unit 5: chemical equations and reactions chemistry cpa winter 2014 callahan, pengitore &...
TRANSCRIPT
Unit Objectives
Unit Objectives: • To relate chemical changes and macroscopic properties (5
signs of a chemical reaction)• To demonstrate how chemical equations describe chemical
reactions• To illustrate how to balance chemical reactions by changing
coefficients• To distinguish between the five major types of chemical
reactions• To classify a reaction as belonging to one of five major types. • To classify factors that influence the rate of reaction.
Unit 5 Standards:
• NJCCCS: 5.1.12.A-D, 5.2.12.A.5, 5.2.12.B.2, 5.2.12.B.3, 5.2.12.D.5
• CCCS: ELA-Literacy.RST.11-12.3, 4, 5, 7, 8, 9, 10
Chemical Equation
• represents a chemical change or reaction
Reactants Products
Reactants – chemicals before the reactionProducts – substance formed in the reaction
• Reactions can be described several ways:1. In a sentence
Copper reacts with chlorine to form copper (II) chloride.
2. In a word equationCopper + chlorine copper (II) chloride
3.Using formulasCu + Cl2 CuCl2
Symbols used in ReactionsSymbol Explanation
+ Used to separate two reactants or two products
Yields, separates reactants and products
(s), (l), (g) State of matter; Fe (s)
(aq) Aqueous solution – dissolved in water
Heat supplied to the rxn
Catalyst used (speeds up the rxn time)
Diatomic Elements
• There are 7 elements on the periodic table that exist in nature bonded in pairs.
• Those elements are:– Hydrogen, Nitrogen, Oxygen, Fluorine, Chlorine,
Bromine, and Iodine.
• Whenever they are referred to as alone or as a gas, i.e, “chlorine gas”, we write them like this:– H2, N2, O2, F2, Cl2, Br2, I2
Diatomic Elements
• To help you remember them, you can use the acronym, “HONClBrIF”
• Or, with the exception of Hydrogen, they make the number “7” on the periodic table starting at Nitrogen, going down to Iodine:
Practice Problem Set:Write the word equations below as chemical equations
1. Zinc and lead (II) nitrate react to form zinc nitrate and lead.
2.Aluminum bromide and chlorine gas react to form aluminum chloride and bromine gas.
3.Sodium hydroxide and carbon dioxide react to form sodium carbonate and water (dihydrogen monoxide)
In a chemical reaction
• Law of Conservation of Matter states that matter isn’t created or destroyed.
• The way atoms are joined is changed
Because of the LAW OF CONSERVATION OF MATTER, we have to BALANCE EQUATIONS!!!
To BALANCE AN EQUATION means to make sure that the NUMBER of atoms of each
element is the same in the reactants and in the products!
Balancing Rules:
1. You may change the coefficients to any number you want, but…
2. You may NEVER change a subscript.
A coefficient is a number written in front of the compound
5 Types of Chemical Reactions
1. Synthesis2. Decomposition3. Single Replacement (Displacement)4. Double Replacement (Displacement)5. Combustion
Synthesis Reaction
Synthesis reaction – 2 substances are combined to form a single product
A + B AB
+
Synthesis Examples
2Mg + O2 2MgOMagnesium and oxygen combine to form
magnesium oxide.
2H2 + O2 2H2OHydrogen and oxygen combine to form
dihydrogen monoxide (water)
Decomposition Reaction
Decomposition reaction – A single compound is broken down into 2 or more products.
AB A + B
+
Decomposition Examples
2NaCl(s) 2Na(s) + Cl2(g)
Sodium chloride (table salt) decomposes into sodium and chlorine gas.
CaCO3 CaO + CO2
Limestone (CaCO3 ) decomposes into lime (CaO) and carbon dioxide.
Single Replacement Reaction
Single Replacement reaction – A single element takes the place of an element in a compound.
A + BC B + AC
+ +
Single Replacement Examples
Mg + BeO Be + MgOMagnesium replaces beryllium in beryllium
oxide to form magnesium oxide and beryllium.
2Na + 2HCl H2 + 2NaCl
Sodium replaces hydrogen in hydrochloric acid to yield hydrogen and sodium chloride.
Single Replacement Demo
• Magnesium reacting with Hydrochloric acid• Compared to Copper reacting with HCl
Double Replacement Reaction
Double Replacement reaction – Elements in 2 compounds switch places to form 2 new compounds.
AB + CD AD + CB
+ +
Double Replacement Examples
MgO + BeS MgS + BeOOxygen and sulfur switch places to form
magnesium sulfide and beryllium oxide.
Na2S + Zn(NO3)2 2Na(NO3) + ZnS
Sulfur and nitrate switch places to form sodium nitrate and zinc sulfide.
Double Replacement Demo
• A double replacement between barium chloride and potassium sulfate
• Potassium Iodide and lead (II) nitrate produces potassium nitrate and lead (II) iodide
Combustion Reaction
Combustion reaction – hydrocarbon (H and C) burn in oxygen to produce water and carbon dioxide. Heat is given off as energy.
CxHy + O2 H2O + CO2
Combustion Examples
CH4 + 2O2 2H2O + CO2
Methane burns in oxygen to produce water and carbon dioxide.
C12H22O11 + 12O2 11H2O + 12CO2
A sugar molecule burns in oxygen to produce water and carbon dioxide
Factors that affect reaction rates
• Temperature– Higher temperature faster reaction
• Concentration– Changing the amounts of reactants– High concentration means more particles per
volume– Example: 3% H2O2 vs. 30% H2O2
• Surface Area – Reactions occur faster when there is more surface
area• Sugar cube vs. sugar packet dissolving
• Catalyst– Used to speed up a reaction without being used
up – Enzymes are examples of catalyst
Can you slow a reaction down?
• Inhibitor – a substance added to slow reactions down– Added to food products
Limiting Reactant• Sometimes, when two or more reactants are
present in a reaction, more than the other is available for reacting.
• The one thing that there is not enough of is called the limiting reactant.
• It is the reactant that is used up first.
Limiting Reactant Example #1:Making a Bicycle
Making a bicycle requires1 frame + 2 wheels 1 bicycle
a)If you have 100 frames and 120 wheels, howmany bicycles can you manufacture? ______a)What is the limiting reactant? _________
Limiting Reactant Example #2:Grilled Cheese Sandwich
Bread + Cheese ‘Cheese Melt’
2 B + C B2C
100 bread 30 slices ? sandwiches
Limiting Reactant Example #3:Chemistry Problem
Hydrogen gas can be produced by the reaction of magnesium and hydrochloric acid, as shown by this equation:
Mg(s) + 2HCl (aq) MgCl2(aq) + H2(g)In particular, 6,000 molecules of HCl were mixed with 1,000
molecules of Mg.
a)Which reactant is limiting? ________________________
a)How many molecules of H2 are formed when the reaction is complete? ______________________________________