CHEMISTRY COMMUNITY

Shimei_2F

W is positive when work is being done ON the system and negative when the system is doing the work.

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If the reaction was at equilibrium, changing the concentrations will shift the equilibrium and change from standard E cell to E cell.

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If the reaction is very fast, the rate changes more rapidly than the time required to measure it. The reaction may be finished before an initial rate can be observed.

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Add the exponents of all the reactants in the rate equation.

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What are the correct units for the answer? In the textbook, it's
2.7x10^10 mol.L-1.s-1 and in the solutions manual it's 2.7x10^10 L.mol-1.s-1

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Organic Chem tutor used k=M^(1-n).s^-1.

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Mass doesn't affect the E(cell) but concentration does.

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You can use rate constant to calculate the rate. Rate constant doesn't change while rate does.

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0.693 came from ln(2) which is in the half life equation for first order reactions. t=ln(2)/k

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You can search up some of the TAs names on Chem Com, go to step-up, or workshops.

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You derive it from the equations: ΔG=ΔG°+RT(ln(Q)) and ΔG=-nFE. You set the two equal to each other to get: -nFE=ΔG°+RT(ln(Q)). Divide both sides by -nF to get: E=(ΔG°/-nF)-RT(ln(Q))/nF) From ΔG°=-nFE°, you change it to E°=ΔG°/-nF to replace the first part of the equation to get: E=E°-(RT/nF) x ln(Q)

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When we write cell diagrams, and there are two ions ex: Fe2+ and Fe3+ both in aqueous solution. I know you don't separate it with the line (|) and instead, you separate it with a comma. But does it matter what order I write them in? Can I write them as either Fe2+,Fe3+ OR Fe3+,Fe2+?

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You can find it by balancing the electrons of the half-reactions and that's the n, the amount in moles of electrons that were transferred.

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If you write out the original reaction, you can see that the oxidation number of Cl doesn't change whereas Fe does.

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Problem asks to write the half-reactions and devise a galvanic cell (write a cell diagram) to study each of the following reactions. (c) Cd(s) + 2Ni(OH)3(s) --> Cd(OH)2(s) + 2Ni(OH)2(s), the reaction in nickel-cadmium cell I found the two half-reactions which were: Cd(s) + 2OH-(aq) --> Cd(OH)2 + 2e-...

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It's 50% to get a C- in the class and he probably rounds your grade at the end if you're really close.

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Is test 2 just going to include the material that wasn't tested on the midterm up to what we learn before the test?

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Our TA said that there's a system that automatically checks your chemistry community posts.

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How does Le Chatelier's Principle apply to cell potentials?

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How do you write the redox reaction or draw cell diagrams when you're given two half-reactions?

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Probably anything from the end of thermodynamics and beginning of electrochemistry.

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When would you use the Van't Hoff Equation and what does it mean?

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Sometimes it's given to you and other times, you're given the information to calculate it.

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Because it relates the difference in Standard Gibbs Free Energy to K.

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Work under constant volume is 0. Under constant pressure, you'd use w=-P(external)Delta V. Under constant temperature when it's reversible and isothermal, you'd use w=-nRTln(Vf/Vi).

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the final temperature would be the same so you set qCu=-qWater and solve.

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For Part 1) You would calculate the heat (q) required to heat the copper kettle and water to 100 C separately. Then you add them together to find the total heat needed to raise the temperature. Use q=nCdeltaT for both. For Part 2) You would divide the heat required to heat the water by the total hea...

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Since it's sealed, no matter can be removed or added but heat can still be transferred so it's a closed sytem.

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These changes occur when reactions require energy or release energy.

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I think it'd be a good idea to know them and how to apply it since Lavelle did assign the reading so it's fair game.

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It means that the constant temperature of the gas is maintained by ensuring that the system is in thermal contact with a constant-temperature water bath at all stages of the expansion. In an isothermal expansion, the pressure of the gas falls as it expands; therefore, to achieve reversible expansion...

