Chemical Reactions. Questions 1.What is the difference between a chemical and physical change?...
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Transcript of Chemical Reactions. Questions 1.What is the difference between a chemical and physical change?...
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Chemical Reactions
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Questions
1. What is the difference between a chemical and physical change?
2. Give an example of a chemical change and a physical change.
3. How can you tell a chemical reaction has occurred?
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Chemical vs. Physical
• ____________________- deals with energy and states of matter. – Ex: Crushing a can, melting an ice cube.
• _____________________- takes place on a molecular level and a new substance is produced.– Ex: Burning, cooking an egg.
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Chemical Reactions
• Chemical Reaction – When two or more substances come together to form a new substance.
• Chemical Reactions are all around us!
• What are some examples of chemical reactions in your life?
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How To Tell A Chemical Reaction Has Occurred
• New substance• Light• Heat• Color Change• Gas• Odour• Sound
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Questions
4. What is a chemical equation? On what side of the equation are the products and reactants located?
5. Describe one chemical reaction that occurs in everyday life.
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Reactions• Chemical Equation – Way of representing a chemical reaction.– Ex:
• _____________________ – substances being brought together to react (before reaction)
• _____________________ – substances formed (after reaction)
Reactants Products
• Reactants yield (produce) the products.– Ex: The reaction of Hydrogen and Oxygen yields Dihydrogen
Monoxide (water)
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Reaction Symbols
• (l) = Liquid
• (g) = Gas
• (s) = Solid
• (aq) = Aqueous Solution (solvent is water)
• = Points in direction of reaction
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Questions
6. What is a diatomic element? Give an example. What is one way of remembering which elements they are?
7. What is the Law of Conservation of Mass?
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Diatomic Elements
• Diatomic Elements are those that occur naturally as two. (Di = 2)–Ex: Hydrogen occurs as H2 not as H.
• There are 7 diatomic elements:
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How to Remember Diatomic Elements
• Use the acronym I Bring Clay For Our New Home:
– I = Iodine – Bring = Bromine – Clay = Chlorine – For = Fluorine – Our = Oxygen – New = Nitrogen – Home = Hydrogen
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Diatomic Elements form a 7 on the periodic table plus Hydrogen in the corner!
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Chemical Equations: In Words
• Write down the following chemical reaction in words:
2 NO + O2 2NO2
• _________________________________________________
_________________________________________________
__________________________________
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Chemical Equations: Balancing
• Law of Conservation of Mass – The mass of the reactants
_______________________________________________.
• In other words, what goes in to the reaction, must come out! Nothing just disappears!
Ex: Formation of WaterH2 (g) + O2 (g) H2O (l)
• There are two hydrogens on both sides, but only two oxygens on the left and one on the right. So the equation needs to be balanced!
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Chemical Equations: Balancing
• In order to balance an equation (have equal number of atoms on each side), you must place coefficients (numbers) in front of the atoms or molecules.
____ H2 (g) + ____ O2 (g) _____ H2O (l)
(you can use an inventory list to help you)
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Balancing Equations• Rules:– Can’t add extra molecules or atoms into the
equation!– Never change molecular formulas!
• Tips:– If an element occurs as a free element, balance
this element last. – Can use fractions to help in balancing, but need to
clear the fractions by multiplying by a common multiplier.
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Questions
8. What does it mean to be an aqueous solution?
9. What are the five different types of reactions?
10. What is a synthesis reaction?
11. What is a decomposition reaction?
12. What is a single displacement reaction?
13. What is a double displacement reaction?
14. What is a combustion reaction?
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Chemical Equation from Words• When writing down an equation, make sure to
write down the states of each element and compound.
Ex: Aluminum reacts with Copper (II) Chloride to form Copper metal and Aluminum Chloride.
Write the balanced equation for this reaction.
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Types of ReactionsYou need to be able to identify the type of reaction and
predict the product(s)
1. _____________________
2. _____________________
3. _____________________
4. _____________________
5. _____________________
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Steps to Writing Reactions
1. Identify the type of reaction2. Predict the product(s) using the type of reaction as a model3. _____________________!!
