CHEMISTRY COMMUNITY

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It auto saves every 2 min and you’ll be able to log back on it once you’ve started it (according to email)

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Rule of thumb for me is that they show up as a reactant first then a product. An intermediate will show up as a product first then a reactant

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Always use kelvin. You won’t get the right answer if you use Celsius

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Standard Gibbs free energy is at constant temp and constant pressure at 1M

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The one with the lower reduction potential is your anode for galvanic cells

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He’s asked for the plots of different orders before but with the online final you might just need to able to recognize them

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If they give you a rate law and ask to find the rate determining step out of given elementary steps, look for the step that has all of the molecules in the given rate law/ match them.

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It’s 3 and a half hours. I believe it will automatically submit when you reach the time limit or at 2:45

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Homework problems have asked to identify the molecularity of chemical reactions, so definitely be able to do that on the final

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Acetic acid will lose its proton/H+ because it’s an acid. Its conjugate base is CH3COO which makes its charge -1

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Not to solve problems or anything, but I think you should at least be familiar with using them in derivations.

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Kw is the equilibrium constant of water. Since it’s neutral Ka and kw = 1 x 10^(-7). When multiplied you get 1x 10^-14 (kw value)

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When you have reactions of different orders, you end up getting mol^n/L^n on the side of k. Since The rate is always mol/Ls, the kr for different orders will change to always cancel out and get mol/Ls for the units of the final answer/rate.

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Since it’s online now, will there still be homework questions on the final?

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Hi Fiona Latifi 1A! When something is below another metal in the elctrochemical series it means that the species that is below is better at reducing the metal that's above. Cathodic protection involves connecting the pipeline to something that's more strongly reducing—that is the metal that is more...

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Luyan Zhang - 2D wrote:
Kevin Antony 2B wrote:We need a solid to be the electrode. As there is no solid on the right hand side, we use Platinum.

Well, there are no solids on the left either, so wouldn't we need to add Pt on the left too?

Hg(l) is an exception. I believe it can conduct electricity on its own

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I’m having trouble understanding why a current flows from cathode to anode, and electron flows from anode to cathode. What is another way to visualize this? Hi there, After reading up, it seems that the current is always flowing in the opposite direction of electrons. Therefore, if electrons flow f...

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For part a, it has: AgBr(s) —> Ag+ + Br-
It has an Ag(s) at the beginning of the cell diagram, on the anode end. Why is this? What rule does it follow?

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Spontaneous reactions can be detected by a negative Gibbs free energy and positive potential difference.

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At standard conditions, each compartment of the cell will be 1M. Assuming that a concentration cell uses the same solutions, then the potential difference at standard conditions is 0.

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When E standard = 0, you have a concentration cell

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I’m having trouble understanding why a current flows from cathode to anode, and electron flows from anode to cathode. What is another way to visualize this?

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What’s happening in the Galvanic Cell when emf is negative and the cell is absorbing energy (Delta G >0)? Whats happening when the cell is absorbing energy?

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What is the difference between formal charge and oxidation number?

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Hi, in my experience step up is usually going over hw problems. Workshops sometimes have worksheets

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I believe O2 and hydrogen peroxide are some exceptions to Oxygen’s -2 rule

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Altamash Mahsud 1I wrote:Potential difference is simply the amount of energy (work) it takes to move a certain amount of charge some distance.

Hi, is this different from one coulomb able to do 1J of work?

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nehashetty_2G wrote:A salt bridge comes is significant to a galvanic cell because it eases the charge buildup. It allows the ions to transfer when which allows the solutions to stay neutral overtime.

Why do the solutions need to stay neutral?

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Can anyone explain what is the difference between electric potential and voltage?

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It’s sealed so no matter can leave or come in. But since it’s not insulated, heat can still be exchanged. So it is a closed system.

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Forming new bonds releases energy. In a synthesis reaction where you’re forming a new product from its reactants, energy will be released because the new product is more stable. Breaking bonds requires energy. In decomposition reactions where you’re breaking apart a molecule into its simpler parts, ...

