CHEMISTRY COMMUNITY

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I don't believe that we are going to be responsible for knowing the steady-state method.

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I think the questions will be similar to the homework problems and the concepts will be taken from the homework, but all of the questions will not come from the homework assigned problems.

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Are the stoichiometric coefficients always used as the order of the reactants?

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Right, generally they are not present in the written form of the overall reaction.

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We also learned how to calculate average rate of reaction. When would we use that equation rather than the instantaneous rate?

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When calculating Gibbs free energy, do you take into account stoichiometric coefficients?

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I believe it is Joules per mol because the constant n in the equation delta G=nFE represents the number of electrons transferred but is represented by a unit less value.

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Are ions that are not involved in the oxidation/reduction half reactions included in cell diagrams? For instance, if there is a cell containing AgNO3(aq), and Ag+ + e- -> Ag(s), would you include NO3-(aq) in the cell diagram ?

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For a first order reaction the [A] v Time plot is a decreasing exponential but what would the graph of [A] v Time look like for a second order reaction?

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In each of the different order reactions, their reaction rates are affected by the concentration of reactants differently or not at all (in the case of zero order).

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It doesn’t matter which you use but I think in lecture he said that biologist usually use log because pH is calculated using log.

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The n in the Nernst equation stands for the number of electrons transferred in the balanced reaction. The book says that the units of n is not moles and is just a unit less number. Then when you solve of delta G you get a value in J/mol since the moles don’t cancel out in your calculation.

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I’m not sure but if the redox number you’re referring to is the E vale of the cell, then you can tell the reaction is favorable if the cell potential (E) is positive.

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Kallista McCarty 1C wrote:It will cover the rest of thermodynamics that was not on the midterm and all of electrochemistry!

Would that just be Gibbs Free Energy as the thermodynamics portion?

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Cu is the anode since it is losing electrons, and M is the cathode since it is gaining electrons. (I remember this by Red Cat and An Ox: Red uction- Cat hode, An ode- Ox idation :)). Eº=Eº(cathode)-Eº(anode), so you would plug in the voltages to solve for Eº(cathode). How do you know Cu is losing e...

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Use H+ to balance the hydrogens first and then add OH- to both sides to balance the H+ ions.

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Yes, add the same number of OH- molecules as you have H+ ions to both sides.

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When electrons move from one solution in the cell, they are replaced by negatively charged ions, and when they move into the solution in the other cell, positively charged ions balance the negative charge.

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Yes, because when the oxidation number increases, that would mean the negatively charged electrons are being lost by oxidation and vice versa for reduction.

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A standard hydrogen electrode models the reduction of H+ to H2 and it is used as a comparison for other redox reactions.

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Use Cv when volume is constant and Cp when pressure is constant.

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I believe you use the initial volume because you are trying to find the number of moles at the beginning of the process.

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In an isobaric system, pressure is constant, so delta P would equal zero. In this case, work can be calculated using the formula w=-PdeltaV and heat can be calculated using q=deltaH.

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Are reversible processes always isothermal?

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Why are standard molar entropies always positive?

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The energy from heat being added to the system is represented by q, while w represents the energy leaving the system due to work.

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How does a system being thermally insulated affect its entropy?

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An expansion is reversible when temperature is constant, but pressure and volume are variables; it is irreversible when pressure is constant and temperature changes.

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The system is in equilibrium, so the Pint and Pext are essentially equal with very small shifts that are balanced by work.

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When calculating the degeneracy (W) of a molecule, using X^N where X=the number of particles and N=the number of energy states, how is N determined? And can you give an example of this?

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When do you use Hess' Law v. Enthalpies of formation?

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When a system has constant pressure, there is no change in pressure. It means the same for volume.

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Because the reaction in that example is between a string acid and a strong base, it is a neutralization acid and forms water. The density of pure water is about 1.0 g/mL.

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What is the difference between delta H and q?

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When given the enthalpy of combustion, you need to write out the combustion equations which would generally by the substance + O2 -> CO2 + H2O and from there you can use Hess' Law to manipulate the equations and add the enthalpies to find the enthalpy of the reaction.

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If it is asking about temperature effects/changes, I would assume that either endo/exothermic or the delta H value will be given and you can determine the other by knowing that exothermic reactions have a negative delta H value and endothermic reactions have a positive delta H value.

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Strong acids dissociate more than weak acids, resulting in a higher hydronium concentration in the solution. Where pH=-log[H3O+] a higher concentration of hydronium correlates to a lower pH value.

