Chemistry Test 1

In a cell, a free amino acid has

four groups bonded to one C, which is called the alpha carbon: charged carboxyl (-COO-) and amine (-NH3+) groups, an H atom, and a side chain, represented by an R

saturated solution

is at equilibrium and contains the maximum amount of dissolved solute at a given temperature in the presence of undissolved solute. Therefore, if you filter off the solution and add more solute the added solute doesn't dissolve

the catalyst is not consumed

it is used and then regenerated

when a gas dissolves in a solid

it occupies the spaces between the closely packed particles

defining characteristics of a mixture

its composition is variable and it retains some properties of its components

Because an elementary reaction occurs in one step,

its rate law, unlike that for an overall reaction, can be deduced from the reaction stoichiometry: reaction order equals molecularity. Therefore, only for an elementary step, we use the equation coefficients as the reaction orders in the rate law

Arrhenius equation

k = Ae^(-E_a/RT) as T increases the value of the negative exponent becomes smaller which means k becomes larger so the rate increases Higher T -> Larger K -> increased rate

Rate law =

k[A]^m[B]^n... k = proportionality constant called the rate constant, that is specific for a given reaction at a given temperature and does not change as the reaction proceeds. m and n = reaction orders, define how the rate is affected by reactant concentration - the balancing coefficients a and b in the reaction equation are not necessarily related in any way to the reaction orders m and n - the components of the rate law - rate, reaction orders, and rate constant - must be found by experiment

solubility in hexane is high for

larger alcohols. In any larger alcohol (n>0) dispersion forces between the hydrocarbon portion and hexane can replace dispersion forces between hexane molecules.

Solubility in water is low for

larger alcohols. n>2 carbons. Those with chains longer than six carbons (N>5) are insoluble in water.

smaller activation energy or higher temperature =

larger fraction of sufficiently energetic collisions, the larger the value of k, and the higher the reaction rate

effective collisions

lead to product because the atoms that become bonded in the product make contact. to be effective, a collision must have enough energy and the appropriate molecular orientation

integrated rate law for a first-order reaction

ln([A]_0/[A]_t) = kt first order reaction reaction; rate = k[A]

two models of enzyme action

lock-and-key model - the "key" (substrate) fits the "lock" (active site) induced-fit model - the substrate induces the active site to adopt a perfect fit

freezing point depression (deltaTf)

occurs because the vapor pressure of the solution is always lower than that of the solvent, sot he solution freezes at a lower temperature; that is, only at a lower temperature will solvent particles leave and enter the solid at the same rate delta Tf is proportional to molal concentration of solute deltaTf = Kfm where Kf is the molal freezing point depression constant delta Tf = Tf(solvent) - Tf(solution)

mole fraction (x)

of a solute is the ratio of the number of moles of solute to the total number of moles (solute plus solvent) mole fraction (x) = amount (mol) of solute/ amount (mol) of solute + amount (mol) of solvent

pressure has little effect on the solubility

of liquids and solids. But it has a major effect on the solubility of gases

semipermeable membrane

one that allows solvent, but not solute, to pass through

ideal solution

one that follows Raoult's law at any concentration

ion-induced dipole forces

one type of charge-inducded dipole force, rely on polarizability. They arise when an ion's charge distorts the electron cloud of a nearby nonpolar molecule, giving it a temporary dipole moment. nonpolar solute in a polar solvent that also contains dissolved ions

a reaction has an individual order "with respect to" or "in" each reactant, and an

overall order, the sum of the individual orders

reaction energy diagram

plots how potential energy changes as the reaction proceeds from reactants to products (the reaction progress). The diagram shows the relative energy level of reactants, products, and transition state, as well as the forward and reverse activation energies and the enthalpy of reaction

soluble proteins have

polar-ionic exteriors and nonpolar interiors.

frequency factor

product of the collision frequency Z and an orientation probability factor p which is specific for each reaction

concentration

proportion of a substane in a mixture, so it is an intensive property (like density and temperature)

enzyme

protein catalyst whose function has been perfected through evolution. they are typically globular proteins with complex shapes and molar masses ranging from about 15,000 to 1,000,000 g/mol.

