Exam 2: Chapter 4,6,7 (Mostly 7) Flashcards
What is current?
- charge / time
I = dQ / dt
What is charge measured in?
coulombs - 1 C = 6.24x10^18 charges
What is current measured in?
Amperes (1A = 1C / 1s)
What is work (electrochemistry)?
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
What is ohms law?
V = RI
What is Joule’s Law?
P = (I^2)(R)
What is power?
Work per unit time
Oxidation is the process that occurs when…
- oxidation number of an element increases
- compound adds oxygen
- compound loses hydrogen
Reduction is the process that occurs when…
- oxidation number of an element decreases
- compound loses oxygen
- compound gains hydrogen
What does oxidation state reflect?
reflects the extent of electron transfer in bonding
How is the oxidation state determined?
- determined by comparing the number of electrons in a lewis structure assigned to an atom with the number of electrons on the free atom
How are electrons split in different bonds?
- 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
What are the rules for assigning oxidation states?
What are non-metal oxidation states?
What is a reducing agent?
- the reactant that reduces another reactant
- the reducing agent contains the element that gets oxidized
What is an oxidizing agent?
- the reactant that oxidizes an element in another reactant
- the oxidizing agent contains the element that is reduced
RedOX reactions must happen ___________
simultaneously
What do voltmeters measure?
voltmeters measure the potential difference but don’t allow current to pass through
What is the measured voltage in an electrochemical cell referred to as?
The electromotive force (EMF) or cell potential
Why do you need a reference electrode?
- 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
Reference electrode is on the _______ side of the cell
left
What is the most standard reference electrode? What is its reduction potential?
How do you know if Ered is + or -?
- 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
What is the E cell equation?
E°cell = E°red(cathode) - E°red(anode) = E°red(cathode) + E°ox(anode)
E°oxidation = - E°reduction
What is important to remember about E values for the half cells?
- when adding do not multiply the half-cell E values even if you need to multiply the half-reactions to balance the equation
What is E° also referred to as?
Reduction potential
What is important to know about reduction potentials of half reactions?
- species with very positive E° accept electrons from other species easily
- (positive E° -> more likely to get reduced)
What is ΔG equal to in regards to work and electricity?
ΔG = W other
W other = W elec = Q x V
What is the difference between ΔrG0 and ΔrG?
- 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
What is the biological standard state and how does it differ from the conventional one?
- 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
In a graph of lnKeq vs T^-1 what is the slope and y intercept?
slope = -ΔH0 / R
y-int = Δ S0 / R
Why does the creation of surface or interface require work to be done? (Explain the origin of surface tension)
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.
Free energy vs extent of reaction graph
Raoult and Henrys law graph
