deck Flashcards
when Kc > 1, is the reaction efficient or inefficient?
efficient
what is happening in a solution with both solid and liquid in it at equilibrium?
ions in the liquid are solidifying (precipitating) at the same rate that the solid is dissolving
on a concenttration/time graph, what does the slope represent?
rate of change
what does Kc tell us?
called the equilibrium concentration constant
tells us how well a reaction proceeds, dependant on reactant concentration and coefficients in equation (more particles = faster rate, larger coefficient = greater effect on rate)
Kc (and K) are different for every reaction
rate varies as [reactants]^(any coefficients)
what is the Kc expression
([C]^c x [D]^d) / ([A]^a x [B]^b)
where C and D are products, A and B are reactants, and the lowercase letters are any coefficients
what is happening in regards to
- amount of reactants/products
- Kc expression
- which side is favoured
- efficiency
when Kc<1?
large amount of reactants, small amount of products
bigger denominator in Kc expression
reactants are favoured
reaction proceeds less than 50%
inefficient reaction
rules for substances included in Kc expression for
H2O
solids
liquids
- include H2O(g)
- in aqueous system, don’t include H2O(l) ([water] = 1)
- don’t include solids (concentration cannot vary)
- in gaseous system, don’t include liquids
what is the rule saying that when a stress is applied to an equilibrium system, the system response is the opposite to minimize the stress?
le chatelier’s principle
true or false, we can determine which side is favoured using equilibrium shift
false, only from Kc value
which direction does equilibrium shift when we add products?
left, towards reactants
what is the system response to adding reactants
concentration of reactants decreases, concentration of products increases
how does system response effect equilibrium
equilibrium shifts towards the side that increased from the system response (THE OPPOSITE SIDE THE STRESS WAS ADDED if the stress was adding reactants of products)
true or false, you cannot change pressure in liquid equilibria
true, only gas equilibria
name the 3 ways you can change pressure in a gaseous system
add/remove a reactant/product - equilibrium shifts away from the side that was added to or towards the side from which was removed
reduce volume of container - equilibrium shift towards the side with fewer gaseous moles (opposite for an increase in volume), if the same then no effect
add an inert gas - no equilibrium shift
true or false, reducing container volume in an equilibrium system shifts equilibrium towards the side with more gaseous moles
false, shifts towards the side with less gaseous moles
true or false, increasing container volume in an equlibrium system shifts equilibrium towards the side with more gaseous moles
true
what can affect the value of Kc and why
only temperature. it is like adding a stress, the energy term will be a reactant or product
add=equilibrium shifts away
remove=towards
when Kc increases as temperature increases, which way does equilibrium shift?
right (towards products)
when Kc increases as temperatire increases, is the reaction endothermic or exothermic?
endothermic
bronsted lowry definition of acid
can donate H+ ions
reacts with water to form H3O+ (hydronium ion) and a conjugate base
bronsted lowry definition of base
can accept protons (like H+), meaning it has a negative charge
reacts with water to produce OH- (hydroxide ion) and a conjugate acid
what is [H+] in a strong acid solution and why
[H+] = [strong acid]
(original concentration of the strong acid)
because it’s 100% ionized
assumption for strong acids reacting with water at equilibrium (amount of reactant and product)
very little reactant (~0%), lots of products (~100% each)
assumption for weak acids reacting with water at equilibrium (amount of reactant and product)
lots of reactant (~99%), very little products (~1% each)
when do you use the forward arrow
reactions with strong acids/bases and water to show that they fully ionize/dissociate
efficiency of strong and weak acid reactions relative to Kc
strong - efficient, Ka>1
weak - inefficient, Ka<1
what is Ka, Kb
Ka is Kc but for acids
Kb is for bases
they are inversely related
what is the net ionic equation for
HCl(aq) + NaOH(aq) <=> H2O(l) + NaCl(aq)
CHEM 30 NET IONIC
H3O+(aq) + OH-(aq) <=> H2O(l) + H2O(l)
2H2O(l) as the product is incorrect
what is a polyprotic acid/base
polyprotic acids can donate more than one H+ to a base (they have more than one acidic H that is not bonded to a C)
polyprotic bases can accept more than one H+ from an acid (they have a charge that is more negative than 1-)
reactions with these happen one proton transfer at a time (multiple reactions)
what is an amphiprotic species/substance and what is the most common one?
they can act as both a base and an acid in different reactions
water is the most common
conjugate acids of a polyprotic base OR conjugate bases of a polyprotic acid
found on both sides of the acid/base table
how are strong acids communicated in net ionic equations?
