CHEMISTRY COMMUNITY

Zaynab Hashm 2I

it basically predicts a system's behavior or "reaction" to certain kinds of stress (or changes) including increasing/decreasing temperature or pressure and increasing/decreasing the concentration of a specific substance; the system could shift either way based on the stress.. -increasing t...

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it's important to know that it means a catalyst is no longer active and cannot function in speeding up a reaction; this could occur due to exposure to certain chemicals

Zaynab Hashm 2I

Jacob Motawakel wrote:So if the catalyst is not present in the products of the final reaction, does that mean it is fully consumed throughout the overall reaction?

a catalyst only speeds up a reaction, but it is NOT consumed!

Zaynab Hashm 2I

805312064 wrote:Okay that makes sense. One more question, what does adhesion/adsorption have to do with catalysts?

it is a term used in heterogeneous catalysis where it is the process by which a catalyst binds (=sits) to surface atoms that are in a different phase than that of the catalyst

Zaynab Hashm 2I

another term used to describe this would be adhesion (ex; a substance adhering to a surface)

Zaynab Hashm 2I

if you mean the part of the reaction (reactants or products) in which heat would be written;

with reactants if delta H is + (meaning reaction is endothermic, thus absorbing heat)
with products if delta H is - (meaning reaction is exothermic, thus releasing heat)

Zaynab Hashm 2I

whenever there isn’t a solid that would be able to conduct electricity in the oxidation/reduction half-reactions, add Pt(s)

p.s. Hg(l) is an expection as it can conduct electricity, so no need to add Pt(s)

Zaynab Hashm 2I

1 Volt = 1 J/C so the units cancel out when you multiply;

substituting the units in for -nFE, you get
-(mol)x(C/mol)x(V=J/C), and you’re left with J for G

Zaynab Hashm 2I

Platinum (Pt(s)) is adder to the cell diagram whenever the oxidation/reduction half-reactions do not have a solid to conduct electricity.

Hg(l) is an exception since it can conduct electricity, so Pt(s) is not needed.

Zaynab Hashm 2I

Yes, I believe it would just depend on which constants you use; so remember that lnQ and logQ are not the same!

Zaynab Hashm 2I

n is calculated in the unit of mole (abbreviated; mol)

Zaynab Hashm 2I

galvanic cells (including concentration cells) always have a positive voltage as they have favorable redox reactions (=spontaneous), while electrolytic cells have a negative voltage as they have unfavorable redox reactions (=nonspontaneous) and must be driven by an external power source

Zaynab Hashm 2I

both concentration and galvanic cells are batteries in which the redox reaction has a positive voltage, however;

concentration cells have the same chemical species (with different concentrations) while galvanic cells have different chemical species

Zaynab Hashm 2I

anode is the electrode where oxidation occurs and cathode is the electrode where reduction occurs;
electrons flow from anode (-) to cathode (+)

Zaynab Hashm 2I

electrolytic cells are used in the process of electrolysis which drives a non-spontaneous redox reaction to decompose chemical compounds using electrical energy

Zaynab Hashm 2I

I believe the only difference is that ΔG° is ONLY in standard conditions (like it is constant/unchanging for specific measures), however ΔG is not specific, it changes depending on other variables!

Zaynab Hashm 2I

just to make sure, you can double check to see which side is oxidized/negative (=anode) and which side is reduced/positive (=cathode)

Zaynab Hashm 2I

electrons always flow from the anode (-) to the cathode (+)
in other words, electrons always flow from the oxidation half cell to the reduction half cell.

Zaynab Hashm 2I

I am not too sure, but I hope this helps a little;

E is the electromotive force (EMF) which equals the potential difference when there is no current flow,
since i represents current, it shows that as the current tends to 0, the potential difference is at a maximum.

Zaynab Hashm 2I

a battery would die at equilibrium because there will no longer be a flow of charge/electrons between the anode and cathode; using a salt bridge (or porous disk) would prevent that

Zaynab Hashm 2I

ΔG denotes conditions that are not at standard state
ΔG° denotes conditions that are at standard state

*standard state: 1 M, 1 atm, and 298 K (= 25°C)

Zaynab Hashm 2I

we use, ΔS° = ΣS°(products) - ΣS°(reactants), and i think we can also calculate ΔS using some of the formulas found on the formula sheet, but that depends on what is known/unknown and the system of the reaction

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when calculating ΔH(rxn), we find that all except for ΔH(zinc) in the products is not in its most stable state and therefore not equal to 0. zinc is also the limiting reagent in that reaction, after finding ΔH(rxn) multiply it by moles of zinc which you can find by dividing by molar mass of zinc. th...