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In lecture this was described as the "conjugate seesaw" where strong acids/bases tend to have a weak conjugate base/acid and vice versa.

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When a reaction is endothermic, it requires heat and has a positive delta H value, so you can think of heat as a reactant in a way. When it is exothermic, heat is given off during the reaction and delta H is negative, so heat can be thought of as a product of the reaction in this case.

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I believe you can use it whenever you are calculating K using ICE table just as long as K<10^-3

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In a reaction where X2 -> 2X is it considered endothermic or exothermic and why? (X stands for any element)

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You can approximate if the x value is less than or equal to 10^-3 I believe.

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I believe you only need to solve partial pressure when asked for the partial P for the individual compounds or if you need to solve for Kp.

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I do not think the equilibrium constant will be different if the gases are in atm, bar, etc. as long as all of the pressure values have the same units because the equilibrium constant is a ration of products to reactants.

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Liquids are not included when calculating Kc, but if you have both aqueous and gaseous compounds you can calculate Kc including all gaseous and aqueous compounds.

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It can be replaced with a 1 because it does not affect the calculation, but also I think it would okay to just not include the l/s molecules in the formula.

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When given the equilibrium constant as K for a reaction with only gases, is it safe to assume that the K value is meant to be the Kp? If not, how do you know whether it is Kp r Kc?

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I think in lecture a "pure" substance was described as that in a liquid or solid state. When calculating the equilibrium constant, solids nor liquids are included in the formula.

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I don't believe a hydrogen bond could form with an O2 molecule because hydrogen bonds are dipole-dipole interactions and O2, as a linear molecule, does not have a dipole moment.

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When Q > K there is a larger amount of products than there are at equilibrium, so the reaction will proceed in the reverse direction to use up the excess products. When Q < K there is a larger amount of reactants than there are at equilibrium, so the reaction will proceed in the forward direction to...

LNgo 1G

The uncertainty, or delta x value, represents the distance that the electron can be located. If the uncertainty is larger in the case of the example that we did in class, that would mean that the electron would exist outside the nucleus of the atom.

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When would you use the -o ending versus the -ido ending when naming ligands? In the practice problems I saw both of them in different examples in the case of the cyanide molecule and cannot tell when to use one or the other.

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There are different components that contribute the acidity of a molecule, but concerning electronegativity, acids containing a central atom with higher negativity allows for a more stable conjugate base, so the acid is more likely to dissociate.

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Since solutions with a pH of 6 are sometimes considered neutral and other times considered acidic, because it is lower than the neutral pH of 7. When the solution is more acidic, the acid dissociates as it gives of a proton (H+ ion), leaving the negatively charged conjugate base in the solution.

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When haming compounds, when would you have an -o ending versus an -ato ending? For example, I have seen cyanide named -cyano- and -cyanato- in different compounds.

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When looking at the reaction equation you can tell which is an acid because it would have donated a hydrogen atom whereas the conjugate base would be the compound that received a hydrogen atom.

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Lewis acids/bases are characterized by the donating or receiving of an electron pair while Bronsted acids/bases are characterized by the donating or receiving of a hydrogen ion.

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Oxides are compounds that include one or more oxygen atom. They are important in acid/base reactions because the oxygen atom forms a bond with one of the hydrogen atoms in a water molecule to create OH- and this reaction is used to characterize bases.

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I believe this would be considered a substitution reaction, so the ions do essentially "switch". The bonds in the molecules break in water due to hydrogen bonding and are reformed in more stable structures.

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This is when there are more than one central atoms that ligands bind too, a good example would be triphosphate where the oxygen atoms are the ligands and the phosphate atoms are the central atoms.

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The bond angles will be >180, 90, and <120 because the lone pairs exerts repulsive forces on the atoms.

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I think the electron repulsion plays a part in orienting the molecule so that the chlorine atoms are not on opposite poles as you might expect, but they are placed next to each other in the molecular structure.

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The melting point is higher if the dispersion forces are stronger because it takes more energy to break stronger interactions between molecules.

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Dissociation energy is the energy required to break a bond. Stronger IMFs, such as ion-ion interactions, have greater dissociation energy and weaker IMFs, such as dispersion forces, have lower dissociation energy because the stronger the bond is, the more energy it takes to break it.

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I don't believe so since hydrogen bonding is a form of dipole-dipole interactions which do not take place in nonpolar molecules since they do not have dipole moments.

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I believe there would be a dipole moment in the direction of the chlorine atoms, which would both be on the same side of the molecule, not at opposite poles.

