types of reactions and balancing. curriculum big idea: chemical reactions are predictable concept:...
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Curriculum
Big Idea: Chemical reactions are predictable
Concept: Common chemical reactions can be categorized as synthesis, decomposition, single replacement, double replacement, or combustion.
PA Standard: 3.2.C.A2 Predict the chemical formulas for simple ionic and molecular compounds.
Today’s Agenda
Opener: What is evidence of a chemical reaction?
Notes on chemical reactionsPractice Determining the Type and
Balancing ReactionsClosure Question (see the last slide)Take Home Assignment: 11.1 Section
Assessment
Word Equations
Reactants productsExamples: Methane + oxygen carbon dioxide + water Hydrogen peroxide water + oxygen Iron + oxygen iron(III) oxide To write a word equation, 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.
Chemical Equations
Chemical Equation – a representation of a chemical reaction; the formulas of the reactants (on the left) are connected by an arrow with the formulas of the products (on the right).
Examples:Fe + O2 Fe2O3
Fe(s) + O2(g) Fe2O3(s)
Catalysts
Catalyst – a substance that speeds up the reaction but is not used up in the reaction (neither a reactant nor a product)
Example: MnO2 is a catalyst in the following reaction:
MnO2
H2O2(aq) H2O(l) + O2(g)
Chemical Reactions
How can we tell a chemical reaction has taken place? Temperature change Color change Odor Gas bubbles Appearance of a solid
Chemical Reactions
Representing chemical reactions Reactants: starting substances Products: substances formed during the reaction Word equation: indicates the reactants and products of
a chemical reaction.
Chemical equations: statement that uses chemical formulas to show the identities of substances.
Diatomics- H2, O2, N2, F2, Cl2, Br2, I2
Chemical Reactions
Practice Write the word equation for the
reaction in which magnesium reacts with chlorine to produce magnesium chloride.
Write the word equation for the reaction in which water decomposed into hydrogen and oxygen.
Chemical Reactions
Balancing Chemical Equations coefficient: the number written in from of the
reactants or products. steps:
1. Write the chemical equation for the reaction. ex. NaOH + CaBr2 Ca(OH)2 + NaBr
2. Count the atoms of the elements in the reactants and the products.
Chemical Reactions
3. Count the atoms of elements in the products.
4. Change the coefficients to make the number of atoms of each element equal on both sides of the equation.
5. Write the coefficients in their lowest possible ratio.
6. Check your work.
Classifying Reactions
Combination Reaction – a chemical change in which two or more substances react to form a single new substance.
Example: 2Mg(s) + O2(g) 2MgO(s)
Classifying Reactions
Decomposition Reaction – a chemical change in which a single compound breaks down into two or more simpler products.
Example:2H2O(s) 2H2(g) + O2(g)
Classifying Reactions
Single-Replacement Reaction – a chemical change in which one element replaces a second element in a compound
Example:2K(s) + 2H2O(l) 2KOH(aq) + H2(g)
Activity Series
Activity Series (p. 333) – lists metals in order of decreasing reactivity. A reactive metal will replace any metal listed below it in the activity series.
Example:Br2(aq) + NaI(aq) NaBr(aq) + I2(aq)
Br2(aq) + NaCl(aq) No reaction
Classifying Reactions
Double Replacement Reaction – a chemical change involving an exchange of positive ions between two compounds
Example:Na2S(aq) + Cd(NO3)2(aq) CdS(s) +
2NaNO3(aq)
Classifying Reactions
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.
Example: 2C8H18(l) + 25O2(g) 16CO2(g) + 18H2O(l)
Learning Check
Classify the following reactions as
1) combination or 2) decomposition:
___A. H2 + Br2 2HBr
___B. Al2(CO3)3 Al2O3 + 3CO2
___C. 4 Al + 3C Al4C3
Learning Check
Classify the following reactions as 1) single replacement 2) double replacement
__A. 2Al + 3H2SO4 Al2(SO4)3 + 3H2
__B. Na2SO4 + 2AgNO3 Ag2SO4 + 2NaNO3
__C. 3C + Fe2O3 2Fe + 3CO
Predicting the Products of a Chemical Reaction
The number of elements and/or compounds reacting is a good indicator of possible reaction type and thus possible products. See pages 338-339.