Unit 3: Chemical Equilibrium

Question 1

Can chemical reactions be undone?

Answer 1

Under the right conditions, they can be undone.

Question 2

What is the “right condition” for most reactions to reverse?

Answer 2

Most reactions are exothermic, meaning that they release energy (energy is removed from the system, negative delta H). So, energy or a catalyst are needed to reverse a reaction (refer to graph in notes)

Question 3

What is notable about equilibrium reaction equations?

Answer 3

They have a double arrow between the products and reactants.

Question 4

What is equilibrium?

Answer 4

Chemical equilibrium is when the forward and reverse reactions are proceeding at the same rate.
It occurs in a closed system (no matter can enter or leave).
No observable changes (the microscopic level is still active).
Two types of equilibrium (phase and dynamic).

Question 5

What is phase equilibrium?

Answer 5

A balance between two phases of matter (like solid and liquid). Refer to the sealed soda container example.

Question 6

What is dynamic equilibrium?

Answer 6

A balance between forward and reverse chemical reactions. The products become the reactants as the reactants become the products.

Question 7

What is Le Chatelier’s Principle?

Answer 7

If stress is applied to a system at equilibrium, a temporary non-equilibrium state will occur. The system will then shift in the direction opposite to the change (returning to equilibrium). There are three stresses that may affect an equilibrium rate: change in concentration, change in volume, and change in temperature.

Question 8

How does a change in concentration affect equilibrium?

Answer 8

The system will react to replace a removed substance or use up an added substance.

Question 9

How does a change in volume or pressure affect equilibrium?

Answer 9

This only affects gasses. Gasses take up the volume that they are in. If volume is increased (pressure decreased), the equilibrium favours the direction that produces more moles of gas. If the volume is decreased (pressure increased) the equilibrium favours the direction that produces fewer moles of gas.

Question 10

How does a change in temperature affect equilibrium?

Answer 10

Every equilibrium has both an exothermic and an endothermic direction. If you add heat, the reaction favours the endothermic reaction (the endothermic reaction removes heat). If you remove heat, the reaction favours the exothermic reaction (releases more heat).

Question 11

What does keq represent?

Answer 11

The equilibrium constant.

Question 12

What represents the equilibrium constant?

Answer 12

Keq.

Question 13

What is keq/the equilibrium constant?

Answer 13

A numerical value (no units) that describes the system once it has reached equilibrium. Keq > 1, products favoured. Keq < 1, reactants favoured.

Question 14

What is the keq expresssion?

Answer 14

keq = ([C]^c * [D]^d) / ([A]^a * [B]^b) where aA + bB <-> cC + dD
Capitals are substances, lowercases are coefficients/amount. Do not include solids or pure liquids, only include gasses (gasses and non-pure liquids have concentration).

The product of the concentration of the products to the power of their amounts divided by the product of the concentration of the reactants to the power of their amounts.

Question 15

What is the product and reactant in an equilibrium expression?

Answer 15

The reactants are always on the left. The reactants are always on the right.

Question 16

What represents the reaction quotient?

Answer 16

Q

Question 17

What does Q represent?

Answer 17

The reaction quotient.

Question 18

What is the reaction quotient?

Answer 18

Like keq, Q is a ratio of the products to reactants. Calculated using instantaneous concentrations. If Q = keq, the reaction is at equilibrium. If not, then you can determine which way the reaction should shift. If Q<Keq, system has more reactants than at equilibrium, so it will move in the forward direction. If Q>Keq, there are more products than at equilibrium, so it will move in the reverse direction.

Question 19

What does I.C.E. stand for?

Answer 19

I: Initial or instantaneous concentrations.
C: Change in concentration.
E: Equilibrium concentration.

Question 20

How do I.C.E. calculations work?

Answer 20

Refer to charts and notes

Question 21

What is solubility?

Answer 21

A measure of the maximum amount of substance that can dissolve in a given amount of solvent

Question 22

What does it mean when a solution is saturated

Answer 22

The maximum amount of substance has been dissolved

Question 23

What is a solute

Answer 23

What is being dissolved

Question 24

What is a solvent

Answer 24

What the solute is being dissolved into

Question 25

What is concentration

Answer 25

A measure of the solute per unit of the solvent C=solute/solvent or C=mol/L

Question 26

What does of mean when something is saturated

Answer 26

The solution has a large amount of solute dissolved in it

Question 27

What does it mean when something is dilute

Answer 27

It has a small amount of solute

Question 28

What does it mean when something is unsaturated

Answer 28

The solution can hold more solute

Question 29

What does it mean when something is supersaturated

Answer 29

The solution is holding more solute than it theoretically can at that temperature

Question 30

What is an alloy

Answer 30

A solution of a metal in another metal

Question 31

What axiom do chemists use to determine whether a solute will dissolve into a solvent?

Answer 31

Like dissolves like Polar solutes tend to dissolve well in polar solvents Non-polar solutes tend to dissolve well in non-polar solvents

Question 32

Why are organic alcohols such great solvents?

Answer 32

They have polar and non-polar properties

Question 33

Why does vitamin a dissolve into fat?

Answer 33

They are both non-polar

Question 34

Why does vitamin c dissolve into water

Answer 34

They are both polar

Question 35

What is dissociation?

Answer 35

Ionic compounds, when dissolving in water, break apart into their ions AnBm(s) <-> NA(aq) + MB(aq)

Question 36

What is ionization?

Answer 36

Dissociation, but with acids. The reactant is a liquid

Question 37

What are electrolytes

Answer 37

Ionic or acidic compounds dissolved in water (they are free to move and they conduct electricity)

Question 38

How do molecular compounds dissolve?

Answer 38

They do not ionize or dissociate, so they do not produce mobile ions They are non-electrolytes (CO2) for example

Question 39

What is solubility

Answer 39

The maximum amount of solute that will dissolve in a given amount of solvent

Question 40

What factors affect solubility rates?

Answer 40

Surface area: more surface area speeds up dissolving Agitation/stirring: Lets solvent particles collide with solute particles more often, speeding up dissolving (collision theory) Temperature: Kinetic energy of particles increases (collision theory)

Question 41

Does increasing temperature increase solubility?

Answer 41

In most cases, yes. Gasses especially decrease in solubility as temperature increases.

Question 42

Conversion of grams and millilitres of water

Answer 42

1g water = 1ml water

Question 43

How much of a solute must dissolve in a solvent for it to be considered soluble?

Answer 43

Usually, More than 1g dissolves in 1L: soluble Less than 1g dissolves in 1L: Insoluble

Question 44

Steps to write a net ionic equation

Answer 44

Complete and balance reaction normally, including all states of matter (don’t break apart aqueous chemicals yet) TI: write all (both sides) aqueous compounds as separate ions NI: cancel ions that appear as both reactants and products, write what remains

Question 45

What is ksp?

Answer 45

Solubility product constant. Describes how well a substance dissolves as a ratio of products to reactants. ksp>1 dissolves well ksp<1 dissolves poorly

Question 46

How do you use ksp to determine whether a precipitate will form?

Answer 46

ksp presents the maximum amount of ions that will dissolve in solution If Q>ksp: precipitate If Q

Question 47

Who proposed ionization and dissociation?

Answer 47

Svante Arrhenius

Question 48

What is wrong with Cl2^-1 (aq)?

Answer 48

Diatomic elements share electrons and do not possess a charge. Ex: MgCl2(s) <-> Mg+2(aq) + 2Cl-1(aq).