H3O+ because they ionize completely
how are weak acids communicated in net ionic equations?
as they are because they don’t create much H3O+ at all
how are strong bases communicated in net ionic equations?
OH- because they dissociate completely
how are weak bases communicated in net ionic equations?
as their anion because they dissolve but don’t make much OH- at all
(ex. NaNO2 would be NO2- in net ionic)
when two amphiprotic species are the reactants in an equation, how do you tell which one donates a H+?
the one that is the stronger acid on the acid/base table acts as the acid and donates the H+ to the other
how to calculate Kb from acid/base table
Kb = (1.0x10^-14) / (Ka)
how to know if a reaction with H3O+ or OH- ions proceeds and which side is favoured
always proceeds with any hydronium or hydroxide ions, the side opposite from these ions is favoured
how to calculate pH given [OH-]
pH = 14.00 - (-log[OH-])
what is the shortcut to solve for [H3O+] in a weak acid
[H3O+] = square root of ([WA] x Ka)
ASSUMING [H3O+] «_space;[WA]
(«_space;means significantly less than)
what is the shortcut to solve for [OH-] in a weak base?
[OH-] = square root of ([WB] x Kb)
ASSUMING [OH-] «_space;[WB]
(«_space;means significantly less than)
true or false, pH is an equilibrium concentration
true
describe the basic steps and formulas to solve this question
the volume of 6.00mol/L NaOH required to neutralize 2.20kg of HN3(l) is ________L.
convert kg to g, find molar mass of HN3, and use n=m/M.
using molar ration (1:1) obtain n for NaOH, use V=n/c to solve.
(answer = 8.52L)
what is the Ka expression for hydroazoic acid
(HN3, H3O+, H2O, and N3- are involved in the reaction)
Ka = ([H3O+][N3-]) / [HN3]
describe the basic steps and formulas to solve this question
there is a .15mol/L concentration of NH3(aq). it’s pH is _____
[WB] = .15mol/L
find Ka of conjugate acid and use Kb = Kw / Ka.
find [OH-] using square root of ([WB] x Kb).
find pOH by taking the -log of that answer.
find the pH by subtracting 14.00 - that answer.
(answer: 11.21)
i hope you know what indicators are
.
basic reactant and product names for a titration
acid + base <=> salt + water
generalizations of the types of acid/base used in sample and titrant
consider acid/base strength, measured concentration (known or unknown), and where the indicator is
sample - generally weak acid/base, unknown concentration, with a pH indicator
titrant - generally strong acid/base, known concentration
what reaction is happening in a weak acid titration when 0mL if titrant is added
WA + water <=> hydronium ion + CB
ex. HCN + H2O <=> H3O+ + CN
where is the starting pH of a weak acid titration and why?
generally between 2 and 6 (never 1 or 7) because a small amount of H3O+ has already formed in reaction with water, but there is not much product in a reaction with a weak acid so it will be higher than 1
what reaction is happening during a monoprotic weak acid titration?
WA + hydroxide ion <=> water + CB
ex. HCN + OH- <=> H2O + CN-
where is the buffer region in a monoprotic weak acid titration and what is present there?
the most flat section of the graph between the starting point and the equivalence point.
1/2 of the sample is the WA, the other 1/2 is its CB
true or false, signifying to us the end of the reaction, the equivalence point has some excess titrant
false, there is no excess titrant at the equivalence point, only after
what is the equation to the equivalence point in a monoprotic weak acid titration
WA + OH- <=> H2O + CB
same equation as what is happening during the titration
how to determine the overall equation for a polyprotic weak acid / weak base titration
add all equivalence point equations (add all reactants on one side, add all products to the other, combining coefficients if needed, likely for water and hydronium/hydroxide)
what can be a buffer
must be a WEAK ACID AND ITS CONJUGATE BASE
true or false, HCl and Cl- is a buffer
false, its a strong acid not a weak acid (must be weak acid)
true or false, H3PO4 and PO4 3- is a buffer
false, not conjugates (must be conjugates)
how to determin e the pH at which a buffer is efective
take Ka of the weak acid form of the buffer, use pH = -log(Ka) to find pH
what is the general equation when solving buffer pH range?
react WA + water <=> CB + H3O+
true or false, water cannot be a buffer with hydroxide ion
true, water does not act as an acid generally
