Exam 2: Chapter 4,6,7 (Mostly 7)

Question 1

What is current?

Answer 1

• charge / time
  I = dQ / dt

Question 2

What is charge measured in?

Answer 2

coulombs - 1 C = 6.24x10^18 charges

Question 3

What is current measured in?

Answer 3

Amperes (1A = 1C / 1s)

Question 4

What is work (electrochemistry)?

Answer 4

One Joule of work is required to raise the electric potential energy of one Coulomb of charge by an electric potential of one Volt
V = W / Q

Question 5

What is ohms law?

Answer 5

V = RI

Question 6

What is Joule’s Law?

Answer 6

P = (I^2)(R)

Question 7

What is power?

Answer 7

Work per unit time

Question 8

Oxidation is the process that occurs when…

Answer 8

• oxidation number of an element increases
• compound adds oxygen
• compound loses hydrogen

Question 9

Reduction is the process that occurs when…

Answer 9

• oxidation number of an element decreases
• compound loses oxygen
• compound gains hydrogen

Question 10

What does oxidation state reflect?

Answer 10

reflects the extent of electron transfer in bonding

Question 11

How is the oxidation state determined?

Answer 11

• determined by comparing the number of electrons in a lewis structure assigned to an atom with the number of electrons on the free atom

Question 12

How are electrons split in different bonds?

Answer 12

• in a covalent bond both electrons are assigned to the more electronegative atom
• in a homonuclear bond the electrons are split evenly between the two atoms

Question 13

What are the rules for assigning oxidation states?

Answer 13

Question 14

What are non-metal oxidation states?

Answer 14

Question 15

What is a reducing agent?

Answer 15

• the reactant that reduces another reactant
• the reducing agent contains the element that gets oxidized

Question 16

What is an oxidizing agent?

Answer 16

• the reactant that oxidizes an element in another reactant
• the oxidizing agent contains the element that is reduced

Question 17

RedOX reactions must happen ___________

Answer 17

simultaneously

Question 18

What do voltmeters measure?

Answer 18

voltmeters measure the potential difference but don’t allow current to pass through

Question 19

What is the measured voltage in an electrochemical cell referred to as?

Answer 19

The electromotive force (EMF) or cell potential

Question 20

Why do you need a reference electrode?

Answer 20

• If you are only interested in the right hand side electrode you couldve chosen any arbitrary left hand side electrode to measure the cell EMF
• Want to use a well-defined electrode to compare between reports and labs

Question 21

Reference electrode is on the _______ side of the cell

Answer 21

left

Question 22

What is the most standard reference electrode? What is its reduction potential?

Answer 22

Question 23

How do you know if Ered is + or -?

Answer 23

• Half-reactions with a stronger tendency toward reduction than the SHE have a + value for E°red
• Half-reactions with a stronger tendency toward oxidation than the SHE have a – value for E°red

Question 24

What is the E cell equation?

Answer 24

E°cell = E°red(cathode) - E°red(anode) = E°red(cathode) + E°ox(anode)
E°oxidation = - E°reduction

Question 25

What is important to remember about E values for the half cells?

Answer 25

- when adding do not multiply the half-cell E values even if you need to multiply the half-reactions to balance the equation

Question 26

What is E° also referred to as?

Answer 26

Reduction potential

Question 27

What is important to know about reduction potentials of half reactions?

Answer 27

- species with very positive E° accept electrons from other species easily - (positive E° -> more likely to get reduced)

Question 28

What is ΔG equal to in regards to work and electricity?

Answer 28

ΔG = W other W other = W elec = Q x V

Question 29

What is the difference between ΔrG0 and ΔrG?

Answer 29

- ΔrG0 = gibbs free energy of reaction at standard state - ΔrG = the gibbs free energy with respect to the extent of the reaction - Example: aA + bB -> cC - ΔrG0 = cΔrGc0 - (a ΔrGa0 + b ΔrGb0) - ΔrG = ΔrG0 + RTlnK

Question 30

What is the biological standard state and how does it differ from the conventional one?

Answer 30

- pH 7, 298K, 1 atm - instead of choosing the conventional standard state which can be easier to calculate (1 bar, 1 M) the biological standard state chooses the state which is more complex but applied to biological environments

Question 31

In a graph of lnKeq vs T^-1 what is the slope and y intercept?

Answer 31

slope = -ΔH0 / R y-int = Δ S0 / R

Question 32

Why does the creation of surface or interface require work to be done? (Explain the origin of surface tension)

Answer 32

Molecules interact equally in bulk, but the molecules on the interface have less neighboring molecules which makes the molecules on the interface associate strongly at its sides. Thus liquids prefer to be spherical to obtain the lowest surface to volume ratio.

Question 33

Free energy vs extent of reaction graph

Answer 33

Question 34

Raoult and Henrys law graph

Answer 34