chem 2 final chap16-20

A chemical equilibrium occurs when the forward reaction rate equal the …

Reverse reaction rate (reaction has not stopped)

Reactants and products are still being converted

Concentrations remain constant

The system is dynamic

aA+ bB → ← cC + dD

K = (C)^c (D)^d / (A)^a(B)^b

Value of k to meaning

K>1 products are favored

K<1 reactants are favored

K=1 similar amounts present

Le chateliers principle

If a stress is applied to a system at equilibrium the system shifts to oppose the stress

Concentration changes

A+B→ ← C+D

Add reactant shifts right which makes more product

Remove reactant shifts left makes more reactants

Add product shift left makes more reactants

Remove product shift right makes more product

Pressure change (gases only)

Increase pressure : shift toward the side with fewer moles of gas ( increase pressure shifts right)

Decrease pressure : shift toward the side with more moles of gas

Temperature change

Treat as a reactant or products

Endo heat +A→ ←B

Add heat shift right Remove heat shift left

Exo A→ ← B+ heat

Add heat shift left. Remove heat shift right

Bronsted Lowry acids and base

Acid- proton H+ donor

Base-proton H+ acceptor

HCl+H2O→H3O+ + Cl-

HCl= acid (donates H+)

H2O= base (accepts H+)

H3O+= conjugate acid

Cl-= conjugate base

Quick tip

Acid loses H+ → becomes conjugate base

Base gains H+→ becomes conjugate acid

Strong acid

Completely ionize in water

HCl, HBr, HI, HNO3

Weak acid

Partially ionize in water

HF, H2CO3, CH3OOH ( acetic acid )

Trends in acid strength

Across a period - acidity will increase from left to right CH4< NH3< H2O< HF

Down a group - acidity increases down the group HF< HCl< HBr< HI

(Larger atoms hold H less tightly)

More oxygen atoms = stronger acid

HClO< HClO2< HClO3< HClO4

2H2O→ ← H3O+ + OH-

Water self ionizes

Ion- product constant

Kw= ( H3O+)(OH-)

Kw= 1.0×10^-14

Ka and acid strength

Large Ka= stronger acid

Small Ka = weaker acid

Ka value — acid strength

>1 — strong acid

10^-2 to 10^-6 — weak acid

<10^-7 — very weak acid

As Ka increases ….

Ionization increases

pH decreases

Acidity strength increases

Strong acid- strong base

Starts very low pH

Sharp rise near equivalence point

Equivalence point pH=7

Weak acid - strong base

Higher starting pH

Buffer region present

Equivalence point pH>7

Electrochemical cells convert between chemical energy and …

Electrical energy

Galvanic (voltaic) cells

Produce electrical energy from a spontaneous redox reaction

Reaction occurs naturally

Used in batteries

🔺G<0

Ecell>0

K>1

Electrolytic cells

Use electrical energy to force a non spontaneous reaction

Require an external power source

🔺G>0

Ecell<0

K<1

Anode and cathode

Anode (AN OX) - oxidation occurs / electrons are released

Cathode (RED CAT) - education occurs / electrons are gained

Salt bridge

Allows ions to flow between halt cells it’s purpose is to maintain electrical neutrality and complete the circuit

External wire

Allows electrons to travel from anode to cathode

Half cells

The two compartments where oxidation and reduction occur

Electron flow

Elections always travel anode → cathode

Oxidation—- reduction

Loss of electrons —— gain of electrons

Oxidizing agent

Causes oxidation in another substance which gets reduced

Reducing agent

Causes education in another substance which gets oxidized

Cell potential (Ecell)

Measure of a cells electrical potential

Units (V) volts

Gibbs free energy and cell potential

🔺G= -n FEcell

+🔺G —→ -Ecell Not spontaneous

-🔺G —→ +Ecell Spontaneous

Nucleus

Center of the atom containing protons and neutrons

Nuclide

An atom with a specific number of protons and neutrons

Isotope

Atoms with the same number of protons but different number of neutrons

Carbon-12

Carbon-14

Radioactivity

Spontaneous emission of radiation from an unstable nucleus

Radioactive decay

Process by which an unstable nucleus becomes more stable

B- emission

B+ emission

Alpha emission

Neutron emission

Proton emission

Alpha , beta(-,+) , proton, neutron emission

Alpha - 2 neutrons and protons = helium

B+ = proton becomes neutron (loses proitron)

B-= neutron becomes proton (loses electron)

P = spits out a proton

N= spits out neutron (only one that doesn’t make new element )

Stable nucleus has:

Proper neutron to proton ratio

Small atoms 1:1

Larger atoms require more neutrons

Stable nuclear forces

Strong nuclear force must balance proton- proton repulsion

Stable energy state

Nucleus has low energy and does not spontaneously decay

Effects of radiation on living systems

Low dose : medical imaging , cancer treatment, sterilization

High dose : cell damage, tissue damage, increase cancer risk

Acute exposure : large does short time = radiation sickness and serve tissue damage

Chronic exposure : smaller dose long time = increase mutation rates and increase cancer risk