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usually in the question, the initial values are given for both P and V, so make sure to use all the initial values (of all variables) at once in the equation to find n

Zaynab Hashm 2I

from lecture notes; "molecules in gaseous phase occupy many more states than liquid and solid"

W(g) > W(l) > W(s) and since S = Kbxln(W) then S(g) > S(l) > S(s)

Zaynab Hashm 2I

Gibbs Free Energy can be calculated by using:

1) ∆G = ∆H – T∆S
2) ∆G = – RT ln(K)
3) ∆G = sum of G(products) - sum of G(reactants)
4) Hess's Method (adding or subtracting ∆G(rxn))

Zaynab Hashm 2I

it would be for an isothermal reaction when the temperature is constant

Zaynab Hashm 2I

we can relate insulation to the effects of temperature on entropy; if a system is insulated, heat cannot be transferred (so temperature won't increase), and therefore there won't be a change in entropy.. hence we can focus instead on how the pressure and volume of such a system would affect entropy

Zaynab Hashm 2I

in general, entropy is a measure of randomness

statistical is when you measure the randomness based on the different microstates that affects entropy
thermodynamic is when you measure the randomness based on the heat transfer that affects entropy

Zaynab Hashm 2I

reversible reactions are when the reactants that formed the products can go back the other way, so that the products can reform the reactants however, that is not possible for irreversible reactions, where the products cannot reform their reactants (for example, most combustion reactions) in other w...

Zaynab Hashm 2I

heat capacity is the amount of heat energy required to raise the temperature of 1 g of a substance by 1 K constant volume heat capacity; there is no work of expansion, so all heat is contained and used to raise the temperature constant pressure heat capacity; there is work of expansion, so some of t...

Zaynab Hashm 2I

I believe some of the important ones are already included on the formula sheet

Zaynab Hashm 2I

delta U = delta H - P delta V comes from the equation U = q + w

since q = delta H (change in enthalpy), and w = - P delta V,
when you plug those in instead of q and w, you will get delta U = delta H - P delta V

Zaynab Hashm 2I

Before releasing the compressed air, the system will have a high internal energy due to the high pressure inside. After releasing, there will be a work of expansion on the surroundings, and this in turn will decrease the internal energy of the system. In other words, the system loses energy.

Zaynab Hashm 2I

an exothermic reaction will release heat which will raise the temperature of the surroundings and an endothermic reaction will therefore do the opposite if heat is released for exothermic rxns why is delta t negative? for exothermic reactions, delta T is positive as temperature increases (due to th...

Zaynab Hashm 2I

delta T (change in temperature) calculated for a system shows whether a reaction is endothermic (absorbs energy) or exothermic (releases energy) if a reaction is endothermic, it absorbs the heat energy, therefore decreases (-) the overall temperature of the system if a reaction is exothermic, it rel...

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steam has "stored" energy in its molecules as they move freely;
when steam condenses upon contact with skin, it release said energy because of the difference in temperatures

simply put, steam can cause severe burns due to its high heat energy

Zaynab Hashm 2I

inert gas is another term used for noble gas as these gases do not undergo chemical reactions under a set of given conditions (=unreactive)

Zaynab Hashm 2I

when pressure increases, enthalpy increases; and when pressure decreases, enthalpy decreases

Zaynab Hashm 2I

the higher the pKa, the weaker the acid (less acidic)

Zaynab Hashm 2I

% ionization = (acid ionized/initial acid) x 100%

so the value of x divided by the initial molarity, multiplied by a 100%

Zaynab Hashm 2I

I'm not sure, but your answer is the same as what I am getting!

