Voltaic Cell Animation

Hey guys! So I found an animation on YouTube that demonstrates what happens in a voltaic cell. If any of you have struggled with understanding this, watching this may help!!
https://www.youtube.com/watch?v=J1ljxodF9_g

Spontaneous Reactions

It was really interesting to see today Kayli's demonstration of what a spontaneous reaction can look like. You know, I can't help but think about how a large majority of reactions we have done in lab are spontaneous reactions. It seems as if a lot of reactions in nature are actually spontaneous, and yet there are still quite a few times in which we have to continually input energy in order to maintain the reaction. It certainly is easy to tell the difference between the two though, since if a reaction starts and keeps going without us doing anything it must be spontaneous. 

But why do you think that might happen? According to the Second Law of Thermodynamics, it seems as if the universe will actually move towards disorder on its own. What do you think this might mean in terms of reactions? What would be classified as "orderly" and "disorderly"?

Just some fruit for thought, see you all either tomorrow in lab or in class on Wednesday.

Matt

Doubt

Verb: feel uncertain about, question the truth or fact of (something), disbelieve (a person or their word), feel uncertain, esp. about one's religious beliefs.

As the definition implies, the word “doubt” carries a substantial negative connotation, especially in reference to religious beliefs.  From a Christian perspective doubt is seen as especially dangerous territory.  One of the twelve disciples has even been labeled as “Doubting Thomas” due to his disbelief in Jesus’ rising from the dead.  Doubt brings questions about a topic or theory to the surface; when the item in question is something as central and important as one’s faith, there is resistance to those questions because there is fear that it could shake one’s faith.  However, in her talk on 3/20, Dr. Francl presented doubt in a far more positive setting.  She proposed doubt as an opportunity to ask questions that enable one to dig deeper and learn more about a topic.  With this approach, we need not see doubt as something that is going to completely change our minds or force us to turn our backs on our faith.  Instead, doubt can be seen as an invitation to investigate a question in order to learn more about an aspect of Christian faith.

Chapter 19 Practice Sheet

Answers: 1. Each of the metals in the complex ions give have CN=4 and a charge of +2. Each is a square planar geometry. 2. d10/zero, d3/3, d8/2, d7/3 unpaired d electrons

LEWIS acids and bases--no conjugates here!

Gilbert N. Lewis is famous for many things, among them is his definition of acid/base chemistry. A Lewis acid is electron deficient. Generally, transition metal cations are considered good Lewis acids. A Lewis base is electron-rich and after collision, can stick to a Lewis acid through sharing an unbonded pair of electrons. When talking about transition metal chemistry, Lewis bases are the ligands that coordinate (bond or stick) with the metal cation. Electron-pair suppliers can come from molecules that contain an atom with a nonbonded lone pair -- such as N in NH3, N in en, O in H2O. Electron-pair suppliers can also come from anions in solution -- such as O in ox, Cl-, N in CN-. Chelating ligands are long and flexible enough to be polydentate. Both en and ox are both important examples of bidentate ligands. They act as Lewis bases and coordinate to a metal in two positions. When Lewis acid/base chemistry happens between a transition metal cation and ligands in aqueous solution, the result is a complex ion, often with a beautiful color. The formation of complex ions is reversible and so a K value (Kf) can describe the equilibrium composition of the mixture of Lewis acid, Lewis base, and the complex ion.

The Intersection of Science and Religion

Hi everyone!

If you made it through the snow to see Dr. Francl's presentation on how she connects her faith to her work in chemistry, you heard quite a great talk! If you missed it, it is definitely something to look into if you are interested!

I thought it was really interesting that Dr. Francl clarified that it's not just that science and religion mesh at any singular points, and it's not that only certain parts of science and religion work together - but rather, that science and religion are completely related. God has created everything, and we as Christians can really look at the world as God's word. By learning and understanding the world, we can learn about God's greatness and can really learn how to fit our faith into our love of science!

Kayli

Weak Bases in Search of H+

Bases move around looking for a partially positive H to snag as H+. H+ is welcome to take the spot at a lone pair site inherent to a weak base (like on N as part of an amine) or a vacant spot by attraction to a negative charge (on anions). If a base collides with the H part of an acid, the base's ability to steal the H+ away is assessed by the value of Kb. A large Kb means the base is a serious thief, a collector of H+. The smaller the Kb (and larger the pKb) means the acid doesn't have to worry too much about acting as an acid. The Kb of the anions of strong bases are so low, that those anions are essentially ineffective as bases (weaker than weak). They are referred to as spectator ions. Can you list the anions of the strong bases you have memorized?

