CHEMISTRY COMMUNITY

Subashni Rajiv 1K

If a reaction is endothermic, you can treat heat as a reactant, but you wouldn't actually write it out.

Subashni Rajiv 1K

As long as you understand the Arrhenius Equation and why it's used, you should be fine. You would be given A or asked to solve for it given the other values.

Subashni Rajiv 1K

I like to use this acronym to help me remember the order of prefixes:
King Henry Died By Drinking Chocolate Milk
Kilo Hecto Deka Base Deci Centi Milli

Subashni Rajiv 1K

Lyndon just posted practice problems for Electrochemistry and Kinetics that can be found if you search up ENDGAME.

Subashni Rajiv 1K

Also, don't forget that pKa and pKb are related to one another. So if you are given the pKb and asked for pH you can convert to pKa and go from there.

Subashni Rajiv 1K

The concentration difference is what gives the cell a current. At equilibrium, the concentrations are the same on both sides, so there would be no current.

Subashni Rajiv 1K

Something to note is that a straight line between to different species can indicate a porous disk while double lines indicate the presence of a salt bridge.

Subashni Rajiv 1K

You could use the Nernst equation depending on what else is given.

Subashni Rajiv 1K

Looking at the Nernst Equation and how the variables related to one another can help you understand the effect of anode/cathode differences.

Subashni Rajiv 1K

Standard conditions are at 25 degrees Celsius and 1M or 1 bar/atm.

Subashni Rajiv 1K

For a concentration cell, the same type of solution is used for both compartments. The only difference is the concentration.

Subashni Rajiv 1K

Electrodes can transport electrons from one half-cell to another.

Subashni Rajiv 1K

The homework problems from section 6K specified whether it was in an acidic or basic solution, so it will be provided.

Subashni Rajiv 1K

You can generally disregard the plutonium when it comes to cell potential calculations.

Subashni Rajiv 1K

Copper is actually the anode, so you would subtract it's cell potential from the cathode's cell potential and set that to the provided cell potential.

Subashni Rajiv 1K

To remember what's being oxidized and what's being reduced, it's helpful to think of the mnemonic LEO says GER. (Lose Electrons Oxidation. Gain Electrons Reduction.)

Subashni Rajiv 1K

It is 0 because no electrons are transferred.

Subashni Rajiv 1K

It's also helpful to know where the salt bridge would be in a typical diagram of a galvanic cell.

Subashni Rajiv 1K

The standard hydrogen electrode is the standard measurement of electrode potential for the thermodynamic scale of redox potentials.

Subashni Rajiv 1K

It does not matter where they are placed in the reaction because the overall reaction stays the same.

Subashni Rajiv 1K

In a closed system, energy cannot be transferred to the surroundings.

Subashni Rajiv 1K

When solving for internal energy, it is helpful to keep track of the terms given in relation to the system and not the surroundings.

Subashni Rajiv 1K

Entropy in increasing order goes solid, liquid, and then gas.

Subashni Rajiv 1K

We do not need to know Ksp, it was not covered in lecture.

Subashni Rajiv 1K

-P delta V is used to calculate work when there is a constant external pressure.

Subashni Rajiv 1K

Based off the second law of thermodynamics I feel like you can make the assumption that it is spontaneous because the total entropy of the universe is always increasing.

Subashni Rajiv 1K

Temperature is measured in Kelvin or Celsius while heat is typically measured in kilojoules or joules.

Subashni Rajiv 1K

Something to remember is that for endothermic reactions, heat can be thought of as a reactant and for exothermic reactions it can be thought of as a product.

Subashni Rajiv 1K

It is where the state is changing. It can be either the solid/liquid in between phase or the liquid/gas in between phase.

Subashni Rajiv 1K

By looking at the ideal gas equation PV=nRT we can see that volume can change if pressure stays constant because the number of moles and temperature can still affect the volume.

Subashni Rajiv 1K

Yes, that'd be correct.

Subashni Rajiv 1K

The Boltzmann constant is only used for gases because it relates the average KE of particles in a gas with the gas's temperature.

Subashni Rajiv 1K

W=-P(DeltaV) is the equation we should be using for problems. It's also found on the equation sheet.

Subashni Rajiv 1K

The change in temperature remains a constant regardless of what temperature unit is used. It's important to keep temperature units the same for each problem.

Subashni Rajiv 1K

Another popular unit the book uses for delta U or internal energy is kilojoules (kJ).

Subashni Rajiv 1K

You would use the Ka or Kb value and use an ice table to solve for x. If you're given the final concentration of any of the products you can work backwards, since the change in product concentration is equal to the final concentration.

