– Summer Institute and Summer Assignment Connections:
Today in class I will be connecting many of the concepts that you initially learned this summer with a discussion that will contain the following:
Many of you came from AP Biology last year and I know a few had Regents Chemistry last year but the year before you had Living Environment. So from AP Biology and Living Environment we can think that Biology essentially can be broken down into really one concept:
Yes DNA is important but it codes for the proteins that gives us our ALLELES or our traits!!
I always say that proteins are the soldiers of the DNA!
Proteins catalyze chemical reactionsthat produce everything that life requires!!
without chemical reactions there is no life!
Proteins help cells identify the world around them as they act as receptors. Without these receptors our immune system would not work and we would all die from the “common cold”!
Proteins are important chemical messengers (hormones like insulin). Without our cell would not be able to transport glucose into our cells and we would not have the free energy to live and survive.
Proteins are help in transporting materials like hemoglobin that transports oxygen (O2) in our blood and transport proteins that help NAD+ or FAD reach the mitochondria. NAD+ or FAD transports electrons to the electron transport chain (in oxidative phosphorylation) in aerobic respiration!
Proteins are used as a nutrient and can feed cellular respiration to provide free energy to living organisms.
Proteins are made from 20 different amino acids that arrange the elements oxygen (O), nitrogen (N), carbon (C), and hydrogen (H) 20 in different 3 – D shapes. The ability of proteins to do their biological job depend on the number and arrangement of these 4 elements! Why these elements? The details of biology are in the chemistry!
Proteins are polymers that are made of monomers called amino acids. Amino acids have a unique group of Carbon, Hydrogen, Oxygen, and Nitrogen elements that give the molecule the properties that make it an amino acid.
The atoms of C, H, O, and N arranged in this fashion create amino acids that create proteins. Atoms and the chemistry behind them ARE the microscopic details of Biology!
The details of Biology are in the chemistry!!!! Why do we require Oxygen in cellular respiration?
If you remember Oxygen pulls electrons electrons through electron transport chain. Once the chain is complete it eventually accepts electrons and 2 H+‘s to become water.
So oxygen is needed to force our cells to produce the most ATP possible by the transport of high energy electrons from glucose using FAD and NAD+ into the matrix of the mitochondria. Without this system there are no complex forms of life! (See Figure 1)
So even though biology macroscopically (large picture) is really about proteins, life’s most important process, cellular respiration boils down microscopically (small picture) to electrons that drive chemical reactions that give cells free energy and the electrons that keep protein’s elements together in chemical bonds.
So chemistry principles are the details of Biology (and electrons are the details of chemistry)!
Figure 1: Oxidative Phosphorylation (electron transport chain of cellular respiration):
So we have learned FROM THE SUMMER INSTITUTE or the SUMMER ASSIGNMENT that Redox reactions are chemical reactions that pass electrons around (which is exactly what happens . Redox reactions are the most abundant chemical reactions that exist. If you ever have any doubt what kind of chemical reaction that is occurring the BEST guess is that it is a redox reaction.
The reason why REDOX is the most abundant is that we naturally have a large number of available elements that have a great ability
to lose electrons = Oxidation
*2/3 of all naturally occurring elements are LARGE ELEMENTS
example from figure 1: NADH —> NAD+ + e-
NADH delivers an electron to the chain and thus is oxidized in the process.
This oxidation cause high energy electrons to pump H+ into the inter membrane space in high concentration. The high H+ concentration diffuses through ATP synthase and makes the protein move to ADD Phosphate ion onto an ADP to make ATP! That is why they call it Oxidation Phosphorylation!!!
and the reason why REDOX is the most abundant is that we naturally have a large number of available elements that have a great ability
to gain electrons = Reduction
*1/3 of all naturally occurring elements are SMALL ELEMENTS but because some these are in high abundance in nature like oxygen in our atmosphere these types of elements are in constant contact.
So because we have these 2 main type of elements (Big and Small) this sets the stage for Redox (transfer of electrons) reactions. How does the size of atoms lead to REDOX or even oxidation phosphorylation in cellular respiration?
