CHEMISTRY COMMUNITY

preyasikumar_2L

Larger, more complex molecules would have more atoms in the molecule. This means that there are more electrons floating around which can result in more intermolecular forces between them and other species nearby. All the atoms would require more bonds to keep everything held together, and thus resul...

preyasikumar_2L

Platinum is the most common electrode used in electrochemical cells when none of the species present are solid metals because it is resistant to oxidation and won't easily react in redox reactions.

preyasikumar_2L

You can look at the graph, the rate law expression (exponent = 1), the rate constant units (s^-1), and the equation (if there's one reactant and its stoichiometric coefficient = 1).

preyasikumar_2L

A catalyst only serves to speed up the rates of the forward/reverse reactions, but those would still be equal, and since catalysts don't change any equilibrium concentration and isn't a reactant since it can be regenerated and reused, the equilibrium constant K would not be affected. Also, K is the ...

preyasikumar_2L

You should always make sure the equation is balanced before trying to do any calculations which require the correct stoichiometric ratios of reactants and products. Since the stoichiometric coefficients are crucial in things like exponents and fractions, and the equilibrium constant K is dependent o...

preyasikumar_2L

The coefficients do not affect the rate constant, it will still be K.

preyasikumar_2L

Since the half-reactions are typically written as reduction reactions, you have to use the cell potentials to understand which one is being oxidized and which one is being reduced.
More positive - reduction, cathode
More negative - oxidation, anode

preyasikumar_2L

It would probably be helpful to at least understand the derivations and why/how they were done to achieve the equations we will use, but we probably would not have to do that whole process on paper for the test, rather just be able to use those equations correctly when required.

preyasikumar_2L

If you can plot the graph then I think you should be able to go backwards and determine the rate of reaction and reaction order from a given graph by looking at the axes and linearity/curve of the line of the graph.

preyasikumar_2L

Don't worry about C, it's a zero order reaction - it will have no effect on the rate. Just focus on solving for A and B.

preyasikumar_2L

Since electrons move from the anode to the cathode, the cathode eventually becomes very negatively charged and would stop electrons from moving from anode to cathode because like charges repel. The salt bridge allows ions to move between the anode and cathode to maintain both solutions in a neutral ...

preyasikumar_2L

Electrons are lost from the anode (which is where oxidation occurs) and travel to the cathode (where reduction occurs).

preyasikumar_2L

Oxidation happens at the anode and reduction happens at the cathode. Electrons leave the anode and go to the cathode.

preyasikumar_2L

In things like ΔH° and ΔG°, the degree symbol just means that those are the standard ΔH and ΔG values, aka the values under "standard conditions" (STP = 1.0 atm and 25°C).
It's used for temperature for degrees Celsius/Centigrade (°C) and degrees Fahrenheit (°F).

preyasikumar_2L

The reducing agent is the species that does the reducing - the reducing agent will reduce the other species by losing its electrons and giving them to the other species so that the other species gets reduced. Thus the reducing agent itself gets oxidized. Vice versa is true for oxidizing agents - the...

preyasikumar_2L

Electrical potential is the ability of an electrochemical/voltaic cell to produce an electric current, while voltage is the difference in electrical potential across different areas/points.

preyasikumar_2L

Platinum is the most common electrode used in electrochemical cells because it is resistant to oxidation and won't easily react in redox reactions.

preyasikumar_2L

Shouldn't the oxidation state of oxygen in O2 be zero? The oxidation state of each individual oxygen in compounds that have other elements of different electronegativity is -2, except in peroxides where it's -1. In O2, where there's no polarity in the bonds shared due to the fact that both oxygen a...

preyasikumar_2L

I don't think he curves tests, but I know that if you get a 50% in the class that's a C.

preyasikumar_2L

When a redox reaction takes place in an acidic or basic solution, there would be an excess of H+ or OH- ions respectively. You need to use H+ to balance the half reactions in acidic solutions, and OH- to balance the half reactions in basic solutions. Also be sure to balance charges on both sides of ...

preyasikumar_2L

A half reaction is either of the reduction (RED) or oxidation (OX) reaction components of a redox reaction.

preyasikumar_2L

I'm pretty sure most entropy, enthalpy, and gibbs free energy values will be given to us, either in the problem or the constants/values/equations sheets. And I mean, know that ΔH of all elements in their standard states is 0, and know the trends for ΔH, ΔS, and ΔG (<0 is spontaneous, decrease in ent...

