CHEMISTRY COMMUNITY

chemoyku dis 1B

Hi! I'm not actually sure if it would be possible in real life or theoretical but the third law of thermodynamics law states that the entropy of a perfect crystal at absolute zero (0 K) is exactly equal to zero. But physically, the law implies that it is sort of also impossible to bring a system to ...

chemoyku dis 1B

Hi

this is because residual entropy looks at the difference in entropy between a non-equilibrium state and crystal state of a substance that is close to absolute zero (at 0 kelvin).

chemoyku dis 1B

Hi! Yep, spontaneous is kind of a different meaning in chemistry. The spontaneity of a system refers to how likely the reaction would occur without the need/ input for energy. This relates a lot with entropy. I think Dr. Lavelle will get into more depth about Gibbs Free energy next lecture as well a...

chemoyku dis 1B

Hi! The equation to calculate heat capacity at constant volume, Cv is delta U/ delta T. this is because if we arrange q = mC deltaT and delta U = q . For constant pressure, Cp it is delta H/ delta T. For an ideal gas, enthalpy is H = U+ PV (using PV=nRT), we can get delta H = delta U +nRT. Therefore...

chemoyku dis 1B

Hi, Delta U only equals 0 in an isothermal process (in an isolated system), the energy exchanged as heat would equal to the amount of work done by the system. Since temperature is constant, the energy change is 0 (U=0.) So, the heat thats absorbed is the work that is done to its surroundings (q= -w)...

chemoyku dis 1B

Is there an equation to calculate enthalpy when you're given the grams and Mr? I couldn't find it in the section 4C of the textbook but they seem to be using an equation in the calculations?

chemoyku dis 1B

Hi! Its the equation on our constants and equations sheet where: q= mc deltaT where q represents heat, m is mass in grams, c is the heat capacity and delta T is the change in temperature in Kelvin. If you rearrange this equation so that it looks like: c= q/(m deltaT) you can find specific heat capac...

chemoyku dis 1B

Hi! If you look at the constants and equations sheet you'll see three values for the R ideal has constant. They want you to use the other values because of the units. You should see which units are in your equation and if they correspond with the right R value on the constants and equations sheet an...

chemoyku dis 1B

Hi!

DeltaHf is the enthalpy of formation which refers to the energy released or consumed when one mole of a substance is created under standard conditions from its pure elements.

Delta Hfusion is the heat required for water to vapourise (change its state from water to gas).

chemoyku dis 1B

Hi! I would start by this equation to make it easier: q (melt ice) + q (heat the melted ice) = -q (heat lost by the water) heat required to melt ice is the same as the heat of fusion of water. Multiplying the fusion of water with the moles of ice + q(ice) = -q(heat lost by water). if you plug in the...

chemoyku dis 1B

Hi! The relative acidity of an acid depends on the extent to which the acid (HA) dissociates to its respective ions (H+ A-) and that is the same for the bases. I think in general you should know a few classic ones and just trends of what compounds typically form stronger bases (group 2 hydroxides...)

chemoyku dis 1B

Hi! This is because Barium is a Group 2 Element meaning that its oxidation number is 2+ (it has 2 valence electrons and it loses these 2 valence electrons to have a full outer shell. Since the hydroxide ion is a -1 compound (OH-), we multiply is by 2 to balance out the charges because its neutral ov...

chemoyku dis 1B

Hi! There are so many terminology in thermochemistry that it gets confusing to understand, totally feel you. Standard enthalpy of formation in simpler terms if we break it down: enthalpy refers to the heat content of a system. formation refers to the formation of compounds from their elements. If we...

chemoyku dis 1B

Hi! The standard reaction enthalpy refers to the chemical change in enthalpy in a reaction under standard conditions (25 celsius, 1 atm for gas, 1M for liquid.) The standard enthalpy of formation which is the energy released or consumed when one mole of a substance is created under standard conditio...

chemoyku dis 1B

Hi! pKA refers to the acid dissociation constant which explains us to what extend the acid ionizes and dissolves (relative acid strength). In simple words, it just shows us how strong/ weak an acid is. To find Ka, it is actually very similar to finding K! acids usually have this equation when dissol...

chemoyku dis 1B

Hi! he mentioned that buffers can be made from weak acids or base and their salts depending on if you would like a basic or acidic buffer. A buffer has a very little change in pH when a small amount of strong acid or base is added to it. So it can prevent any change in the pH of a solution. This is ...

