chapter 17/18

Question 1

What is the first law of thermodynamics?

Answer 1

Energy cannot be created or destroyed

Question 2

What is a spontaneous change?

Answer 2

Occurs without a continuous input of energy from outside the system

Question 3

What is required for a nonspontaneous change to occur?

Answer 3

The surroundings must continuously supply energy tot he system

Question 4

A spontaneous change in one direction must be what in the opposite direction?

Answer 4

Nonspontaneous

Question 5

What is an endothermic process and what is one example?

Answer 5

An endothermic process is a chemical/physical process that absorbs heat from its surroundings. Melting is an endothermic process

Question 6

What happens to the particles in a system when a spontaneous endothermic process occurs?

Answer 6

An increase in freedom of motion (and more dispersed energy of motion.

Question 7

What is a microstate?

Answer 7

Each quantized energy state for a system of particles (the arrangement of molecules/atoms within a system at a specific point in time)

Question 8

At a given set of conditions, what is true about each microstate?

Answer 8

Each microstate has the same total energy as any other. As such, each microstate is equally likely

Question 9

As the number of possible microstates increases, what becomes true about the energy of the system?

Answer 9

The larger the number of possible microstates, the larger the number of ways in which a system can disperse its energy.

Question 10

How is entropy related to microstates?

Answer 10

The number of micfrostates in a system (W) is directly related to entropy via the following equation: S = kB*lnW
Kb is the Boltzman constant.

Question 11

What is the boltzman constant?

Answer 11

The bolztman constabt (kB) relates the number of microstates in a system to the entropy of the system. the boltzman constant is 1.38 * 10^-23 J/K

Question 12

What does it mean for entropy and enthalpy to be state functions?

Answer 12

Entropy and enthalpy depend on the state of the function, not on the path they took to achieve said state.

Question 13

What is a reversible process?

Answer 13

A process that occurs in such tiny increments that the system remains at equilibrium. The direction of the change can be reversed by infinite reversal of conditions.

Question 14

When considering both the system and the surroundings, what is true about all real processes that occur?

Answer 14

They occur spontaneously in the direction that increases the entropy of the universe.

Question 15

When is a process spontaneous?

Answer 15

When a decrease in entropy of the system is offset by a larger increase in the entropy of the surroundings.

Question 16

How are delta S universe, system, and surrounding related?

Answer 16

deltaS univ = deltaS sys + deltaS surr
> 0

Question 17

What is S nought?

Answer 17

The standard molar entropy of a substance, measured for a substance in its standard state in units of J/(mol*K)

Question 18

What are the conventions for defining a standard state?

Answer 18

1 atm for gases, 1M for solutions, and the pure substance in its most stable form for solids and liquids.

Question 19

What factors affect entropy?

Answer 19

Temperature, physical state, the formation of a solution, atomic size and molecular complexity.

Question 20

During phase changes from solid to liquid to gas, how does entropy change?

Answer 20

Entropy increases.

Question 21

What are the two characteristics of a phase change process?

Answer 21

The process happens @ constant temperature (melting point, freezing point, etc.), and the process absorbs or releases large amounts of energy.

Question 22

How/why does entropy change as a salt is dissolved in a solvent.

Answer 22

Entropy of salt solutions is usually greater than that of the solid and water, but it is affected by the organization of the water molecules around each ion.

Question 23

How does atomic size affect delta S nought?

Answer 23

Delta S nought is higher for larger atoms/molecules of the same type.

Question 24

For allotropes, how does delta S nought differ?

Answer 24

For allotropes, delta S nought is higher in the form that allows the atoms more freedom of motion.

Question 25

As chemical complexity increase does delta S nought increase or decrease?

Answer 25

Increases

Question 26

How are the number of atoms in a molecules, vibrational modes, and microstates related?

Answer 26

More atoms in a molecules = more vibrational modes = more microstates = higher entropy

Question 27

What is the standard entropy of reaction and what is its equation?

Answer 27

Refers to the entropy change that occurs when all reactants and products are in their standard states.
Delta S nought rxn = the sum of the delta S nought products (* moles) - the sum of the delta S nought reactants (*moles)

Question 28

What are some things that can help us predict the sign of delta S nought rxn?

Answer 28

Positive if the amount of gas increases, negative if the amount of gas decreases, likely positive if the new structure has more freedom of motion

Question 29

At a constant temperature, what do the surroundings function as?

Answer 29

A heat source or heat sink

Question 30

In an exothermic process, how do the system and surroundings interact?

Answer 30

The surroundings absorbs the heat released by the system, and Ssurr increases.
qsys < 0; qsurr > 0, and deltaS surr > 0

Question 31

In an endothermic process, how do the system and surroundings interact?

Answer 31

The surroundings provides the heat absorbed by the system, and Ssurr decreases.
qsys > 0; qsurr < 0, and deltaS surr < 0

Question 32

For any reaction, how are qsys and qsurr related?

Answer 32

qsys = -qsurr

Question 33

Is delta S nought dependent on temperature at which heat is transferred?

Answer 33

Yes

Question 34

When the surroundings are at a lower temperature, is the impact on the surrounding larger or smaller? Why?

Answer 34

It is larger because there is a greater relative change in Ssurr

Question 35

What is the equation relating change in entropy of surroundings, change in enthalpy, and temperature

Answer 35

Change in entropy of surroundings = - change in enthalpy of system / temperature
AKA delta S surr = - delta H sys / T

Question 36

What must be true about change in enthalpy of the universe for a spontaneous reaction?

Answer 36

Delta S nought univ > 0 for a reaction to occur spontaneously

Question 37

When are exothermic reactions spontaneous?