Talking Chemistry

I have begun to look at the homework for next Friday, and it appears to be similar to what we have been practicing in class. If any of you have questions or would like an explanation of how to do something, please comment or something and we can figure out an answer!!
Dr. Bundens does love when we talk chemistry.

"Practice pH" answers

Here are the answers (and some other thoughts) to the worksheet on pH calculations: 1. [H+] = 2.5 x 10-6 M while [OH-] = 4.0 x 10-9 M. There are two ways of figuring out [OH-]... first, convert pH to pOH and proceed or second way, use [H+] and Kw to get it. Try both ways and become an expert! Note: Rain water is naturally acidic due to various gases in the air (like CO2) that become weak acids when hydrated in clouds. (Recall: Dry ice (CO2) becomes carbonic acid (H2CO3) when bubbled through water :-). "Acid Rain" is when pH is lower than about 5.0 or 4.7. This happens when moisture in the air reacts with specific gases like SO2 and NO2 to form Strong acids (sulfuric and nitric). SO2 is produced when burning coal in many of our nation's power plants and is of real concern in producing Acid Rain. 2. pH = 14.8. Strong base!! Yes, you can have pH greater than 14 and even less than zero (negative!). The pH scale extends in both directions. For this question, there are two ways to get pH from [OH-]... first, take pOH and subtract from 14, or second way, get [H+] with Kw and take pH. Which way do you prefer??

Le Chatelier is fun to say!

Disturb a stable chemical equilibrium system, and you'll put it in opposite world. Le Chatelier observed that the system wants to re-store itself to a happy equilibrium balance and will do so by minimizing the disturbance. Don't we all want this? Balance, harmony, peace, with minimal disturbances... If you increase the pressure on an equilibrium system containing gases, then the road to re-storing equilibrium necessitates relieving at least some of the pressure if possible. Do this by making fewer molecules of gas in the closed mixture. If you crank up the heat on a reversible reaction that has worked so hard to achieve equilibrium status, then it will counter by absorbing some of the heat to promote the product of an endothermic direction. Products of endothermic reactions have absorbed more heat energy than its reactants. So then, what happens if you coooool down a reversible reaction? How will the substance counter this disturbance in order to re-establish an equilibrium balance? If you remove product from an equilibrium reaction, then when equilibrium is restored, the composition will have more product than there was before the disturbance. Removing product "favors" product formation. Removing reactant "favors" reactant formation. The more you remove, the more you'll form (but still less than you remove -- there is no *exact* opposite behavior). "Shifting" means "Favoring" a direction of change... changing into more products than in the original equilibrium or changing into more reactants than in the original equilibrium. It is the composition of the mixture that "shifts"! Of all these disturbances, ONLY TEMP can change the value of the equilibrium constant K. The other disturbances can change the product-to-reactant composition, but the overall value of K remains the same -- 2/1 is the same as 12/6 and 20/10, but each ratio is still 2 overall.

Le Chatelier's Principle

Hey everyone,

So today's lecture was really interesting with Le Chatelier's Principle and the entire concept behind it. It really does make sense how if you increase the concentration of a product, then the concentration of the reactants will then increase while the products decrease in order to maintain that equilibrium constant.

Personally, I kind of like to think of it as a sort of see-saw where if one side goes up, it then must come down while the other side goes up. Not to mention the fact that when you increase the temperature of the system, the endothermic reaction will increase while the exothermic reaction will decrease and vice versa. It truly is a case of where in order to get a certain result you have to do the exact opposite.

Looking forward to seeing you all either tomorrow or Wednesday.

Matt

Back to Thermodynamics

Why is equilibrium such a central concept in chemical thermodynamics? Well, equilibrium describes what happens to reversible reactions, and reversible reactions are prevalent in God's world. We need useful tools to describe what we observe. Among other things, this helps us predict and even control outcomes. Molecules and particles are constantly moving at the temperatures of our experiments and life around us. Their collisions can lead to reaction. Once product is formed, it doesn't just sit there. Product substances collide, too, and can result in re-forming reactant. There they are -- reactants and products co-existing in a mixture, and still undergoing changes. This can keep going on... to a point. Once the rate at which reactant forms product matches the rate at which product changes back to reactant (rate slower than the initial activity of the reaction), the dynamic mixture achieves a balance point. Ongoing reactions, but no increased amounts of anything produced. The composition of the mixture is static. Good, then we can measure or calculate how much of any reactant or how much of any product is in the equilibrium mixture! K helps us. K is the ratio of products over reactants. Multiply ALL the product amounts and divide that by the multiple of ALL the reactant amounts. So, since products are in the numerator of this ratio, then a large K value (> 1) means there are more products in the mixture than reactants! It is useful to know the value of K for any equilibrium reaction. Ka is the value give to an acid in water equilibrium reaction. Different acids will have different Ka values. In class examples (and in lab), we will calculate K given the equilibrium amounts of reactants and products. We will also do the opposite -- calculate equilibrium amounts by using a known K value -- this type is more involved (and often needs the wonderful quadratic formula :-).