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In the first equation, you're calculating for the heat capacity of the Calorimeter using the heat put into the Calorimeter which is why it's qcal. In the second equation, you use it to calculate the heat of the overall change in internal energy from the 2 rises in temperature.

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The three ways to change the energy of a system is heat, work, and mass flow.

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An ideal gas in a cylinder was placed in a heater and gained 5.50 kJ of energy as heat. If the cylinder increased in volume from 345 mL to 1846 mL against an atmospheric pressure of 750. Torr during this process, what is the change in internal energy of the gas in the cylinder?

How do we solve this?

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Problem: A constant-volume calorimeter was calibrated by carrying out a reaction known to release 3.50 kJ of heat in 0.200 L of solution in the calorimeter (q 5 23.50 kJ), resulting in a temperature rise of 7.32 C. In a subsequent experiment, 100.0 mL of 0.200 m HBr(aq) and 100.0 mL of 0.200 m KOH(a...

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If X is less than 5% of the initial, you should be on the right track!

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I think it's helpful to know the generic formulas for liquid to vapor, solid to liquid, and solid to vapor which make up the formula (Delta H sublimation)=(Delta H fusion) + (Delta H vapor).

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Exothermic reactions have a negative value because it releases energy so products are lower than reactants. Vice versa for endothermic reactions which have a positive value because it requires energy so the reactants are lower than the products.

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A state function is not dependent on the path taken to obtain that state. One example is density which only depends on the initial and final, not the path taken.

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Usually, you shouldn't get a negative number inside the square root. Outside the square root, it can be positive and negative.

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I think the midterm and final is cumulative but not the tests.

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K is used when a reaction is at equilibrium. Q can be used at any arbitrary stage of a reaction.

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Raising the temperature of an exothermic reaction lowers the K value and shifts to favor the production of reactants. On the other hands, raising the temperature of an endothermic reaction raises the K value and shifts to favor the production of products.

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You're allowed to approximate X while doing ICE tables if the K constant is less than 1.0x10^-3. If the answer is less than 5% of the initial molarity, then the approximation is okay.

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A reaction shifts left or right in order to reach equilibrium again if something such as concentration or temperature changed.

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Usually, temperature should be given so you can use PV=nRT to solve for pressure.

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It should be given usually.

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What exactly is Le Chatelier's Principle?

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I don't think so, we should be given it on exams.

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When there is more product than reactants and the reverse reaction is favored.

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If the pH of the titration is >7, it's basic. If it's <7, it's basic. If pH is 7, it's neutral.

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Delta X is the uncertainty in position.

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use these when the ligand already has a prefix of bi- tri- tetra- etc.

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When we name coordination compounds on the final, would writing (en) in place of ethylenediamine or (dien) in place of diethylenetriamine be acceptable?

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Lavelle doesn't bruincast his lectures but his website does have modules that you might find helpful.

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Strong acids completely ionize in solution while strong bases completely ionize in water.

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Stronger acids have higher kA and lower pKA while weaker acids have lower kA and higher pKA.

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The equilibrium constant kA is a quantitative measure of the strength of an acid in a solution. The pKa is used to indicate the strength of an acid.

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Go to Lyndon's review sessions!

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A bronsted acid is a substance that gives up or donates hydrogen ions during a chemical reaction.

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Yes, Lavelle has mentioned in class before that the final will be cumulative of everything we've learned this quarter.

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As the orbitals in the bond have more s character, the bond length generally decreases so the strength increases.

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K3[Cr(CN)6]

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Does anyone have the answers to Lydon's worksheet this week?

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Yes because the molecule with the lone pair would create repulsion that would alter the degrees of the bond angles.

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The electronic arrangement factors in both bonding pairs and lone pairs. The molecular shape takes into consideration of the lone pairs. So an atom's electronic arrangement and molecular shape can be the same if there aren't any lone pairs.

