Reactions happen everywhere, but how do we know there is a reaction? Visual signs are key ways to tell if there has been a reaction.
4 Common "Driving Forces" For Reactions:
- Formation of a solid (ex precipitation)
- Formation of water (ex. combustion)
- Transfer of electron (ex. oxidation-reduction)
- Formation of gas (ex. combustion)
Chemical Equations:
- Reactants -----> Product
- (s)- solid
- (l)- liquid
- (g)-gas
- (aq)- aqueous solution
It's great to know and understand how to balance a chemical equation because it is important to have a balanced equation that satisfies the conservation of mass law. Now to predict the product. First things first the solubility rules will be very important:
Now that you can sing the solubility rules it's time to work some problems:
- Based on the reactant, what is the product using the solubility rule.
- AgNO3 (aq)+ NaCl(aq) ->
- Since this will be a double displacement,
- Ag+ will go with Cl-
- Na+ will go with NO3-
- The molecular equation is
- AgNO3 (aq)+ NaCl(aq) -> AgCl + NaNO3
- Now we need to determine the physical state( aq or s)
- We look back to the rules to determine the states:
- 1. Most nitrate (NO3 -1) are soluble
- 2. Most salts of Na+,K+ and NH4+ are soluble
- 3. Most chloride salts are soluble.
- exception: Ag+, Pb2+, Hg2 +2
- 4. Most sulfates salts are soluble
- exception:Ba2+, Pb2+ , Ca2+
- 5. Most hydroxide (OH-)compounds are insoluble
- Exception- ions in rule number 2 and Ba/Ca
- 6.Most sulfides, carbonate, phosphate are insoluble
- Exception- ions in rule number 2
- The answer is: AgNO3 (aq)+ NaCl(aq) -> AgCl(s) + NaNO3(aq)
3 Ways to Write a Chemical Equation!
Molecular Equation
- No charges are showing. Only compounds
- AgNO3 (aq)+ NaCl(aq) -> AgCl(s) + NaNO3(aq)
Complete Ionic Equation
- All (aq) compounds will disassociate “break” into their ions
- Ag+(aq) +NO3- (aq)+ Na+(aq) +Cl-(aq) -> AgCl(s) + Na+ (aq) +NO3-(aq)
Net Ionic Equation
- Find the solid and then write the ions in the reactants that makes up the product
- Ag+(aq) + Cl-(aq)-> AgCl(s)
Spectator Ions
- Based one the chemical equation, What is the spectator ion?
- AgNO3 (aq)+ NaCl(aq) -> AgCl(s) + NaNO3(aq)
- First look for the compound with the physical state of aq in the product.In this example, it is NaNO3(aq)
- Next, give the ions that form the aqueous compound.
- In this example Na+ and NO3-
- Na+ and NO3- are the spectator ions.
Types of Reactions
- Combustion.
- CH4+O2 -> CO2 + H2O
- Always look for in the reactant a carbon source and oxygen gas and in the product CO2
- CH4+O2 -> CO2 + H2O
- Synthesis
- Adding elements and/or compounds to form a new single compound
- example: H2 +O2-> H2O
- Decomposition
- Breaking a compound into simpler parts
- Example: H2O-> H2 +O2
- Single displacement
- One element/compound replaces another one.
- note only a cation can replace a cation and an anion can only replace an anion
- example: Zn +FeCl2-> Fe + ZnCl2
- Double displacement
- Elements/compounds switches partner to form 2 new compound.
- Example: AgNO3 (aq)+ NaCl(aq) -> AgCl(s) + NaNO3(aq)
- Acid/ base reaction
- In the reactant, there must be both an acid(H) and a base(OH).
- example: HNO3 + NaOH->H2O + NaNO3
- Precipitation reaction:
- Formation of a solid when two or more aqueous solution are combined
- AgNO3 (aq)+ NaCl(aq) -> AgCl(s) + NaNO3(aq)