6.67x10^-15 seems right because Kw = [H3O+][OH-] = 10^-14

and when you multiply the concentrations, you only get the right value if you use 6.67x10^-15 instead of 1.50x10^-14

Zaynab Hashm 2I

6A.19 is asking to calculate the molar concentration of OH- given the molar concentration of H3O+, in part c) [H3O+] = 3.1 mol.L^-1 using [H3O+] [OH-] = 10^-14 (Kw), i keep getting 3.2 x 10^-15 mol.L^-1 (i checked that it is 3.2 x 10^-12 mol.L^-1 in the solution manual) would that be a solution manu...

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Bronsted-Lowry Acid: H+ donor
Bronsted-Lowry Base: H+ acceptor

Arrhenius Acid: produces H+ in H2O
Arrhenius Base: produces OH- in H2O

Lewis Acid: electron pair acceptor
Lewis Base: electron pair donor

hope this helps a little!

Zaynab Hashm 2I

pH is a measure of the concentration of H3O+ or H+, so it basically measures the concentration of hydronium ions in a solution. strong acids dissociate/ionize way more compared to weak acids, and therefore release more H+. since pH measures the concentration of H+ in the solution; 1. stronger acids ...

Zaynab Hashm 2I

We calculate Q the same way we calculate K, and we account for both aqueous and gaseous states. However, liquids and solids are disregarded when calculating the constants. The only difference is that Q indicates the change in the reaction/system at any time before reaching equilibrium, but K is at e...

Zaynab Hashm 2I

Solution Manual Errors (7th Edition) have been posted on Professor Lavelle’s website:

https://lavelle.chem.ucla.edu/wp-conten ... rs_7Ed.pdf

I’m not quite sure where you made a mistake, but if you don’t find the error in this PDF, try to solve it again.

Zaynab Hashm 2I

5G.1 is true/false c) if one starts with a higher pressure of reactant, the equilibrium constant will be larger d) if one starts with a higher concentrations of reactants, the equilibrium concentrations of the products will be larger my question is, why is c) false and why is d) true, what would the...

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During today's lecture, a student asked what would we change X to if PCl3 had a stoichiometric coefficient of 2 instead of 1, I think Professor Lavelle said that it would be 2X. Is that right? (I wanted to check if my notes were correct!) Also, when would it be 2X^2 for PCl3? (he mentioned it, but I...

Zaynab Hashm 2I

can someone please explain the reason why when;

1) Q<K, there is more reactant

2) Q>K, there is more product

anything explaining what results in Q<K or Q>K would help!

Zaynab Hashm 2I

If you mean why we have to use partial pressure, it's because the question mentions that they're in a gas-phase equilibrium. We use partial pressure for gases.

Zaynab Hashm 2I

why do we not include the concentrations of solids or liquids in the equilibrium constant expression, k?

* do we only account for concentrations in the aqueous state?

Zaynab Hashm 2I

to help you figure those out, you must know that;

in c (en) = bidentate
in d (edta) = hexadentate

*count as binding sites to get the coordination number

Zaynab Hashm 2I

yes, every molecule has london dispersion forces

Zaynab Hashm 2I

we only add the suffix -ate to indicate that the coordination compound has a net negative charge

Zaynab Hashm 2I

I believe it's because both lone pairs are on the same (one) oxygen atom, so there would only be one binding site for the metal (since in this case, the metal would only bind to one atom)

Zaynab Hashm 2I

pentaamminesulfatocobalt (III) ion

Zaynab Hashm 2I

in addition to the answer above, I have noticed two more things:

weak acids usually have carbon or phosphorus in them (ex. carboxyl group COOH)
weak bases usually have nitrogen in them (ex. amine group NH2 or NH3)

but again, this ISN'T a guideline you should always depend on!

Zaynab Hashm 2I

a chelate consists of a central metal atom binding to a ligand (polydentate: meaning it has multiple binding sites) in a ring structure *a ligand can only chelate a metal atom if it has multiple binding sites (=polydentate) p.s. in that specific question, you must know that the binding sites must be...

Zaynab Hashm 2I

**i noticed this was question J.7 (b) zinc nitrite (not zinc nitrate) a neutralization reaction is a reaction between an acid and a base to produce a salt and water we know the products: the salt produced is zinc nitrite which is written as Zn(NO2)2 and water H2O now, we have to figure out the acid ...