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Why is delta H always q but q is not always delta H? What exactly does he mean by that? The definition of enthalpy is energy/heat absorbed or released at constant pressure (state function). So delta H is always q. Heat only describes energy transfer due to a temperature difference. Heat can be exch...

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DHavo_1E wrote:Hello,

Could I ask whether anyone could give an example of a closed system? Thank you!

Hi, an example of a closed system is a closed beaker. matter can't enter or leave the system, but the beaker isn't insulated to heat can still be exchanged. Hope this helps!

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I'm not sure if this is the answer you're looking for, but you can't break one bond of a double bond. You have to break the whole thing and reform it as a single bond. You'll have different bond enthalpies for the same atoms bonded with a single bond versus a double bond.

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It's because you're measuring the change in units. It doesn't really matter whether you're using one unit or another. There is no difference between going up 1 unit of kelvin and going up 1 unit of Celsius because the change is still one unit.

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Nick Lewis 4F wrote:So all energetically favorable reactions are spontaneous but not all spontaneous reactions are energetically favorable?

Yes. Energetically favorable reactions don't require energy input so they are exothermic reactions. But not all exothermic reactions occur spontaneously.

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It's because the integral calculates the area under the curve. In the pressure v volume graph, calculating the area under the curve will give you the amount of work done to the surroundings.

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In expansion work, the work done to the surroundings is the energy lost to push against the external pressure. This is one way you can change the energy of the system.

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VLi_2B wrote:Can someone please give an example of an isolated system that is not a bomb calorimeter or a hydroflask?

The universe since energy is conserved.

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A closed beaker is an example of a Closed system. Matter can't leave/enter but the beaker isn't insulated so heat can still be transferred.

The bomb calorimeter is an example of an isolated system. No heat or matter can be exchanged.

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Molar heat capacity deals with 1 mole so it will use moles. Specific heat deals with 1 gram of a substance so it will use grams in its units.

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^^ What he said. If it's at equilibrium, it's reversible because it's done in infinitesimally small amounts.

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At constant pressure, enthalpy is the amount of heat released or absorbed by the reaction.

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Enthalpy doesn't have to be at constant pressure. It's just that at constant pressure, enthalpy will just be the heat released or absorbed by the reaction. All of the work will be done will be to change the volume of the system. We just use constant pressure to relate heat to enthalpy. Most reaction...

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State functions don't depend on the "path" they take. Usually they'll usually just involve the intial and final states. Some examples are enthalpy, temperature, density, volume, and pressure. Nonexamples have many parameters/variables in their equations because we have to consider them whe...

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It's because on a pressure vs volume graph, calculating the area under the curve gives you the amount of work done to the surroundings. For reversible expansions, this is the entire area under the curve from V1 to V2. For irreversible expansions, it's gonna be the rectangle formed from V1 to V2 at t...

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Intensive properties don't depend on how much material you have in the system. Some examples are temperature, density, molar heat capacity, and pressure. Extensive properties do depend on how much material you have in the system. Examples are volume, mass, enthalpy, entropy, heat capacity, and inter...

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Lavelle says to memorize all the strong acids and bases so that anything else you see, you immediately know is weak. Also, as someone mentioned above, having ka or kb as a given means you have a weak acid or base. Remember that strong acids and bases completely disassociate, giving an infinity disas...

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its the conjugate base/original acid or conjugate acid/original base. What it's really comparing is the original acid/base you started with and how many of those gained/lost a proton to become its conjugate. The formula gives you a ratio/percent

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In this scenario, I think of heat as a product. This will make sense as to why it shifts left. On the molecular level, heat is added to the products side of the equation so when heat goes up it increases the number of collisions of products to become reactants.

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What helps me is to look at the formula of heat and enthalpy. Enthalpy can be calculated using the initial and finals states. Heat is calculated using a bunch of parameters meaning it depends on the path taken.

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Enthalpy is a state function because it does not depend on the path taken, only the initial and final values matter.

