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Flashcards in Test 3 Deck (34):
1

Chemical Equilibrium

Achieved when the rates of the forward and revers reactions are equal and the concentrations of the reactants and products remain constant.

2

Equilibrium constant expression in terms of concentration

Kc = ([C]^c[D]^d) / ([A]^a[B]^b)

for any reaction at equilibrium, that is:
aA + bB cC + dD

Do not include solids and liquids in the expression, only aqueous solutions and gases.

3

Equilibrium constant expression in terms of pressure

Kp = ((P^c) of C) * ((P^d) of D) / ((P^a) of A) * ((P^b) of B)

P = partial pressure

4

Equation for relationship between Kc and Kp

Kp = Kc(RT)^change in n

Kp = equilibrium constant in terms of pressure
Kc = equilibrium constant in terms of concentration
R = 0.0821
T = temperature in Kelvin
change in n = change in moles of system = moles of gaseous products - moles of gaseous reactants

5

How to convert Celsius to Kelvin

C + 273

6

Physical Equilibrium

Changes that occur between two phases of the same substance are physical processes.

7

Homogeneous Equilibrium

Reactions in which all reacting species are in the same phase.

8

What is R?

R = 0.0821

9

Heterogeneous Equilibrium

Results from a reversible reaction involving reactants and products that are in different phases.

10

Multiple Equilibria Equation

Kc = K'c * K''c

Kc = overall equilibrium constant in terms of concentration
K'c = equilibrium constant in terms of concentration for first reaction
K''c = equilibrium constant in terms of concentration for second reaction

11

Rules for Writing Equilibrium Constants

1.) When the equation for a reversible reaction is written in the opposite direction, the equilibrium constant becomes the reciprocal of the original equilibrium constant.
2.) Each concentration term in the equilibrium constant expression is raised to a power equal to its stoichiometric coefficient...
doubling a chemical equation throughout = original Kc^2
tripling a chemical equation throughout = original Kc^3
halving a chemical equation throughout = original square root of original Kc
third a chemical equation throughout = cube root of original Kc

12

Reaction Quotient (Qc)

Found by substituting the initial concentrations into the equilibrium constant expression.

If Qc < Kc:
The ratio of initial concentrations of products to reactants is too small. To reach equilibrium, reactants must be converted to products; the system will shift from left to right.

If Qc = Kc:
The initial concentrations are equilibrium concentrations.
The system is at equilibrium.

If Qc > Kc:
The ratio of initial concentrations of products to reactants i too large. To reach equilibrium, products must be converted to reactants; the system will shift from right to left.

13

Quadratic Equation

x = (-b +- square root of (b^2 - 4ac)) / 2a

14

Le Chatlier's Principle

If an external stress is applied to a system at equilibrium, the system adjusts in such a way that the stress is partially offset as the system reaches a new equilibrium position.

15

Exothermic Reaction

Occurs when change in heat < 0
OR
When heat is considered a product (heat is released in this case)

16

Endothermic Reaction

Occurs when change in heat > 0
OR
When heat is considered a reactant (heat is used up in this case)

17

How does change in total pressure affect an equilibrium?

Only gaseous molecules are affected.

If increasing pressure, the system will adjust to decrease the pressure by shifting to the side of the equation that has fewer moles of gas.

If decreasing pressure, the system will adjust to increase the pressure by shifting to the side of the equation that has more moles of gas.

18

Strong Acids

Strong electrolytes that are assumed to ionize completely in water (H+)
Hydrochloric acid - HCl
Hydrobromic acid - HBr
Hydroiodic acid - HI
Nitric acid - HNO3
Perchloric acid - HClO4
Sulfuric acid - H2SO4
Chloric acid - HClO3

19

Ionization reactions of strong acids in water

HCl(aq) -----> H+(aq) + Cl-(aq)
HBr(aq) -----> H+(aq) + Br-(aq)
HI(aq) -----> H+(aq) + I-(aq)
HNO3(aq) -----> H+(aq) + NO3-(aq)
HClO4(aq) -----> H+(aq) + ClO4-(aq)
H2SO4(aq) -----> H+(aq) + HSO4-(aq)
HClO3(aq) -----> H+(aq) + CLO3-(aq)