A solution usually has higher entropy than the

pure solute and pure solvent because the number of ways to distribute the energy is related to the number of interactions between different molecules

a solution boils at a higher temperature than the

pure solvent. This colligative property results from the vapor pressure lowering

solubility is a quantitative term but dilute and concentrates are

qualitative, referring to the relative amounts of dissolved solute

tonicity

refers to the tone, or firmness of a cell. placing a cell in an isotonic solution, one that has the same concentration of particles as the cell fluid, maintains the cell's normal shape when water enters and leaves the cell at the same rate. hypotonic solution has a lower concentration of particles, so water enters the cell faster than it leaves, causing the cell to burst. hypertonic solution has a higher concentration of particles, so the cell shrinks because water leaves faster than it enters

boiling point elevation (deltaTb)

results because a higher temperature is needed to raise the solution's vapor pressure to equal Pext boiling point elevation is proportional to the concentration of solute deltaTb = Kbm where Kb is the molal boiling point elevation constant and m is molality deltaTb = Tb(solution) - Tb(solvent)

the amino acid sequence of a protein determines its

shape, which determines its function

lipid bilayer

sheetlike double layer of phospholipids, with the tails of the two layers touching and the heads in the water. These structures are favored energetically because of their intermolecular forces: * Ion-dipole forces occur between polar heads and water inside and outside * Dispersion forces occur between nonpolar tails within the bilayer interior * Minimal contact exists between nonpolar tails and water

average rate

slope of the line joining two points along the curve over a given period of time

rate-determining step (or rate-limiting step)

slower step than other elementary steps. limits how fast the overall reaction proceeds. Therefore, the rate law of the rate determining step becomes the rate law for the overall reaction

active site

small part of an enzyme's surface that is a region whose shape results from the amino-acid side chains involved in catalyzing the reaction. Often far apart in the sequence of the polypeptide chain, these groups lie near each other because of the chain's three-dimensional folding.

Solubility in water is high for

smaller alcohols. n= 0, 1, or 2 carbons

just as separate molecules attract each other,

so do distant groups on the same molecule

the solvent is the most abundant component but in some cases the substances are miscible meaning

soluble in each other in any proportion

suspension

a heterogeneous mixture containing particles large enough to be visibly distinct from the surrounding fluid

strong electrolytes

soluble salts, strong acids, and strong bases -dissociate completely, so their solutions conduct well

hydration

solvation in water.

osmotic pressure

a net flow of solvent into the more conentrated solution causes a pressure. Net flow of water into a solution increases its volume and thus decreases the concentration

Alcohols are organic compounds that have a dual polarity

a polar hydroxyl (-OH) group bonded to a nonpolar hydrocarbon group. The OH portion interacts through strong H bonds with water and through weak dipole-induced dipole forces with hexane The hydrocarbon portion interacts through dispersion forces with hexane and through very weak dipole-induced dipole forces with water

the backbone of a protein is

a polypeptide chain: an alpha-carbon connected through a peptide bond to the next alpha carbon, and so forth

Chemical kinetics

the study of how fast changes occur in chemical reactions, it focuses on the reaction rate

half-life

the time it takes for the reactant concentration to reach half its initial value

a catalyst causes a lower total activation energy by providing a different mechanism for the reaction

the total of the activation energies for both steps of the catalyzed pathway is less than the forward activation energy of the uncatalyzed pathway

Raoult's law

the vapor pressure of solvent above a solution (Psolvent) equals the mole fraction of solvent (Xsolvent) times the vapor pressure of the pure solvent (P*solvent) delta P = P*solvent - Psolvent = Xsolvent x P*solvent

volume percent [% (v/v)]

the volume of solute in 100 volumes of solution volume percent = volume of solute/volume of solution x 100

oil is insoluble in water because

the weak dipole-induced dipole forces between oil and water molecules cannot replace the strong H bonds between water molecules or the extensive dispersion forces within the oil

ion-dipole forces

attractions between ions and polar molecules. they are the principal force involved when an ionic compound dissolves in water. Two events occur simultaneously: * Forces compete * Hydration shells form. Ionic solute in a polar solvent

Hydrogen bonding

attractions between molecules with an H atom bonded to N, O, or F. It is the principal force in solutions of polar, O- and N-containing organic and biological compounds, such as alcohols, amines, and amino acids.

