CHEMISTRY COMMUNITY

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Expansion causes an increase in work because of the equation -PdeltaV in which more volume causes more work.

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Delta s total is the sum of delta s of surroundings and system.

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Yes, you would place platinum electrodes in the sides with no solid electrodes, but other electrodes would be preferred depending on what's in the solution like iron electrodes are preferred if the solution contains iron and so on.

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Yes, anodes are the ones that are oxidized so they have lower concentrations while the cathodes are reduced so they have the greater concentration.

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Cells need solids electrodes in both sides to work, so if there is no solid electrode on any side, you place solid platinum to fulfill that necessity.

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The instantaneous rate applies to a specific point in time which is more useful than an average rate as the graph may not be as consistently simple in which the average rate can be very different as to what the actual rate is.

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Intermediates aren't included in the expression due to how it's produced in one step to be entirely consumed upon the next.

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Q is the ratio of concentrations and/or partial pressures of products over reactants where the individual coefficients are to be used as exponents for each individual reactant/product. You can use Q to find other values of variables that are also on the Nernst equation if given enough additional inf...

HuyHa_2H

I believe they rounded at a certain point during the problem. I didn't round until the very end and got 756 seconds as well so you should be fine.

HuyHa_2H

You first find the concentration of A after B undergoes the change which is 0.153 M of A - (2 mol of A divided by 1 mol of B)*(0.034 mol of B per liter) which gives you 0.085 M of A afterwards. Then plug this concentration as well as the initial concentration into the rate law of the first order and...

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It tripped me up trying to comprehend this but I kind of think of them as opposites. So, the oxidizing agents are reduced and the reducing agents are oxidized.

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Yes, it's absolutely critical that the anodes are placed on the left side of the salt bridge and cathodes on the right side of the salt bridge.

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I thought it was a typo and others looked up the equation where the chemical equation appears to be Cl2 -> HClO + Cl- instead. So, the oxidation equation is 2H2O + Cl2 -> 2e- + 2HClO + 2H+ and the reduction equation is 2e- + Cl2 -> 2Cl-. Combine the equations, and you'll get H2O +Cl2 -> HClO + H+ + ...

HuyHa_2H

Oxidizing agents are what's being reduced thereby gaining electrons where vice versa, reducing agents are what's being oxidized thereby losing electrons.

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For both acidic and basic solutions, you add H20 to balance the oxygens. Afterward for acidic solutions, you add H+ to balance the hydrogens; as for basic solutions, you add H20 to balance out the hydrogens but then add the same amount of OH- to the opposite side to maintain balance.

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For electrochemistry in this case, you can identify the n (as moles/electron in this case) from balancing your redox reaction since redox reactions involve the transfer of electrons.

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Salt bridges are present in order to maintain charge balance because in the case of charge imbalance, the reaction would essentially stop.

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Yes, they essentially have the same roles of keeping the cells neutral but the only difference is that with a porous disk, you don't place the anode and cathode in different beakers but rather together in the same solution.

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What I usually do is identify the ones that are unchanging like how oxygen and ozone have oxidation numbers of zero. From, there I'd find the oxidation numbers for the transition metals or whatever other element/compounds there are. Based on the changes in oxidation numbers of some species in the re...

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Oxidizing agents gain electrons and are reduced in a reaction whereas reducing agents lose electrons and are oxidized in a reaction.

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Extensive properties are dependent upon the amount that you have like density whereas intensive properties aren't dependent on the amount present at all like specific heat capacity.

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Work is negative when a system is doing work because that's what it loses hence the negative. Conversely, it's positive if something else is doing work on the system.

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Pressure and volume are inversely proportional to each other therefore depending on what you're given, the ratio will always be V2/V1 or P1/P2.

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The effects can be seen in the equation deltaG = -RTlnK. If K is greater than 1, then delta G is negative indicating spontaneity whereas if K is less than 1, then delta G is positive indicating a nonspontaneous process.

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Elements in their most standard state (pure elements) possess an enthalpy of formation of 0 like graphite.

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The equation has to always be balanced to find both K and Q. The only difference is that K is for when it's at equilibrium whereas Q is not.

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Adiabetic essentially means that no heat is entering or exiting, therefore it'd equate to 0 which would make deltaU equal to work.

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It's best to memorize them, but something like the pH scale and dissociability can indicate the strengths of acids/bases if given.

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Volume and pressure are inversely proportional so if volume increases, pressure must decrease and vice versa, but just remember that pressure can increase without changing volume by adding inert gases.

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Enthalpy is a state function therefore the total enthalpy can be summed up which allows Hess's law to be used.

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We will eventually have to calculate the enthalpy of sublimation and is represented by the sum of the heat of fusion and the heat of vaporization.

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Delta U is the internal energy. Q represents heat. Utilizing the two is through the equation: Delta U = q + w where w is the net work.

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Looking on a heating curve, as the temperature reaches a certain point, it will remain constant before increasing again. That constant temperature is where the phase change occurs.