20

Strong Bases

Strong electrolytes that ionize completely in water (OH-)
Lithium hydroxide - LiOH
Sodium hydroxide - NaOH
Potassium hydroxide - KOH
Calcium hydroxide - Ca(OH)2
Strontium hydroxide - Sr(OH)2
Barium hydroxide - Ba(OH)2

21

Ionization reactions of strong bases in water

LiOH(s) -----> Li+(aq) + OH-(aq)
NaOH(s) -----> Na+(aq) + OH-(aq)
KOH(s) -----> K+(aq) + OH-(aq)
Ca(OH)2(s) -----> Ca^2+(aq) + 2OH-(aq)
Sr(OH)2(s) -----> Sr^2+(aq) + 2OH-(aq)
Ba(OH)2(s) -----> Ba^2+(aq) + 2OH-(aq)

22

Ion-product Constant

Kw; the product of the molar concentrations of H+ and OH- ions at a particular temperature.

For any aqueous solution at 25 degrees Celsius:
Kw = [H+][OH-] = 1.0 * 10^-14

[H+] < [OH-]
Basic solution

[H+] = [OH-]
Neutral solution

[H+] > [OH-]
Acidic solution

23

pH

The negative logarithm of the hydrogen ion concentration in M (mol/L)

pH = -log[H3O+] or pH = -log[H+]

Acidic solutions: [H+] > 1.0 * 10^-7 M; pH < 7.00
Basic solutions: [H+] < 1.0 * 10^-7 M; pH > 7.00
Neutral solutions: [H+] = 1.0 * 10^-7 M; pH = 7.00

[H+] = 10^-pH

24

pOH

The negative logarithm of the hydroxide ion concentration in M (mol/L)

pOH = -log[OH-]

[OH-] = 10^-pOH

25

Equation for relationship between H+ and OH- ion concentrations

pH + pOH = 14.00

26

Conjugate acid-base pair properties

1.) If an acid is strong, its conjugate base has no measurable strength, i.e., it is extremely weak.
2.) Strong acids react completely to form H+ and their conjugate base. Weak acids react to a much smaller extent, producing H+ and their conjugate base WHILE the equilibrium of the reaction lies primarily to the left (reactant side)
3.) #2 applies to strong and weak bases (forms conjugate acid and OH-)

27

Equilibrium expression for acid ionization

Ka = ([H+][A-]) / [HA]

Ka = acid ionization constant = the equilibrium constant for the ionization of an acid

28

Percent Ionization

percent ionization = (ionized acid concentration at equilibrium / initial concentration of acid) * 100%

For a monoprotic acid:
percent ionization = ([H+]/[HA] initial) * 100%

29

Relationship between the ionization constants of acids and their conjugate bases

Kw = Ka * Kb

Kw = water ionization constant
Ka = acid ionization constant
Kb = base ionization constant

The stronger the acid, the weaker the conjugate base and the stronger the base, the weaker the conjugate acid.

30

Molecular structure and the strength of acids

Hydrohalic Acids
Acids increase in strength moving down the group

Oxoacids with different central atoms from the same group
Acid strength increases with increase in electronegativity (movement to the right in the periodic table)

Oxoacids having the same central atom but different numbers of attahced groups
Acid strength increases with increasing oxidation number (more oxygen atoms in the molecule)

31

Salt Hydrolysis

The reaction of an anion or a cation of a salt, or both, with water

32

Salts that produce neutral solutions

Salts containing an alkali metal ion or alkaline earth metal ion (except Be^2+) and the conjugate base of a strong acid (for example, Cl-, Br-, and NO3-).

Strong base and a strong acid

33

Salts that produce basic solutions

The solution of a salt derived from a strong base and a weak acid, is basic.

34

Salts that produce acidic solutions

The solution of a salt derived from a strong acid and a weak base.