Chem Test III
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When calculating K you must make this kind of table
If K is very small...
the equilibrium mixture will contain mainly reactants.
The equilibrium constant, K, allows us to do two things
- 1. predict the direction in which a reaction will proceed to reach equilibrium.
- 2. Calculate the concentrations of the reactants and products when equilibrium has been reached.
What is the reaction quotient, Q?
- a number obrainted by substituting a rea tant and produce concentrations or pp at any point in the reaction into and equilibriumm constant expression.
- Q= [D]d[C]c/[A]a[B]b
What three realtionships does Q have with K?
- Q=K where the Q must be at an equlibrium state.
- Q>K where the products are too large and that the reaction moves from right to left to establish equilibrium.
- Q<K where the reactants are too large and the reaction moves from left to right to establish equilibrium.
What is the quadratic equation?
x is equal to a negative b plus or minus the square root of b-squared minus 4ac, all over 2a
Le Chatelier's principle is?
if a system of equilibrium is changed by temp, pressure, or concentration in one of the components the system will shift its equilibrium position so as to counteract the effect of the disturbance.
What three ways can an equilibrium be disturbed?
- 1. concentration
- 2. pressure by changing the volume
- 3. temperature
When there is a concentration change what will happen?
the system reacts to consume some of the substance, or produce some.
When there is a pressure change what will happen?
- Changing the volume to change the pressure causes the moles of gas to reduce in a gaseous reaction.
- K is not effected but the partial pressures of the reaction do change.
When the temperature is changed what happens in an exo and endo thermic reaction?
- endo: reactants+ heat = products
- exo: reactants = products + heat
How does temperature changes effect K?
- endo: increasing T increases K
- exo: decreasing T decreases K
What is the effect of a catalyst on an equilibrium reaction?
A catalyst increase the rate at which the reaction will occur but it does not change anything else.
The arrhenius definitions of acid and base?
- - an acid is a substance that, when dissolved in water, increases the concentration of H+ ions.
- - a base is a substance that, when dissolved in water, increases the concentration of OH- ions.
Bronsted-Lowry acid and base definitions.
- -acid is a substance that donates a proton to another substance.
- -base is a substance that accepts a proton from another substance.
Acids and bases always work together in which was according to Bronsted-Lowry?
to complete and equilibrium the two substance involved has to take on the described roles of an acid and a base.
What is an amphiprotic substance?
a substance that can act as a acid or a base. This is determined by the other reactant and whether it is more basic or acidic than the amphiprotic substance.
Conjugate acid base pair is what?
and acid and a base such as HX and X- that only different from the present of a hydrogen proton.
Conjugate base is what?
what is left after the hydrogen proton is donated, every acid as one.
What is a conjugate acid?
is formed by adding a proton to a base. every base has one.
How do different strengths of acids and bases affect their conjugate part?
the stronger the acid the weaker the conjugate base; the stronger the base the weaker the conjugate acid.
A strong acid does what?
it completely transfers its protons to water and its conjugate base has a negligible tendancy to be protonated (to abstract protons).
A weak acid does what?
It only partially dissociates in aqueous sol'n and therefor exists as a mixture of acid molecules and their constituent ions. The conjugate base is a weak base as well.
a negligible acid does what?
Its conjugate base is a strong base which reacts completely with water, to form OH-ions
What does the position of the equilibrium favor when it comes to acid-base reactions?
the transfer of one proton of a stronger acid to a stronger base creating a weaker acid and a weaker base. Therefore, at equilibrium the mixture contains more weaker acid and base that stronger.
What is autoionization?
the process where water spontaneously forms low concentraions of H+ and OH- ions by proton transfer from one water moleculte to another.
What is the ion-product constant for water at 25 degrees?
What is pH and how it is effected by concentration of H+?
- pH= -log[H+]
- if the concentration increases pH decreases.
What is pOH?
What is pKw?
pKw= -log[H+] + -log[OH-]
p scales are useful with what equation?
Strong acids and bases are what that exist in (aq) entirely as ions?
What is Ka?
- The acid-dissociation constant.
- The larger the value of Ka the stronger the acid.
What is percent ionization and what is the relationship between the conc. of H+ and the conc of the weak acid?
- Percent ionization= [H+]eq/[HA]initialX 100%
- the percent ionization decreases as the concentration increases therefore the conc of H+ is not directly proportional to the conc. of the weak acid.
What is a general rule when deciding to use the quadratic formula or not?
if the quanitiy of x is more than 5% of the initial value it is better to use the quadratic formula.
What is a polyprotic acid?
an acid that has more than one donatable H+ (H2SO4)
What is Kb?
- Kb= [BH+][OH-]/[B]
- it is the base-dissociation constant.
What are amines?
A compound that has an available area for an H+ ion to attach. (NH3)
What is the relationship between Ka, Kb, and Kw?
Kw= Kax Kb=1.00x10^-14
What is the relationship between pKw= pKa x pKb ?
pKw= pKa x pKb = 14.00 @ 25 degrees
What is hydrolysis?
- Hydrolysis is the ability for ions to react with water to generate H= or OH- ions.
- If a hydrolysis reaction we are able to predict the pH
if Ka > Kb?
The solution is acidic.
The solution is basic
What are the rules on predicting whether a reaction with be acidic, basic or neutral?
- 1. the anion of a stong acid will not effect the pH.
- 2. the anion of a weak acid with cause the pH to increase.
- 3. a cation of a weak base will cause the pH to decrease.
- 4. The cations of group 1A and 2A will not affect pH because they are stong bases.
- 5. Other metal ions will cause a decrease in pH
- 6. When a there is a weak acid and weak base present in the solution the solution will follow which ever K is bigger.
What are the Lewis definitions of acid and base?
- Lewis Acid is an election-pair acception.
- Lewis acid is an election-pair donor.
How can hydrolysis be described in lewis acid base interaction?
The metal ion acts as a lewis acid and the whater molecule acts as lewis bases.
Whe does the acid-dissociation constats for hydrolysis reactions generally increase?
with increase charge of ions and decreasing radius of the ion.
Common strong acids are?
HCl, HBr, HI, HNO3, HClO3, HClO4, and H2SO4
Common Strong bases are ?
ionic hydroxides of alkali metals and heavy alkaline earth metals. such as NaOH, KOH, Ca(OH)2,
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