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A calorimeter is just a "thermally insulated container" to measure changes of heat while a bomb calorimeter is the same thing but can withstand more pressure.

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Enthalpy is just the heat absorbed or released during a reaction and you can just consider the internal energy as just the sum of all of the total energy contained in the system.

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The two aren't numerically equal as there's a 273.15 difference between Celsius and Kelvin, but it'd probably be more useful if Kelvin were to be used as it's often compatible with many equations that involve temperature.

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Adding the signs would be necessary otherwise people can't really tell if the reaction is endothermic or exothermic.

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Water is a solvent, indicating that it's a liquid which won't affect the equilibrium. Only aqueous and gaseous reactants or products can affect it.

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Increasing the partial pressure of something from one side causes the partial pressure of whatever else is on that same side to decrease and everything on the opposite side increases, and vice versa to maintain the proper ratio.

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You can think of partial pressure as relating to individual reactants or products while pressure applies to the entire system simultaneously.

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Just as confirmation, you know to use ICE tables if you're given K and the initial concentrations/pressures correct? Is there anything else to identify in the problem to know if ICE charts should be used?

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You just look at the K value and compare them. Smaller K values indicate more thermodynamical stability and the opposite if the K value is bigger.

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You use the 5 percent rule to make sure that the approximation that you made where x is 0 in the denominator when k is less than 10^-3 is valid and should be used every time you solve for equilibrium concentrations using the ICE chart.

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There are two equations that can be made for this problem because it's polyprotic. The first equation is H2SO4 + H2O = H3O + HSO4. But because it can still deprotonate, the second equation is HSO4 + H2O = H3O + SO4. You then make an ICE chart for this where the initial concentration of HSO4 and H3O ...

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The ideal gas law is typically used to convert between pressure and concentration. So, if you're given concentration and you're supposed to find Kp or vice versa, you know that you have to apply the equation.

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Yes, because the equilibrium constant will never change so you must maintain the product to reactant ratio. So if the reactant were to increase then the products would increase to maintain the proper ratio.

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Yes, because the equation used to find both are the exact same. The K value is when the reaction is at equilibrium so if Q equates to that then the reaction is definitely at equilibrium as well.

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If Q<K, then the forward reaction is favored, resulting in more product to reach equilibrium while if Q>K, then the reverse reaction is favored which results in more reactants to reach equilibrium.

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I'd assume that it'd be Kp because units of pressure is given, but I don't think it should be too concerning because you can convert between concentration and pressure anyways.

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The equilibrium constant is just the ratio of product to reactant. With the constant, you can determine the concentration or partial pressure for either one when given the constant and the reactant or product. Also, if either reactant or product changes to a certain amount, you can determine the amo...

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If you draw out the proper shape, then obviously the molecule will be polar because of dipoles that aren't canceling each other out. So, it's only if the molecules are the same where the dipoles would cancel each other out.

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You should see if the dipoles cancel out in the molecule. If they cancel, then it's nonpolar and if they don't then it's polar.

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You would typically only find the hybridization for the most stable resonance structure so I don't think you'd need to show the other resonance structures only the stable one.

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The more stable structure would be preferred. So, it's the one where S has two double bonds each connected to an O and a lone pair on top of S as well. Count the sigma and pi bonds for that structure.

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Yes, they do because they're also electron groups.

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pH measures acidity whereas pOH measures basicity. Both are primarily measured on a scale from 0-14 so if the pH is 4 then the pOH is 10 and so on.

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Cl is less electronegative than F which makes it easier to dissociate which makes HCl the stronger acid.

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A Lewis acid accepts an e- pair while a Lewis base donates an e- pair. Bronsted acids donate protons while bronsted bases accepts protons.

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I think you're supposed to use the hybridization of the most stable resonance structure which you can find through formal charge.

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Bronsted Acids donate protons and Bronsted Bases accepts protons.

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Formal charge tells you which resonance structure is more stable so with it you'll be able to find the preferred form of a molecule

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Both SiH4 and SiF4 are nonpolar which mean that they only display LDF forces. So when both molecules have LDF you look at the size. The F is more bigger than H so SiF4 is the bigger one of the two which makes it have stronger LDF forces so higher boiling point.

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You don't need to order the bonds. Just know how many sigma and pi bonds are present in each kind of bond (Triple Bond = 1 Sigma Bond and 2 Pi Bonds,etc.)

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Each lone pair is a potential hydrogen bonding site, so in your case a nitrogen atom with TWO lone pairs would have TWO potential hydrogen bonding sites.

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You would consider the weight if both molecules are not polar which is not the case here. AsF3 displays dipole-dipole interactions which indicates it's polar while AsF5 only displays LDF forces so it's not polar. Dipole-dipole is stronger than any LDF so AsF3 would have the higher boiling point.

HuyHa_2H

Just for confirmation, what do you generally look at in a VSEPR model to determine polarity of a molecule?

