Test #1: Chemical Kinetics and Solubility

chemical kinetics

study of the speeds of reactions and the nanoscale pathways or rearrangements by which atoms and molecules are transferred from reactions to products

chemical kinetics synonym

reaction kinetics

homogeneous reactions

reactants and products are in the same phase

heterogeneous reactions

species are in multiple phases and react at interfaces

enzyme reaction classification

heterogenous

factors affecting the speed of reactions

\-properties of reactants/products

\-concentration

\-temperature

\-catalysts

\-surface area

what properties of reactants/products affect rates the most

structure and bonding

when is a reaction fastest?

when only the reactants are present

catalysts

\-change path to products

\-their concentration affects speed as well

surface area

\-important for heterogenous reactions

\-greater contact leads to faster reactions

reaction rate

change in \[reactant\] or \[product\] per unit time

reaction rate equation

change in concentration/unit time

stoichiometry of reaction rates

coefficient represents concetration

reaction rate is proportional to…

concentration and growth of products

rate law

rate = k\[A\]^m\[B\]^n

m+n =

overall order of chemical reaction

rate determining step

the lowest part of the reaction sequence

half lives are constant for…

first order reactions

average rate

using the concentrations at the beginning and end of a time period over which the reaction rate is changing

instantaneous rate

the rate at which a reaction is proceeding at any specific time, given by the slope of the tangent line

initial rate

instantaneous rate when t=0

zero order equation

\[A\]t = -kt + \[A\]o

zero order graph

linear, negative slope

first order equation

\[A\]t = \[A\]oe^-kt or ln\[A\]t = ln\[A\]o^-kt

first order graph

nonlinear

second order equation

1/\[A\]t = kt + 1/\[A\]o

half life

constant for first order reactions because it is independent of initial concentration

half life for second order rxns

constantly changing

half life equation

ln2/k

unimolecular reactions

a single particle rearranges into one or two particles

unimolecular reaction examples

isomerization, fluorescence and radiation

bimolecular reactions

two particles collide and rearrange

bimolecular reaction example

bond formation

order of solvents

always pseudo first order

elementary reactions

occur as written

complex reactions

occur as a series of elementary steps

optical isomers

L vs. R handed, each have the same physical properties

geometric isomers

have different physical properties

activation energy

minimum energy needed to form products

transition state

occurs at the top of the activation barrier and can form products for fall back to reactants

transition state synonym

activated complex

transition state time period

a few fs

energy of products

less than that of the reactants

speed of reverse reactions

slower

stability of products

more stable than reactants

caviat of bimolecular reactions

must collide with enough energy and in the right location to cause and inversion

fractional factor

steric factor

rise in temperature

speeds up most reactions

Arrhenius equation

k = Ae^(-Ea/RT)

order of unimolecular reactions

first

order of bimolecular reactions

second

collision theory first postulate

the rate of reaction is proportional to the rate of reactant collisions

collision theory second postulate

the reacting species must collide in an orientation that allows contact between the atoms that will become bonded together in the product

collision theory third postulate

the collisions must ccur with adequate energy to permit mutual penetration of the reactant species’ valence shells so that electrons can rearrange and form new bonds

intermediates

species that are produced in one step and consumed in a subsequent step

termolecular reactions

involves the simultaneous collision of 3 atoms, molecules, or ions

reaction mechanism

provides detail regarding the precise, step by step process by which a reaction occurs

rate limiting step

the slowest step in a sequence

catalyst

increases the reaction rate without being consumed and lowers the activation energy

catalysts do not affect…

delta H, delta S, delta G, initial/final energies

enzymes

very large proteins that serve as a catalyst for one or more reactions

substrate

molecule that attaches itself to the enzyme

cofactor

small organic or inorganic molecule required for an enzyme to work

volume of first order reactions

less than second order

common cofactors

Mg, K, Na

active site

part of the enzyme that interacts with the substrate

enzymes at high temperature

denature

solution

homogeneous mixture of substances

solvent

component in the greatest amount

solute

component in lesser amounts

ideal solution

solute is surrounded by only solvent and is formed without energy change

possible solvent phases

solid, liquid, or gas

Like dissolves like

solute and solvent will mix if they share similar primary intermolecular forces

polar dissolves…

polar

nonpolar dissolves…

nonpolar

Solvation

solvent-solute attraction > solute-solute and solvent-solvent attraction

miscible

dissolve in all proportions

immiscible

do not dissolve but form distinct layers, separated by density

partially miscible

can only mix in certain proportions

alcohols

solubility in water decreases as they grow larger

alcohol head

hydrophilic

alcohol tail

hydrophobic

delta Hsoln =

delta Ha + delta Hb + delta Hc

thermo of favored solubility

negative H and positive S

forming a solution is almost always…

spontaneous (entropically favored)

unsaturated solution

solute < solubility

saturated solution

solute = solubility

supersaturated solution

more than the equilibrium amount is dissolved

concentrated solution

almost saturated

dilute solution

almost completely unsaturated

dynamic equilibrium

solute moves constantly in and out of the solution

dissolution of ionic solids in liquids

\-must overcome lattice energy to become hydrated

\-cations and anions break and become free floating

enthalpy of hydration

= -Lattice Energy + delta Hhyd (cations) + delta Hhyd (anions)

ionic solutes dissolve in…

polar liquids

gas solubility decreases as…

T increases

solid solubility increases as…

T increases

gas solubility increases as…

partial P increases

Le Chatelier’s Principle

if more gas is on the reactant side, it will shift toward the products

Henry’s Law

gas solubility is directly proportional to the pressure of the gas

Henry’s law equation

Cg = kPg