a substance dissolved in water]
• Example: Fe (s) + O2 (g) → Fe2O3 (s)• Catalyst is a substance that speeds up the
reaction but is not used up in the reaction.• A catalyst is neither a reactant nor product and is
written above the arrow.
5
6
Types of equations• Word equation
– Carbon Dioxide + Water Glucose + Oxygen
• Skeletal equation– CO2 + H2O C6H12O6 + O2
• Skeletal equation with phases– CO2 (g) + H2O (l) C6H12O6 (s) + O2 (g)
• Balanced equation– 6CO2 + 6H2O C6H12O6 + 6O2
7
Types of Reactions
1. Combination (synthesis) reaction is a chemical change in which two or more substance react for form a SINGLE NEW SUBSTANCE.– Example: 2H2 + O2 → 2H2O– Combination reactions are easy to recognize because they
have two reactants and one product.
2. Decomposition reaction is a chemical change in which ONE SUBSTANCE reacts to form TWO or more new substance.– Example: 2H2O → 2H2 + O2 – Decomposition reactions are easy to recognize because
they have one reactants and two or more products.
8
Types of Reactions3. Single replacement reaction is a chemical change in which
ONE ELEMENT replaces another element in a COMPOUND. – you can recognize a single replacement reaction because both the
reactant and the product have an element and a compound– example: 2K + 2H2O → 2KOH + H2
4. Double-replacement reaction is a chemical change involving an exchange of positive ions between two compounds.– you can recognize a double-replacement reaction because both
the reactants and the products are two compounds– They generally take place in aqueous solutions, and often produce
a precipitate, a gas, or a molecular compound such as water.– FeCl3 + NaOH → Fe(OH)3 + NaCl
9
Types of Reactions5. Neutralization Reaction is a special type of double-
replacement reaction. It is a chemical change where an acid and a base react to form water and a “salt”– Most bases are hydroxides, example: sodium hydroxide {NaOH}– Most acids start with hydrogen, example: hydrochloric acid {HCl},
sulfuric acid {H2SO4}– Salts are defined as ionic compounds– Example: NaOH + HCl → H20 + NaCl
6. Combustion reaction is a chemical change in which an element or a compound reacts with oxygen often producing energy in the form of heat and light. – Often the other reactant is a hydrocarbon or an alcohol and the
products are carbon dioxide and water.– Example: CH4 + O2 → CO2 + H2O
10
Types of Reactions SummaryType of Reactants Reaction Type Products
2 elements ONLY Combination or synthesis
Compound
1 compound ONLY Decomposition Elements
C, H, O and O2 ONLY Combustion CO2 + H2O
ALWAYS
1 element and 1 compound
Single replacement 1 compound and 1 element
2 compound Double Replacement 2 compounds
Acid + Base Neutralization H2O + “salt”
11
Types of Reactions Practicea. Al + CH3OH (CH3O)3Al + H2
b. Ba(NO3)2 + CuSO4 BaSO4 + Cu(NO3)2
c. N2 + H2 NH3
d. H2O (l) + SO3 (s) H2SO4 (aq)
e. KOH + H3PO4 K3PO4 + H2O
f. C4H10 + O2 CO2 + H2O
g. H2O2 H2O + O2
h. KI + Cl2 KCl + I2
i. AgNO3 + KCl AgCl(s) + KNO3
j. NaHCO3(s) Na2CO3(s) + H2O(l) + CO2(g)
a. Single Replacement
b. Double Replacement
c. Combination
d. Combination
e. Neutralization
f. Combustion
g. Decomposition
h. Single Replacement
i. Double replacement
j. Decomposition
12
Balancing chemical Reaction
• The law of conservation of mass states that matter is not created or destroyed it merely changes forms.
• In order to show that mass is conserved the amount of products and reactants MUST equal.
• Once a word equation is turned into chemical formulas it must be balanced.
13
Balancing Chemical Equations
• Coefficients are small whole numbers that are placed in front of the formulas in an equation in order to balance it.
