CHEMISTRY COMMUNITY

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Glass electrodes are used to measure pH and Ecell measurements are converted to [H+] concentrations.

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The overall order is equal to all the exponents on the reactant concentrations added together.

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Both ways do work, but the easier method is generally to split up the half reactions and balance it that way depending on whether it is a basic or acidic solution.

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Work is positive when it is being done on the system (eg. compression) while work is negative the system is doing work on the system (eg expansion).

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catalysts are used up and then reformed so they start in the reactants of one reaction and are reformed in the products of another reaction.

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k' is the rate constant of the reverse reaction. So at equilibrium, k[A][B]=k'[C][D]

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A galvanic cell have a positive standard Ecell while an electrolytic cell have a negative standard Ecell and it is not spontaneous.

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In the beginning of a reaction, there are no products present so we use the initial concentrations of the reactants because only the forward reaction occurs.

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Changing the mass would not affect the Ecell because in the Nernst equation, which is used to calculate the Ecell, the mass is not incorporated into the equation.

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The units for the rate of a reaction are moles per liter per unit of time.

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The pt(s) is an inert metal inserted as an electrode because the other elements are not solids, so it should not be included in the balanced equation. The other elements in the cell diagram should be included in the balanced equation.

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The graph of ln(reactant) and time is a straight line and the slope is linear.

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The cell diagram is written as the anode (oxidation reaction) first on the left side followed by the cathode (reduction reaction) similar to how a cell would be drawn.

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The half reactions are balanced when they have an equal number of e- charges on the reactant and product sides.

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A conjugate acid is the acid when it loses its H+ ion, so it should have a one less charge than the acid. A conjugate base is the base when it gains an H+ ion, so it should have one more charge than the base.

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A basic solution contains less H+ ions, so more OH- ions, so a basic solution should be balanced with the OH- ions.

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The Van't Hoff equation is used to calculate K (equilibrium constant) at different temperatures if the change in enthalpy is known.

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At equilibrium, the forward and reverse reactions occur at the same right which means that they are at their lowest energy states. As a result, the Gibbs free energy of the reactants and products has to be the same at equilibrium.

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Gibbs Free Energy is the amount of free energy available to do work. It is a state function, so only the initial and final amounts matter.

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iso means same and choric means volume, so isochoric means constant volume.

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Delta S is the entropy of the system. Delta S surroundings is the entropy of the surroundings. Delta S total is the entropy of the surroundings and system combined.

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An isolated system, like combustion in a bomb calorimeter, is when nothing changes with the surroundings. A closed system, like a sealed beaker, is when only energy can exchange with the surroundings.

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when something is being compressed, work is done by the system, so it is positive. When something is expanding, work is done on a system, so it is negative.

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Increasing the pressure will shift the reaction to the side with fewer moles of gas and decreasing the pressure will shift the reaction to the side with more moles of gas. If there is an equal number of moles on the reactants and products, then there will be no change.

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When you are expanding a gaseous mixture, you are increasing the volume, so decreasing the pressure, so the reaction would proceed to the side with more moles of gas.

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The formula for calculating W is (# of microstates)^#atoms/molecules. So for part a, if the nano structure is aligned in the same direction, the number of microstates is 1 and the number of molecules is 64, so W would be 1^64 which is one. For part b, the number of microstates is 4 and the number of...

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Because work is equal to -p delta V, to find the volume of the pump, you need to use the formula for calculating the volume of a cylinder which is pi (r)^2 X height, with the height being -20 because the pump is being compressed. Using the volume and the given pressure, you can plug the values into ...

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If they are all aligned in the same direction, then the microstate would be one.

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Change in internal energy is equal to q(heat)+w(work).

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In a closed system, energy can exchange with the surroundings. An example is a sealed beaker of water.

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A negative delta H is exothermic because energy is released.

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work of expansion will be a negative value because the change in volume is positive, while work of compression will be a positive value because the change in volume is negative.

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P is pressure in atm, V is volume in liters, n is the number of moles, R is the gas constant 8.206 x 10-2 L·atm·K-1·mol-1, and T is the temperature in Kelvin.

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Only moles of gas are accounted for because it is the ideal gas law.

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Because enthalpies of different reactions can be added together, it is said to be additive.

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I think you should just know that the enthalpy is positive for all the phase changes.

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Since work is the energy required to do something, it is measured in joules.

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No because it requires heat energy to go from a solid to a liquid to vapor so the reactions would be endothermic.