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Generally, you can't really determine polarity just off of the molecular formula which is why you use the VSEPR models to determine it as it is the actual accurate representation of the molecule.

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Depending on which two atoms that have bonds together, they may have a single bond (1 sigma bond), a double bond (1 sigma and 1 pi bond), or a triple bond (1 sigma and 2 pi bonds).

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Symmetry shouldn't really be what you're looking for to determine polarity but rather use the VSEPR models instead because VSEPR models are the actual representation and Lewis structures are just inaccurate base models.

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Bent and angular are the same thing, but I'd probably use angular just because it's how the book calls it.

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Dipole-dipole is when the positive end of a molecule and the negative end of another molecule attract, LDF is when electrons create temporary dipoles, and hydrogen bonds is when a hydrogen atom bonds with a highly electronegative atom (N,F,O). In terms of energy needed to break these interactions, L...

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It's when a molecule with a dipole comes in contact with an atom with no dipole. The electrons in the atom then react to the molecule to create a dipole in the atom itself.

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The bigger the electronegativity difference, the greater the dipole moment will be. And yes, if there if is any difference in the electronegativity, then you should consider that there is a dipole moment.

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Ionization is the process of forming ions by losing or gaining electrons, electron affinity is like how likely the atom is to gain an electron, and electronegativity is how likely the atom would take an electron.

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Aside from looking at the electronegativity aspect, I think of it as how covalent bonds pretty much involve the sharing of electrons whereas ionic bonds involve the attractions of opposite charged ions which makes it much more harder to break.

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Anions gain electrons whereas cations lose electrons so basically anions get heavier and cations get lighter.

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The electron with the least electronegativity is the one that is the central atom but pretty much most of the time it's the element with the least amount of atoms in the molecule.

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Electrons don't really leave, but rather they are shared among atoms to form ions.

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Pretty much single bonds contain one sigma bond, double bonds contain a sigma and a pi bond, and triple bonds have one sigma and two pi bonds.

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Yeah, you pretty much use the De Broglie equation when you're given or given enough to find either the mass, velocity, or wavelength of an object that is not massless.

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Noble gases have full valence shells which make them not needing to take or give any electrons which exclude them from the trends.

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Electrons in any element or whatever else they're present in all have the same size which is 9.10938356 × 10^-31 kilograms.

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Formal charge is calculated by utilizing the formula: Valence Electrons - (# of Lone Electron Pairs + # of Bonding Electrons/2).

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The further the electrons are from the nucleus, the less the force of attraction is from the protons to the electrons, hence the further electrons are easier to remove.

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Electromagnetic radiation move at the same speed as the speed of light hence we use the constant 2.998 x 10^8 m/s for both subjects.

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Each series has their own range of wavelengths. Once you've found the wavelength the photon's at, then you can just link them to whichever series involves that range.

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To add on to that, each orbital is placed one electron at a time. When all of the orbitals have been placed and there are still more electrons, then each one will be paired up with each electron that was already placed in the orbitals.

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Photons don't have mass so the equation isn't applicable for it.

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Wave functions just tell us what the shape of the orbitals so you can basically tell where the electron's going to be.

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Honestly, any unit of distance in the metric system per a unit of time is fine because they can all be converted anyway, but normally people write it as m/s or maybe unless otherwise stated.

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Amplitude just indicates how high or low the waves themselves travel. But in terms of its relationship to frequency and wavelength, it probably doesn't matter as amplitude isn't present in the equations that we've been using so far.

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More specifically, it's thermal electromagnetic radiation.

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The speed of light won't because it's a constant but sometimes they might be displayed differently due to sig figs and rounding and whatnot.

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When the electron reaches an excited state, it jumps to a higher energy level where they release photons to go back to the original state.

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The relationship is displayed in E(energy)=h(Planck's constant)v(frequency). Planck's constant is the constant of proportionality which shows the direct relationship between energy and frequency. The higher the frequency, the higher the energy output, and vice versa. The Planck's constant doesn't re...

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Percent yield is basically the ratio of actual yield to theoretical yield, and theoretical yield is the maximum amount of product that you can possibly get based off of your limiting reactant.

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Usually when you're adding or subtracting you tend to round your answer to the least number of places to the decimal point in the problem. Ex: 1.234+1.2 gives you 2.434 but you round it to 2.4. And as for multiplying or dividing you literally just use the smallest number of sig figs out of the value...

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Most of the problems you'll do will require you to write out chemical equations so yeah, you'll pretty much have to remember polyatomic ions especially in case the question won't give you the chemical formula for the compounds that you'll need.

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Typically, if you can't use a whole number as a stoichiometric coefficient for whatever it is you're balancing is when you use a fraction. It's so you can just multiply every coefficient in the equation with the denominator of the fraction to get all the coefficients as whole numbers without messing...

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I thought they were due this Friday, but apparently it's due this Sunday.

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