CHEMISTRY COMMUNITY

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At the same concentration, weak acids will not dissociate as much as strong acids will. This means that weak acids have lower concentrations of H3O+ and therefore their pH will be closer to 7 while strong acids will have much lower pH because of their higher hydronium concentration.

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Solids and liquids are not factored into the calculations for equilibrium constants (and therefore in ICE tables) because their concentrations are not changing.

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Work of expansion at constant pressure has to incorporate volume because expansion is a change in volume. So, to calculate the work needed to change the volume,the integral should involve the volumes.

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The area under the reversible expansion curve is the work done during the expansion. You can solve for this using the integral formula for reversible expansion, as the definition of an integral is the area underneath the curve.

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As long as you have the corresponding reaction rate and the concentrations of the reactants/products, you can use any trial to determine k.

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The reason termolecular reactions are so rare is that three molecules must collide simultaneously for it to occur. The more molecules needed, the lower the probability of the reaction occurring, which is why termolecular reactions are very uncommon.

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Why aren't the fast steps also factored into the overall reaction rate law?

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When can we assume that a reaction has microscopic reversibility?

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How would you calculate the value of A to put in the Arrhenius equation? Would it need to be given to you?

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What is the Nernst Equation derived from?

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Differential rate laws are a function of the concentration of the reactant. So, the differential rate laws compare Rate vs. [R].

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Rate 2 is divided by Rate 1. Since the concentration of [NH4+] stays the same in reactions 1 and 2, these values and their units cancel out. k also cancels out when the two rates are divided. So, the only components left in the calculation are initial rate 2/initial rate 1 (which is equal to 2) and ...

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This above method can also be used to determine the order of the reaction. The order of the reaction can be calculated by adding together the exponents of the reactants (n, m...).

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We focus more on [R] than [P] because it is easier to observe the initial rates of the reaction when t is very close to t=0. There are more reactants present than products at the beginning of the reaction so it is easier to measure the initial reaction rate if we examine [R].

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A first order reaction has a reaction rate in the form of k[A]^1.

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When comparing temperatures, deltaS and deltaH are assumed to stay constant for both temperatures which could be why deltaS/R seems to be ignored.

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The second page of outline 4 will be on test 2. This includes Gibbs Free Energy, the van't Hoff equation, work, and understanding how to implement these concepts in organic reactions, and environmental and biological examples.

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If the two were in different phases, would there then need to be a 'I' separating them?

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What is the difference between a salt bridge and a porous disk?

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A salt bridge helps the two solutions in a Galvanic cell maintain neutrality through ion transfer, thus preventing charge buildup.

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W, or degeneracy, is defined as the number of ways of achieving a given energy state. It can be calculated by counting the number of particles and the number if arrangements/states they could be in. For example, if 2 particles could be in one of two states, W=4, or 2^2. The number of particles is ra...

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Residual entropy (the remaining entropy of molecules when thermal entropy is ignored) is calculated using the equation S= kB lnW.

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The Boltzmann equation is used to represent the relationship between degeneracy, w, and entropy. Degeneracy is the number of ways of achieving a given energy state. The Boltzmann equation also includes the Boltzmann constant which is 1.381*10^-23 J*K^-1. Can we calculate degeneracy? If so how? Dege...

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Step one is raising the temperature of the reactants to 200C. Step 2 is the actual reaction at 200C (deltaH is given). Step 3 is cooling the products back down to 37C. Add all these values together to get the total change in enthalpy of the reaction. What equations would you use to raise the temper...

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Why does Lead have a higher molar entropy than Carbon?

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I'm pretty sure that generally, nonlinear molecules will have higher molar heat capacities than linear molecules. For example, in 4C.1 from the textbook, NO2 (bent) has higher molar heat capacity than NO (linear).

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On the learning outcomes sheet for "Thermochemistry and the First Law of Thermodynamics" from Dr. Lavelle's class website, it says we should "understand the environmental impact of burning fossil fuels, and the use of alternative fuels as energy sources." Can someone explain how ...

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When heating a substance, for example, water, the heat energy is used to first raise the temperature to the boiling point. When the temperature gets to that point, the heat energy is then used to complete the phase change instead of raising the temperature further. So, the boiling water would stay a...