• Balanced equation is a chemical equation in which each side of the reaction has the same number of atoms of each element and mass is conserved.
• To write a balanced chemical equation, first write the skeleton equation. Then use coefficients to balance the equation so that it obeys the law of conservation of mass.– In every balanced chemical equation each side of the
equation has the same number of atoms of each element.
14
Steps to balancing chemical equations
1. Create a T-chart and List the elements in the chemical formulas on each side in the SAME order
2. Count the number of atoms of each element on each side
3. See what elements don’t match in your T-chart4. Add coefficients in front of one substance at a time,• Start by balancing the most complex compound first, • general rule of thumb is to save Hydrogen and Oxygen
until the end to balance.
5. recount number of atoms of each element6. Repeat 3, 4 & 5 until all elements are balanced.
15
Counting Atoms
• In order to balance chemical reactions you MUST first know how to count atoms.
• Subscripts multiply what ever they are beside• If a subscript is beside parentheses it multiplies
everything in the parentheses. • Coefficients multiply everything immediately
H | H– Pick an element to start balancing with, I pick N• Least common multiple between 1 and 2 is 2
– Add 2 in front of product side and recount– N is balanced so now look at H• Least common multiple between 2 and 6 is 6
– Add 3 in front of reactant H and recount– Now both sides are equal so it is a balanced equation
= 2= 2
= 1= 3
2
= 2= 6
3
= 2= 6
18
Balancing Chemical Reactions Practice
• Is a trial and error process
Example 1: NaHCO3 Na2CO3+ H2O + CO2
Na | Na
H | H
C | C
O | O• Count Atoms of each element• Start balancing the most complex item (reactant)
Na = 1 | Na = 2 H = 1 | H = 2 C = 1 | C = 1+1 =2 O = 3 | O = 3 + 1 + 2 = 6
Na = 2 | Na = 2 H = 2 | H = 2 C = 2 | C = 1+1 =2 O = 6 | O = 3 + 1 + 2 = 6
2
19
Balancing Chemical Reactions Practice
• Is a trial and error process
Example 1: C4H10 + O2 CO2+ H2O
C | C
H | H
O | O• Start balancing the most complex item (reactant)• Leave H and O until the end– Have to use whole number and currently have no whole
number… trick: Double all current coefficients and recount.It is Now Balanced
C = 4 | C = 1 H = 10 | H = 2
O = 2 | O = 2 +1 = 3
4
C = 4 | C = 4 H = 10 | H = 2
O = 2 | O = 8 +1 = 9
5
C = 4 | C = 4 H = 10 | H = 10
O = 2 | O = 8 +5 = 13
1082
C = 8 | C = 8 H = 20 | H = 20
O = 2 | O = 16 +10 = 26
13
C = 8 | C = 8 H = 20 | H = 20
O = 26 | O = 16 +10 = 26
20
Balancing Reaction Practice – Polyatomic• Balancing reactions with polyatomics can be a bit complicated
but if the polyatomic is the same on BOTH sides of reaction you can treat it like a special element.
FeBr3 + Ba(OH)2 → BaBr2 + Fe(OH)3
• When counting Atoms put a box around JUST the polyatomic• Count like normal and balance using these count• Br is 1st thing that don’t balance, common multiple between 2
and 3 is 6
Fe 1 | Fe 1Br 3 | Br 2Ba 1 | Ba 1(OH) 2 | (OH) 3
2 3
Fe 1 2 | Fe 1 Br 3 6 | Br 2 6Ba 1 | Ba 1 3(OH) 2 | (OH) 3
Fe 1 2 | Fe 1 2 Br 3 6 | Br 2 6Ba 1 | Ba 1 3(OH) 2 | (OH) 3 6
23
Fe 1 2 | Fe 1 2 Br 3 6 | Br 2 6Ba 1 3 | Ba 1 3(OH) 2 6 | (OH) 3 6
• When counting Atoms put a box around JUST the polyatomic• Count like normal and balance using these count• Na is 1st thing that don’t balance, common multiple between 2
and 3 is 6.• Fix each side and recount• Mg is next thing that don’t balance, common multiple between
1 and 3 is 3.