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Synthesis Reactions• Synthesis reactions occur when two substances
(generally elements) combine and form a compound.
Reactant + Reactant 1 Productor
• Examples:
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Practice• Predict the products. Write and balance the
following synthesis reaction equations.• Sodium metal reacts with chlorine gas
• Solid Magnesium reacts with fluorine gas
• Aluminum metal reacts with fluorine gas
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Decomposition Reactions• Decomposition reactions occur when a
compound breaks up into the elements or to a few simpler compounds
• 1 Reactant Product + Product or
• Examples:
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Decomposition Exceptions• Carbonates and chlorates are special case
decomposition reactions that do not decompose into their elements.
• Carbonates (CO32-) decompose to carbon dioxide and a
metal oxide• Example:
• Chlorates (ClO3-) decompose to oxygen gas and a metal
chloride• Example:
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Practice
• Predict the products. Then, write and balance the following decomposition reaction equations:
• Solid Lead (IV) oxide decomposes PbO2 (s)
• Aluminum nitride decomposes AlN (s) 2
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Single Displacement Reactions
• Single Displacement Reactions occur when one element replaces another in a compound.
• A metal can replace a metal (+) or a nonmetal can replace a nonmetal (-).
• element + compound element + compound (if A is a metal)
(if A is a nonmetal)
*Remember the cation (+) always goes first in a compound*
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Single Displacement Reactions
• Write and balance the following single displacement reaction equation:
• Zinc metal reacts with aqueous hydrochloric acid
Note: Zinc replaces the hydrogen ion in the reaction
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Single Displacement Reactions• Sodium chloride solid reacts with fluorine gas
*Note that fluorine replaces chlorine in the compound*
• Aluminum metal reacts with aqueous copper (II) nitrate
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Double Displacement Reactions• Double displacement Reactions occur when a
metal replaces a metal in a compound and a nonmetal replaces a nonmetal in a compound
• Compound + compound compound+ compoundor
• Examples:
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Double Displacement PracticePredict the products and balance the equations.
1. HCl(aq) + AgNO3(aq)
2. CaCl2(aq) + Na3PO4(aq)
3. Pb(NO3)2(aq) + BaCl2(aq)
4. FeCl3(aq) + NaOH(aq)
5. H2SO4(aq) + NaOH(aq)
6. KOH(aq) + CuSO4(aq)
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Combustion Reactions• Combustion reactions occur when a hydrocarbon
reacts with oxygen gas.
• Also called burning!• You need three things to burn something:
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Combustion Reactions• In general:
• Products in combustion are always carbon dioxide (CO2) and water (H2O).
• Incomplete burning causes byproducts such as carbon monoxide.
• Combustion is used to heat homes and run automobiles (octane, as in gasoline, is C8H18)
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Combustion Reactions
• Example:
• Write the products and balance the following combustion reaction:• C10H22 + O2
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Questions
15. What is an exothermic reaction? Give an example.
16. What is an endothermic reaction? Give an example.
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Endothermic vs. Exothermic
• Reactions can be classified as either Endothermic or Exothermic depending on whether it gives off energy or takes energy in.
• Energy can be in theform of light or heat.
• Energy Change is denoted by ∆H.
• ∆H = kJ/mol
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Exothermic Reactions
• Exothermic Reactions are those that give off energy (light or heat).
• Reactants Products + Energy
• Ex: In the formation of water2H2 + O2 2H2O + 483.6 kJ
• ∆H = - 483.6 kJ/mol
• ∆H is negative in exothermic reactions because energy is given off or lost.
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Exothermic Reactions
• Some examples are:
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Endothermic Reactions• Endothermic Reactions are those that
absorb energy (heat and light).
• Ex: In the melting of ice6.00 kJ + H2O(s) H2O(l)
∆H =• ∆H is positive in endothermic reactions
because it is energy needed for the reaction to occur.
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Endothermic Reactions
• Some examples:– Melting– Baking– Cooking– Ice Packs