Answers for Pink Practice Sheet and MCAT questions

If you are working through the pink practice problems in preparation for the exam, here are some answers for you to compare... 2. Yes since k changes with temperature., 3. 250 kJ/mol, 4.a 103 kJ, c first, d 779 sec, e 2.36 x 10-3 M/s, 5.b 344 (L/mol)^3/2(1/s), c 24.0 M/s, 6.a X, b 40 kJ, c -30 kJ, d 70 kJ, e Y, f X, g Y, h both. For the heat of reaction practice problem, both methods happen to give the same answer. If you have worked on the MCAT questions on this material, here are some answers: Passage 16 A, D, C, D, A, B, C, Passage 18 C, A, D, C, C, D, Passage 24 D, A, D, A

Break for Kinetics

If changes in thermodynamic state functions do not depend on how reactants convert to products, then we can't use them to tell us about a reaction's in-between details. Studies in Kinetics (motions of molecules) can lead us toward this information. Empirical Kinetics is all about trying to come up with a rate expression (rate law) for a chemical reaction of interest. A rate expression (law) is a general summary of how dependent a reaction's rate is on the concentration of each reactant at a specified temperature. To come up with a rate expression, we need to determine the order with respect to each reactant, and then get a value for the rate constant (k) of the reaction at the given temp. How to do? 1. Use the method of initial rates: You did this in lab. Get initial rate vs. [reactant] data, or 2. Try to plot different [reactant] vs time plots to see if data matches up with one of the "integrated rate equation" cases Kayli outlined in the previous post for m = zero, first or second order. Then you can get a value for rate constant (k) from the slope of the straight-line plot at a given temperature. Sound easy enough? Let's try to avoid other cases :-)

Integrated Rate Equations

Hi everybody!

Today we learned about the different graphs for different orders of reactions. A zero order reaction rate has [A] on the y-axis and time on the x-axis. A first order reaction rate has ln[A] on the y-axis and time on the x-axis. Lastly, a second order reaction rate has 1/[A] on the y-axis and time on the x-axis.

A way that may help you remember that the first order has the ln[A] on the y-axis is that the 'l' in 'ln' looks like a 1! Hope that helps a little bit!

Hess's Law

A scientific law is a simplified, general summary of what we can readily observe in God's world -- His ordinary way of sustaining and governing the creation. Hess observed that changes in state properties like enthalpy can be determined either directly or by adding together a series of steps in an overall change in any order. In your experiment, you switched the order of the three reactants to test this observation. Was the overall deltaH per gram of NaOH about the same regardless of the order in which you mixed reactants? Hopefully! Hess's observation and the idea of state property are two somewhat redundant concepts. We can observe what Hess did BECAUSE of state properties. Any property that can be calculated simply as a change between final (products) and initial (reactants) states is a state property. H, T, P, V... are all state properties. q and w are path properties. Heat and Work are the pathways of energy transfer so we don't talk about delta q or delta w. Either energy is transferred in an organized way or a disorganized way. There is no meaning to a change in the transfer of energy -- transfer IS the change. Hess's Law allows us to cleverly calculate properties such as deltaH of a reaction (heat of reaction) using heats of formation values. It is "clever" since we do not have to carry out a direct reaction, instead we relate experimental values indirectly to get what we want. We end up with a more general and accurate method for heat of reaction than by worrying about gas-phase average Bond Enthalpies. We'll use Hess's Law as a tool to determine values for other state property changes like entropy (S) and Gibbs free energy (G) coming up...

Upcoming Quiz

Hey guys!
So we have a quiz coming up on Friday on Thermochemistry, and I am sure we are all nervous, myself included.
I would say that one of the best ways to study is to get together with a group of people and to talk about the concepts. Being able to think and fully explain a concept to someone else is one of the best ways to integrate the material into your mind.
Also, one of the best things for me, personally, is just to do practice problems.  Go beyond the homework. Practice the others from the book that are similar to those that you have problems on. It is a HUGE help.