Subashni Rajiv 1K

The chemical equations will be given to us.

Subashni Rajiv 1K

Attendance is not taken at discussion, however homework is returned and turned in during discussion sections. If you were planning on missing, someone in the class can turn it in for you.

Subashni Rajiv 1K

Polyprotic acids typically have multiple Hydrogens allowing the Hydrogen to donate its proton in each reaction. The conjugate base resulting will contain one less Hydrogen and therefore, an additional negative charge.

Subashni Rajiv 1K

Since strong acids dissociate completely, there will be a greater amount of products versus reactants. Since the Ka is the ratio of products to reactants, the Ka will be high for strong acids.

Subashni Rajiv 1K

Energy is required to break a bond.

Subashni Rajiv 1K

Percent ionization is the amount dissociated (concentration) over the initial concentration multiplied by 100.

Subashni Rajiv 1K

Typically, if the problem gives concentration, then Kc is used. In most cases, it will be easy to know what you are asked for, if not specified.

Subashni Rajiv 1K

Yeah, when I did this problem, I got 3.2x10^-15.

Subashni Rajiv 1K

When given problems regarding Le Chatelier's Principle, we are to assume that the products and reactants are in excess.

Subashni Rajiv 1K

Ksp is not on the outline for chemical equilibrium found on Dr. Lavelle's website, only Kc and Kp.

Subashni Rajiv 1K

Whatever side is favored has a greater number of moles and a higher concentration than the other side.

Subashni Rajiv 1K

When the concentration of the reactants increase, the reaction rate increases and vice versa when the concentration of the reactants decrease.

Subashni Rajiv 1K

A catalyst is a substance that speeds up a chemical reaction by lowering the activation energy.

Subashni Rajiv 1K

For part b, the reactant concentrations are excluded because they are in the solid and liquid forms.

Subashni Rajiv 1K

At Lyndon's workshop on Monday, he gave us a worksheet called Acids and Bases Fundamentals. On it the list of common strong acids and bases included HCl, HBr, HI, HNO3, H2SO4, HCLO4, LiOH, NaOH, KOH, RbOH, CsOH, Ca(OH)2, Sr(OH)2, and Ba(OH)2.

Subashni Rajiv 1K

The lewis structure can actually be drawn with the Chlorine atoms across from each other. Although symmetrical, because not all atoms surrounding the central atom are the same, it is a polar molecule.

Subashni Rajiv 1K

The melting and boiling points rise across the three metals because of the increasing strength of their metallic bonds.

Subashni Rajiv 1K

Drawing the lewis structure of the molecule can help you figure out the intramolecular forces. From there, the stronger the forces/bonds, the higher the boiling point.

Subashni Rajiv 1K

If the pH of the acid and conjugate base are known, you can use the equation pH = pKa + log [A-]/[HA].

Subashni Rajiv 1K

The "ate" suffix is typically used to denote the compound's net negative charge.

Subashni Rajiv 1K

These can be found in the handout Dr. Lavelle shared with us through email a few days ago.

Subashni Rajiv 1K

I think there would be a heavy emphasis on the newer content, but we should be given a practice final that includes all the content from the course.

Subashni Rajiv 1K

We should know how to get the molecular formula from the name and then draw the lewis structure based off of the molecular formula.

Subashni Rajiv 1K

You would not be marked down because they're interchangeable.

Subashni Rajiv 1K

Yes, the partial positive of the Hydrogen atom is attracted to the partial negative or the Oxygen, Fluorine, or Nitrogen atom, creating a Hydrogen bond.

Subashni Rajiv 1K

It's much lower energy to combine a single sigma bond and a single pi bond than trying to force two sigma bonds between two atoms.

Subashni Rajiv 1K

The lone pair causes the angle to be slightly less than 90 degrees.

Subashni Rajiv 1K

A single bond indicates sigma bond while a double bond means one sigma bond and one pi bond. The electron of the pi bond is loosely bound and therefore weak . The pi bond is easily shifted to any one of the two atoms. Due to the shifting of the pi electron, polarity comes up in the molecule with les...

Subashni Rajiv 1K

Larger anions are more polarizable because they have more electrons over protons. The outer electrons are more loosely held together and can be easily distorted by the cation.

Subashni Rajiv 1K

A helpful way I found to learning how to come up with the VSEPR formula for a molecule was by looking at different examples of lewis structures and their corresponding formulas.

Subashni Rajiv 1K

No, the test covers topics covered after midterm content to Friday's lecture.

Subashni Rajiv 1K

The Hydrogen attaches to the Carbon with a single bond and the Oxygen attaches to the Carbon with a double bond.

