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Chem 2 Heider > Ch 14 - Chemical Equilibrium > Flashcards

Ch 14 - Chemical Equilibrium Flashcards

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1
Q

Equilibrium Constant

A

how far a chemical reaction goes based on an experimentally measurable quantity

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2
Q

What does a large equilibrium constant mean?

A

Nearly all reactants proceed to products

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3
Q

A reaction with can

A

reach an equilibrium

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4
Q

K

A

an equilibrium constant

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5
Q

Larger K value =

A

more reaction proceeds towards the products

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6
Q

Hb + O2 HbO2

A
  • hemoglobin attached to blood and oxygen are an equilibrium process
    - in the lungs O2 is high so reaction shifts right creating more HbO2 blood
    - stores it with blood and move it to muscles
    - in the muscles the oxygen is low and the Hb releases O2 to restore equilibrium
    - hemoglobin binds oxygen when the surrounding concentration is high, but releases oxygen when the surrounding oxygen concentration is low
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7
Q

How does a fetus get O2 in the womb?

A

maternal and fetal circulation never mix but the fetal K is different allowing oxygen to be “handed off” from the mother circulation at very close proximity

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8
Q

Reversible

A

a reaction that can proceed in both the forward and reverse direction

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9
Q

Dynamic equilibrium

A

for a chemical reaction this is the condition in which the rate of the forward reaction equals the rate of the reverse reaction

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10
Q

Why in dynamic equilibrium products and reactants continue to

A

occur simultaneously but at the same rate

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11
Q

What is not true with dynamic equilibrium?

A

the products and reactants ARE NOT the same amount necessarily

Same rate NOT amount

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12
Q

As the amount of reactants goes down the amount of products goes up leading to

A

a slower rate of reactants(assuming non zero order rxn)

  • the pool of reactants gets smaller
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13
Q

the rate of a reaction is direction proportional to the pool of reactants so as the pool decreases the rate goes down and likewise as…..

A

the amount of products increases the rate increases

  • eventually the slow down of the rate of reactants and the speed up of the rate of products reaches an equilibrium
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14
Q

What is the equilibrium constant used for?

A

a way to quantify the concentrations of the reactants and products at equilibrium

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15
Q

Equilibrium Constant(K)

A

the ratio at equilibrium of the concentrations of the products raised to their stoichiometric coefficients divided by the concentrations of the reactants raised to their stoichiometric coefficients

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16
Q

Law of mass action

A
  • K = ([C]^c[D]^d)/([A]^a[B]^b)

- products/reactants raised to their coefficients

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17
Q

K &laquo_space;1(equilibrium to the left)

A
  • reverse reaction is favored
    - forward reaction does not proceed very far
    - more reactants than products
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18
Q

K = 1(equilibrium in the middle)

A
  • neither direction is favored

- forward reaction proceeds about halfway

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19
Q

K&raquo_space; 1 (equilibrium to the right)

A
  • forward reaction is favored
    - forward reaction proceeds essentially to completion
    - more products than reactants
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20
Q

reverse the equation, invert the equilibrium constant

A
  • A + 2B 3C
    - Kforward = [C]^3/([A][B]^2)
    - 3C A + 2B
    - Kreverse = ([A][B]^2)/[C]^3
    - Kreverse = 1/Kforward
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21
Q

if you multiply the coefficients in the equation by a factor, raise the equilibrium constant to the same factor

A
  • A + 2B 3C
    - K = [C]^3/([A][B]^2)
    - nA + 2n B 3n C
    - K’ = [C]^3n/([A]^n[B]^2n)
    = ([C]^3/([A][B]^2))^n
    = K^n
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22
Q

If you add two or more individual chemical equation to obtain an overall equation, multiply the corresponding equilibrium constants by each other to obtain the overall equilibrium constant

A
  • A2B
    - K1 = [B]^2/[A]
    - 2B 3C
    - K2 = [C]^3/[B]^2
    - sum: A3C
    - Koverall = [C]^3/[A]
    - Koverall = (K1)(K2)
    - ([B]^2/[A])([C]^3/[B]^2)
    = [C]^3/[A]
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23
Q

For gaseous reactions the partial pressure of a particular gas is….