Henry's law

expresses the quantitative relationship between gas pressure and solubility: the solubility of a gas (Sgas) is directly proportional ot the partial pressure of the gas (Pgas) above the solution: Sgas = kH x Pgas kH is the henry's law constant and is specific for a given gas solvent combination at a given temperature with Sgas in mol/L and Pgas in atm.

homogeneous catalyst

exists in solution with the reaction mixture, so it must be a gas, liquid, or soluble solid

rate law (or rate equation)

expresses the rate as a function of concentrations and temperature.

reaction order from concentration and time data in a graph

first order - straight line when you plot ln [reactant] vs t second order - straight line when you plot 1/[reactant] vs t zero order - straight line when you plot [reactant] vs t

transition state theory

focuses on the high-energy species that exists at the moment of an effective collision when reactants are becoming products

II(atm) = MRT =

nsolute/Vsoln x RT

Tyndall effect

the scattering of light by a colloid

solubility in hexane is low for

the smallest alcohol

units of rate constant k =

(L/mol)^order-1 divided by unit of t

dipole-dipole forces

(attractions between polar molecules), in the absence of H bonding, allows polar molecules like propanal to dissolve in polar solvents like dichloromethane.

Unit for the rate of change of concentration/time =

(mol)/(L*s) or any unit of time that is convenient for the reaction

Membrane proteins, which play countless essential roles, differ fundamentally from soluble proteins in terms of their dual polarity:

* Soluble proteins have polar exteriors and nonpolar interiors. They form ion-dipole and H-bonding forces between water and polar groups on the exterior and dispersion forces between nonpolar groups in the interior * Membrane proteins have exteriors that are partially polar (red) and partially nonpolar (blue). They have polar groups on the exterior portion that juts into the aqueous surroundings and nonpolar groups on the exterior portion embedded in the membrane. These nonpolar groups form dispersion forces with the phospholipid tails of the bilayer. Channel proteins also have polar groups lining the aqueous channel.

drawbacks of molarity

* effect of temperature - heat affects volume * effect of mixing - volume is not additive

advantages of molality

* effect of temperature - mass is not affected by temperature * effect of mixing - mass is additive

colloidal particles range in diameter from

1 to 1000 nm. a colloid has a very large total surface area

steps for studying the kinetics of a reaction

1. series of plots of concentration vs time determine slope of tangent at t0 for each plot 2. initial rates compare initial rates when [A] changes and [B] is held constant and vice versa 3. reaction orders substitute initial rates, orders, and concentrations into rate = k[A]^m[b]^n and solve for k 4. rate constant (k) and actual rate law

three common approaches to measuring concentration as a reaction proceeds

1. spectrometric methods - measure the concentration of a component that absorbs (or emits) characteristic wavelengths of light. Known amounts of reactants are injected into a tube of known volume within a spectrometer which is set to measure the wavelength and intensity of the color. The rate of formation is proportional to the increase in that intensity over time. 2. conductometric methods - rely on the change in electrical conductivity of the reaction solution when nonionic reactants form ionic products, or vice versa. The more dissociation the more ions form so the conductivity of a reaction mixture increases. 3. Manometric methods - employ a manometer attached to a reaction vessel of fixed volume and temperature. The manometer measures the pressure change in the vessel due to a reaction that involves a change in the number of moles of gas. The rate is directly proportional to the increase in pressure as gas forms

three criteria for a valid mechanism

1. the elementary steps must add up to the overall balanced equation 2. the elementary steps must be reasonable. They should involve one reactant particle (unimolecular) or two (bimolecular) 3. the mechanism must correlate with the rate law, not the other way around

integrated rate law for a second-orer reaction

1/[A]_t - 1/[A]_0 = kt second-orer reaction; rate = k[A]^2

rate =

1/mol of concentration * change in concentration/change in time

integrated rate law

A mathematical expression for reactant concentration as a function of time

Which ion has greater charge density in each following pair: Na+ or Cs+ Sr+ or Rb+ O2- or F- K+ or Cl- Mg or Cs

Charge density decreases down a group and right on a period. Higher charge density means higher deltaH. Larger the charge higher the charge density. Charge is more important than volume Charge/Volume Na+ Sr2+ O2- K+ (has a smaller volume. and greater ability to attract ions) Mg

change in Hrxn =

Ea(fwd) - Ea(rev)

Zero order

If the rate does not change when [A] doubles, the rate does not depend on [A], but we express this fact mathematically by saying that the rate depends on [A] raised to the zero power. [A]^0. The reaction is zero order in A and zero order overall: rate = k[A]^0 = k

First order

If the rate doubles when a reactant doubles, the rate depends on the reactant raised to the first power. Thus the reaction is first order in (or with respect to) the reactant and first order overall: Rate = k[A]^1 = k[A]

Which of the following statements describing solutions is NOT true?