This lead us to the one concept that Chemistry is all about!
Like Biology (which is about proteins)Chemistry is about electronsor better yet how electrons are attracted to the positive nucleus.
The details of Biology is Chemistry!
The details of the Chemistry are the Physics
or the physical laws that govern all matter (atoms), specifically how electrons (that are negatively charged are attracted to the positive nucleus (made of protons).
The physical law that governs all of chemistry isCoulombs Law!
Coulombs Law = F = Kq1q2
F = Force of Electrostatic Attraction
K = proportionality constant ( I will explain this later)
q1 = size of negative charge
q2 = size of the positive charge
d2 = distance between the 2 opposite charges squared
The Force (F) of attraction between 2 point points charges of opposite charge (q1 & q2) is directly proportional to the size of the charges and inversely related to the square of the distance between these charges.
Directly proportional to the size of the charges –
-IF the size of the opposing point charge increases then the Force of Attraction will be greater proportionally.We will see this in insoluble salts (ionic compounds) that cannot dissolve in a couple of weeks.
Example: NaCl (s) —> Na+ (aq)+ Cl– (aq)
sodium chloride can break into its ions in water because the Coulombic force between positive and negative ions in the crystal of NaCl are weak compared to the ions attracted to water. Water which we will learn has a positive and negative area (its polar) and so its positive area can attract the Na+(aq)ion enough to pull it away from the Cl–(aq) ion that it is attracted to to make the compound. When this happens we say it is soluble (meaning water can break the electrostatic attraction between the negative part of the salt and the positive part of the salt.
We say they are soluble since water will break apart the ionic solid – which is called dissolving
Please watch this animation to see what I am talking about:
This is an example of spontaneous physical reaction.
Now MgO is not soluble and does not dissolve in water because the coulombic force between the to ions of different charges are too large! If I made an animation of water trying to dissolve MgO it would be boring as no salt would dissolve.
This would be an example of a non-spontaneous physical reaction.
MgO (s) —>does not break apart into its ions in water
This is because the Mg+2 and O-2 ions have HIGHER point charges THUS the Force (F) between the ions is TOO LARGE for water to break apart thus it is insoluble and remains as solid in water.
Inversely related to the square of the distance between these charges-
– IF the distance increases between the 2 point charges then the F decreases (inverse square relation). We will look at this inverse square in our atomic structure discussion later in the course. But in terms of the outermost negative electrons ( Q1) and their Proximity (d) to the positive nucleus (Q2) the farther away the electrons the lower the Coulombic attractive force that these electrons feel, thus these elements generally lose electrons (oxidize). We see this in the sodium metal demo in water.
WATER easily pulls an electron away from the sodium metal
What I am showing you is a half reaction because Na is oxidized
while the water is reduced. I am only showing you half of the redox as
I am omitting the reduction.
Oxidation : Na —> Na+1 + 1 e– + Energy
The reason Na can lose electrons (LEO) and oxidize in water is because the size of the Na atom is so big that is outermost electron (valence) feels the positive nucleus less and can be removed.
The electrostatic forces are weaker between the negative electron and the positive nucleus. Larger the atom the weaker the electrons are held!
Notice the lowered Force is amplified because of the squaring of the larger distance that metals have between their nucleus and outermost (valance electrons). Increasing the size of the denominator will always Increase the entire value of the formula.
Here is my demonstration of adding sodium metal atoms into water:
This is an example of aspontaneousreaction.
IF the distance decreases between the 2 point charges then the Electrostatic Force (F) increases . In terms of the outermost negative electrons (Q1) and the Proximity (d) to the positive nucleus (Q2) the CLOSER the electrons are to the nucleus, the greater the coulombic attractive force that these electrons feel, thus these elements generally gain electrons (reduce). We see this every time you see a combustion reaction where oxygen grabs electrons from metals causing them to corrode or change into a new compound or in combustion when oxygen grabs electrons from carbon (bigger nonmetal)
Here are 2 examples of combustion reactions:
Combustions reactions are guess what??
