ch. 4 chemical reactions homework: 4.17, 4.18, 4.30, 4.33, 4.43, 4.45, 4.49, 4.55, 4.60, 4.62, 4.63,...
TRANSCRIPT
Ch. 4 Chemical Reactions
Homework: 4.17, 4.18, 4.30, 4.33, 4.43, 4.45, 4.49, 4.55, 4.60, 4.62,
4.63, 4.73, 4.78, 4.100
Chemical Reactions• In a chemical change, also known as a
chemical reaction, one or more of the starting materials, called reactants, are converted into one or more products
• There are 3 aspects of a chemical reaction:1) Mass relationship
2) Types of Reactions
3) Heat gains and loses
Background for Mass relationships
• Formula Weight- the sum of the atomic weights in amu of all atoms in the compound’s formula
• Formula weight applies to ionic compounds, and covalently bonded molecules
• Molecular Weight- means the same thing but only applies to molecules
The mole
• Mole- the amount of substance that contains as many atoms, molecules, or ions as there are atoms in 12 grams of carbon 12.
• A mole always contains the same number of formula units
• That number, known as Avogadro’s Number, is 6.02 x 1023
Molar Mass• Molar Mass- the mass of one mole of any
substance is the formula weight expressed in grams.
• To convert between grams and moles, we use the Molar Mass as the conversion factor:
Writing Chemical Equations
• We use the formulas for the reactants and products
• We use an arrow to show the direction of the reaction
• We also designate the state of all reactants and products!!– (s)=solid, (l)=liquid, (g)=gas, (aq)=aqueous – (aqueous means the substance is dissolved in
water)
• Example:
• Chemical Equations must be balanced!!!!
• This means there must be the same number of atoms on the left as on the right
• To balance equations, we put coefficients in front of the formulas until we have the same number of each type of atom on both sides.
Guidelines for balancing Eq.
1) Begin with atoms that appear in only one compound on the left and right
2) If an atom occurs as a free element, balance this element last
3) You can only change coefficients, NOT FORMULAS!!!!!
4) A balanced equation is always written with the lowest possible set of coefficients.
Stoichiometry
• Stoichiometry- the study of mass relationships in chemical reactions
• The balanced equation gives us the molar ratios of the reactants and products.
• We can use this information to calculate the mass of starting material needed to produce a certain amount of product or vice versa.
Percent Yield
• Actual Yield- the mass of a product formed in a chemical reaction that is physical carried out
• Theoretical Yield- the mass of product that SHOULD form according to the stoichiometry of the balanced equation
• Percent Yield- The actual yield divided by the theoretical yield time 100%
Combination Example• A student combusted 6.0 grams of C3H8 in
the presence of 30 grams of O2. 7.2 grams of water was captured. What was the percent yield for the reaction?
Ionic Reaction in Aqueous Solutions
• When positive and negative ions are placed in water, the ions are separated
• This is called dissociation
• Ions in water react with each other in solution only when one of the following can happen:
Types of Reactions
1) Two ions form a solid that is insoluble in water
2) 2 ions form a gas that escapes from the reaction mixture as bubbles
3) An acid neutralizes a base
4) One of the ions can oxidize the other
Ion Solubility Rules1) All compounds containing Na+, K+, or NH4
+ are soluble in water
2) All nitrates(NO3-) and acetates(CH3COO-) are
soluble in water
3) Most Chlorides(Cl-), and Sulfates(SO42-) are
soluble in water. EXCEPTIONS: AgCl, BaSO4, PbSO4
4) Most Carbonates(CO32-), phosphates(PO4
3-), sulfides(S2-), and hydroxides(OH-) are insoluble in water. EXCEPTIONS: LiOH, NaOH, KOH, NH4OH
Oxidation Reduction Reactions
• Oxidation- is the loss of electrons
• Reduction- is the gain of electrons
• And Oxidation/Reduction reaction, aka Redox reaction, involves the transfer of electrons from one species to another.
• These reactions are not independent of one another
• Something can’t gain electrons from nowhere!!!
Organic Definitions• In organic Chemistry, it is very hard to figure
out what lost electrons and what gained them, so we use different definitions:
• Oxidation- a reaction in which there is an increase in the number of bonds to Oxygen and/or a decrease in the number of bonds to Hydrogen.
• Reduction- a reaction in which there is an increase in the number of bonds to Hydrogen and/or a decrease in the number of bonds to Oxygen.
Categories of Redox Reactions
1) Combustion-What ever is burned is oxidized by O2
2) Respiration-O2 oxidizes carbon containing molecules to produce
CO2 and water, much like a combustion but much slower and lower temperature
3) Rusting-Iron is oxidized to Iron Oxide
4) Bleaching
-Most bleaching involves oxidation
5) Batteries
- The reaction in the battery is a redox reaction.