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What does it mean when properties are intensive vs extensive? For example, what makes entropy extensive?

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What makes an expansion reversible vs irreversible?

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To change the energy of a system, you can add or remove the amount of the substance in the system, although this only applies to open systems. The second way to change energy is heat or cool the system (for a closed system). The third way to change the energy of a system is to do work on the system/...

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It is important to know what kind of system is present because the type of system will determine whether energy and pressure have to be constant or if they can change so that you can complete accurate calculations and choose the correct equations to use.

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Why is bond formation exothermic?

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When you are calculating the enthalpy of a reaction, sometimes the reactants or products will be in the liquid form. Since predetermined enthalpy values of elements are usually given in the gas phase, you must add/subtract the enthalpies of the phase changes to these values to determine what they ar...

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When water is boiled to 100 degrees C, some of it is converted to steam. Water as steam has more energy than liquid water because it requires additional energy as enthalpy of vaporization as it turns to gas. So, steam at 100 degrees Celsius has the energy of water at 100 degrees C plus the enthalpy ...

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K does give the relative concentrations of products to reactants when the equation is at equilibrium. This is because it is calculated using [Products]/[Reactants], thus showing us the ratio of products to reactants. A large K value (greater than 10^3) means more products at equilibrium than reactan...

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Speeding up the reaction would not influence the concentrations of the reactants nor products at equilibrium. Equilibrium is not affected by the speed of the reaction.

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If K is a large number (larger than 1 x 10^3), then that means at equilibrium, more products are present than reactants and the equilibrium is shifted right. If K is a small number, (smaller than 1 x 10^-3), then at equilibrium, more reactants are present than products and the equilibrium is shifted...

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How is K affected when the chemical equation it's based on is multiplied by a factor?

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The value of Kw for water at body temperature (37 C) is 2.1 x 10^14. (a) What is the molar concentration of H3O+ ions at 37 C? (b) What is the molar concentration of OH- in neutral water at 37 C? In this problem, how would you find the molar concentration of H3O+ ions? Would the concentrations of H...

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The purpose of a buffer is to resist PH changes in a solution, helping to keep the solution's PH constant despite additions of acids or bases. A buffer can be made from a weak acid or a weak base and their respective salts, or from a combination of 2 salts that form a conjugate acid-base pair.

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The most important part of the conjugate seesaw is that the strength of an acid determines the strength of its conjugate base. A stronger acid will have a weaker conjugate base, and a weak acid will have a strong conjugate base. The same applies to bases and their conjugate acids. A strong base will...

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Why does the temperature change the value of K while pressure and concentration don't?

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Why do we see if our approximation is correct by checking if the final answer is less than 5% of the initial? Is there a particular reason we use 5% as the cutoff?

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K is calculated with the concentration of the products over the concentration of the reactants at equilibrium. Since solids and liquids in a reaction do not change concentrations, they would just cancel out when calculating the equilibrium constant. So, only gases are considered when calculating K.

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Both Q and K are calculated the same way. Both are the concentration of the products over the concentration of the reactants. K is that value when the reaction is at equilibrium and Q is that value at any other time.

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Chatelier's principle can be used to see which direction a reaction will proceed in response to a change in concentration or pressure. For example, if more reactants are added, therefore increasing concentration, Le Chatelier's principle tells us that the reaction will move forward in order to minim...

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PV=nRT is the ideal gas equation. it can be used to convert between partial pressure and concentration for a gas, which means it can help us find Kc from Kp and vice versa.

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The notation of K depends on what information they give you in the equation and what phase it occurs in. If the problem gives you the partial pressures of the gases in the reaction, you would be using Kp. If the molar concentrations are given, then Kc. Either way, K always stands for the equilibrium...

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PranaviKolla2B wrote:What are partial pressures?

If you have a mixture of gases in a container, the partial pressure would be the pressure each individual gas exerts on the container. The partial pressures added together equals the total pressure of the mixture.

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What is the biological importance of the heme complex?

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What is the function of hemoglobin and myoglobin?

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An example of this that was used in class is cisplatin and transplatin. In cisplatin, the Cl atoms are on one side of the central Pt and the NH3 molecules are bonded the opposite side. In transplatin, one Cl and one NH3 switch places so that the Cls and NH3s are diagonal from each other instead of s...