REDOX reactions that use oxygen (a small atom) that is able to attract electrons so well because of its small size (d2) and it large number of protons (q2).
Making the proton number larger (numerator) and the denominator smaller leads to a LARGE F or electrostatic force!
This is why oxygen is the earths most important oxidizer!!
It cause other atoms, molecules, or ions to lose electrons. Oxygen causes oxidation!
Why don’t you think they call the losing of electron Oxidation
Here are 2 examples of combustion (or REDOX reaction that uses Oxygen as the oxidizer):
2Fe + O2—> 2FeO+ Energy
Pure Iron RUST
C6H10O5 + 6O2 —>6CO2 + 5H2O + Energy
This second reaction is cellular respiration!! Why do we need to breath oxygen?? To get the high energy electrons out of glucose to make ATP and those high energy electrons that was put their by photosynthesis!! Everything is connected!
Reduction half reaction for both: O + 2e–—> O-2
In both cases Oxygen became reduced or pulled the electrons because of its higher coulombic attraction due to electrons Closer to the nucleus (smaller d) in part due to the atomic radius being smaller. In the case of the combustion reaction of the cotton ball oxygen has both smaller d and greater (Q2) due to having a greater nuclear charge (more protons) than carbon. That is how Oxygen (a nonmetal) can pull an electron from another nonmetals (carbon)!!!!!!!
Now lets get back to size of atoms and how we can predict their type of chemical reactivity. We now know why oxygen takes electrons from things like metals based on Coulombs Law( to make rust ) but we have not figured out why oxygen is so small in the first place. We saw that Na is large and due to Coulombs law it tends to lose electrons (oxidize) unlike Oxygen which is small and tends to gain electrons (reduce).
If we look at periodic chart of elements and use their relative atomic radii (size compared to each other) we can see a trend:
The elements are arranged according to their the number of their number of protons (q2) andthe electron shells (row number) they have.
Protons increase left to right and then start a new row.
Example: H has 1 proton, while He has 2 and Li has 3 and so forth…
The proton number changes the numerator in Coulombs Law!
Every additional shell is farther away (d2)from the nucleus that contains protons.
Example: Na has electrons in 3 shells while K has electron in 4 shells .
The proton number changes the numerator in Coulombs Law!
Notice as you move across the Periodic Table the atomic radius generally decreases because you are adding more electrons in the same electron shell. Notice F (fluorine) is smaller than oxygen because it has more protons. This causes F to reduce better than O. If we breathed in F instead of oxygen the electron would not move through the electron transport chain. They would immediately be sucked up by F. This is one of the reasons that F2 gas is toxic!!!
Notice are you move down the Periodic Table (in the same column) the atomic radius generally increases as you are adding additional shells of electrons. Shells are determined by the row number. Na (sodium) is in row 3 and thus has 3 shells of electrons while K (potassium) is in row 4 and thus has one more shell of electrons that is father away from the nucleus than Na. This explains why K loses electrons or oxidizes more than Na.
Thelarger elements like Na are bottom leftand thesmaller elements light oxygen are top right.
Theelements that oxidize are bottom leftand theelement that reduce are top right.
Thelarger elements are metalsand thesmaller elements are nonmetals.
Metals oxidizeandNonmetals reduce.
Metals are reducing agents and Nonmetals are oxidizing agents
Elvira the outermost electron: (start at 6:20)
So lets put this all together in a chemical reaction that represents a great example of a Redox reaction that features a metal and a nonmetal.
2 Na (s) + 2 Cl2(g) —> 2NaCl (s)
Metal Nonmetal Ionic Compound (salt)
Large atom Small atom
Loosely held electrons Tightly held electrons
Loses electrons Gains electrons
Gets oxidized Gets Reduced
acts as the reducing agent acts as a the oxidizing agent
*notice the 2 half reactions are written so that the electrons are cancelled out.
Electrons lost = Electrons gained.
*notice that the electrons on each side cancelled out!