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Because an exothermic reaction releases energy and the energy of the products is lower than the energy of the reactants, the enthalpy is negative. An endothermic reaction absorbs energy so the energy of the products is higher than the energy of the reactants, so the enthalpy is positive.

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Yes, you should leave out H2O because we assume that it is in excess so the concentration doesn't affect the reaction.

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The Kw value is a constant value of 1.0 X 10^-14 and it is used to either find the concentration of [OH-] or [H3O+] if either of the concentrations of the acid or base are given.

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When the temperature increases and the reaction is endothermic, the amount of reactants increases, so to balance out to equilibrium, the reaction will shift towards the products.

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An increase in pressure will favor the side of the reaction with less moles of gas and an decrease in pressure will favor the side of the reaction with more moles of gas. However, if an inert gas is added to the system, there is no change in the reaction.

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When doing an ICE table, solving for x requires using a quadratic equation. However, if the K value given is less than 10^-3, then we can assume that the x value in the denominator is so close to zero that we can ignore it.

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If Q>K then the reaction moves to the left because the concentration of products is greater than the concentration of reactants so the reaction would move towards the side of the reactants to reach equilibrium. If Q<K, then the reaction moves to the right because the concentration of reactants is gr...

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Usually they should be given or you might have to convert from moles to pressure using the ideal gas equation.

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PV=nRT, the ideal gas equation, can be used to solve for any of the values in the equation if a question asks for it or converting between pressure and molarity.

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Kp is used when the products and reactants are in the gaseous phase. Kc is used when the products and reactants are in the aqueous phase, so they have a concentration.

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The ratio (PO2)^3/(PO3)^2 represents the equilibrium constant K so it stays the same. As a result changing the concentrations of the products and reactants would not change the constant.

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Yes each heme complex binds to one O2- molecule which is why myoglobin only transports one oxygen molecule at a time.

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It is the negative log of the Ka value. A lower pka indicates that an acid is stronger because it shows that the acid more fully dissociates.

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It is an amphoteric oxide because it falls under the amphoteric band on the periodic table.

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No, but you can differentiate between an acidic, normal, and basic salt. A salt formed from a strong acid and weak base is normally acidic and a salt formed from a strong base and a weak acid is normally basic.

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If the electronegativity difference between two atoms is greater than 2, then the bond is normally ionic and if the difference is less than 1.5 then the bond is normally covalent.

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In oxacids, increasing the number of oxygen atoms distributes the negative charge over more atoms so the proton is less attracted to only one oxygen so the acid becomes stronger.

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The more polarizable an anion, the more stable it is, so the more electronegative an atom, the more stable the anion.

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The Ka equilibrium constant represents the strength of an acid in a solution based on how well it can dissociate. Lavelle mentioned that if a Ka value is given, it usually indicates that the element is a weak acid because a strong acid that dissociates completely would have a Ka of close to 1.

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Some examples of a weak base are ammonia (NH3) and methylamine (CH3NH2) and examples are a weak acid are carbonic acid (H2CO3) and vinegar (C2H4O2).

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Examples of a lewis acid, but not a bronsted acid are BF3, AlCl3, and metal cations like Mg2+, Li+, Na+ because they accept an electron pair, but don't necessarily donate a proton.

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Drawing the molecules based on its organic structure will not be covered in 14A, so I don't think you will need to know it for the final.

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Hybridization occurs when an atom creates a bond using electrons from both the s and p orbitals. As a result, there is an imbalance in the energy levels, so to equalize it, the s and p orbitals are combined to create hybrid orbitals.

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The bond angles are less than 120 degrees on the equatorial and less than 90 degrees on the axial.

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A bronsted acid is a molecule that gives up a proton, or a hydrogen atom, to another molecule.

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A single bond is a sigma bond and any additional bonds after that connecting the same elements are pi bonds.

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We should know the bond angles for the shapes that do not have lone pairs because the angles are constant. However, for the shapes with lone pairs, we need to know that the bond angles for trigonal pyramidal are less than 109.5 degrees.

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Electronegativity is the ability of an atom to attract electrons to itself while electron affinity is the energy released when an electron is added to a neutral atom.

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Noble gases from the 3p orbital onwards are able to have an expanded octet because the electrons can expand into the d subshell. As a result, xenon is able to form a covalent bond because it can expand its octet.

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The ones we have gone over in lecture are bent, trigonal pyramidal, see-saw, and square planar.