Zaynab Hashm 2I

that appears to be the net chemical equation

C5H5NHCl dissociates and forms Cl- ions that appear on both sides of the equation, but because the Cl- ions don't affect the overall interaction with water, they would be "removed" from both sides in the net chemical equation

Zaynab Hashm 2I

I think it's actually the same concept for both, but the difference would be;
atomic spectroscopy: of atoms (a single atom)
molecular spectroscopy: of molecules (two or more atoms)

Zaynab Hashm 2I

even if you put them opposite to each other, remember that tetrahedral structures have bond angle 109.5 degrees, and so they won't even be in complete symmetry to cancel the dipole moments here's a tip; all carbon atom tetrahedral structures are polar, unless the carbon atom is surrounded by 4 atoms...

Zaynab Hashm 2I

hybridization is a concept used for mixing or overlapping s and p orbitals, and since hydrogen only has a 1s orbital, it doesn't hybridize.

Zaynab Hashm 2I

the arrow/dipole points towards the δ- charge

Zaynab Hashm 2I

Be would form two bonds (one with each CH3).

If it asked about the shape with respect to the central atom (Be), it would be linear (this would also be the shape of the overall structure).
BUT,
If it asked about the shape with respect to the carbon atom, it would be tetrahedral.

Zaynab Hashm 2I

because diethyl ether can't form hydrogen bonds with other diethyl ether molecules, but butanol can, and so the more the intermolecular forces, the bigger the attraction, and it gets harder to break the molecules apart (leading to a higher boiling point)

Zaynab Hashm 2I

can someone please explain why bond angles may differ slightly for molecules with the same formula and general shape?

thanks in advance!

Zaynab Hashm 2I

I believe you would count that as a one region of electron density

Zaynab Hashm 2I

H and He only require 2 electrons for their highest energy shell to be full (they only have 1s that needs to be filled with only 2 electrons rather than 8). Li and Be are metals that tend to lose electrons rather than gain them to get a positive charge, hence going back to the lower noble gas config...

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bond length in increasing order is: triple bond < double bond < single bond

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NaCl is an ionic bond, HCl is a covalent bond. Ionic bonds are stronger than coverlet bonds, and due to the higher attractions, they have a higher melting point.

Zaynab Hashm 2I

yes, because the rod-shaped molecules have a greater surface area than spherical-shaped molecules, allowing more contact points for attraction forces between molecules (more attraction forces = stronger).

Zaynab Hashm 2I

yes, kilo is always 10^3 in unit conversions. 1 kJ = 1000 J.

Zaynab Hashm 2I

eV (electron volt) is a unit of energy which equals to approximately 1.602×10−19 J, and is commonly used to measure the energy of particles including photons.

Zaynab Hashm 2I

polarizability is the measure of how easily the electron cloud is distorted, so the higher the polarizability, the stronger the dispersion force because the larger electron clouds allow for more effective overlap resulting in a higher attraction between the molecules.

Zaynab Hashm 2I

generally the trend for polarizability is related to the atomic radii trend; it increases down a group and decreases across a period on the periodic table.

the larger the anion, the more polarizable; they would be arranged like so O2-<N3-<Cl-<Br-

Zaynab Hashm 2I

ionization energy increases across a period and decreases down a group, so if you look at the periodic table it is clear that helium is the element that has the highest first ionization energy

Zaynab Hashm 2I

Do you mean delocalization of electrons? If yes, it is when the electric charge is spread over the atoms in a certain bond (usually over a few of the atoms and not all of them) as the electrons can move freely and transfer within the structure. For example, in the Lewis structure of CN2(2-) rather t...

Zaynab Hashm 2I

Generally, ionic bonds are stronger than covalent bonds as they are harder to break.
Double bonds are stronger than single bonds as they are shorter (the shorter the bond, the stronger).

Zaynab Hashm 2I

Yes, for example when a compound has an overall charge on it like the 2- in SO3(2-); where the sulfur and one of the oxygen atoms will have a formal charge of 0 , and the other two atoms of oxygen will have a formal charge of -1 each. We must try to get the FC that is closest to zero to make sure it...

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I think they could, but they wouldn't be stable then! Since they can use their d-orbitals to expand on the octet rule, these elements can have more than 8 valence electrons to be in their most stable form.