How many different modules did I interconnect today?? Could you have understood any of this if you did complete the Summer Institute?
Today’s Lecture that you can use instead of reading above:
This is the end of week 1 notes!
*Connections: Spontaneity – week 2 stuff below this point!
In all chemical reactions there is possibility that the reverse reaction could occur. A chemical reaction that reaches equilibrium is one where the forward reaction occurs at the same rate as the reverse reaction. For example:
2NO2 (g) <=> N2O4 (g)
NO2 (g) + NO2 (g) <=> N2O4 (g)
Now this reaction reaches equilibrium and because the rate or speed of the forward reaction equals the rate of speed of the reverse reaction the amount of each chemical stays constant. If we were to put NO2 only in the reaction vessel and seal the container, a graph of the changes in concentration (Molarity or partial pressure) would like the following.
Notice that concentration of the NO2is large initially and decreases as the reaction proceeds.
Notice the initial concentration of N2O4 is zero (it has not been made yet) and increases as the reaction proceeds.
Both NO2and N2O4 eventually level out and at this point equilibrium has been reached!
If the rate of 2NO2combining to make N2O4 (forward reaction) is as fast as rate of N2O4 decomposing into 2NO2 (reverse reaction) then the concentration of both chemicals become CONSTANT at equilibrium.
So what does this look like? Well it is pretty boring in that it appears that nothing is going on because the reactants and products stay constant. In truth there plenty going on because forward reaction and the reverse reaction atr continuously going on but there is no NET change.
Also notice part people that the reactants (NO2) and products ( N2O4 ) ARE NOT Equal at equilibrium. IN this example or reaction NO2 is favored at equilibrium. Why would nature favor the NO2? Which of the 2 chemicals has the greatest dispersed energy? The 2 pieces ( NO2) or the larger whole (N2O4)?
The 2 smaller pieces!! Nature favors energy that spreads out.
Nature favors a pathway that has the greatest amount of dispersed energy. We call this Entropy (S)! So we know that the universe works by always providing a pathway for energy to go from a high concentrated source to a lower energy source. In other words, Chemical or physical processes can only occur if the universe provides a pathway for it to happen. This pathway is dependent upon the Entropy (S) to increase in the universe or an increase in the change of Entropy (ΔS). This is the second Law of Thermodynamics!
ΔSuniverse = increase ( IF There is a pathway!!)
That is why Heat flows to Cold always!! There are limits to what can be done with matter and it all depends on Energy dispersing! If Energy is being diluted or dispersed into the Universe then the process is SPONTANEOUS under a set of defined conditions.
If the Energy is not dispersing into the universe then there is NO PATHWAY for the reaction or process to occur!! This process is NONSPONTANEOUS under a set of defined conditions.
If you think of it this way then you can understand why a change of how fast a reaction occurs (RATE) has nothing to do with spontaneity. In the case of the reaction above 2 particles (NO2) combine to make larger one (N2O4) or 1 particle breaks into 2 particles in the reverse. This ratio is upheld no matter how many more of these multiples I have. If I have 20 pieces (NO2) I will make 10 larger one (NO2 ) and if it occurs faster by adding a catalyst then whole number ratio is upheld!
Now in getting back to the equilibrium condition in above diagram or the reaction:
2NO2 (g) <=> N2O4 (g)
The forward reaction is moving as fast as the reverse. Since there is no net change there is no increase in Entropy in the universe or there is no real preferred pathway when equilibrium is reached. At this position the Energy has been dispersed already!!! This is the death of the chemical reaction in one direction!! All reactions move in a direction to exhaust there energy into the universe until it empties! That point is equilibrium!!!!
Thus all reactions move toward equilibrium, and thus get less spontaneous over time as they approach equilibrium or reach the death of the chemical reaction! The father away a reaction is from equilibrium the more spontaneous it is!!
