Chemistry Unit 3

Rate of a chemical reaction
speed a chemical change takes place; how fast or how slow a reaction goes to completion (does not determine how much of a product is made)
Measured as change in number of moles of a reactant or product per unit time.
Activation Energy
• Activation energy (Ea¬) – minimum energy required to initiate a reactive collision
NOTE: Activation energy is inverse to the rate of reaction. In a given chemical reaction, if the Ea is lower, the faster the reaction or if the Ea is higher, the slower the reaction
Endothermic Chemical Reaction –
Diagram represents potential energy (y-axis) of the chemical reaction and progress of reaction (x-axis).
a.Energy of the product formation is greater than that of the reactants.
b.Heat is absorbed (gained) to system from surroundings.
c.Activation energy (Ea) in red on endothermic diagram
d.Energy difference between reactants and products is the Heat of Reaction (?Hrxn) is positive
•Written as: ?Hrxn = + (positive)
• ENERGY + reactants ? products ?Hrxn = +
Exothermic Chemical Reaction
Diagram represents potential energy (y-axis) and progress of reaction (x-axis).
a.Energy of the product formation is less than that of the reactants.
b.Heat is evolved (released or lost) from system to surroundings.
c.Activation energy (Ea) in red on exothermic diagram
d.Energy difference between reactants and products is the Heat of Reaction (?Hrxn) is negative
•Written as: ?Hrxn = – (negative)
• reactants ? products + ENERGY ?Hrxn = –
Dynamic Equilibrium
Dynamic Equilibrium – state or condition where two opposing processes take place at the same rate at a given temperature.
a.Simultaneous opposing processes; forward and reverse reactions.
LeChatelier’s Principle
LeChatelier’s Principle – if a system at equilibrium is disturbed (stressed), the system will adjust so as to counteract the disturbance and restore the system to equilibrium; temporary displacement from equilibrium.
Weak Acid
aqueous solutions of these substances only partially dissociates in water to form hydronium and hydroxide ions, respectively.
Weak Base
aqueous solutions of these substances only partially dissociates in water to form hydronium and hydroxide ions, respectively.
Example of weak acids
a.Hydrogen cyanide (HCN), hydrofluoric acid (HF)
b.Oxoacids that fail the “test” such as nitrous acid (HNO2), hypochlorous acid (HClO), sulfurous acid (H2SO3), phosphoric acid (H3PO4)
c.Organic compounds containing the carboxyl functional group (– COOH) form acids like ethanoic acid (CH3COOH) or methanoic acid (HCOOH).
Example of weak bases
Organic compounds containing nitrogen are weak bases such as methylamine (CH3NH2), trimethylamine
(CH3)3 N
Bronsted-Lowry Theory
Bronsted-Lowry Theory – way to describe a chemical reaction that results in a proton transfer from one reactant species to another reactant species.
Properities of acids
Acids
When dissolved in water, produces hydronium ions (H3O+) or (H+)
Neutralize bases to produce water and salts
Taste tangy or tart
Solutions turn blue litmus paper red
pH range: 0.00 – 6.99
Properties of bases
Bases
When dissolved in water, produces hydroxide ions (OH-)
Neutralize acids to produce water and salts
Taste bitter
Solutions turn red litmus paper blue (blue is base)
pH range: 7.01 – 14.00
Conjugate base
Conjugate base – species formed when an acid donates a proton.
Conjugate acid
Conjugate acid – species formed when a base accepts a proton.
Titration
Titration – an analytical technique to determine the exact concentration of a particular substance in a neutralization reaction.
equivalence point
When the reactants have combined exactly, there must be a way to determine this complete combination known as an equivalence point or end point of the titration.
Strong acid
compound that produces hydrogen ions when dissolved in water. Chemical Formula usually HX(X = monatomic or polyatomic ion). Chemical formula = H+
Strong base
a compound that produces hydroxide ions when dissolved in water. Bases are named as if they were ionic compounds (the name of the cation followed by the name of the anion).
hydroxide ion
A water molecule that loses a hydrogen ion and thus becomes negatively charged. Hydroxide ions are denoted OH-. (Do not conf. with hydronium ion)
Hydronium ion
A water molecule that gains a hydrogen ion and thus becomes positively charged. Hydronium ions are denoted H3O+. (Do not conf. with hydroxide ion
Ion Production Constant for Water
pH
the negative logarithm of the hydrogen-ion concentration. pH=-log[H+]. Always express in scientific notation
x

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