Na 3 | Na 2PO4 1 | PO4 2Mg 1 | Mg 3SO4 1 | SO4 1
2 Na3PO4 + MgSO4 → Mg3(PO4)2 + Na2SO4
Na 3 6 | Na 2PO4 1 2 | PO4 2Mg 1 | Mg 3SO4 1 | SO4 1
• Predicting the products of a chemical reaction involve 1st determining the type of reaction that is occurring.– Combination: starts with 2 elements – Decomposition: starts with 1 compound– Single Replacement: Starts with 1 element & 1
compound– Double Replacement: starts with 2 compounds– Neutralization: starts with 2 compounds that are an
ACID and a BASE– Combustion: starts with O2 and a compound
containing C, H and/or O.
23
Predicting Products identifying types of reaction practice.
____Al + ____Cl2
___Mg(OH)2 + ___HCl
___Zn + ____HCl
___C2H6 + ___O2
___Al2O3
__Ba(NO3)2 + __Na2SO4
Combination
Neutralization
Single replacement
Combustion
Decomposition
Double replacement
24
Predicting Products
• Predicting the products of a chemical reaction involve next determine the products that would be produced based on a balance of charge. – Combination: ends with 1 compound– Decomposition: ends with 2 elements– Single Replacement: ends with 1 element & 1
compound– Double Replacement: ends with 2 compounds– Neutralization: ends with H2O and a “salt”
– Combustion: ends with CO2 and H2O
Predicting Products____Al + ____Cl2
Is a combination reaction so the product is a compound between aluminum and chlorine. MUST BALANCE CHARGES!Al+3 and Cl-1 form compoundAlCl3
____Al + ____Cl2 ____ AlCl3 still needs number of atoms to be
balanced___Mg(OH)2 + ___ HCl
Is a neutralization reaction so the product is water and a salt. The salt would be formed between the element at the beginning of the base and the element at the end of the acid. Think square dance!! MUST BALANCE CHARGES!Mg +2 and Cl-1 form compoundMgCl2 and H2O___Mg(OH)2 + ___HCl __ MgCl2 + __ H2O still needs number
of atoms to be balanced
26
Predicting Products
__Al2O3 Is a decomposition reaction so the product is just
elements. Don’t forget diatomic elements. Al and O2 (is a diatomic element) __Al2O3 __ Al + ___ O2
__Ba(NO3)2 + __Na2SO4 Is a double replacement reaction, the positive ions switch partners. MUST BALANCE CHARGES!__Ba(NO3)2 + __Na2SO4 __BaSO4 + __NaNO3 still needs to be balanced
27
Predicting Products ___Zn + ____HCl
Is a single replacement reaction so the element replaces an element in the compound
Generally the 1st element in compound is the one that leaves. MUST BALANCE CHARGES!
___Zn + ____ HCl ___ZnCl2 + ___H2
___C2H6 + ___O2Is a combustion reaction, and can only make carbon dioxide and water.___C2H6 + ___O2 ___ CO2 + _____H2O
28
Predicting Products SummaryMake sure to BALANCE charges for ALL ionic and acid compoundsTransition Metals use the reactant to determine the charge and assume that it stays the same.Once you BALANCE CHARGES do NOT change the subscripts.Don’t forget your 7 diatomic elements:
When they are not in compounds they are in pairsN2, O2, F2, Cl2, Br2, I2, H2
ALL other elements are single elements when not in compoundsJust because an element has a subscript on the reactant side, does NOT mean it will have the same subscript on the product side.
29
Word Equations
• When balancing reactions that are word equations you MUST first write BALANCED chemical formulas.
• Remember to check the ions that each forms for Ionic compounds and Acids
• Once you have a balanced chemical formula DO NOT change the formula (i.e. change subscripts)
• DON’T forget your 7 diatomic elements.
30
Word Equations• Example 1: solid calcium hydroxide reacts with sulfuric acid to
produce aqueous calcium sulfate and water.• Pick out the chemical names in the reaction and turn them into