chemoyku dis 1B

Hi! Kw means the equilibirum constant of water, aka the dissociationn and ionization of water which is 10^-14 at 25 celsius. In pure water [OH-] = 10^-7 [H3O+] = 10^-7. Kw can be expressed as [OH-][H30+] or if -log is used = pKW = pOH +PH. I hope this explained some of the relationship that helps de...

chemoyku dis 1B

Hi! In the question we are given that Ka = 3.69 and that the acid is placed in a solution with a PH = 2.48. Since the pH is lower than the Ka, the acid would not dissociate to produce the charged deprotonated species, A- . To make the PH and pKa equal, the acid would remain as its neutral species in...

chemoyku dis 1B

Hi! It would look something like this: 2HCl (g) ⇌ H2 (g) + Cl2 (g) I the pressure of HCL 0 0 C -2x + x x E Pressure - 2x x x It would just look like your typical ICE table! then by the given K value you can set up an equation of reactants/products. I hope this helped.

chemoyku dis 1B

Hi!

To figure out concentrations at equilibrium, K, you would have to use the ICE table.

So you can use the initial concentrations of reactants to find the equilibrium.

Q also uses the same equation as the equilibrium constant.

I hope this helped somehow...

Kind regards.

chemoyku dis 1B

Hi!

It's just asking that you add up all the values of partial pressure of reactans and products at equilbrium (total pressure in the system). That's it :)

I hope this helped.

chemoyku dis 1B

Hi, This was a challenging question, I feel you! Whenever you see "at equilibrium" and concentrations with a question asking for K, always remember using the R=P, K= [products]/ [reactants] equation. So to find the answer you'd just put the concentration of NO2 to the power of 2 (because t...

chemoyku dis 1B

Hi! I understand the way it can be confusing. From the equation and your question, you said that the reactants had a total of 7 moles of gas on the reactants and 4 moles of product. Your TA mentioned that increasing pressure would favour the products (the forward reaction). This is because there are...

chemoyku dis 1B

Hi! K generally refers to both Kc and Kp. I do think that in our achieve assignments it would be specified but if it isnt I would recommend looking at the units in the question. If it is talking about an equation/ reaction with the states of reactants and products in gas, we would assume that it is ...

chemoyku dis 1B

Hi! As Emaad mentioned above, that is basically how to derive PV=nRT, but you do not need to worry about the derivation of the Ideal Gas Equation. However, this equation comes from the ideal gas law where it explains the relationship between the pressure, volume and temperature for an ideal gas. P s...

chemoyku dis 1B

Hi! You don't need to worry about activity in this moment. However, Lavelle wanted to explain us the origin of K. The equilibrium constant actually calculates the activity of reactants/ activity of products. However, activity does not have a unit to measure. Therefore, molar concentration is used in...

chemoyku dis 1B

Hi!

A polydentate ligand has more than 2 lewis base sites, such as multiple lone pairs on different atoms. For example, EDTA has six atoms that can bind with electron pairs that can be used to bond to a central metal atom or ion.

I hope this helps.

chemoyku dis 1B

Hi! When we are looking at enthalpy of vapourisation, we are looking at its interaction with neighbouring atoms. This is where the intermolecular forces come in. Rather than bond strength/length, we look at the intermolecular forces that exist between the molecules. For example water has hydrogen bo...

chemoyku dis 1B

Hi! I would say you don't have to memorise them, but a general idea works. Amphoteric oxides are usually transition metals (d-block elements) or metalloids (between the metals and non-metals). An amphoteric oxide can neutralise both acid and a bases. So to identify if a compound is amphoteric, you c...

chemoyku dis 1B

In the lecture, Prof. Lavelle gave example of NiCl2 as aqueous state. and it was Ni in the central atom, four water molecules in horizontal square planar, and two Cl atom vertically attached to Ni. To draw the lone pair electrons of water here, will each water molecule still have one pair of remain...

chemoyku dis 1B

Hi!

NH4ClO4 can be represented in an equation like this:

NH3 + HClO4 = NH4ClO4

Since its parent molecule NH3 is a weak base and HClO4 is a strong acid, the salt overall would be acidic.

I hope this helps.

chemoyku dis 1B

Hi! Amphoteric refers to species that is able to act as both a base and acid (lewis, arrhenius, bronsted...) , so it means that it can accept and donate a proton. In fact, it is also amphiprotic (species that can only behave as bronsted lowry acids and bases). So HCO3- can become CO3^2- or H2CO3. Th...

chemoyku dis 1B

Hi!

