Friday 1/20 List the different elements in the chemical reaction. How many of each do you have on each side? Why do you think that is?

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: 2H2O 2H2 + O2 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. Temperature change Color change Gas production (odor, bubbles) 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 CS2 (s) + O2 (g) → CO2 (g) + SO2 (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

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

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!

cont… Are the following equations balanced? 2 2 2 4 2 H2O2 (aq) O2 (g) + H2O (l) 2 2AgNO3 + H2S Ag2S + HNO3 2 4 MnO2 + HCl MnCl2 + H2O + Cl2 2

Types of Reactions 2 2 2 2 Mg (s) + O2 (g) MgO (s) 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… 2 Mg (s) + O2 (g) MgO (s) 2 CaO (s) + CO2 (g) CaCO3 (s) 2 KNO2 (s) + O2 (g) KNO3 (s) 2

2 2 2 HgO Hg + O2 HNO3 N2O5 + H2O DECOMPOSITION… - opposite of synthesis - one reactant breaks down (decomposes) into two or more products. Ex… 2 HgO Hg + O2 2 2 HNO3 N2O5 + H2O

2 2 Mg + Zn(NO3)2 Mg(NO3)2 + Zn Cl2 + KI KCl + I2 SINGLE DISPLACEMENT… - one element in a compound is displaced (kicked out) by another (more reactive) element . - reactants =1element &1compound …products = 1element & 1 compound. Ex… Mg + Zn(NO3)2 Mg(NO3)2 + Zn Cl2 + KI 2 2 KCl + I2 ** metals can only replace metals and vice versa for non-metals!

3 2 6 NaCl + AgNO3 AgCl + NaNO3 Ca(OH)2 + H3PO4 H(OH) + Ca3(PO4)2 DOUBLE DISPLACEMENT… - cations of two different compounds trade places. - reactants = 2 compounds …products = 2 different compounds Ex… NaCl + AgNO3 AgCl + NaNO3 3 Ca(OH)2 + H3PO4 2 6 H(OH) + Ca3(PO4)2 (H2O)

5 3 4 6 6 6 C3H8 + O2 CO2 + H2O C6H12O6 + O2 CO2 + H2O 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 O2 …products = H2O and CO2 Ex… C3H8 + O2 CO2 + H2O 5 3 4 C6H12O6 + O2 CO2 + H2O 6 6 6

identify the following types of rxns… Pb(NO3)2 + K2CrO4 PbCrO4 + 2KNO3 double displacement 2Al(OH)3 Al2O3 + 3H2O decomposition CH4 + 2O2 CO2 + 2H2O combustion 4Li + O2 2Li2O synthesis 2Al + 3CuSO4 Al2(SO4)3 + 3Cu single displacement