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You should familiarize yourself with the strong acids and strong bases. There's a list online and videos on youtube to help you memorize. Like what people said, you could also look for acids and bases using the Lewis and Bronsted-Lowry definitions. But I think to prepare for the test, knowing that l...

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Kp is the specific notation used for gases or when given partial pressures.

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if you calculate q and it equals k then it is at equilibrium. If they don't equal, then it's not and the reaction is still occurring. From there you can compare q and k to determine which way the reaction will proceed to reach equilibrium.

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No lavelle just does to build on 14a material and for visualization, but on the test you won't get extra points for it. You could anyway if it helps to understand the chemistry

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If it does, it will be in the context of converting partial pressure to concentration or vice versa

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Ferrate follows the rule of naming anions with adding -ate at the end, but use the latin name for Iron just cause it sounds better.

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I just count the electron density regions from s, p2, p3, d, d2, d3. Rarely if ever do I go higher than that.

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I believe he wants us to use Nitro for NO2 and nitrito for ONO

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When would we get positive values when using -hR/n^2? Or is it always negative? Does emission/absorption change the sign?

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When we are given the value for the uncertainty in position, when do I multiply it by 2? Sometimes the solution will require double the uncertainty given and other times it's not.

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TO find ph, take the negative log of the base concentration (pOH) then subtract that amount from 14 to give you pH.

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Yes. If you draw a Lewis structure with a dipole it is polar. Sometimes, a molecule will have dipole movements but cancel each other out. In this case, the molecular is going to be non polar.

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I think it’s going to be more calculation heavy based on the midterm mixed with conceptual questions so I wouldn’t neglect studying them.

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Hello, I have a question about the difference between 2sp3 and sp3. How do you know if the "2" in front of the sp3 is supposed to be there? What's the difference between the two? It’s the quantum number of the central atom when you’re talking about the hybridization of a molecule. Describ...

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Both bent and angular refer to the same shape

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Hydrogen bonding: H bonded to FON with a LP. Only H bonded to FON will be attracted to other regions with H bonded to FON Ions can have: ion-dipole, ion-ion anything with dipole moments will have: dipole-dipole molecule w dipole + molecule w no dipole = dipole-induced-dipole All Molecules (polar and...

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I don't know if big molecules are going to be tested, but it'd only be helpful to know how to draw any lewis structure and determine polarity.

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it's because d is a lower energy state than p or s. When we do electron configuration, it's why we do n-1 when passing thru the transition metals/d block.

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I noticed he likes to use those as examples in questions he gives out. I would study concepts around these examples since they seem to be fair game.

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Yes, T shape has 5 bonding regions giving it bipyramidal geometry. And 2 Lone pairs that push/repel the 3 bonding regions into a T shape.

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I thought CH3 would be trigonal pyramidal because of its tetrahedral geometry and 1 LP bonding region but it's trigonal planar.

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Greater. A lone pair will increase e- repulsion, causing the bond angles to be slightly smaller than if there was an atom in place.

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A linear molecule can have 3 lone pairs with a geometry of trigonal pyramidal (5 bonding regions). The lone pairs will push the bonds into a linear shape. Same thing with 4 lone pairs with a geometry of an octahedral. The 2 bonding regions will be farthest apart in a linear shape.

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intermolecular = between molecules (attractive forces)
intramolecular = between atoms (bonds)

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Bent = 1 or 2 LPs
trigonal pyramidal = 1 LP
linear = when 3 or 4 LPs
See-saw = 1 LP
T shaped = 2 LPs
Square planar = 1 LP
Square pyramidal = 2 LP

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ShreyaKannan1B wrote:Which elements does hydrogen form hydrogen bonds with?

FON - Fluorine, oxygen, and nitrogen

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Yes, whether they are polar or nonpolar. Or noble gas or not.

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It's because they're shorter that makes them stronger. More shared electrons create a stronger bond because more electrons are present that can pull on the nuclei which means the atoms get even closer and stronger bond forms.

