Chemical Reactions Three areas of focus Rearranging the building blocks of chemistry (atoms/ions/ molecules/electrons) Force & energy is what decides if the reaction occurs and how fast Mathematics helps you keep an inventory of all the starting and ending materials
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Three areas of focus Rearranging the building blocks of chemistry (atoms/ions/ molecules/electrons) Fo rce & energy is what decides if the reaction occurs.
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Chemical Reactions
Three areas of focus Rearranging the
building blocks of chemistry (atoms/ions/ molecules/electrons)
Force & energy is what decides if the reaction occurs and how fast
Mathematics helps you keep an inventory of all the starting and ending materials
Objectives
Recognize Evidence of a chemical change. Represent chemical reactions with equations. Change word equations into formula equations. Given a description of a reaction, write a word and
formula equation. Balance chemical equations. Translate a formula equation into a sentence. Define and give a description of the major types of
chemical reactions. Classify reactions as one of five major types. Predict the products of simple reactions when given the
reactants. Understand, explain, and apply the activity series of the
elements.
Skills
Memorize the diatomic elements Memorize the symbols used in chemical equations. Use the Activity Series for single replacement reactions Use the Solubility Chart for Double Replacement Reactions Know common gases Memorize substances that decompose
The process by which one or more substances are rearranged to form different substances is called a chemical reaction.
Also called a chemical change
We are making something new!
Equations show
the reactants which enter into a reaction.
the products which are formed by the reaction.
the relative amounts of each substance used and each substance produced.
Two important principles to remember
Every chemical compound has a formula which cannot be altered.
A chemical reaction must account for every atom that is used. This is an application of the Law of Conservation of Matter which states that in a chemical reaction atoms are neither created nor destroyed.
Evidence of a Chemical Reaction
Evidence of a Chemical Reaction
Production of a Gas Temperature Change Color Change Production of a Solid (precipitate) Production of Water or other unionized
The diatomic elements are always written H2, N2, O2, F2, Cl2, Br2, I2
The sign, → , means "yields" and shows the direction of the action.
A small delta, ( ), above the arrow shows that heat has been added.
A double arrow, ↔ , shows that the reaction is reversible and can go in both directions.
Word Equations
Using words in equation form to represent a chemical reaction
iron(s) + chlorine(g) iron(III) chloride(s)
Skeleton Equation
uses chemical formulas instead of words
Fe (s) + Cl2 (g) ----- FeCl3 (s)
Practice
Chemical Equation
In order to obey the Law of Conservation of Mass equations must be Balanced:
Coefficients: number written in front of
a chemical formula to indicate the smallest number of particles involved in the reaction.
Steps for Balancing
Write skeleton equation. Change the coefficients to make the
number of atoms of each element equal on both sides of the equation. NEVER CHANGE A SUBSCRIPT!!!
Write the coefficients in the smallest ratio possible.
Check your work.
Helpful hints for balancing chemical equations
Start with “Big Formulas” C2H6O2
Save single elements for last O2 or Cu Balance hydrogens second to last Balance oxygens last Check for lowest ratio Do not change your subscripts Balance the polyatomic ions as one unit
Metal + nonmetal → salt 2 Na(s) + Cl2(g) → 2NaCl(s)
A few nonmetals combine with each other 2P(s) + 3Cl2(g) → 2PCl3(g)
These two reactions must be remembered: N2(g) + 3H2(g) → 2NH3(g) NH3(g) + H2O(l) → NH4OH(aq)
Decomposition Reactions
AB A + B Compound Cmpd/Elem + Elem/Cmpd One Reactant
Examples of Decomposition Reactions AX → A + X
Metallic carbonates, when heated, form metallic oxides and CO2(g)
CaCO3(s) → CaO(s) + CO2(g)
Most metallic hydroxides, when heated, decompose into metallic oxides and water Ca(OH)2(s) → CaO(s) + H2O(g)
Metallic chlorates, when heated, decompose into metallic chlorides and oxygen 2KClO3(s) → 2KCl(s) + 3O2(g)
Some acids, when heated, decompose into nonmetallic oxides and water H2SO4 → H2O(l) + SO3(g)
Some oxides, when heated, decompose 2HgO(s) → 2Hg(l) + O2(g)
Some decomposition reactions are produced by electricity 2H2O(l) → 2H2(g) + O2(g) 2NaCl(l) → 2Na(s) + Cl2(g)
Summary
A + B AB (synthesis)AB A + B (decomposition)A + BC B + AC(single replacement)AB + CD AC + BD(double replacement)Hydrocarbon + oxygen CO2 + H2O(combustion/oxidation)