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I believe that we should know that as bond strength increases, bond length decreases.

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Dipole moments result from differences in electronegativity as more electronegative atoms pull the electrons of less electronegative atoms closer to them. This same effect also makes a molecule polar as electrons are being shared unequally.

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Dipole moments are created from differences in electronegativity, so since Cl is more electronegative than C and H, there will be a dipole moment in the direction of the Cl atoms.

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I believe it would because O is an electronegative atom which would form H bonds with the H from other CH3CHO molecules.

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When drawing the Lewis structure for a radical molecule, how do you know which atom the single lone electron belongs to?

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Which bonds are stronger: ionic or covalent?

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Hydrogen bonds are very strong dipole-dipole interactions that occur due to the attraction between partial charges.

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Phosphorus can only have 5 bonds total since there are only 10 electron places in the d shell that it uses to expand its octet.

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The most stable structure will have the most atoms with lower formal charges, closest to or equal to zero.

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Resonance occurs when the Lewis structure of a molecule has double or triple bonds that can be applied amongst different atoms, yielding multiple different forms.

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Elements that can expand their octet are able to do so because they have the d-orbital to use to hold electrons.

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The resonance form with the most formal charges equal to zero means that there is a more equal sharing of electrons since there are no partial charges on the atom(s).

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The stability of the half-full d orbital may be attributed to the electron shielding effect since the half-full shell allows for a more stable placement of electrons with respect to electron repulsive forces.

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The more electronegative atom pulls the electrons closer to it, resulting in a partial negative charge on that atom and a partial positive charge on the other.

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Elements in period 3 have access to the d-block orbital which allows them to hold more than the 8 electrons that the period 1 and 2 elements can.

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Technically it doesn't matter whether the arrow is up or down because it just represents electrons with opposite spins, not in any specific direction, but generally the up arrow goes first.

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It depends how many electrons are in the d orbital. If there are 5 or 10 electrons in the d orbital the d will go before the s because it is more stable due to electron shielding; otherwise the s goes before the d orbital.

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Ionic bonds are stronger because they involve the giving and accepting of electrons between atoms while in covalent bonds, the electrons are only shared.

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The molecule shifts between all three structures based on where it will be most stable, so it results in the measurement of “partial double bonds”

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Atoms in the same energy level are close together on the spectrum which would explain the chunks. The gaps represent the jump between energy levels since they are quantized rather than continuous.

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If given the wavelength, how can you tell which series (Lyman, Balmer, etc.) a photon falls under?

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Wave functions are the path that electrons travel around the nucleus. They can be represented by sin/cos graphs because the electron oscillates as it moves in a circular orbit, not just in a straight path. In chemistry, wave functions can be used to determine the shape of different types of electron...

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I think that the points or planes that mark the separation of these lobes are called nodal planes and since s-orbitals have only a single lobe, there is no point of separation in the orbital. Hope this helps!

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Quanta is the general term for particles or pieces that make up a whole, like how quantum mechanics refers to the mechanisms behind very small objects. Photons are a quantum measurement of light.

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You divide the molar mass given by the empirical mass and then multiply the subscripts of the empirical formula by this number to get the molecular formula.

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You can use stoichiometry to calculate the amount of the excess reactant that is used in the reaction with the amount of the limiting reactant that you have. Then subtract the value of the excess reactant used in the reaction from the amount given.

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You divide the given molar mass by the empirical mass. The empirical mass will always be smaller than the molecular mass because it is the smallest ratio of the atoms so you can try to remember that you divide by the smaller number.

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I believe the uncertainty would be 5.0. The plus and minus signs just mean that the variation can go either direction.

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You can use the mole ratios of the individual ions to the compounds given to find the moles of each ion in the solution and divide by volume to get the concentration from there.

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You use Avogadro's number when you are trying to find the number of particles, atoms, or formula units of a substance.

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I do the limiting reactant problems a little differently. So instead of comparing the moles, I just calculate how many moles of the product each reactant can produce. The reactant that produces the least amount of product is the limiting reactant.

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This is a dissociation equation, so it does split into ions, but you might have to take into consideration the solubility of the solution to see how much of the solution dissolves and how much solid is left.

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It is okay to use fractions when balancing equations; you can compute them into integers by multiplying the entire equation by the denominator. Technically you can't have a fraction of an atom because atoms are the smallest basic units of matter, so generally chemical equations only have whole numbe...

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Using the empirical formula makes it easier to name compounds and to determine the composition of a substance because it represents the smallest whole number ratio of the individual atoms.

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