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When you draw the lewis structure, you see that xenon has an expanded octet which means that there are six bonding regions including the two lone pairs on the xenon and the four bonding pairs to the fluoride. so the shape would be octahedral.

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Usually, you only want to find formal charges if the question asks for it, but when drawing lewis structures with or without a charge, you want to calculate the formal charge of each atom and see if all the formal charges add up to the charge of the molecule.

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It is derived from the equations E=momentum * speed of light and E= hc/wavelength. Combining both of those, you get wavelength= h/momentum. You use the de Broglie equation for any particle with momentum and wavelength properties.

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The ones you probably need to know for this class would be sulfur, phosphorus, chlorine, and silicon because their electrons expand into the 3d orbital.

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Ionization decreases down a group and increases across a period. The ionization energy decreases down a group because as the number of shells increases, the electrons are shielded from the nucleus, so it takes less energy to remove the last electron. The ionization energy increases across a period b...

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Expanded octets usually occur for phosphorus, sulfur, chlorine, and silicon. The number of electrons that a molecule with an expanded octet usually depends on the total number of valence electrons present in the entire molecule and the overall charge of the molecule. An expanded octet usually occurs...

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Yes, we did a problem like this in one of the review sessions, and we used the equation En=-hR/n^2 to solve for the change in energy.

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Oxygen has a lower ionization energy because when you add an electron, it is added to an already half full orbital while for nitrogen, only half the orbital is full. As a result, there is electron-electron repulsion which lowers the ionization energy for oxygen.

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Lavelle said in the lecture that only the information up to 2D exercises in the textbook will be covered.

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You would only have to calculate it if it is specified, but you should calculate the formal charge of the structure to find out if the structure is in its most stable state.

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You will normally be given the threshold value, but it is not a constant value. Also, it is hvphoton= threshold +1/2mv^2.

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Ionic bonds occur between a metal and a nonmetal and a covalent bond is between two nonmetals.

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Yes, I believe so because you remove electrons from the farthest orbital usually.

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You count the number of electrons that aren't shared in a bond between another molecule. For example in a C-O (single) bond, the oxygen has 3 lone pairs and Carbon has 3 lone pairs.

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No, I don't believe so because a formal charge is a charge assigned to an atom assuming that electrons are equally shared within a chemical bond.

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Is there a rule for choosing the central atom? And are there some atoms that will always be the central atom?

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According to the Pauli Exclusion Principle, if 2 electrons are in the same orbital, then the spin is paired which means they spin in the opposite direction. Usually the spin starts up.

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If you are given the value of one of the quantum numbers, you can figure out the specific value for the other quantum numbers. For example if you are given a value for n, you can find the possible values of l and ml.

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The Stern and Gerlach experiment revealed how electrons don't have the same spin which differed from the classical prediction. Since electrons can be spun up or down, we use a 4th quantum number, ms which is the spin magnetic number.

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I believe the mass of the electron is given on the formula sheet. I don't think you will need to know the mass of a proton or a neutron, unless it is given in the problem.

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I remember Lavelle telling us that the homework due for week 3 should only be on the quantum topics.

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The DeBroglie Equation is only used for any moving particles with momentum and has wavelike properties with wavelength. Light does not have any mass so it cannot be used to calculate momentum.

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The Bohr Frequency Condition is used when a high energy electron drops to a lower energy level and the difference in energy is given off as a photon.

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The periodic table given on the test was the one on his website, so I would use that one. I would also go to the last decimal place given on the periodic table and not round your final answer till the end.

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I'm not sure if he posts power points of the slides, but I know he has modules for each of the quantum lessons on his website that you can take notes on.

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A black body is a physical body that absorbs all electromagnetic radiation regardless of frequency.

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V1 is usually the initial volume that you use to create the second molarity, so if you are solving for V2, you use the smaller volume in the equation for M1.

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I balance the element that occurs the least in the equation. For example, if hydrogen occurs two times in the reaction and it is the least occurring element, I balance that first and then move on to the next element that occurs the least. If there's an odd number of moles of an element, you balance ...

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usually you have a margin of error or plus or minus .1. it also depends on what you are using it for. FOr empirical/molecular you can round like 3.8 to 4 (from what I have been told)

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i start with the elements that are not carbon and then the rest before balancing hydrogen and oxygen

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There is a formula sheet that will be given for the test, but on the safe side, you should memorize the list of polyatomic ions.

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If the question asks for it, then you should subtract the grams of the amount of the excess reactant from the grams of the limiting reactant already calculated.

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