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I like to think of viscosity as how easily a liquid flows. Something that has high vicosity, like molasses, has strong intermolecular forces. Something with high viscosity is also described as being really thick, like molasses. Water has lower viscosity and flows much easier than molasses because it...

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Dipole moments exist because electrons move in a cloud. Electrons occupy one side over another at random times, producing a temporary separation of charge. Molecules with no charges still experience attraction on the intermolecular level because of these temporary dipoles. The tendency of electrons ...

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Ionic bonds form crystalline lattices in their solid form. Forming bonds releases energy (they become more stable). If a molecule has ionic bonds (cation and anion) and is in the gas phase, the amount of energy released as it condenses into a solid is called lattice energy.

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It depends. If the difference is really big, the atom w the higher electronegativity will literally "pull" electron(s) from the other atom. The result is a cation and anion, and an ionic bond forms because of electrostatic forces between opposite charges (another way of saying opposites at...

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I just count across the period. For transition metals, if they ask, go off the number of electrons in the highest principle quantum number. If they ask for the d block electrons, then add those in too. Problem 2A1 letter c is an example. Mn is said to have 7 VE - 2 from 4p2 and 5 from 3d5

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I dont think so either. But it would be good to know that the formula just says that as the radius gets bigger, the electrostatic/Coulomb's force decreases.

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Heisenberg's uncertainty principle is different from Bohr's (classical) model. Bohr's model assumes that electrons are orbitting an electron and that is not the case. Electrons are really moving in a "cloud". So if you wanna know its position, that means you have to stop the electron so yo...

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I like to think of light intensity a how strong a light shines - the number of photons a light emits. If it changed frequency, i'd see a different color light. But Einstein's experiment shows that's what you need to do to knock off more electrons because colors with higher frequencies (lower wavelen...

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When molecules have resonance their e- exist in a hybrid of their lewis structures. Their e- can make those bonds (delocalized) to lower their repulsion. The result is a more stable atom. A molecule with more Lewis structures is more stable.

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It's valence electrons. They could ask you for isoelectronic atoms (like as anions or cations) given a periodic table but idk

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The Lewis structure isn't perfect & sometimes we're able to draw many Lewis structures for a molecule. This is called resonance. In this case, the molecule actually exists as a hybrid of all its resonance structures. And probably not, and he's said that he'll accept any correct structure.

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E=pc is especially helpful to find the momentum of light which does not have rest mass (so you can't use p=mv). Light has no rest mass but does have momentum in the form of energy.

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We remove electrons from the highest energy subshell because these electrons are the most unstable and the atom will readily give them up to become more stable.

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We use the wave function to find the probability of where an electron is going to be. As we get down to the very small, light acts more like a wave. The wave function helps us model the location of the electrons and determines which orbitals are going to be present.

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Light doesn't have rest mass at least. So we can't really use the mv equation. But it does have momentum in the form of energy. We can use another equation instead to find its momentum, E=pc where E is the energy of the photon, and c is the speed of light.

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wavelength is just measuring one peak to the next so this distance is in meters

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This is my method: I put the units that i have on the bottom, and the units i want on top. I put a 1 next to the bigger units. Then for the smaller units, I subtract the scientific notations of the bigger unit from the smaller unit. Then I multiply these factors. Ex: 18.2 nm in cm? 18.2 x 1 cm/10^7 ...

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when you say energy is quantized, this means energy can only be absorbed or emitted in specific (discrete) amounts. This means at some point, you can't divide energy into smaller amounts.

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7.00 x 10^3 has three sig figs because when there is a decimal, all the zeroes are significant (including those inbetween integers and after them). 700 is another way of saying the same thing, but only has 1 sig fig because when there are no decimals, only 0s in between numbers are significant, not ...

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In the context of the photoelectric effect and experiment, the work functions describe the minimum energy a photon needs to knock off an electron so that the electron can overcome it's an attraction to the plate. Some electrons are more attracted to the metal than others. Those with the highest max ...

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