Solutions are colorless. True statements are - The particles in a solution are atomic or molecular -Making a solution involves a physical change - Solutions are homogeneous mixtures

When a solid dissolves, each particle/ion is removed from the crystal by interaction with the solvent to form a complex (e.g. dissolution of NaCl). This process of surrounding each ion with solvent molecules is called

Solvation (hydration)

k (rate constant) increases exponentially as

T increases

integrated rate law fora zero-order reaction

[A]_t - [A]_0 = -kt zero-order reaction; rate = k[A]^0 = k

ionic atmosphere

a cluster of ions of net opposite charge surrounding a given ion in solution

colloids

a dispersed (solute-like) substance is distributed throughout a dispersing (solvent-like) substance. The particles are larger than simple molecules but too small to settle out. They are classified by the physical state of the dispersed and dispersing substances. Foams - gas dispersed in a liquid Styrofoam is a solid foam, a gas dispersed in a solid sols, solids dispersed in water emulsion, liquid dispersed in another liquid

Dna exists as two chains wrapped around each other in

a double helix that is stabilized by intermolecular forces * On the more polar exterior, negatively charged sugar-phosphate groups interact with the aqueous surroundings via ion-dipole forces and H bonds * In the less polar interior, flat N-containing bases stack above each other and interact by dispersion forces. *Bases form specific interchain H bonds; that is, each base in one chain is always H bonded with its complementary base in the other chain. Thus, the base sequence of one chain is the H-bonded complement of the base sequence of the other.

A catalyst speeds up the forward and reverse reactions thus

a reaction has the same yield with or without a catalyst, but the product forms faster

reaction mechanism

a sequence of single reaction steps that sum to the overall equation

fractional distillation

a solution of two or more volatile components is attached to a fractionating column packed with glass beads, which increases surface area; the column is connected to a condenser and collection flask. As the solution is heated and the vapor mixture meets the beads, numerous vaporization-condensation steps enrich the mixture until the vapor leaving the column, and thus the liquid finally connected, consists only of the most volatile components

reaction intermediate

a substance formed in one step of the mechanism and used up in a subsequent step during the reaction. intermediates are less stable than the reactants and products, but unlike much less stable transition states, they have normal bonds and can sometimes be isolated

catalyst

a substance that increases the reaction rate without being consumed. Each catalyst has its own specific way of functioning, but in general a catalyst provides a different reaction mechanism with a lower activation energy, which in turn makes the rate constant larger, and thus the reaction rate higher: catalyst -> lower Ea -> larger K -> higher rate

entropy (S)

a thermodynamic quantity related to the number of ways the energy of a system can be dispersed through the motions of its particles

Reaching the transition state does not guarantee that a reaction will proceed to products because

a transition state can change in either direction

amino acids

about 20 different amino acids occur in porteins, which range in size from about 50 amino acids to several thousand

Dipole-induced dipole forces

also based on polarizability, arise when a polar molecule distorts the electron cloud of a nonpolar molecule. They are weaker than ion-induced dipole forces because the charge of each pole is less than an ion's. The solubility in water of atmospheric O2, N2, and noble gases, while limited, is due in part to these forces. a nonpolar solute in a polar solvent

vapor pressure of nonvolatile nonelectrolyte solutions

always lower than the vapor pressure of the pure solvent. the fundamental reason for this lowering involves entropy, specifically the relative change in entropy that accompanies vaporization of solvent versus vaporization of the solution. A liquid vaporizes because a gas has higher entropy.