preyasikumar_2L

Yes, but you may need to multiply the half reactions by constants in order to get electrons or repeating reactants and products equal in order to cancel out completely.

preyasikumar_2L

The concentrations of reactants and products at equilibrium changes when temperature changes, so the value of K will also change when temperature changes.

preyasikumar_2L

The temperature gets cancelled out:

ΔG = ΔH − TΔS = -RTlnK

lnK = (ΔH − TΔS)/(-RT) = ΔH/(-RT) − TΔS/(-RT) = -ΔH/(RT) + ΔS/R

preyasikumar_2L

∆S is related to ∆H by ∆S=∆H/T (from ∆G = ∆H - T∆S, when ∆G = 0)

preyasikumar_2L

I believe that's correct - heat of fusion is the enthalpy when something changes state from solid to liquid, so the sign would be switched for the heat of solidification (liquid to solid) but still the same magnitude.

preyasikumar_2L

ΔG = 0 means that the system is at equilibrium - the forward and reverse reactions are occurring at the same rate at the same time.

preyasikumar_2L

I'm pretty sure we need to have the small list of strong acids and bases memorized. The list was provided to us last quarter or you can just find it online. You'll know if something is a weak acid/base if it's not something from that list - you don't need to memorize weak acids and bases because it ...

preyasikumar_2L

△G < 0 means that the forward reaction is spontaneous, exothermic
△G = 0 means that the reaction is at equilibrium, reversible
△G > 0 means that the forward reaction is not spontaneous, endothermic

preyasikumar_2L

Yes, Delta E and Delta U are essentially the same thing and can be used interchangeably.

preyasikumar_2L

ΔH = ΔU + PΔV

ΔU is only equal to ΔH when the pressure is constant and the change in volume ΔV = 0.

preyasikumar_2L

From the pKb you can find the value of Kb. Kb = 10^(-pKb) From the Kb you can find the value of Ka. Ka = Kw/Kb You can find the equation of Ka using the reaction and ICE table, and solve for the missing x values of the substances at equilibrium using the value of Ka and the equation. From there, you...

preyasikumar_2L

You multiply 300kJ/mol by 0.05 mol to get the mol units to cancel out and get a result of 15 kJ for the enthalpy of reaction.

preyasikumar_2L

Yeah, I think for now we can assume that reactions in calorimeters suggest that the system is isolated. According to Dr. Lavelle's examples of open, closed, and isolated systems, he said that the combustion of glucose in a bomb calorimeter is an example of an isolated system where no energy or matte...

preyasikumar_2L

If you're asked for the molar concentration of H₃O⁺ or OH^- you can leave your answer in terms of mol/L. Only when they ask for the pH or pOH do you have to think about taking the logarithms of those values.

preyasikumar_2L

At different temperatures, the pH scale can go beyond the standard 0 to 14, because at different temperatures the autoprotolysis value of water is different from 10^-14, but we do not need to worry about this in this class (for now).

preyasikumar_2L

Strong acids and bases completely dissociate in water, while weak acids and bases only partially dissociate. There's a fairly small/easy to learn list of strong acids and bases that you can memorize (that was provided to us last quarter or you can just find online). You'll know if something is a wea...

preyasikumar_2L

A buffer is an aqueous solution that is a mixture of a weak acid/base and its conjugate base/acid, and it can resist change in pH when an acid or base is added to it. It is able to (mostly) maintain the pH of the solution because it is able to neutralize small amounts of the added acid or base becau...

preyasikumar_2L

The x is only negligible when adding/subtracting if the K value is very small (<10 -3 ) or when the change in the concentrations/partial pressures is less than 5% of the original concentration/partial pressure. You will not always have a small K value, and the stoichiometric coefficients will not al...

preyasikumar_2L

It probably depends on what you are given in the problem (the partial pressures or the concentrations). You could do either Kp or Kc, as long as you keep track and do not confuse the two because the values will not be the same. And in Wednesday's lecture Lavelle showed us how to convert between Kp ...

preyasikumar_2L

I'm pretty sure K c , K p , K w , K eq , K a , K b , etc are all different ways to clarify K, the equilibrium constant, by what is being used to calculate that value. K c is the equilibrium constant that is calculated using the concentrations of aqueous substances or gases of a system at equilibrium...