A chelate is a ring-like complex structure that is formed by the bonding of chelating ligands (ligands that have many lone pairs that can bond to more than one site on the metal) bonding to the central metal.

I hope this helps.

chemoyku dis 1B

Hi, I don't know how to do the question the way you did it but with what I know i'll try to explain how it works! The salt NH4Br is made from the parent molecules NH3 and HBr as you mentioned. NH3 is a weak base as you mentioned. HBr is a strong acid, this is because of the large atomic radius and s...

chemoyku dis 1B

Hi!

This is because the complex coodination compound overall is neutral. Therefore, the complex inside the square brackets is 3+ charge and Br3 was added so that it could neutralise it with a 3- charge.

I hope this helps.

chemoyku dis 1B

Hi! H2SO4 is a strong acid (bronsted lowry polyprotic acid, it has two H+). So H2SO4 would dissociate into its respective ions: Since it says aqueous solution, it occurs in water: (1) H2SO4 + H2O = (double headed arrows) HSO4- + H3O+ The conjugate base of H2SO4 is HSO4- and this is because HSO4- if ...

chemoyku dis 1B

Hi, bond strength is the more significant factor in determining if the acid is strong or not. If the atoms are small, the bond length will be short and the bond will be short as well, leading to a weak acid because the bond cannot be broken easily. You can also look at electronegativity in a way tha...

chemoyku dis 1B

Hi, what are the ways to differentiate a base, an acid, and a neutral elements ? Hi! Depending on the definitions of acids and bases yes. Lewis acids and bases are about the exchange of e-. A lewis base will typically have a lone pair (or might have more) to donate to the lewis acid. A lewis acid w...

chemoyku dis 1B

Hi! Just a general question, the names of VSEPR geometry shapes tend to repeat. For example, there are three different linear shapes or two different bent structures. Why not have a different name. And do we differentiate them by first stating the electron-pair geometry and then the molecular geome...

chemoyku dis 1B

How do you determine the strength of oxyacids based on their formula? Hi, in the achieve homework, since the oxygen numbers are the same, you'd look at the halogens. Electronegativity is significant in labelling an acid weak or strong. HClO would be the most acidic and this is because Cl is the mos...

chemoyku dis 1B

Hi! The amount of oxygen oxyacids have determine how strong an acid is. The more the number of lone oxygens, the stronger the acid would be. This is because the oxygen is slightly negative and it pulls electrons, delocalising electrons through a larger area, stablising the anion formed when H+ is lo...

chemoyku dis 1B

Hi! There are ways you can determine strong acids, for example H-Cl is a strong acid because it has a polar bond where Cl is delta negative and H is slightly delta positive. So it pulls the electrons to Cl and H becomes easier to lose. Furthermore, when an acid has many oxygens, it makes the O-H bon...

chemoyku dis 1B

Hi!

A conjugate base is an acid. A Bronsted lowry acid is a proton donor.

Therefore, the conjugate base of HSO4- would be SO4-.

chemoyku dis 1B

Hi! This is because NaF is made from a strong base and weak acid. the cation Na+ comes from the parent molecule, NaOH which is a strong acid because it is a group 1 hydroxide. The anion F- comes from the parent molecule, HF which is a weak acid because of its small radius and high electronegativity ...

chemoyku dis 1B

Hi! Polyprotic acids refer to acids that have more than one proton. For example sulfuric acid is, H2SO4 (it has 2 protons which it loses one by one.) The acidity decreases as you remove the H+ from polyprotic acids because in this example we would form the conjugate bae HSO4 -. The negative charge f...

chemoyku dis 1B

When determining the hybridization of a molecule, do double and triple bonds count as one or multiple? For example, if a carbon atom had a double bond and two single bonds, would its hybridization be sp3 or sp3d? Hi! Nope, multiple bonds such as triple and double bonds count as one electron domain....

chemoyku dis 1B

Ariella Sassover 3E wrote:What does [A-] represent in the formula pH=pKa + log[A-]/[Ka]?

Hi!

[A-] represents the anion that is formed when the acid is dissociated.

