Chemistry > Exam 3 > Flashcards

Exam 3 Flashcards

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1
Q

Brønsted-Lowry Acids

A

chemical species that donates H+ ions

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2
Q

Brønsted-Lowry Bases

A

chemical species that accepts H+ ions

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3
Q

What happens to a strong acid or base when in an aqueous solution?

A

it completely dissociates

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4
Q

What happens to a weak acid or base when in an aqueous solution?

A

it partially dissociates

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5
Q

Ka (4)

A
  • equilibrium constant for acid
  • represents the strength of an acid
  • only reported for weak acids
  • [H3O+][A-]/[HA]
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6
Q

Kb (4)

A
  • equilibrium constant for base
  • represents the strength of a base
  • only reported for weak bases
  • [HA][OH-]/[A-]
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7
Q

Conjugate Pair

A

two species that differ by one proton

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8
Q

pH

A

measure of the proton concentration in a solution

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9
Q

pOH

A

a measure of the hydroxide concentration in a solution

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10
Q

What is the relationship between pH and pOH?

A

pH + pOH = 14

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11
Q

What is the equilibrium reaction for a generic acid?

A

HA (aq) + H2O (ℓ) ⇌ H3O+ (aq) + A- (aq)

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12
Q

What is the relationship between pKa and Ka? (2)

A
  • pKa= -log[Ka]
  • Ka=10^-pKa
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13
Q

What is the equilibrium reaction for a generic base?

A

A- (aq) + H2O (ℓ) ⇌ HA (aq) + OH- (aq)

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14
Q

What is the relationship between pKb and Kb? (2)

A
  • pKa = -log[Kb]
  • Kb=10^-pKb
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15
Q

What happens when a strong acid and strong base are mixed together?

A

they neutralize each other and form water and a salt

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16
Q

What happens when a strong base and weak acid are mixed together?

A

they will react completely and form the conjugate weak base of the acid, which will then establish an equilibrium in the aqueous solution

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17
Q

What happens when a strong acid and a weak base are mixed together?

A

they react completely and form the conjugate weak acid of the weak base, which will then establish an equilibrium in the aqueous solution

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18
Q

Buffer

A

a solution with approximately equal concentrations of conjugate acid and conjugate base that is capable of resisting change in pH upon addition of an acid or base

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19
Q

What equation is used to calculate the pH of a buffer?

A

Henderson-Hasselbalch

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20
Q

Henderson-Hasselbalch Equation

A

pH = pKa + log[A-/HA]

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21
Q

What happens when the concentrations of conjugate acid and conjugate base are equal?

A

pH = pKa

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22
Q

What happens when a strong acid is added to a buffer?

A

the strong acid will react with the weak base and form the conjugate weak acid

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23
Q

What happens when strong base is added to a buffer?

A

the strong base will react with the weak acid and form the conjugate weak base

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24
Q

Buffer Capacity

A

a measure of the amount of acid or base that can be added to a buffer while maintaining the pH

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25
What is happening at the buffer region in a titration graph?
the weak acid reacts with the strong acid to make more weak base or vice versa
26
What is happening at the midpoint in a titration graph?
the moles of weak acid and base are equal to each other
27
What is happening at the equivalence point in a titration graph? (2)
- the moles of weak acid is equal to the moles of strong base or vice versa - the reaction is complete
28
What is happening at the initial point in a titration graph?
the strong base is the limiting reactant or vice versa
29
What is happening at the final stage in a titration graph?
the weak acid is the limiting reactant or vice versa
30
What would happen if a strong base was titrated into a strong acid?
the pH would be neutral (7) at the equivalence point
31
Indicators (2)
- chemical species with a physical property that changes abruptly near the equivalence point - the end point is signaled by the indicator's color change
32
pico- conversion
1 x 10^-12
33
nano- conversion
1 x 10^-9
34
micro- conversion
1 x 10^-6
35
milli- conversion
1 x 10^-3
36
kilo- conversion
1 x 10^3
37
Reaction Quotient (3)
- describes reaction mixtures under non-equilibrium conditions - represented by Q - Q = [C]^c[D]^d/[A]^a[B]^b
38
What does the value of Q compared to Keq tell us?
the direction of spontaneity
39
Direction of Spontaneity
the direction in which the reaction will proceed to reach equilibrium
40
What does it mean if Q < Keq?
the reaction must be shifted to the right (towards the products) to reach equilibrium
41
What does it mean if Q > Keq?
the reaction must be shifted to the left (towards the reactants) to reach equilibrium
42
What does it mean if Q = Keq?
the reaction is at equilibrium
43
In what ways do chemical reactions proceed?
spontaneously in order to move the system to a lower energy state
44
Gibbs Free Energy (2)
- quantity used to describe the energy changes of a chemical reaction - represented by G
45
ΔGrxn (2)
- the change in free energy associated with a chemical reaction - depends on the molar amounts of the chemical species
46
When is ΔGrxn spontaneous?
when ΔGrxn < 0 at a constant temperature and pressure
47
When is ΔGrxn non-spontaneous?
when ΔGrxn > 0
48
What is the lowest energy state in a reaction? (2)
- the equilibrium state - mixture of both products and reactants
49
What are standard state conditions? (3)
- 1 atm pressure - 1 M concentrations - 298 K
50
What is ΔG°rxn used for?
when a reaction is at equilibrium
51
What is the value of R for the ΔGrxn and ΔG°rxn equations?
8.314 J/molK
52
Enthalpy (H) (2)
- related to the energy associated with making and breaking chemical bonds - represented as ΔH
53
Entropy (S) (3)
- related to the disorder of a system - represented as ΔS - tends to increase spontaneously
54
Bond Enthalpy (2)
- a measure of how much energy is required to break a bond - kJ/mol
55
What is involved in breaking bonds?
an input of energy
56
What is involved with making bonds?
an output of energy
57
What happens to bonds during a chemical reaction?
reactants are broken, then new bonds are formed to make the products
58
ΔHrxn
approximately equal to the difference between the energy needed to break bonds in reactant and the energy released upon formation in the products
59
Exothermic
- reaction gives off heat - ΔH < 0
60
Endothermic
- reaction absorbs heat - ΔH > 0
61
When is entropy spontaneous?
ΔS > 0
62
What happens to entropy when there is equilibrium? (2)
- ΔS = 0 - there is a pure, perfectly crystalline substance at 0 K
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