Reaction Types and Balancing

Essential Questions: Chemical Reactions What is a chemical reaction? How do we know when they happen? How do we communicate about them? Why must we balance chemical equations?

What is a chemical reaction? The process by which the atoms of one or more substances are rearranged to form different substances. Example: 2H 2 O 2H 2 + O 2 A chemical change Chemical bonds are broken or made

How do we know when a chemical reaction has happened? Evidence! There are 4 major indicators of chemical change. 1.Temperature change 2.Color change 3.Gas production (odor, bubbles) 4.Solid formation

How do we communicate about chemical reactions? Sentences Solid carbon disulfide reacts with oxygen gas, producing carbon dioxide gas and sulfur dioxide gas. Word Equations carbon disulfide (s) + oxygen (g) → carbon dioxide (g) + sulfur dioxide (g) Chemical Equations CS 2 (s) + O 2 (g) → CO 2 (g) + SO 2 (g)

Chemical Equations Symbols to indicate the state of reactants and products: –(g) gas –(l) liquid –(s) solid –(aq) aqueous –Δ (over arrow) It means: requires heat Other symbols: + : Must be included between each distinct reactant or product →:Means “to yield” separates reactants from products

Tek 8D Reactants vs. Products In a chemical reaction, reactants are chemically combined or broken down to make (produce) products. arrow always points toward products! reactants products

Tek 8D: Writing and Balancing Equations Chemical equations need to be balanced to comply the Law of Conservation of Mass matter cannot be created or destroyed # of atoms for each element must = each other on both sides of rxn. ** use coefficients (moles) to balance. -Coefficients are the large # in front of compound - must be whole numbers start from far left and work your way to the right!

Tek 8 cont… Are the following equations balanced? H 2 O 2 (aq) O 2 (g) + H 2 O (l) 22 2AgNO 3 + H 2 S Ag 2 S + HNO 3 2 MnO 2 + HCl MnCl 2 + H 2 O + Cl 2 2 4

Types of Reactions There are five different types of reactions… - - synthesis, decomposition, single displacement, double displacement, combustion SYNTHESIS… - - two or more reactants combine to produce one product. Ex… Mg (s) + O 2 (g) MgO (s) Mg (s) + O 2 (g) MgO (s) CaO (s) + CO 2 (g) CaCO 3 (s) CaO (s) + CO 2 (g) CaCO 3 (s) KNO 2 (s) + O 2 (g) KNO 3 (s) KNO 2 (s) + O 2 (g) KNO 3 (s)

DECOMPOSITION… - opposite of synthesis - - one reactant breaks down (decomposes) into two or more products. Ex… HgO Hg + O 2 HgO Hg + O HNO 3 N 2 O 5 + H 2 O HNO 3 N 2 O 5 + H 2 O 2

SINGLE DISPLACEMENT… SINGLE DISPLACEMENT… - one element in a compound is displaced (kicked out) by another (more reactive) element. Ex… Ex… Mg + Zn(NO 3 ) 2 Mg + Zn(NO 3 ) 2 Mg(NO 3 ) 2 + Zn Cl 2 + KI Cl 2 + KI KCl + I ** metals can only replace metals and vice versa for non-metals! ** metals can only replace metals and vice versa for non-metals! - reactants =1element &1compound …products = 1element & 1 compound.

DOUBLE DISPLACEMENT… DOUBLE DISPLACEMENT… - cations of two different compounds trade places. - reactants = 2 compounds …products = 2 different compounds Ex… Ex… NaCl + AgNO 3 NaCl + AgNO 3 AgCl + NaNO 3 Ca(OH) 2 + H 3 PO 4 Ca(OH) 2 + H 3 PO 4 H(OH) + Ca 3 (PO 4 ) 2 H(OH) + Ca 3 (PO 4 ) 2 (H 2 O) 3 6 2

… COMBUSTION … - generally involves the burning of a hydrocarbon. - fires generally need oxygen to burn (reactant). - fires generally release water and carbon dioxide (products). - reactants = hydrocarbon and O 2 …products = H 2 O and CO 2 C 3 H 8 + O 2 CO 2 + H 2 O C 3 H 8 + O 2 CO 2 + H 2 O Ex… C 6 H 12 O 6 + O 2 CO 2 + H 2 O C 6 H 12 O 6 + O 2 CO 2 + H 2 O 6 6 6

identify the following types of rxns… Pb(NO 3 ) 2 + K 2 CrO 4 PbCrO 4 + 2KNO 3 double displacement double displacement 2Al(OH) 3 Al 2 O 3 + 3H 2 O decomposition decomposition CH 4 + 2O 2 CO 2 + 2H 2 O combustion combustion 4Li + O 2 2Li 2 O synthesis synthesis 2Al + 3CuSO 4 Al 2 (SO 4 ) 3 + 3Cu single displacement single displacement