This diagram illustrates what I am talking about:
At point C, there 100% NO2 and 0% N2O4 thus there is no competing reaction because there is no NO2 to combine to make the N2O4. The reverse reaction is at it maximum spontaneity and the forward reaction is at its minimum. There is a Shift in the reaction to move in the reverse. Over time its spontaneity will steadily decrease until it reaches the point of equilibrium and the “death of the reaction”.
Notice that the equilibrium position is at the bottom!! This is where the death of the reaction or where there is ZERO Spontaneity or No more release of energy into the Universe.
ΔSuniverse = O
At point A we have 100% NO2and 0% N2O4. At this point there is tremendous pathway to go forward! There is No competing backwards reaction!! The reverse reaction is impossible here. It so spontaneous in the forward that the reverse is impossible!
At point B, there is 60% NO2 and 40% N2O4. Here we have a competing reaction reverse reaction thus the forward reactions is not as spontaneous and the reaction is getting closer to its death. The reverse reaction is still not as spontaneous as the forward but it is closing in, thus the overall Net direction is still forward but this pathway is not nearly as great as point A.
This shift is what we learn in Le Chateliers Principle –
Regents definition: When a stress is placed on a reaction at equilibrium, the reaction will shift forward of reverse to regain its balance.
REAL Definition: When a stress (a change in concentration) is placed on a reversible reaction the reaction will become more spontaneous in one direction in order to keep dispersing energy until it is run out (and no more work can be done). In a battery this means 0.00 volts!!
We have learned that voltage is the Energy to move current or charge around circuit either by the pushing of chemicals that spontaneously oxidize and in combination with chemicals that pull charge by spontaneously reducing. The voltage of a half reaction tells us about the spontaneity, ability to reduce or oxidize, or the pathway to do so based on the amount of dispersed energy that get released into the universe! Voltages give us a measured value of the available pathway for the redox reaction to occur.
So my question is, Why does a battery have a voltage drop? Why does it die?
Equilibrium and the death of chemical reaction is NOT unique to chemical changes only!
In physical changes (no bonds broken just attractions) equilibrium also will STOP phase changes!
That is why the melting point stays at one Temperature!
Example: Heat + H2O (s) <—> H2O (l)
If you start with a cooler of just ice AND ASSUME NO HEAT enters your cooler what will Happen?
At first when you have 100% ice and 0% liquid water and there WILL HAVE the greatest spontaneity 0r PATHWAY to melt or go forward.
The cooler will eventually get to the point where there is ice and water mixture and reaches equilibrium and thus the rate of melting equals the rate of freezing (or refreezing). At this point no more can be work is done there is no more spontaneity in either direction. If no heat leaked into the cooler then then you would have an the same amount of ice and liquid water in the cooler forever.
freezing melting equilbrium animation:
Because heat leaks into the container (darn entropy!) the forward reaction becomes more spontaneous because of Le Chateliers Principle and eventually all ice will melt because at higher temperatures liquid water can disperse its energy (is more random) than the ice.
Ok then can we manipulate the physical process? We do this all the time. How about placing salt on ice?
H2O (s) <—> H2O (l)
We all know that salt will melt ice BUT WHY?
How can I manipulate the above physical process so that the Ice will melt even if it is currently at equilibrium?
We make the forward direction move spontaneous!!! We help give the forward process an increased pathway!!
Remember that ice and water at equilibrium and if we can BLOCK the water molecules from refreezing the RATE of melting will now exceed the RATE of refreezing and melting will occur!!
Freezing Point Depression animation
Salt will physical get in the way of liquid water reaching the crystal pattern of the ice MORE than the ice crystals melting!
H2O (s) <—> H2O (l)
So really we limiting the reverse pathway!! Hey if we make the reverse pathway less favorable don’t we make the forward MORE FAVORABLE AND MORE SPONTANEOUS!!!
Below is for class:
MAIN FOCUS: To apply the basics of equilibrium, voltage from Standard Reductions Table,spontaneity, solubility to the voltaic cell.
1. Review the Voltaic Spontaneity HW Form- with key
Skills: Solubility, Spontaneity, Equilibrium,
How concentration of soluble ions in a voltaic cell affect its voltage.