A

proportional to its concentration.

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24
Q

Can the equilibrium constant be expressed in terms of the partial pressures of the reactants and products?

A

Yes

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25
Q

Kc = ([SO2]^2[O2]/[SO3]^2)

find Kp

A

Kp = ((Pso2)^2(Po2))/(Pso3^2)

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26
Q

Kp =

A

the equilibrium constant with respect to partial pressures

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27
Q

What is the difference with Kp compared to Kc?

A

Kp takes the form of the expression for Kc except it uses partial pressure for each gas in place of concentration

28
Q

Kp = Kc(RT)^delta(n)

A
  • R = .08206 (Latm/molK)
    - T = temp kelvin
    - delta n = change in moles of the reaction
    - Product stoichiometric coefficient – reactant stoichiometric coefficient
    - Kp = equilibrium constant with respect to partial pressure
    - Kc = equilibrium constant with respect to concentration
29
Q

as long as concentration units are expressed in molarity for Kc and atm for Kp you do not need to

A

write their corresponding units

- 1.5 M or 1.5 atm becomes 1.5

30
Q

solids are not included in the equilibrium expression because their constant value is incorporated into the value of K

A
  • the concentration of a solid DOES NOT change
  • 2Co(g) CO2(g) + c(s)
    - Kc = [CO2]/[CO]^2
    • similarly pure liquids are omitted from the expression
31
Q

the most direct way to obtain an experimental value for the equilibrium constant of a reaction is to measure the

A

concentrations of the reactants and products in a reaction mixture at equilibrium

32
Q

H2(g) + I2(g) 2HI(g)

A
  • Kc = [HI]^2/([H2][I2])
    - Kc = .78^2/(.11)(.11)
    = 5.0 * 10^1
    - always in M though not written(unitless)
33
Q

ICE Table

A(g) 2B(g)

A

[A] [B]

  • Initial 1.00 0.00
  • Change -0.25 +0.50
  • Equilibrium 0.75 0.50

K = [B]^2/[A] = .5^2/.75 = .33

34
Q

reaction quotient(Qc)

A

the ratio – at any point in the reaction – of the concentrations of the products raised to their stoichiometric coefficients divided by the concentrations of reactants raised to their stoichiometric coefficients

35
Q

When K and when Q?

A
  • K at equilibrium

- Q not at equilibrium

36
Q

the value of Q relative to K is a measure of the progress of the reaction toward equilibrium

A
  • at equilibrium Q = K
37
Q

Q < K

A

reaction goes to the right(towards products)

38
Q

Q > K

A

reaction goes to the left(towards reactants)

39
Q

Q = K

A

reaction is at equilibrium

40
Q

ICE table with x

A(g) 2B(g) and K = 0.33

A

[A] [B]
Initial 1.0 0.0
Change -x +2x
Equil 1.0 – x 2x

  • K = [B]^2/[A] = 2x^2/(1.0-x) = .33
    = 4x^2/(1.0-x) = 0.33
41
Q

Le Chatelier’s Principle

A

when a chemical system at equilibrium is disturbed, the system shifts in a direction that minimizes the disturbance
- a system at equilibrium tends to maintain equilibrium and bounces back when disturbed

42
Q

What does a system do with disturbances?

A

when a system is disturbed the system reacts to counter the disturbance

43
Q

3 main types of system disturbances

A
  • change in concentration of a product or reactant
  • change in volume or pressure
  • change in temperature
44
Q

Change in concentration of product or reactant:

N2O4(g) 2NO2(g)

Add NO2

A

if NO2 is added the reaction will shift left(proceeds in the reverse direction) consuming some No2 and creating more N2O4 to bring the NO2 concentration down until a new equilibrium is reached

		- Before adding NO2: Q = K
		- Immediately after addition of NO2: Q > K
		- Reaction shifts left to reestablish equilibrium
45
Q

Change in concentration of product or reactant:

N2O4(g) 2NO2(g)

Add N2O4

A

if N2O4 is added the reaction will shift right to reestablish equilibrium

		- before adding N2O4: Q = K
		- Immediately after addition of N2O4: Q < K
		- Reaction shifts to right to reestablish equilibrium
46
Q