Zaynab Hashm 2I

Can someone explain what resonance is and what the importance of it is? Resonance is a way of describing bonding that might form different structures of a certain molecule or ion where the chemical connectivity is the same but the electrons are distributed differently around the structure. It basic...

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What kind of questions might there be regarding the Aufbau Principle on a test? Questions regarding the electron configurations of elements. So you must be able to know the principles in order to determine the correct electron configurations or to figure out whether or not the electron is in a grou...

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It is much easier to remove an electron from a neutral atom using the first ionization energy, however, after you take the first electron, the atom becomes positive in charge. The positive charge of the atom creates a higher attraction that becomes rather hard to break apart. Therefore, it requires ...

Zaynab Hashm 2I

This is the equation used to show the electrostatic (Coulomb) potential energy for multi-electron atoms (basically non-hydrogen atoms). Each q indicates a charge (typically different level charges), and the r is the distance between the charges. The equation shows that the charges and the distance b...

Zaynab Hashm 2I

I know that atomic radii increase down a group, but decrease across a period; and ionization energy decrease down a group, but increase across a period.

My question is what is the case for electron affinity? What would be the trend down a group and across a period? And why?

Thanks in advance!

Zaynab Hashm 2I

These can be described by quantum numbers; specifically the magnetic quantum number (ml). The Px, Py, and Pz describe the orientation (on the 3D axis).

For example; Px has ml = -1, Py has ml = 1, and Pz has ml = 0.

Hope that helps!

Zaynab Hashm 2I

It's basically the orbital. The 2 is the shell (energy and size) determined by the principle quantum number (n), the p is the subshell (shape) determined by the angular momentum quantum number (l), the x is the orbital (orientation) of a subshell determined by the magnetic quantum number (ml).

Zaynab Hashm 2I

use the following equation; λ = h/mv to find the wavelength.

m is mass of electron which = 9.109 x 10^-31 kg
v is the speed given which = 3.6 x 10^6 m/s

Zaynab Hashm 2I

We're actually supposed to use Δv= 10, there's an error in the solutions manual for this question!

Zaynab Hashm 2I

You first convert the Watts to Joules of energy by multiplying 32 Watts (J.s^-1) by time which is 2 seconds; the units cancel and you're left with Joules of total energy (lamp). Then use E = hc/λ to find the energy of a photon. Now you can divide the total energy (64 J) by the energy of a photon (gi...

Zaynab Hashm 2I

The 102.6 nm here indicates the wavelength (λ) which you'll need to use in the c = λv equation to find the unknown frequency. Then you can plug the values in the Rydberg equation to solve for n2.

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An electron shell is the outside part of an atom that surrounds the atomic nucleus (almost like an outer cloud), and it is where electrons are found. The wave function for an electron in an atom is basically an atomic orbital where electrons are found, that's why there's a high probability of findin...

Zaynab Hashm 2I

You should be able to get the answer first converting mass into kilograms (=0.146 kg), and the speed which is given in miles per hour to meters per seconds (=41.1 m/s), (make sure you're using the right converting factors). Then use De Broglie's equation with the given or known values in order to so...

Zaynab Hashm 2I

You don't always have to multiply it by 3, it could be 2, for example. You just have to make sure you multiply by the smallest number possible to get whole integers.

Zaynab Hashm 2I

You use the formula E (kinetic energy) = 1/2mv^2. The velocity is already given, but the mass you should use is the mass of an electron (a constant) which is 9.11 × 10^-31 kilograms.

Zaynab Hashm 2I

Yes, the shorter the wavelength, the higher the energy; and the higher the frequency, the higher the energy. We get that by the inversely proportional relationship between wavelength and frequency. You can figure out through different formulas that there is a specific constant so only the wavelength...

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You basically have to follow certain rules/principles to see which state they would be in. If they follow the rules/principles, they are in a ground state, if not, then they are in an excited state. For 1E.7, you are given four different examples; the rule to be followed in order to be considered in...

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When it is already given in a percentage (of a hundred), we assume it is a 100g sample and use the numbers as they are given. But when you are given a sample of a different mass that is not 100g total, then you have to convert the individual masses by finding their mass percent composition for easie...

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