HA + H2O = (double headed arrow) A- + H30+

or

HA = (double headed arrow) A- + H+

chemoyku dis 1B

What does a delocalized pi bond mean in Question 16 of the Achieve homework from Weeks 7 and 8? And can sigma bonds be delocalized? Hi! A delocalised pi bond exists in resonance structures. This is when there is a sea of electrons that are free to move in the molecule, between the atoms. I believe ...

chemoyku dis 1B

Hi! You can identify if a salt is acidic or basic or neutral like this: 1) Example: If we look at NaCl, we know that salts are made from the neutralisation of acid + base = salt + water. So, the parent atoms of NaCl must be acids and bases. The acid that contributed in this equation must be NaOH whi...

chemoyku dis 1B

Hi!

It is because [H+][OH-] = 1.0x 10^-14
or that can be written as pOH + pH = 14

you can also use
-log[H+] = pH

[H+] = 10^-pH

I hope this helped.

chemoyku dis 1B

When pKa is less than pH, is a conjugate produced or does it make it a weak base? If the PKa is less than the pH it is in a more acidic solution. This means that in the B + H2O = BH+ +OH- equation, the equilibrium will lie to the left so the protonated base (BH+) will increase more to neutralise th...

chemoyku dis 1B

How does light act as a wave? I know that light has wave-like properties, but which properties of waves does light possess and does this mean that electrons must have wave-like properties also? Hi! So quantum mechanics actually tells us that light can behave as waves but also as particles. When lig...

chemoyku dis 1B

What is the difference between Bronsted Acids/Bases and Lewis Acids/Bases and what is an example of them? Hi! Bronsted and Lowry Acids/Bases refer to the exchange of protons (H+) Bronsted Lowry acids are H+ donors (you can usually identify them because they have H+) Bronsted Lowry bases are H+ acce...

chemoyku dis 1B

When writing electron configurations, what does it mean when 2 electrons are paired? What does it mean when 2 electrons are parallel? More specifically, what does it mean for their spin? Hi! in orbitals, Pauli's exclusion principle states that there can only be two electrons. An unpaired electron i...

chemoyku dis 1B

Hi,

I was wondering why SO2 is not a resonance structure because it can have one oxygen bond and oxygen-oxygen double bond. Is it because of the formal charge of the atoms?

chemoyku dis 1B

I’ve seen how to calculate Ka , but not not kB. How would you go about doing this? Hi! It has the same logic behind it. If we represent the reaction with a base and water (base dissociating in water to become aqueous): B + H20 = (double headed arrows) BH+ + OH- Since we learnt KA = products/ reacta...

chemoyku dis 1B

Paloma Sanchez 2G wrote:At what pH value is something considered neutral?

Hi!

At pH=7, this is because pOh+ Ph = 14 and so therefore if the values are 7, that means that there is equal concentration of [H+] and [OH-]

I hope this helps!

chemoyku dis 1B

Oh wow, this makes sense because I would have assumed that the two forces pointing to each other would make it non polar but Since it’s towards the central I see why it would be polar. For clarification, had the arrows been pointing away from the central atom, it would be no polar? Hi! For example,...

chemoyku dis 1B

Thank you! Adding on though, the third part of this question asks to find the [H+], [OH−], with only the pH given? How do I find [H+] and [OH−]? Hi! pOH + pH = 14 to find the concentration of H+ ions (aka [H+]) you can do 10^-pH. to find pOH you can do, 14- pH and to find concentration of OH- = pOH...

chemoyku dis 1B

Hi! Perhaps someone else has already asked this but I was wondering, what exactly is a chelating ligand? :( Hi! a ligand is a neutral molecule or an ion that binds to a central metal atom to form complex coordination compounds. They are lewis bases because they contain at least one pair of electron...

chemoyku dis 1B

Hi, bond strength is the more significant factor in determining if the acid is strong or not. If the atoms are small, the bond length will be short and the bond will be short as well, leading to a weak acid because the bond cannot be broken easily. you can also look at electronegativity in a way tha...

chemoyku dis 1B

Hi, I'm not sure what you mean but I don't think so but I would double check with your TA/Dr. Lavelle. Wavelength is the distance over which the wave repeats, so I don't think it could have low wavelength and high wavelength at the same time. But you're right about low wavelength being dangerous! I ...

chemoyku dis 1B

Hi! Every bond you see in this picture has sigma bonds. This is because a single bond is created when s-orbitals overlap/ when p-orbitals overlap horizontally which creates a sigma bond. However, for pi bonds, they are created by the side-by-side overlap of p-orbitals. Pi bonds occur in double bonds...

chemoyku dis 1B

Hi, You are right about the first sentence! It is favourable when most of the formal charges are 0 because the molecule is more stable. However, the reason for the achieve homework questions is because electronegativity increases from the left to the right of the periodic table. Therefore, the most ...

chemoyku dis 1B

Hi, I'm not sure what exactly cross links are but I'm going to try to help! In hydrogen bonding, so for hydrogen bonds to form there are a few requirements: 1) there must be an electronegative atom of NOF 2) there must be an electronegative atom with a lone pair/lone pairs bonded to a H 3) a partial...

chemoyku dis 1B

Hi!