1/30 Thoughts

Hey everyone, so I don't know about you but it was pretty interesting to see today how there is a huge difference between the average bond enthalpy values and the change of energy of the formation of a compound at SATP. Who would have thought that the averages would cause such a large difference when conducting calculations.

What I find interesting is the fact that no matter how many steps you take in order to attain a certain product, the change in enthalpy will stay the same since any compounds formed between steps will simply cancel one another out. We should be really thankful that enthalpy is a state function since that saves us a lot of effort. This was probably in Hess's mind when he was developing his law and it is extremely useful since as chemists we tend to be lazy. What do you all think about this?

Heat of Reaction Practice

1. The heat of reaction using the heat of formation method is -137 kJ while the heat of reaction using the bond enthalpy method is -127 kJ. The results are similar but not exactly the same. This is mainly due to the error inherent to the bond enthalpy method. BE data are average bond strengths rather than specific to this reaction. 2. The standard heat of reaction is -354.8 kJ which is exothermic. 3. The standard heat of formation for Al2O3 is -1675.7 kJ/mol. So the formation of Al2O3 from Al (s) and O2 (g) is an exothermic process. 4. The heat of reaction for the Hall Process is given as endothermic at +2170.9 kJ for every 4 moles of aluminum refined. This is 2170.9 kJ/4 mol Al. If you convert 4 mol Al to grams of Al using molar mass, you get 20.12 kJ/g. So for 5.000 g, the endothermic reaction involves 100.6 kJ of energy. Much less energy is involved for 5 g Al than for 4 moles of Al!

Calorimetry Practice

Check your practice work (beige sheet)... 1.(a) deltaE = -38.9 kJ (sign is important), (b) 1.32 x 10^3 kJ released, and (c) the heat capacity (C) works out to be 27.2 kJ/oC. 2. The minimum heat is 2.64 kcal.

Nitroglycerin problem

Did you calculate 780 Liters of gas produced? All products in the detonation of nitroglycerin are gases. You need to determine the total moles of gas produced from the reaction with 1 kg of reactant...

Imagining Gas Behavior

Tiny particles so far from each other cannot interact very much. Things are less complicated then. Like most stars in space. Vast distances between them. We can imagine a gas particle as a point, traveling on and on until it bumps into something exerting a tiny pressure -- on its container or another particle. If a collision with another happens fast, then any sort of polarized interaction is insignificant. But what if the collision is a slower event? A low temperature, say lower than room temp, is a measure of slower collisions. When we all slow down, we can interact more, get to know each other, build social networks. So much interaction leads to stronger ties -- binary stars maybe, or liquid networks. Get those tiny particles to SLOW down enough and gases can even become liquids - AND/OR - PUSH those tiny particles close enough and gases can become liquids. Slow speeds measured by low temperatures, and crowding measured by high pressures and small volumes -- lead to interactions. Things get complicated. I'm not saying it's all fun and games attractions, those repulsions are important too! You can get too close. PV won't exactly predict the value of nRT. Our class experiments involved room conditions. We observed a simple relationship between P,V, n and T. How marvelous to summarize our observations on vast collections of these tiny particles designed by God with simple math! No harm in starting out simply -- we can include more complexity later if needed. Models in science -- start with simple observation, add a deeper layer when needed. The process becomes experiment, theorize, experiment again, modify the theory, repeat, repeat... No theory is without "holes".

Molecular Interpretations

For a given amount of trapped gas, we can readily observe the effect of pressure on volume with no change in temperature. If we compress a container and force gas particles into a smaller space, then they will collide more frequently with the container even though they still move with the same average speed (same temp). More collisions result in a greater internal pressure. So, if a container under this increased pressure cannot withstand it, then it will crack or maybe explode! If the "system" happens to be some air trapped behind food stuck in a choking victim's trachea, then abdominal thrusts (Heimlich maneuver) are a good way to compress the volume of this trapped air behind the food. This results in more pressure exerted by the air trapped behind the food -- hopefully enough to force the food up and out and save the person (my husband had to do this once in a public restaurant to someone we didn't know… saved her life!). This is all kind of like the motion of a piston in a cylinder...

Welcome to our class blog!

We hope the conversation here will enrich your experience in second semester general chemistry at Eastern University. When you read postings such as this one, you are very welcome to add your comments and follow up on what interests you. Here is to a great semester!