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Why are Ka calculations are only used for weak acid and bases?

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What is the difference between a carboxylic acid and an oxoacid? How can you tell which is which?

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Oxoacids are oxygen-containing inorganic acids. The strength of an oxoacid depends on the number of oxygens (more O atoms = stronger), the electronegativity of the center atom (Higher EN = stronger), and the oxidation number of the center atom (bigger # = stronger).

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A conjugate acid is what is created when the base receives a proton as it dissociates in an aqueous solution. Conjugate acids are weak acids because they can now donate the proton they received back to where they received it from to become a base again (this act of donating a proton makes it an acid...

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This pretty much means that oxoacids can dissociate better and thus are stronger acids when, after giving off a proton, they are able to delocalize the negative charge. This means that oxoacids composed of atoms with similar electronegativities (and therefore would delocalize the charge) will be mor...

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Strong acids are able to completely dissociate in a solution to donate their protons. Most strong acids are inorganic.

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Can someone explain why you have to take the negative log of the H+ concentration to find pH? Why is it negative?

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Yes, H20 is amphiprotic because it can can accept or donate a proton.

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The coordination number is the number of bonds around the central metal in the coordination compound.

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A ligand is an ion or molecule with at least one lone pair of e- that forms a coordinate covalent bond with a central metal atom.

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The number of hybridized orbitals is equal to the number of atomic orbitals around the central atom. So, the hybridization is sp3 to match the four atomic orbitals around the central atom that is seen in its Lewis structure.

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Yes, the hybridized orbitals are an average of the s, p, and d orbitals which means they should be weighed equally.

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In order of most repulsion strength to least repulsion strength according to the VSEPR model, the order is lone pair-lone pair > Lone pair-bonding pair > Bonding pair-bonding pair.

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If two lone pairs were added to the central atom, the molecule would then have four areas of electron density and so the electron geometry would be tetrahedral and the molecular geometry would then be bent since there are 2 bonding pairs. So, a molecule can only be linear if the central atom only ha...

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There are four regions of electron density, which means the electron geometry is tetrahedral. Since one is a lone pair, the molecular geometry is trigonal pyramidal.

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A trigonal planar molecule must have no more than three areas of electron density, and all three must be bonding pairs. SO3 (2-) has three bonding pairs, but since it also has a lone pair, it would then be trigonal pyramidal since the lone pair would repulse the bonding pairs away from it.

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The lone pairs in H2O are not opposite each other because H2O has four areas of electron density and therefore is in tetrahedral electron geometry. It would not matter which two pairs of electrons are the lone pairs because no matter what the molecular geometry will be bent.

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The kintetic energy (Ek) would be equal to zero because if you want to find the longest wavelength of light that is able to eject an electron, that means that there is no energy left over (Ek) because all of it is used to eject the electron (the work function). So, set the energy of the photon (Ep) ...

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Is this the only exception to the general trend for ionization energy? ( That ionization energy increases across a period and decreases down a group?) Or do all group 16 elements have lower ionization energies than their preceding group 15 element?

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The more electronegative atom will carry the negative charge because it wants to have more electrons.

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Covalent bonds have ionic characteristics if they share their electron unequally (if one element is more electronegative than the other, but not enough to become completely ionic). This is called a polar covalent bond. One side of the molecule is more positively charged and one side is more negative...

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In a way, you have to use the electronegativities of the elements in order to make the lewis structures. So, electronegativity is definitely an important component when it comes to determining dipole moments.

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It's also important to remember that if you are drawing an ion, the total formal charges should add up to the overall charge of the ion.

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Covalent bonds can have ionic characteristics if the atoms in the molecule share the electron unequally (have different electronegativities/electron affinities). Atoms with higher electronegativity will pull the shared electrons closer to it, thus making it slightly negative. The element that has th...

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Does the polarity/dipole moments of molecules play a role when we draw its Lewis structure?

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Also, how do you find the number of degenerate orbitals an atom has?

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The hybridization and mixing of orbitals in period 3 or larger atoms are part of the reason why some atoms can have expanded octets. This is because orbitals in the same shell can mix together because they are similar in energy, which means they can have more orbitals available to fill during bonding.