That is because hydrogen is more electronegative than Boron and in metals in general. So when it is bonded with non-metals it'll have a +1 oxidation number, but if it is bonded with a metal it will have a -1 oxidation number.

I hope this helped :)

chemoyku dis 1B

Hi! When it's talking about the two unpaired electrons its referring to the orbital Aufbau's diagram we draw to represent the electron configurations of atoms. If you remember Hund's rule where orbitals are filled singly before they must be paired up, this should explain why e- exists separately. I ...

chemoyku dis 1B

Hi,

A refers to the central atom so you're right! I think the book was just referring to the electrons only since X represents the bonding electrons and E represents the lone pairs.

I don't think you have to worry about your answer tho :)

chemoyku dis 1B

Hi, I like the way you are thinking about the structure involving the same atoms and you're right! This question does depend on the position of certain atoms. When there are polar bonds for example in this case a C - Cl bond is polar. However, you can still have a non polar molecule with polar bonds...

chemoyku dis 1B

Because water has two lone pairs surrounding the central oxygen atom, these will cause repulsion against the bonded hydrogen atoms. Because lone pair-lone pair repulsion is the strongest out of all, this will cause the hydrogen atoms to be pushed from the linear axial plane (electrons try to spread ...

chemoyku dis 1B

I would not say that there is a "rule" but think of formal charge as being a general guide. The formal charges show us the most favorable structure which is the structure that contributes the most to the actual real-world structure. It is important to consider electronegativity so I like t...

chemoyku dis 1B

Hi, I'm going to try to explain as much as I can so I hope it helps! 1)He used the equation wavelength(lambda) = h(plancks constant)/ mass x volume. 2)Next, he plugged the values for all the constants with the wavelength being 1.4 x 10^-10 m. 3) The conclusion he reaches (so, the Yes it can be detec...

chemoyku dis 1B

when something is directly proportional you can write an equation like this to represent is y= k.x

however, if its indirectly proportional you can express it like this: y=k/x

I hope this helps.

chemoyku dis 1B

Hi!

Electromagnetic energy is quantised in units of photons which contributes to the overall energy.

The wavelength and frequency are set properties and values. So, each photon making the same pulse would have the same wavelength and frequency.

chemoyku dis 1B

Hi! 1) First you'd want to use E=hv and plug in the planck's constant and the frequency in the question to get the energy of photons and also divide by 100 to change cm into meters. 2) next the equation for the work function is (I recommend memorising it since it is not on the sheet!!) Energy of pho...

chemoyku dis 1B

Hi! When you talk about energy if you mean energy of photons as in the (E=hv) you can calculate the moles of photons by multiplying the energy of photons by Avogadro's number. I don't think that there is an equation but multiplying E in joules/photons with 6.022x 10^23 photons/moles = number of phot...

chemoyku dis 1B

Hi! I would think of doing something like this: 1) Starting off with the Rydberg's equation E = -h (planck's constant) R(rydberg's constant)/n^2 2) Plug in the equation the planck's constant values and rydberg's constant. The n in the equation would be 3-1 because the electron is moving from n=3 to ...

chemoyku dis 1B

Yes! You'd just need to divide it by 100 or multiply by 1/100.
Example: 300cm(1m/100cm).

PS. Writing the units will help you cancel them off.

chemoyku dis 1B

When a metal was exposed to photons at a frequency of 1.03×1015 s−1, electrons were emitted with a maximum kinetic energy of 3.80×10−19 J. Calculate the work function, Φ, of this metal. By using E=hv and then the work function Ephotons - Φ - KE, I found the value of Φ which was 6.8289x 10^-19. What ...

chemoyku dis 1B

A liquid is exposed to infrared radiation with a wavelength of 8.24×10−4 cm. Assume that all the radiation is absorbed and converted to heat. How many photons are required for the liquid to absorb 48.62 J of heat? I've started with using the E=hv formula but because there is wavelength I used E = hc...

Search found 80 matches