Answer 37

When deltaS system > 0 (size of deltaS surrounding isn’t important because deltaS surrounding > 0 for all exothermic reactions). When deltaS system < 0, deltaS surr must be larger than deltaS sys for the reaction to be spontaneous.

Question 38

When are endothermic reactions spontaneous?

Answer 38

When deltaS system > 0, deltaS surr must be smaller than deltaS system for the rxn to be spontaneous. DeltaS surr is always < 0 for endothermic reactions. Typically deltaS sys > 0 because endothermic reactions absorb heat from the surroundings (leading to an increase in the disorder of the system).

Question 39

What is the Gibbs free energy equation?

Answer 39

Combines enthalpy and entropy of a system. G = H - TS

Question 40

When is does delta G (free energy change) indicate spontaneity vs nonspontaneity?

Answer 40

DeltaG < 0 for spontaneous process
DeltaG > 0 for nonspontaenous
DeltaG = 0 for equilibrium

Question 41

How can deltaG nought rxn be calculated using standard free energy formation of the components? (Answer with the formula)

Answer 41

DeltaG nought rxn = the sum of the delta G nought of the products (multiplied by moles) - the sum of the deltaG nought values of the reactants (multiplied by moles).

Question 42

How are gibbs free energy, Q and K related (conceptually)?

Answer 42

If Q and K are very different, deltaG has a very large value (positive or negative). The reaction releases or absorbs a large amount of free energy.
If Q are nearly the same, deltaG has a very small value (positive or negative). The reaction releases or absorbs very little free energy.

Question 43

What do voltaic cells do?

Answer 43

They use a spontaneous redox reaction (deltaG < 0) to generate electrical energy. (The system does work on the surroundings)

Question 44

What do electrolytic cells do?

Answer 44

They use electrical energy to drive a nonspontaneous reaction (deltaG > 0). The surroundings do work on the system.

Question 45

How are both electrolytic and voltaic cells constructed (basic components that both have)?

Answer 45

Using two electrodes placed in an electrolyte solution.

Question 46

In electrochemical cells, what happens at the anode and cathode?

Answer 46

The anode is where oxidation occurs, and the cathode is where reduction occurs.

Question 47

How are voltaic cells constructed?

Answer 47

Each reaction takes place in its own half cell (rxns are physically separate). Each half cell consists of an electrode in an electrolyte solution. The half cells are connected by the external circuit, and a salt bridge completes the electrical circuit.

Question 48

What happens in voltaic half cells as the reactions occur?

Answer 48

Oxidation occurs at the anode, which is therefore the source of e. The anode decreases in mass and the electrolyte solution increases.
As for the cathode, reduction (gain of e-) occurs here, where the e- are used up. The electrolyte in the half cell decreases and the mass of the cathode increases.

Question 49

What happens to the charges of the electrodes in voltaic cells?

Answer 49

The anode produces e- by the oxidation. The anode is the negative electrode in a voltaic cell. Electrons flow through the external wire from the anode to the cathode, where they are used to reduce ions. The cathode is the positive electrode in a voltaic cell.

Question 50

In voltaic cells, how does the salt bridge work?

Answer 50

The salt bridge completes the electrical circuit and allows ions to flow through both half cells. For the voltaic cell with zinc and copper, as zn is oxidized at the anode, zn2+ ions are formed and enter the solution. cu2+ ions leave solution to be reduced at the cathode. The salt bridge maintains electrical neutrality by allowing excess zn2+ ions to enter from the anode, and excess negative ions to enter from the cathode. A salt bridge contains nonreacting cations and anions (dissolved in a gel or soaked onto filter paper).

Question 51

Describe the flow of charge in a voltaic cell

Answer 51

Electrons flow from from the anode to the cathode. Cations move through the salt bridge from anode to cathode (solutions). Anions move through the salt bridge from cathode to anode (solutions)

Question 52

What is an active electrode?

Answer 52

An active component in its half cell and a reactant/product in the overall rxn

Question 53

What is an inactive electrode?

Answer 53

An electrode that provides a surface for the rxn ad completes the circuit. Does ot participate actively in the overall rxn. They are necessary when none of the reaction components can be used as an electrode. (Usually unreactive substances like graphite or platinum)

Question 54

How do voltaic cells use deltaG?

Answer 54

They convert the deltaG of a spontaneous redox rxn into the kinetic energy of electrons.

Question 55

What is cell potential of a voltaic cells otherwise known as?

Answer 55

Voltage of the cell or electromagnetic force (emf)

Question 56

What is standard electrode potential?

Answer 56

The potential of a given half reaction when all components are in their standard states

Question 57

Are all standard electrode potentials for half reactions written as reductions or oxidizations?

Answer 57

Reductions

Question 58

What does a higher standard potential mean?

Answer 58

A higher standard reduction potential indicates a higher tendency for a half reaction to undergo the reduction rxn. (if given two half cells, higher reduction potential means it is the cathode).

Question 59

What is the standard hydrogen electrode?

Answer 59

Half cell potentials are measured relative to a standard reference. The standard hydrogen electrode has a standard electrode potential defined as zero.

Question 60

For a spontaneous redox reaction, how is cell potential defined (formula)?

Answer 60

E cell = E cathode (reduction) - E anode
(oxidation)

Question 61

What is a concentration cell?

Answer 61

It exploits the effect of concentration changes on cell potential. The cell has the same half reaction in both compartments, but with different concentrations of electrolyte. As long as the concentrations of the solutions are different, the cell potential > 0 and the cell can do work

Question 62

In an electrolytic cell, where are the positive and negative charges coming from?

Answer 62

External source supplies cathode with electrons, which is negative, and removes them from the anode, which is positive.