Molarity (M) =

amount (mol) of solute/ volume (L) of solution

if reactant molecules collide with a certain minimum energy, they reach

an activated state, from which they can change to products; collisions that occur with an energy below this minimum leave the reactant unchanged

Activation energy (Ea)

an energy threshold that the colliding molecules must exceed in order to react

polar and ionic groups

attract water but nonpolar groups do not

a key function of a cell membrane is to

balance internal and external ion concentrations: Na+ is excluded from the cell, and K+ is kept inside. Gramicidin A and similar antibiotics act by forming channels in the cell membrane of a bacterium through which ions flow. Two helical gramicidin A molecules, their nonpolar groups outside and polar groups inside, lie end to end to form a channel through the membrane. The nonpolar outside stabilizes the molecule in the cell membrane through dispersion forces, and the polar inside passes the ions along using ion-dipole forces, like a bucket brigade.

reaction orders cannot be deduced from the

balanced equation but must be determined from experimental data

for nonpolar or slightly polar gases

boiling point generally correlates with solubility in water. A higher boiling point is an indication of stronger intermolecular forces, which result in a greater solubility in water

If the rate limiting step in a mechanism is not the initial step, the product of the fast initial step

builds up and starts reverting to reactant. With time, this fast, reversible step reaches equilibrium, as product changes to reactant as fast as it forms.

State which solute is more soluble in the given solvent and why: 1-butanol (CH3CH2CH2CH2OH) or 1,4 butanediol (HOCH2CH2CH2CH2OH) in water. chlorform (CHCL3) or carbon tetrachlorid (CCl4) in water

butanediol has more HO groups which makes it able to create more hydrogen bonds so it is more soluble CHCL3 is polar like water so it is more soluble

If we use the product to determine the rate then the formula is

change in concentration/change in time no negative sign because concentration 2 is greater than concentration 1 which will result in a positive answer

substrates

collide with the active site and become attached through intermolecular forces causing the chemical change to begin

nonelectrolytes

compounds such as sugar and alcohol do not dissociate into ions at all and do not conduct a current

For the rate of a reaction, we measure the changes in

concentrations of reactants or products per unit time: reactant concentrations decrease while product concentrations increase as the reaction proceeds -(change in concentration (M)/change in time) It is negative because reaction rate must be positive but the 2nd concentration is lower than the 1st one.

an aqueous solution of electrolytes

conducts a current because the solute separates into ions as it dissolves

unsatured solution

contains less than the equilibrium concentration of dissolved solute; add more solute, and more will dissolve until the solution is saturated

supersaturated solution

contains more than the equilibrium concentration and is unstable relative to the saturated solution. You can often prepare a supersaturated solution if the solute is more soluble at higher temperature. While heating, dissolve more than the amount required for saturation at some lower temperature, and then slowly cool the solution. If the excess solute remains dissolved, the solution is supersaturated. Add a "seed" crystal of solute or tap the container, and the excess solute crystallizes immediately, leaving behind a saturated solution.

nucleic acids

contains the chemical information that guides the design and construction, and therefore the function, of all proteins. They are unbranched polymers made up of smaller units called mononucleotides. Each mononuicleotide consists of an N-containing base, a sugar, and a phosphate group.

dispersion forces

contribute to the solubility of all solutes in all solvents, but they are the principal intermolecular force in solutions of nonpolar substances

in a protein, the carboxyl group of one amino acid is linked

covalently to the amine group of the next by a peptide bond

gas solubility in water

decreases with rising temperature. when the temperature rises, the average kinetic energy increases, allowing the gas particles to easily overcome these forces and re-enter the gas phase

for ionic compounds in water, the heat of solution is the lattice energy (always positive) plus the combined heats of hydration of the ions (always negative)

delta H soln = deltaH lattice + deltaH hydr of the ions

heat or enthalpy of solution (delta H solution)

delta H solution = delta H solute + delta H solvent + delta Hmix

heat (or enthalpy) of hydration (deltaH hydr)

deltaH solution = deltaH solute + deltaH hydr

half-life of a second-order reaction

depends on reactant concentration t_1/2 = 1/k[A]_0 the half-life is inversely proportional to the initial reactant concentration

vapor pressure lowering (delta P)

difference in vapor pressure

half-life of a 0 order reaction

directly proportional to the initial reactant concentration t_1/2 = [A]_0/2k zero-order process; rate = k

oil is soluble in hexane because

dispersion forces in one can replace the similar dispersion forces in the other

The heat of hydration is a key factor in

dissolving an ionic solid. Breaking the H bonds in water is more than compensated for by forming the stronger ion-dipole forces, so hydration of an ion is always exothermic