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The Davisson–Germer experiment confirmed the de Broglie hypothesis that matter has wave-like behavior.

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The areas of electron density and lone pairs affect bond angles while atomic radius affects the bond length.

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Test 2 will cover anything that wasn't tested on the midterm up to sigma and pi bonds which he will discuss in class on Monday I believe.

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The oxidation number of an atom is the charge that an atom would have if the compound was composed of ions. The oxidation number of each atom can be calculated by subtracting the sum of lone pairs and electrons it gains from bonds from the number of valence electrons.

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It depends on what element it is. Common examples of elements that can form an expanded octet is sulfur, phosphorus, silicon, and chlorine.

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Electronegativity measures the tendency of an atom to attract a bonding pair of electrons. Electron affinity is the change in energy of a neutral atom when an electron is added to the atom to form a negative ion. Electron affinity and electronegativity both increase from left to right in a period an...

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I think I am if I get the class!

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The ionization energy trend in the periodic table has a few exceptions with oxygen and nitrogen being one of them. The ionization energy of oxygen is lower than nitrogen because each p-orbital in a nitrogen atom is occupied by one electron but in oxygen, the first orbital is occupied by a pair of el...

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Electronegativity is a measure of how strongly atoms attract bonding electrons to themselves.

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The Aufbau principle states that lower energy orbitals fill before higher energy orbitals. Hund's Rule states that one electron goes into each orbital until all of them are half full before pairing up.

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Yes, you remove an electron from the highest energy level.

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My TA said that we should write 3d first so the shells are in chronological order.

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The central atom is usually the least electronegative atom with the most unpaired valence electrons. If carbon is present, often times, the central atom is carbon. However, hydrogen can never be a central atom.

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The net electrical charge of an anion is negative and a cation is positive. For example, sulfate is an anion and ammonium is a cation.

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Usually, you remove electrons from the farthest orbital so yes, you do.

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Metalloids can form covalent and ionic bonds. They can form covalent bonds by sharing electrons or ionic bonds by either losing or gaining electrons.

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Dr. Lavelle said during lecture to use the least electronegative atom as the central atom. In the case that carbon is present in the ion, it's usually the central atom.

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Electronegativity describes the likelihood of an atom to attract a shared pair of electrons towards itself. It increases from left to right because of a greater charge on the nucleus which causes the electron bonding pairs to be attracted to atoms placed further right on the periodic table.

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Electron configuration is the distribution of electrons of an atom or molecule in atomic or molecular orbitals. It tells you how many electrons there are in each of the different orbitals and at which energy level.

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The unit for hertz is the number of cycles per second which basically measures frequency.

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Finding the limiting reactant helps to determine the amount of a product that can be produced or how much of a reactant will react with the limiting reactant.

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It basically says that in an atom or a molecule, 2 electrons can’t have the same four electronic quantum numbers. The two electrons in an orbital must have opposite spins.

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yes, m is the mass of the particle.

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You should be using the periodic table on Lavelle's website to familiarize yourself with it since that's the one we'll be using on all of our tests.

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If a photon has less energy than the work function, it would not be able to eject electrons.

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No I don't think he does. You can check the different links he has on his website if you're uncertain.

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A photon is a particle representing a quantum of light or other electromagnetic radiation. It carries energy proportional to the radiation frequency but has zero rest mass.

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Use the periodic table Lavelle put on his website. It's the one that they gave us on the test.

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it depends on what the question is asking for. Usually you would use the smaller one

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it is used to find E=hv. It can be used with c=lv to calculate and find values
h is planck's constant

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Yes, my TA told our discussion section that they're modeled after the homework questions. So, only free response.

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in the textbook, there is a page under the fundamentals section that goes over how to name ionic and covalent compounds. Also it has a list of the most common polyatomic ions like chlorate, carbonate, sulfate, nitrate, and etc.

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you start with carbon, then hydrogen and the rest after

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