chemical reactions. all chemical reactions involve changes in substances reactants – starting...
TRANSCRIPT
Chemical Reactions
Chemical Reactions All chemical reactions involve
changes in substances Reactants – starting substances Products – new substances formed Reactants Products
Example:Iron + Oxygen Iron (III) oxide
(Rust)
In all chemical reactions:
Bonds are broken and new bonds form
Law of Conservation of matter is supported
Atoms are not created or destroyed – just rearranged
During an ordinary chemical change, there is no detectable increase or decrease in the quantity of matter
Symbols in Chemical Reactions + used to separate two products
or reactants yields (s) subscript – represents a solid (l) subscript – represents a liquid (aq) subscript – represents an
aqueous solution (g) subscript – represents a gas
Symbols (cont.) replaces (s) to represent a precipitate
replaces (g) to represent a gas
Symbols (cont.)
Fe indicates the use of a catalyst (in this case iron)
heat or indicates that heat is supplied to the reaction
Examples:
Zn(s) + 2HCl(aq) H2 + ZnCl2(aq)
2H2O2(l) KI O O2(g)2(g) + 2H + 2H2OO(l)
Pb(NO3)2 (aq) + 2KI(aq) PbI2(s) + 2KNO3 (aq)
Chemical Equations Use formulas to represent
elements and compounds Atoms must balance on both sides
of the equation Atom inventories are helpful
Rules for Balancing Chemical Equations Determine the correct formulas for all
reactants and products in the reaction Reactants go on the left side of the
equation Products on the right side of the equation Count the atoms of each element in the
reactants and products Balance the elements one at a time by
changing the coefficients (NOT subscripts)
Balancing Equations (cont.) Tricks that help
Save uncombined elements for last Use least common multiple to balance
elements that have odd and even atoms on opposite sides
Remember polyatomic ions often remain intact in a reaction count them as a single part
Write water as HOH in acid/base reactions
Balancing Equations (cont.) Check each atom or polyatomic ion
to be sure that both sides are equal
Make sure coefficients are in the lowest possible ratio
Now lets practice! Potassium chlorate is heated and
breaks down into potassium chloride and oxygen gas – Write the balanced equation for this reaction.
Hydrochloric acid reacts with zinc to produces hydrogen gas and zinc chloride solution, write the chemical equation for this reaction.
6 Types of Chemical Reactions Synthesis (combination) Decomposition Single Replacement Double Replacement Combustion Acid/Base
Synthesis Reactions Two or more substances react to
form a single substance Two or more simple compounds
combine to form a more complicated one
Examples of Synthesis Reactions 2Mg(s) + O2(g) 2MgO(s)
8Fe(s) + S8(s) 8 FeS(s)
Decomposition Reactions A single compound is broken down
into two or more simpler substances
a complex molecule breaks down to make simpler ones
Examples of Decomposition Reactions 2 H2O (l) 2H2(g) + O2(g)
2KClO3(s) 2KCl(s) + 3O2(g)
CaCO3(s) CaO(s) + CO2(g)
Single Replacement Reactions Atoms of an element replace the
atoms of a second element in a compound
Element 1+ Compound 1 Element 2 + Compound 2
http://www.marymount.k12.ny.us/marynet/stwbwk05/05flashchem/avreaction/avreaction.html
Examples of Single Replacement Reactions
2Al(s) + 3NiSO4(aq) Al2(SO4)3(aq) + 3Ni(s)
2Fe(s) + 6HBr (aq) 2FeBr3 (aq) + 3H2(g)
Cl2(g) + 2KI(aq) 2KCl(aq) + I2(s)
Double Replacement Reactions
Involves the exchange of the positive ions between two compounds
Also called metathesis
http://www.marymount.k12.ny.us/marynet/stwbwk03/03hchem/nfreaction/nfreaction.html
Examples of Double Replacement Reactions
CaCl2 (aq) + K2CO3 (aq) CaCO3 (s) + 2KCl(aq)
3AgNO3 (aq) + FeCl3 (aq) 3AgCl(s) + Fe(NO3)3
(aq)
Combustion Reactions Oxygen reacts with another
substance usually producing energy in the form of heat and/or light
Examples of Combustion Reactions
CH4(g) + 2O2(g) ---> CO2(g) + 2H2O(g) + heat
2C2H6(g) + 7O2(g) ---> 4CO2(g) + 6H2O(g) + heat
C6H12O6(s) + 6O2(g) ---> 6CO2(g) + 6H2O(g) + heat
4C2H5OH(l) + 13O2(g) ---> 8CO2(g) + 10H2O(g) + heat
Acid/Base Reactions acid with a base produces a salt
plus water
The cation in the salt comes from the base; the anion comes from the acid
Examples of Acid/Base Reactions
2HCl (aq) + Ca(OH)2 (aq) CaCl2 (aq) + 2H2O (l)
Acid + Base Salt + Water
3H2SO4(aq) + 2Fe(OH)3(s) Fe2(SO4)3(aq)+ 6H2O(l)
Acid + Base Salt + Water