Chapter 15

Question 1

When a reaction is in equilibrium…

Answer 1

• The rate at which products are formed from reactants equals the rate at which reactants are formed from products.
• Concentrations cease to change
• The reaction appears to stop before completion has been reached

Question 2

Chemical Equilibrium

Answer 2

Takes place when the forward and reverse reactions proceed at EQUAL RATES

Question 3

Dynamic Equilibrium

Answer 3

A state of equilibrium in which the forward and reverse processes take place at equal rates so that NO NET CHANGE OCCURS

Question 4

Static Equilibrium

Answer 4

A state of equilibrium in which the object DOES NOT MOVE (like the rope in tug of war)

Question 5

Equilibrium State

Answer 5

A mixture of reactants and products whose concentrations no longer change with time

Question 6

Equilibrium is expressed in a reaction by:

Answer 6

2 arrows pointing opposite directions (left and right)

Question 7

Both the forward and reverse reactions in an equilibrium reaction…

Answer 7

Are elementary

Question 8

The rate constant for a forward reaction is expressed by:

Answer 8

Kf

Question 9

The rate constant for a reverse reaction is expressed by:

Answer 9

Kr

Question 10

Kf / Kr gives you…

Answer 10

a constant

Question 11

*****True or False: When a reaction reaches equilibrium, Kf and Kr are equal

Answer 11

FALSE!

Question 12

*****True or False: When a reaction reaches equilibrium, The forward and reverse reaction RATES are equal

Answer 12

TRUE!

Question 13

*****True or False: When a reaction reaches equilibrium, the concentrations of the reactants and products are equal

Answer 13

FALSE! They no longer change once equilibrium is reached, but this does NOT mean that their concentrations are equal

Question 14

Why does the rate of the forward reaction slow down as the reaction proceeds?

Answer 14

Because the concentration of reactants is decreasing, which reduces frequency of collisions, and hence the rate of the forward reaction decreases.

Question 15

At equilibrium, the concentrations of reactants and products…

Answer 15

No longer change

Question 16

*****True or False: For equilibrium to occur, neither reactants nor products can escape from the system

Answer 16

TRUE!

Question 17

At equilibrium, a particular ratio of concentration terms equal…

Answer 17

a constant

Question 18

True or False: Whether the reaction starts out with only products or only reactants, the equilibrium condition can be reached

Answer 18

TRUE!

Question 19

True or False: You cannot determine if equilibrium has been reached by monitoring the concentration of a single reactant

Answer 19

FALSE! You CAN tell based on a single reactant

Question 20

What is the equilibrium constant represented by?

Answer 20

Kc

Question 21

The equilibrium constant expression (Kc = [D]^d[C]^c/ [A]^a[B]^b) depends ONLY on:

Answer 21

The stoichiometry of the reaction

Question 22

The value of Kc depends on…

Answer 22

TEMP, NOT INITIAL CONCENTRATIONS OF REACTANTS AND PRODUCTS

Question 23

What are the units for Kc?

Answer 23

Kc DOES NOT HAVE UNITS

Question 24

True or false: The value of Kc depends on starting concentrations

Answer 24

FALSE

Question 25

For GASES, the equilibrium constant and equilibrium-constant-expression can be written in terms of

Answer 25

Partial Pressures!

Question 26

The units used for partial pressure are...

Answer 26

ATM!!!!

Question 27

Do Kp and Kc generally have the same numerical values?

Answer 27

NO! But conversions can be made between the two

Question 28

*****When does Kp equal Kc???

Answer 28

When the number of moles of gaseous products and number of moles of gaseous reactants are equal

Question 29

What are "activities"?

Answer 29

Equilibrium constants derived from thermodynamic measurements

Question 30

If a reaction is exothermic and produces large quantities of heat reaching equilibrium, its equilibrium constant must be...

Answer 30

GREATER THAN ZERO

Question 31

If K>>1...

Answer 31

Large K Equilibrium lies to the RIGHT PRODUCTS PREDOMINATE

Question 32

If K<<1...

Answer 32

Small K Equilibrium lies fo the LEFT REACTANTS PREDOMINATE

Question 33

The equilibrium constant of a reaction in the reverse direction is...

Answer 33

the INVERSE (or reciprocal) of the equilibrium constant in the forward direction

Question 34

The equilibrium constant of a reaction that is multiplies by n is in fact...

Answer 34

raised to the POWER OF n

Question 35

The equilibrium constant for a net reaction made up by adding two or more reactions is...

Answer 35

the PRODUCT of the equilibrium constants for the individual reactions

Question 36

Homogeneous Equilibria is defined as

Answer 36

Equilibrium that takes place between substances that are ALL IN THE SAME PHASE (solid, liquid, gas)

Question 37

Heterogeneous Equilibria is defined as

Answer 37

Equilibrium that takes place between substances that are in different phases

Question 38

True or False: the concentrations of pure solids and pure liquids are expressed in the equilibrium-constant-expression

Answer 38

FALSE! Whenever a pure solid or pure liquid is involved in a HETEROGENEOUS equilibrium, its concentration is NOT included in the equilibrium-constant-expression

Question 39

If a reaction is exothermic and produces large quantities of heat reaching equilibrium, its Kc will be...

Answer 39

Greater than zero!