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The number of valence electrons depends on where the element is in on the periodic table. For neutral atoms, it is the element's main group number (1-8). Group 1 elements have 1 valence e-, Group 2 had 2 valence e-, and so on. But, if the atom has a charge, then you would take the element's main gro...

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P-block metals have high ionization energies, which means it is more difficult for them to lose electrons. But, for some elements in the p-block, this does not necessarily mean that they are less reactive. For example, group 17 elements have high electron affinity, which means that they have a high ...

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A double bond is shorter than a single bond because although there are more electrons that would want to repulse each other, the electrostatic pull between the positive nuclei and the now more negatively charged (with 2 electrons shared instead of 1) double bond will overcome this. The pull between ...

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Sometimes, if the structure has resonance, the double bond may not be much longer than the single bond. This occurs only if a species is resonant because all of its possible resonant structures blend, thus creating a partial double bond structure and making the double bond shorter than it otherwise ...

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The majority of elements are most stable when they have 8 valence electrons, filling up their outer shell. So, elements will either try to lose or gain electrons based on how many electrons they have in their valence shells to begin with. The reason metals will lose their valence electrons to form c...

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If you remember the blocks on the periodic table as previously mentioned, you can write the electron configuration of the elements. You mostly need to remember that the electrons will fill up the smaller shells first until all the orbitals are full and then will expand to larger shells.

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n is the principal quantum number, which describes the electron's energy and size (which shell it's in). l is the Angular Momentum Quantum number, which describes the shape of the orbital of the electron. In this class, we will likely only see l = 0 (s-orbital), 1 (p-orbital), 2 (d-orbital), or 3 (f...

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I believe that every time he added another electron, he was diagramming the electron configuration of the next element on the periodic table. He was showing the order of which orbitals get filled up first by electrons.

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Thanks! So to clarify, when filling up a subshell, one electron will be in each orbital (parallel to each other) until each orbital is occupied and then after that, the electrons will start pairing up?

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What is the difference between when electrons are paired vs parallel? How can you determine this?

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As long as you have two of the three variables (mass, velocity, or wavelength), you can use De Broglie's Equation to solve for the remaining one. Usually, questions will ask to solve for the wavelength, but the equation could also be manipulated to solve for m or v as well.

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Typically, if the calculated De Broglie wavelength of an object is less than 10^-15 m, its wave-like properties are not detectable. Electrons and other small particles would have a wavelength that is higher than 10^-15m, so only typically in smaller objects would this be used.

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In my notes, it says that diffraction patterns may result from constructive or destructive interference. What is the difference between these two and do they result in different diffraction patterns?

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During the lecture, Dr. Lavelle was trying to demonstrate how a stream of water may seem like it is continuous, but if you zoomed in close enough, it is actually made of molecules as the smallest "transferrable" unit. So, the mass of the water poured has to go up by at least one molecule a...

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It depends on which levels the electron is jumping to and from. This will determine the amount of excess energy which will then determine the wavelength of light emitted. The color of the light depends on its wavelength. Sometimes, the light emitted will not be in the visible spectrum and so it will...

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If there was a decimal point at the end (8340. ), then there would have been 4.

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An empirical formula is the relative number of atoms a molecule has. In other words, it's the proportion of each element in a molecule. For example, glucose's empirical formula would be CH2O because for every carbon atom in a glucose molecule, there are 2 hydrogens and 1 oxygen. A molecular formula ...

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For this problem, a good trick to remember is that you should always start balancing the equation with the elements that appear the least number of times. In this case, Fe and C both appear once on the reactant side and once on the product side, while oxygen appears twice on the left and once on the...

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I think that understanding the most common prefixes for SI units would not be a bad thing to study, not just for this test but for the entire rest of the class! Being familiar with kilo (10^3), centi (10^-1), milli (10^-3), micro (10^-6), nano (10-9), and pico (10^-12) would be the most helpful so t...

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Yes, the amplitude corresponds directly with the intensity of light. So, having a high amplitude would mean the light has high intensity. On the other hand, wavelength (distance between between the peaks) tells you what type of light it is.

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