Change in concentration of product or reactant:

increasing the concentration of one or more of the reactants(makes Q<K) causes

A

the reaction to shift to the right(in the direction of the products)

47
Q

Change in concentration of product or reactant:

increasing the concentration of one of more of the products(makes Q>K) causes

A

the reaction to shift to the left(in the direction of the reactants)

48
Q

Change in concentration of product or reactant:

decreasing the concentration of one or more of the reactants(makes Q > K) causes

A

the reaction to shift to the left(in the direction of the reactants)

49
Q

Change in concentration of product or reactant:

decreasing the concentration of one or more of the products(makes Q<K) causes

A

the reaction to shift to the right(direction of the products)

50
Q

The effect of a volume(or pressure) change on equilibrium

A
  • a decrease in volume causes an increase in pressure

- an increase in volume causes a decrease in pressure

51
Q

The effect of a volume(or pressure) change on equilibrium:

N2(g) + 3H2(g) 2NH3(g)

A

PV=nRT where lower mols of gas(n) = lower pressure(P)

		- 4 mols on left and 2 mols on right
			- higher pressure will shift the system to the right to minimize the equilibrium disturbance
		- If the volume is increased then the equilibrium will more left converting 2mols back to 4 mols
		- what happens if an inert gas is added to increase the pressure?
			- NOTHING!  The overall pressure increased but the partial pressures of the reactants and products did not change so equilibrium is not disturbed
52
Q

The effect of a volume(or pressure) change on equilibrium:

decreasing the volume causes

A

the reaction to shift in the direction that has the fewer moles of gas particles

53
Q

The effect of a volume(or pressure) change on equilibrium:

increasing the volume causes

A

the reaction to shift in the direction that has the greater number of moles of gas particles

54
Q

The effect of a volume(or pressure) change on equilibrium:

if a reaction has an equal number of moles of gas on both sides of the chemical equation then

A

a change in volume produces no effect on the equilibrium

55
Q

The effect of a volume(or pressure) change on equilibrium:

adding an inert gas to the mixture at a fixed volume has

A

no effect on the equilibrium

56
Q

Exothermic Reaction

A

A + B C + D + heat

57
Q

Endothermic Reaction

A

A + B + heat C + D

58
Q

The Effect of a Temperature Change on Equilibrium:

at constant pressure(exothermic reaction) raising the temperature

A

of an exothermic reaction(adding heat) is similar to adding more product, causing the reaction to shift left(absorbing heat and producing more reactants)
- unlike adding more product the change in temperature will change the value of the equilibrium constant(add heat = smaller K)

59
Q

The Effect of a Temperature Change on Equilibrium:

(exothermic reaction)at constant pressure, lowering the temperature causes

A

the reaction to shift to the right, releasing heat and producing more products

60
Q

The Effect of a Temperature Change on Equilibrium:

endothermic reaction)at a constant pressure, raising the temperature(adding heat

A

causes the reaction to shift right to absorb the added heat

61
Q

The Effect of a Temperature Change on Equilibrium:

endothermic reaction) at a constant pressure, lowing the temperature(removing heat

A

causes the reaction to shift left, form less products, and lowering the value of K

62
Q

The Effect of a Temperature Change on Equilibrium:

in an exothermic chemical reaction

A

heat is a product

A + B C + D + heat

63
Q

The Effect of a Temperature Change on Equilibrium:

In an endothermic chemical reaction

A

heat is a reactant

A + B + heat C + D

64
Q

The Effect of a Temperature Change on Equilibrium:

increasing the temperature causes an exothermic reaction to

A

shift left(towards reactants); the value of the equilibrium constant decreases

65
Q

The Effect of a Temperature Change on Equilibrium:

decreasing the temperature causes an exothermic reaction to

A

shift right(towards products); the value of the equilibrium constant increases

66
Q

The Effect of a Temperature Change on Equilibrium:

increasing the temperature causes an endothermic reaction to

A

shift right(towards products); the equilibrium constant increases

67
Q

The Effect of a Temperature Change on Equilibrium:

decreasing the temperature causes an endothermic reaction to

A

shift left(towards reactants); the equilibrium constant decreases

Chem 2 Heider (9 decks)

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