Unit 1- Chemical Equilibrium

Question 1

Define Equilibrium

Answer 1

A state of physical balance.

Question 2

Define Reversible Reaction

Answer 2

A reaction that can proceed in both the forward and the reverse directions.

Question 3

What happens when the rate of the forward reaction and the rates of the reverse reactions are the same?

Answer 3

The concentration of the products and the reactants remains constant.

Question 4

Define Chemical Equilibrium

Answer 4

A chemical reaction is said to be at equilibrium when the rates of the forward reaction and reverse reactions are equal and therefore the concentrations of reactant and product species remain constant in time.

Question 5

How do the products and reactants behave at equilibrium with respect to concentration?

Answer 5

Their concentration remains constant.

Question 6

How is the fluctuation in dynamic equilibrium affected with increasing number of molecules?

Answer 6

There is a decrease in fluctuations in dynamic equilibrium.

Question 7

What is entailed by static equilibrium?

Answer 7

There is a state of physical balance in between particles that are not moving.

Question 8

What is entailed by dynamic equilibrium?

Answer 8

Imagine there are some people on the sand in the beach and there are some number of people in the water; individuals are constantly moving from one section to another so there are a fixed number of people at a given time.

Question 9

In the example of the reversible reaction between dinitrogen tetroxide and nitrogen dioxide, does the reactions stop at equilibrium; what can be said about the rate of decomposition and the rate of formation?

Answer 9

The reaction has not stopped at equilibrium and the rate of formation and the rate of decomposition are equal.

Question 10

Suppose you have a vacuum chamber at room temperature and you place some liquid water inside the chamber keeping it sealed. What ends up happening and why?

Answer 10

The water molecules will immediately begin to enter the gas phase. As the concentration of the gas phase increase, the gas phase water molecules begin to return to the liquid phase. As soon as the liquid is placed in the water, due to the reduction in pressure, the water starts evaporating. Since the container is closed, the evaporated water molecules condense and come into the liquid phase. Ultimately, a dynamic equilibrium is established where the rate of evaporation is equals to the rate of condensation and this is equilibrium pressure that is called vapor pressure.

Question 11

TRUE OR FALSE: a dynamic equilibrium is established once enough water molecules have entered the gas phase to reach the vapor pressure.

Answer 11

TRUE

Question 12

What is the equation for determining the reaction quotient using molar concentrations and partial pressure?

Answer 12

Both of them are the same in many respects; it involves a fraction where the numerator involves the concentration/partial pressures of the products raised to the power of their coefficients multiplied by each other divided by the concentration or partial pressure of the reactants raised to the power of their coefficients and multiplied by one another.

Question 13

What does it mean when the value of the reaction quotient is zero?

Answer 13

It means that the reaction hasn’t started yet and that there are only reactants present.

Question 14

What happens as the reaction proceeds in the scenario where the reaction begins with a mixture comprised of ONLY reactants?

Answer 14

The reactant concentration decreases; the product concentration increases. Thus, the value of the reaction quotient increases over the course of time.

Question 15

What happens as the reaction proceeds in the scenario when the reaction only begins with the products?

Answer 15

Product concentration decreases and the concentration of the reactants increases. Thus, over the course of time, the value of the reaction quotient decreases.

Question 16

What can be said about the graph of time vs the value of the reaction quotient when you only begin with reactants?

Answer 16

The graph increases over the course of time and eventually flatlines/

Question 17

What can be said about the graph of time vs. the value of the reaction quotient when you only begin with products?

Answer 17

The value of the reaction quotient decreases over time and the graph eventually flat lines.

Question 18

Define Equilibrium Constant

Answer 18

The constant value of Q exhibited by a system at equilibrium is called the equilibrium constant which is denoted by K.

Question 19

Define the Law of Mass Action

Answer 19

The law of mass action states that the reaction quotient for a system at equilibrium is constant at a given temperature.

Question 20

What does the value of Kc reflecting?

Answer 20

It reflects the composition of a reaction mixture at equilibrium.

Question 21

What does it mean when there is a large Kc value?

Answer 21

The equilibrium favors the products; this means that more products are going to be present compared to reactants.

Question 22

What does it mean when there is a small Kc value?

Answer 22

The equilibrium favors the reactants; this means that there are more reactants present than products.