preyasikumar_2L

I think last class Dr. Lavelle mentioned that there are three(?) ways of calculating delta H and that he'd teach us how to do it (if not now then eventually). However, for now it is important to know that positive delta H means that the reaction is endothermic and that heating the system will shift ...

preyasikumar_2L

Yes, ICE tables can be set up to determine the Initial, Change in, and Equilibrium concentrations (of aqueous substances or gases) or partial pressures (of gases).

preyasikumar_2L

You calculate Q the same way as you'd calculate K, using the gases and aqueous substances involved in the reaction. The only difference between Q and K is that Q can be different values since it can be calculated at any point during the reaction, while the K for a reaction at a specific temperature/...

preyasikumar_2L

You would only use the gases to write the one (1) Kc equation. Liquids and solids are not included. For calculating Kc, you only take gases and aqueous solutions into consideration.

preyasikumar_2L

If K is small, there are more reactants present at equilibrium, which means that the system sits/lies to the left at equilibrium and strongly favors the reactants. If K is large, there are more products present at equilibrium, which means that the system sits/lies to the right at equilibrium and str...

preyasikumar_2L

It probably depends on what you are given in the problem (the partial pressures or the concentrations). You could do either Kp or Kc, as long as you keep track and do not confuse the two because the values will not be the same. And in Wednesday's lecture Lavelle showed us how to convert between Kp a...

preyasikumar_2L

K is the equilibrium constant which is calculated when the system is at equilibrium, and Q is the reaction quotient that can be calculated at any point in the reaction. They are both calculated in the same manner though and by comparing the Q and K values you can determine where the reaction lies.

preyasikumar_2L

It doesn’t matter what units of pressure you use as long as you use the appropriate value of R that works with those units.

preyasikumar_2L

Le Chatelier's principle states that if the equilibrium of a system is disturbed (caused by changes in temperature, pressure, volume, or concentration) the position of equilibrium will “shift” to counteract the changes and reestablish equilibrium in ways that we can predict.

preyasikumar_2L

When a weak acid reacts with an equivalent amount of a weak base, it won't neutralize completely -- it depends on the equilibrium constant K for the reaction. But if the concentrations of a weak acid and strong base are equal then more volume of the weak acid would be needed to neutralize that stron...

preyasikumar_2L

Some weak bases include ammonia (NH 3 ), ammonium hydroxide (NH 4 OH), pyridine (C 5 H 5 N), and conjugate bases of weak acids. I think you determine which weak base is weaker/stronger in a similar manner to how you would determine which acid is stronger/weaker --> based on bond length and resulting...

preyasikumar_2L

Yes, you can use the abbreviations when naming the compound and also when writing out the formula.

preyasikumar_2L

For pH and pOH, you worry about sig figs after the decimal point. Don't worry about it though until you have your answer.

preyasikumar_2L

The conjugate base is what is left of an acid when an H+ is removed, and the conjugate acid is what becomes of a base when an H+ is added.

preyasikumar_2L

Usually the cation is written first before the anion, it's just standard convention. I don't think there's anything wrong with switching that order other than it would look weird.

preyasikumar_2L

You add the oxidation number in parentheses after the transition metal if they have multiple oxidation states. Ex: iron(II) oxide and iron(III) oxide

preyasikumar_2L

That and pH+pOH=14, and perhaps equations relating to Ka.

preyasikumar_2L

You just need to know how to calculate pH and pOH from the [H+] and [OH-] given, and vice versa. pH = -log([H+]) and pOH = -log([OH-]) = 14 - pH

preyasikumar_2L

Ka is the acid dissociation constant. pKa is the -log of this constant.

preyasikumar_2L

I believe there are 2 lone pairs of electrons around the O, making that part bent, not trigonal planar, which is why it would be <109.5 degrees not 120 degrees.

preyasikumar_2L

Diamagnetic atoms/compounds (and atoms) have paired electrons and are repelled from magnetic fields. (Paramagnetic atom/compounds are the opposite)

preyasikumar_2L

Paramagnetic atoms/compounds have unpaired electrons, and are attracted to magnetic fields. (Examples: Cu²⁺,Fe³⁺)

preyasikumar_2L

Sigma bonds are stronger because the bonding pair of electrons in sigma bonds is localised closer to the nuclei of the bonded atoms (on average). There is greater overlap.