Subashni Rajiv 1K

Lone pairs weaken the bond because of electron repulsion. And, the weaker the bond, the longer the bond.

Subashni Rajiv 1K

Small cations have a high polarizing power while large anions have high polarizability.

Subashni Rajiv 1K

Another helpful tip when it comes to figuring out which elements should have the extra electron is not only the more electronegative one, but also the extra element is found on the elements that are at the ends of the lewis structure.

Subashni Rajiv 1K

Scientific notation is most commonly used with numbers that have powers greater than or equal to +/-3

Subashni Rajiv 1K

Scientific notation is most commonly used with numbers that have powers greater that or equal to +/-3

Subashni Rajiv 1K

For this midterm, I believe that we don't need to know how to name molecules and that the chemical formula will be provided unless it's something like CO2 or H2O.

Subashni Rajiv 1K

I think you should have a general idea of what black body radiation is, however I don't think we will be tested on the law.

Subashni Rajiv 1K

Yes, we'll be given the same equation sheet that was given to us for test 1.

Subashni Rajiv 1K

Delocalized electrons are electrons in a molecule, ion or solid metal that are not associated with an atom or covalent bond.

Subashni Rajiv 1K

Coordinate covalent bonds occur when one atom provides a lone pair of electrons to the bond.

Subashni Rajiv 1K

If the last orbital has an odd number of electrons in the configuration, then this is an indication that there is an unpaired electron.

Subashni Rajiv 1K

A radical is an atom, molecule, or ion that has an unpaired valence electron.

Subashni Rajiv 1K

They generally have an inverse relationship.

Subashni Rajiv 1K

In a ground-state of an atom, all electrons are in the lowest possible energy levels.

Subashni Rajiv 1K

Yes! The octet rule is applicable to most elements, including the ones past the second period.

Subashni Rajiv 1K

Another way to remember this is that the noble gases are very stable therefore they have 8 valence electrons, the most stable configuration.

Subashni Rajiv 1K

It should be from either the Quantum World or Chemical Bonds section.

Subashni Rajiv 1K

Typically when moving down the periodic table and towards the left corner, the atomic radius gets bigger.

Subashni Rajiv 1K

It'd be helpful to know the spectrum because questions we've had include knowing if the wavelength is visible or what type of electromagnetic radiation our answer deals with (like is it gamma or x-ray...). You should also know the wavelength range for the visible light spectrum and the order of the ...

Subashni Rajiv 1K

I attended a step-up session and it really helped reinforce important topics that will appear on tests and midterms. I highly recommend it!

Subashni Rajiv 1K

Amplitude and frequency are independent of one another. Larger amplitude means higher energy and lower amplitude means lower energy. Higher frequency means more energy and lower frequency means lower energy using the E=h(frequency) equation.

Subashni Rajiv 1K

Part C is asking for the wavelength of the electromagnetic radiation that hits the metallic surface. The energy of the incoming photon, E, is the work function and kinetic energy of the electron added together because the energy going into the surface is a part of the work function and the excess in...

Subashni Rajiv 1K

In an email Dr. Lavelle sent on October 5th he mentions that Homework #3 is only on quantum topics.

Subashni Rajiv 1K

If you're an AAP member you can attend peer learning sessions that are weekly that are really helpful. If you don't know if you are eligible or if you are not and still want to apply, Campbell Hall has resources that can help you join the program and gain access to the sessions.

Subashni Rajiv 1K

First convert the given wavelength of 420 nm to m (420 x 10^-9) and multiply the given 32 W to joules (32 J/s). Since the problem tell us it's in 2 seconds, multiply the time with the Joules/sec to give 64 total Joules. Now, use the E=hc/lambda equation and substitute 420 x 10^-9 m for lambda. You s...

Subashni Rajiv 1K

The most important thing to know for a combustion reaction is that O2(gas) is always a reactant and the products are always H2O and CO2.

Subashni Rajiv 1K

Another way to think of it is that electromagnetic radiation isn't a single flow. It is made up of quanta of energy, the size of which involves Planck's constant.

Subashni Rajiv 1K

Posts for the week count from Monday at 12:00am to Sunday at 11:59pm.

Subashni Rajiv 1K

I believe the closest to 100% is preferred but from 70% and up is acceptable.

Subashni Rajiv 1K

You generally use sig figs when dealing with number with 2 or more powers of 10.

Subashni Rajiv 1K

I'm pretty sure the positively charged elements are placed first and then the negatively charged ones.

Subashni Rajiv 1K

This Friday, you'll probably turn in homework at the beginning of lecture in the front. There are usually separate piles based on your discussion section so make sure you know what section you're in.

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