the same forces that act between separate molecules are responsible for a protein's shape because

distant groups on the protein chain end up near each other as the chain bends

molality (m)

does not contain volume in its ratio; it is the number of moles of solute dissolved in 1000g (1kg) of solvent molality (m) = amount (mol) of solute/ mass (kg) of solvent

colloid

heterogeneous mixture. Has two or more phases. They may be visibly distinct or not. In a colloid the particles are typically macromolecules or aggregations of small molecules that are dispersed so finely they don't settle out

most solids are more soluble at

higher temperatures. However, there are some exceptions

solution

homogenous mixture; it exists as one phase. In solution, the particles are individual atoms, ions, or small molecules

van't Hoff factor

i = measured value for electrolyte solution/ expected value for nonelectrolyte solution

elementary reactions (or elementary steps)

individual steps that make up a reaction mechanism. Each describes a single molecular event - one particle decomposing, two particles combing, and so forth.

unimolecular reaction

involves the decomposition or rearrangement of a single particle

the number of solute particles, not their chemical identity

makes a difference in the colligative properties

all gases are

miscible with each other

alloys

mixtures of elements that have a metallic character, are solid-solid solutions two categories: substitutional alloy - atoms of one element replace atoms of the main element. this occurs when the atoms of the elements in the alloy are similar in size. interstitial alloy - atoms of an element (nonmetals are typical in this type of alloy) fill some spaces (interstices) between atoms of the main element in the body-centered array

mole percent (mol %)

mole fraction x 100

concentration affecting rate

molecules must collide to react. A major factor influencing reaction rate is reactant concentration. Rate is proportional to collision frequency which is proportional to concentration

temperature affecting rate

molecules must collide with enough energy. Temperature affects reaction rate by increasing the frequency and more importantly the energy of collisions

physical state affecting rate

molecules must mix to collide. collision frequency, and thus reaction rate, also depends on the physical state of the reactants, which determines how easily the reactants mix. When reactants are in the same phase, random thermal motion brings them into contact, but gentle stirring mixes them further. When the reactants are in different phases, contact occurs only at the interface between the phases so vigorous stirring or even grinding may be needed.Thus, the more finely divided a solid or liquid reactant, the greater its surface area, the more contact it makes with the other reactant, and the faster the reaction occurs.

vapor has a higher mole fraction of the

more volatile component

phospholipids

most abundant molecules in cell membranes. Like soaps they have a dual polarity - a nonpolar tail consists of two fatty acid chains, and an organophosphate group is the polar-ionic head

amino acids can be classified by the polarity or charge of their side chains:

nonpolar, polar, and ionic

heterogeneous catalyst

speeds up a reaction in a different phase. Most often solids interacting with gaseous or liquid reactants, these catalysts have enormous surface areas. Very early in the reaction the rate depends on reactant concentration, but almost immediately, the reaction becomes zero order: the rate-determining step occurs on the catalyst's surface, so once the reactant covers it, adding more reactant cannot increase the rate further

all enzymes catalyze by

stabilizing the reaction's transition state

Formation of a solution

step 1. Solute particles separate from each other. This step involves overcoming intermolecular (or ionic) attractions, so it is endothermic: solute (aggregated) + heat -> solute (separated) delta H solute > 0 Step 2. Solvent particles separate from each other. This step also involves overcoming attractions so it is endothermic. Solvent (aggregated) + heat -> solvent (separated) delta H solvent > 0 Step 3. Solute and solvent particles mix and form a solution. The different particles attract each other and come together, so this step is exothermic: Solute (separated) + solvent (separated) -> solution + heat DeltaH mix < 0 The overall process is called a thermochemical solution cycle

like dissolves like

substances with similar types of intermolecular forces dissolve in each other

Solution formation involves the interplay of two factors

systems change toward a state of lower enthalpy and higher entropy, so the relative sizes of deltaHsoln and deltaSsoln determine whether a solution forms

half life for first-order

t_1/2 = ln2/k = 0.693/k first-order process; rate = k[A] because no concentration term appears, for a first-order reaction, the time it takes to reach one-half the starting concentration is a constant and, thus, independent of reactant concentration

energy of collisions

temperature affects the kinetic energy of the molecules. Rate is proportional to collision energy which is proportional to temperature

a reversible reaction has two activation energies.