preyasikumar_2L

Linear will have ONLY those two bonded atoms around the central atom, or the two bonded atoms and enough lone pairs around the central atom that would cause the dipole moments created from the lone pairs to cancel out, while bent would have the two bonded atoms around the central atom AND lone pairs...

preyasikumar_2L

Yes, a hydrogen bond is a strong dipole-dipole interaction between a slightly positive hydrogen on one molecule and a slightly negative O, N, or F on another molecule.

preyasikumar_2L

VSEPR stands for "Valence shell electron pair repulsion" but we do not need to memorize the full form of that acronym. However, we need to understand the theory and molecular geometries.

preyasikumar_2L

You can put the subscript 1 on the E, but you don't have to. E₁ and E are the same thing, so the 1 is pretty unnecessary, but if it helps you, it's okay.

preyasikumar_2L

You should just memorize the generic ones: linear=180 degrees, trigonal planar=120 degrees, tetrahedral=109.5 degrees, trigonal bipyramidal=90 and 120 degrees, and octahedral=90 degrees. However, you should also know that having lone pairs will cause the bond angles to be less than the basic amounts...

preyasikumar_2L

You can somewhat tell whether molecules are polar or nonpolar by whether or not their Lewis structures are symmetrical or not. Symmetrical = nonpolar, asymmetrical = polar (in general) Polar molecules must have polar bonds (bond between two different elements) with dipoles that do not cancel. Non-po...

preyasikumar_2L

Yes, London dispersion forces are intermolecular forces that occur between all atoms/molecules. They occur due to the temporary attraction that results from temporary dipoles due to electron movement within the clouds.

preyasikumar_2L

Electronegativity is affected by the size of the atom, not the other way around. In fact, they're somewhat inversely proportional - as atom size increases, electronegativity decreases because it is easier for smaller atoms to attract electrons since the nucleus would be much closer to the electron c...

preyasikumar_2L

Cl only has one unpaired electron in its valence shell and would thus typically and ideally only form a single bond with other elements, so if possible, a double bond with Cl is avoided.

preyasikumar_2L

Electronegativity and electron affinity are not the same thing. The difference between the two is that electronegativity is the chemical property that shows how well an atom can attract electrons, while electron affinity is the amount of energy released when an electron is added to a neutral atom to...

preyasikumar_2L

Permanent dipoles form when the electronegativity differences between the atoms bonded in a molecule is very great that some atoms are slightly positively charged and some are slightly negatively charged - for example, in water, there's a permanent dipole between the bonded hydrogens and oxygen such...

preyasikumar_2L

MeV is mega-electron volts. This is a unit of energy equal to 1000000 eV.

preyasikumar_2L

11d. " How many orbitals are in subshells with l equal to (a) l = 0 --> s --> 1 orbital (b) l = 2 --> d --> 5 orbitals (c) l = 1 --> p --> 3 orbitals (d) l = 3 --> f --> 7 orbitals N = shell number, you can figure that out by what period (row) the element is in (EX: Na has 3 shells, n = 3. it's...

preyasikumar_2L

I think the fundamentals are the main high school review topics, so I'd say it's pretty important to be confident with that for the midterm. But the midterm most likely will include everything we've learned so far as well from the quantum and chemical bonds sections.

preyasikumar_2L

I think you just need to redraw the structures with the different double bonds. If the question asks to, then you would find the most ideal structure using formal charge and just draw that one.

preyasikumar_2L

An ionic compound is usually made from a metal and a non-metal, and a covalent/molecular compound is usually made from two non-metals. Sometimes you can determine ionic or covalent bonds by how far apart horizontally the elements are placed on the periodic table - the farther they are suggests great...

preyasikumar_2L

It's pretty important to understand the ionization energy trends when looking at a periodic table - ionization energy increases from left to right across a period and decreases move down groups. It is measured in joules (J) or electron volts (eV), and is calculated by subtracting 1 from the atomic n...

preyasikumar_2L

Bond strength and length will typically be given to you in the problem, on an information sheet, and certain ones might be required to be memorized. However, it's important to remember that triple bonds are stronger than double bonds, which are stronger than single bonds, and triple bonds are shorte...

preyasikumar_2L

All the resonance structures of compounds that have resonance structures are equally accurate, but you would most likely have to draw all the resonance structures when asked to draw the Lewis structures for those compounds. However, you also use formal charges to determine which Lewis structure is m...