Question 23

Does the value of Kc say anything about how rapidly equilibrium is reached?

Answer 23

NO

Question 24

How do you determine the direction of a reaction that is reversible?

Answer 24

You compute the value for Qc; if Kc is bigger than Qc, then the reaction proceeds in the forward direction. If Kc is smaller than Qc, then the reaction proceeds in the reverse direction.

Question 25

Define Homogenous Equilibrium

Answer 25

An equilibrium in which all of the reactants and products are present in the same phase (liquid or gaseous phases).

Question 26

In examples of homogenous equilibria, is water as a reactant or product include in the calculation of Kc? What are the rules for calculating Kc in this case?

Answer 26

No, water is not used; only include the concentration or pressure terms for gaseous or solute species.

Question 27

What is the relationship between Kp and Kc?

Answer 27

Kp= Kc(RT)^Delta N where delta N is the difference in the molar amounts of product and reactant in the gas phase.

Question 28

Define Heterogenous Equilibrium

Answer 28

Involves reactants and products in two or more different phases.

Question 29

What happens when you stress an equilibrium system?

Answer 29

The net reaction will occur in the direction of the greater rate; the reaction will proceed until equilibrium has been re-established.

Question 30

Define Le Chatalier’s Principle

Answer 30

If an equilibrium system is stressed, the system will experience a shift in response to the stress that re-establishes equilibrium.

Question 31

Where will the reaction shift if you add more reactant?

Answer 31

To the right (product side)

Question 32

Where will the reaction shift if you add more product?

Answer 32

The reaction will shift to the left (reactant side).

Question 33

How do we stress a system?

Answer 33

Rate Laws: Reaction rates change with concentration
Arrhenius Equation: Reaction rates change with temperate.

Question 34

Where will the reaction shift if we remove product? What about if we remove reactants?

Answer 34

If we remove products, it will shift to the right (product side), making more products.
If we remove reactants, it will shift to the left (reactant side), making more reactants.

Question 35

Changes in pressure correspond directly to changes in _____, resulting in the same influence of equilibria.

Answer 35

Concentration.

Question 36

In situations where there are different numbers of moles of gas on the reactant and product side, what will shift the equilibrium?

Answer 36

Changes in Volume

Question 37

Where does the equilibrium shift when the volume is decreased?

Answer 37

To the side of the reaction where there are fewer moles of gas present.

Question 38

Where does the equilibrium shift when there is an increase in volume?

Answer 38

It will shift towards the side of reaction where there are more moles of gas present.

Question 39

Where will the equilibrium shift with increasing/decreasing the volume of the reaction if there are equal moles of gas present on both sides?

Answer 39

There will be NO SHIFT in equilibrium.

Question 40

Does increasing/decreasing the volume of a reaction containing non-gas species shift the equilibrium?

Answer 40

NO

Question 41

Do rate constants vary with temperate?

Answer 41

Yes

Question 42

In predicting shifts in equilibrium with temperature, how can we consider heat if DELTA H is positive? What if it is negative?

Answer 42

If DELTA H is positive, we can consider heat as a reactant; if it is negative, we will consider it as a product.

Question 43

How does increasing/decreasing heat affect shifts in equilibrium?

Answer 43

It depends on if heat is a product or a reactant; from there, increasing/decreasing the heat ACTS THE SAME WAY as when you increase/decrease the concentration of a reactant/product.

Question 44

Does the value of the equilibrium constant change when products are added/removed and reactants are added/removed? What about the reaction quotient?

Answer 44

No-Yes

Question 45

Do solid substances have an affect on the equilibrium position?

Answer 45

No

Question 46

Consider the following reaction initially at equilibrium in a fixed container at 25 degrees Celsius: P4 + 5O2 —->P4O10. If Ne (g) is introduced into the vessel, keeping the volume constant, such that the total pressure of the vessel increases, the rate of the forward reaction will _____ and the system will _____.

Answer 46

Not Change-Not Change ; for a fixed volume, the partial pressure of the species do not change when you add a non-reactive gas. Therefore, the rates of the forward and the reverse reaction do not change.

Question 47

What are important things to remember regarding the construction of ICE Tables?

Answer 47

The change that is enacted must be proportional to the moles of the substance present; additionally, the signs for the product must be opposite of that of the reactants.