the activation energy for the forward reaction, Ea(fwd) is the energy difference between the activated state and the reactants; the activation energy for the reverse reaction, Ea(rev), is the energy difference between the activated state and the products

reaction rate

the change in the concentration of reactants (or products) as a function of time. Different reactions have different rates: in a faster reaction (higher rate), the reactant concentration decreases quickly, whereas in a slower reaction (lower rate), it decreases slowly

At a given temperature, when solid is dissolving at the same rate as dissolved particles are recrystallizing

the concentration remains constant and undissolved solute is in equilibrium with dissolved solute

Four factors that affect rate that we can control

the concentrations of reactants, their physical state, the temperature of the reaction, and the use of a catalyst

initial rate

the instantaneous rate at the moment the reactants are mixed (t=0).

salts are soluble in water because

the ion-dipole attractions between ion and water are similar in strength to the strong attractions between the ions and the strong H bonds between water molecules, so they can replace each other

salts are insoluble in hexane because

the ion-induced dipole forces between ion and nonpolar hexane are very weak and cannot replace the strong attractions between the ions

solubility (s) of a solute

the maximum amount that dissolves in a fixed quantity of a given solvent at a given temperature, when an excess of the solute is present

molecularity

the number of reactant particles in the step. characterizes elementary steps.

hydration shells

the oriented cluster of water molecules that surrounds an ion in aqueous solution. In the innermost shell, normal hydrogen bonding between water molecules is disrupted to form the ion-dipole forces. But these water molecules are H bonded to others in the next shell, and those are H bonded to others still farther away.

physical state of the solvent usually determines

the physical state of the solution

osmotic pressure (II)

the pressure that results from the ability of solvent, but not solute, particles to cross a semipermeable membrane. The pressure required to prevent the net movement of solvent across the membrane osmotic pressure is proportional to the number of solute particles in a given volume, that is, to the molarity

solvation

the process of surrounding a solute particle with solvent particles deltaHsolvation = deltaH solvent + deltaH mix

A solution freezes at a lower temperature than

the pure solvent, and this colligative property also results from vapor pressure lowering.

instantaneous rate

the rate at a particular instant during the reaction. The slope of a line tangent to the curve at any given point gives the instantaneous rate at that time

Second order

the rate quadruples when [A] doubles, the rate depends on [A] squared, [A]^2. In this case, the reaction is second order in A and second order overall: Rate = k[A]^2

the factor p is related to the structural complexity of the reactants. p is

the ratio of effectively oriented collisions to all possible collisions

charge density

the ratio of its charge to its volume -heat of hydration for an ion is dependent on it In general the higher the charge density, the more negative deltaHhydr is.

soap

the salt formed when a strong base (a metal hydroxide) reacts with a fatty acid, a carboxylic acid with a long hydrocarbon chain. a typical soap molecule is made up of a nonpolar "tail" 15-19 carbons long and a polar-ionic "head" consisting of a COO- group and the cation of the strong base. The cation greatly influences a soap's properties.

in a tiny fraction of collisions in which molecules are moving fast enough

their kinetic energies push them together with enough force to overcome the repulsions and surpass the activation energy. And, in an even tinier fraction of these sufficiently energetic collisions, the molecules are oriented effectively. At some point during this smooth transformation, a species with partial bonds exists that is neither reactant nor product. This very unstable species called the transition state (or activated complex) exists only at the instant of highest potential energy. Thus, the activation energy of a reaction is used to reach the transition state.

bimolecular reaction

two particles collide and react

colligative properties of solutions

vapor pressure lowering, boiling point elevation, freezing point depression, and osmotic pressure

proteins

very large molecules (called polymers) formed by linking together many smaller molecules called amino acids

to find the values of m an dn

we run a series of experiments in which one reactant concentration changes while the other is kept constant, and we measure the effect on the initial rate in each case

weak electrolytes

weak acids and weak bases- dissociate very little, so their solutions conduct poorly

mass percent [% (w/w)]

with respect to solution, mass percent means mass of solute dissolved in 100 parts by mass of solution mass percent = mass of solute/ mass of solute+mass of solvent x 100 = mass of solute/mass of solution x 100