preyasikumar_2L

Cations are positively charged ions - these are atoms which have lost one or more electrons. Some examples of cations include K + , Na + , and Ca 2+ . Anions are negatively charged ions - these are atoms which have gained one or more electrons. Some examples of anions include F - , Cl - , and O 2- ....

preyasikumar_2L

Nonmetals do not form cations because they are more electronegative than metals and attract electrons more strongly/readily, since they want to gain electrons to fill their octet. Metals also hold their valence electrons more loosely (which is why they're better conductors of electricity), so it is ...

preyasikumar_2L

You use the noble gas from the period above the element you're writing the electron configuration for because noble gases have a full octet of electrons, and so the remaining electrons of the element you're configuring would be valence electrons. Noble gases have a full octet of electrons, so the no...

preyasikumar_2L

I think there is a maximum size, but I don't think we know what it is. Not going by the Heisenberg Uncertainty Principle and just going by nuclear attractive forces, bigger nuclei are unstable, which is why they are short-lived and decay quickly. There will be a point where if you keep adding proton...

preyasikumar_2L

It's the probability of an electron being present at a specific location, aka in a specific orbital. The reason this is uncertain and not exact is because the exact position and momentum of an electron cannot be determined at the same time. Electrons are just too small and fast, man.

preyasikumar_2L

Objects that have a rest mass behave like waves. That is the big concept of the De Broglie equation. So this equation is used to solve for the wavelength (or mass or velocity, depending on what the question is asking for and how the equation is rearranged) of any object that has momentum, or a mass ...

preyasikumar_2L

Using the De Broglie equation λ = h/mv and the masses of a proton (1.6726*10^-27 kg) and a neutron (1.6750*10^-27 kg) that you find by looking them up (I think, unless it's given or you've memorized them)

preyasikumar_2L

For rounding numbers that end in 5 in chemistry you want to try to round it to the nearest even number. 0.55 would round up to 0.6, 0.65 would round down to 0.6, etc. Usually when you have many numbers like this, rounding in this manner can somewhat "average" everything out. You would not ...

preyasikumar_2L

Frequency is the number of waves per a unit of time (usually seconds), and wavelength is the length of one wave from crest to crest or trough to trough. Frequency times wavelength equals the speed of the wave, and in the case of light, we have c = λν. Frequency and wavelength are inversely proportio...

preyasikumar_2L

if the light energy is not great enough then electrons will not be excited. And if they aren't excited, then they can't escape from the pull of the metal.

preyasikumar_2L

All matter has wavelike properties, but the wavelike properties are only noticed for moving objects with an extremely small mass (like electrons). This can be proven with the De Broglie equation, λ = h/mv --> if the mass is too large, the wavelength will be really small and thus the wavelike propert...

preyasikumar_2L

a) I think this is supposed to be something that we have memorized, perhaps from the polyatomic ions (nitrate = NO3-). I know for me in AP Chem we had to memorize strong acids and bases and polyatomic ions, but I'm sure it wouldn't matter if you looked up the formula --> Nitric acid = HNO3 b) For th...

preyasikumar_2L

It usually doesn't really matter what order the elements are in a compound, as long as the subscripts are correct. According to the Hill system, in compounds with carbon and hydrogen, you typically write carbon first, and then hydrogen, and then the remaining elements in alphabetical order. Another ...

preyasikumar_2L

The question is asking for how many moles of SO3 are in 7.00 x 10^2 mg of SO3. It's easier to look at everything in grams so 7.00 x 10^2 mg is the same as 7.00 x 10^2 x 10^-3 g, which is the same as 7.00 x 10^-1 g, or 0.700 g. Converting that into moles using the molar mass of SO3, which is 80.06 g/...

preyasikumar_2L

I'm also not completely sure what you mean, but if given a series of reactions, I'd assume that those reactions are like intermediate steps that would get you from the reactants in the first reaction to the products in the last reaction. As long as you're being careful and are able to keep everythin...

preyasikumar_2L

Yes, it's usually a lot easier to understand and use even numbers, so for rounding numbers that end in 5 in chemistry you want to try to round it to the nearest even number. 0.55 would round up to 0.6, 0.65 would round down to 0.6, etc. Usually when you have many numbers like this, rounding in this ...

Search found 101 matches