CHEMISTRY COMMUNITY

Zoya Mulji 1K

a higher difference in concentrations would mean that a reaction between the two would probably be stronger and have a greater change in temperature.

Zoya Mulji 1K

when work is done on the system it is + and when work is done BY the system it is -. I think in physics, they use the opposite equation where U=q-w which is why that might be opposite, but in chem we use U=q+w.

Zoya Mulji 1K

even if you have cases where the cathode is lower, Q=[anode]/[cathode]

Zoya Mulji 1K

you should probably always keep it in Kelvin just to be safe because if it cancels out it won't matter anyways.

Zoya Mulji 1K

How do you know how the rate of a reaction will be affected if you double/halve/ etc. the amount of a product or reactant?

Zoya Mulji 1K

the units will depend on the rate law and the order of the reaction because that will influence the power to which the units are multiplied. I would find the answer and then write out the formula with just the units to calculate/find what those would be.

Zoya Mulji 1K

because you want to look at the equation like an mx+b equation so that it's easier to graph. In this case, the ln[A] is the b.

Zoya Mulji 1K

might be extra thermo on there since we didn't cover it that much on the midterm

Zoya Mulji 1K

Hannah's peer learning sessions in young are great!

Zoya Mulji 1K

you should try to go to the peer learning sessions in young during the day! you can usually fit them in in between classes and there are never that many people.

Zoya Mulji 1K

If you are just using the cathode - anode equation you don't need to flip any numbers because the minus sign takes care of that. But, if you are using the method of writing out the half reactions and making the net equation, you'll have to make sure you flip the E for the oxidation half reaction.

Zoya Mulji 1K

If you look at the curve graph for the concentration v. time, you can tell that the rate is very quick at first when the concentration is high and decreases as time increases.

Zoya Mulji 1K

How do you format a cell diagram when the states are the same v. when the elements are in different states?

Zoya Mulji 1K

because it is more accurate since you can get the rate of a reaction at a certain time by taking the slope of a tangent line

Zoya Mulji 1K

you should only leave out the Pt because you're only adding that in the cell diagram when you have all aqueous/ gaseous solutions. All other elements in the cell diagram should usually be included.

Zoya Mulji 1K

even though the book wrote the cell diagram like that, you have to look at what is being reduced/ oxidized and then rewrite the cell diagram based on that. Also since the given Ecell is negative, you know that the given isn't spontaneous so you need to switch the Cu and M to make it spontaneous.

Zoya Mulji 1K

the anode is also drawn on the left of a cell picture and on the left of a cell diagram.

Zoya Mulji 1K

up until the beginning of lecture on Wednesday

Zoya Mulji 1K

If the rates of reactions are the same, the free energies on both sides of the equation should be the same.

Zoya Mulji 1K

What topics/outlines is Test 2 going to be on?

Zoya Mulji 1K

What do all of the variables in the Nernst equation mean?

Zoya Mulji 1K

Can someone explain what each part of the galvanic/voltaic cell is and what function it serves (ex. salt bridge)?

Zoya Mulji 1K

Which method/ equation can we use without changing the signs of the cathode/anode?

Zoya Mulji 1K

Since e- move from left to right, eventually, the e- would build up on the right side and that would cause the battery to stop working/ make the e- stop moving. To avoid this, the salt bridge allows for the movement of ions so that e- don't build up on the right side.

Zoya Mulji 1K

I think he talked about biological examples with glycolysis/ cellular respiration and energy production

Zoya Mulji 1K

usually you should choose from the outline that we left off on/ were recently on

Zoya Mulji 1K

going from a liquid to a gas also has greater entropy increase than going from a solid to a liquid

Zoya Mulji 1K

I think the last question was about finding entropy in both an irreverisble and reversible expansion. You approach both using the entropy formula (i believe it was the change in volume formula) but this will only give you the answer to deltaS. To find deltaSsurrounding and deltaStotal you had to kno...

Zoya Mulji 1K

Can someone show me step by step on how to solve for number 10. I did not understand why q(ice)=q(water). CHEM MOD: q(ice) = -q(water) DO NOT forget the negative sign. The heat released from one material in a system is absorbed by the other material in the system. For #10, why do we have to convert...

Zoya Mulji 1K

i'm pretty sure it should always tell us reversible or irreversible to indicate which equation to use.

Zoya Mulji 1K

if you use deltaU=q+w then w is negative when work is done by the system and w is positive when work is done on the system (if you are taking the perspective of the system)

Zoya Mulji 1K

do we ever need to use the integral for calculating work of expansion or can we always use the equation w/o it?

Zoya Mulji 1K

along with isothermal, i think we also need to isobaric (constant pressure) and isochoric (constant volume)

Zoya Mulji 1K

for the reasons above liquids also have higher entropy than solids so entropy increases from the solid state to liquid state to gaseous state.

Zoya Mulji 1K

I'm pretty sure that we will be given the multiple rxns and their enthalpies for Hess's Law.

Zoya Mulji 1K

Why do we add a negative in the work of expansion at constant pressure equation?

Zoya Mulji 1K

Can someone review how you can change the energies of the three types of systems?

Zoya Mulji 1K

Did we go over the equation for work done by expansion when P is not constant? Is that the same work equation with the integral included?

Zoya Mulji 1K

In a perfect system, what would/ should the values of q be?

Zoya Mulji 1K

enthalpy is a state property which is a property that is not dependent on the path taken to obtain that state. This means that state properties can be added or subtracted and this like work or heat are not state properties.

Zoya Mulji 1K

i think the method you use just depends on the information you are given and since bond enthalpy values are usually something you can look up/ would be given, you could use this method if you are not given the information for Hess's Law.

Zoya Mulji 1K

enthalpy is the study of heat released or absorbed in chemical reactions and physical changes --> the amount of heat released or absorbed at a constant pressure is called enthalpy

Zoya Mulji 1K

The third method was just using the formula where you sum the standard enthalpy of formation of the products and subtract the sum of the standard enthalpy of formation of the reactants from that.

Zoya Mulji 1K

Hess's Law shows you that enthalpy changes are additive because enthalpy change at each stage can be added to give total enthalpy change.

Zoya Mulji 1K

How would you change the yield of a product without adding more reactants?

Zoya Mulji 1K

How do you do the calculations for the ICE table without using the quadratic formula?

Zoya Mulji 1K

How does the concentration change when the pH value changes by a certain value?

Zoya Mulji 1K

With acid and base equilibrium reactions, why do you not include water in the equilibrium constant equation?

Zoya Mulji 1K

If the reaction gives off heat while forming the product, then the heating will favor reactant formation (because additional heat is used) and this is exothermic.

Zoya Mulji 1K

Can someone summarize what the different ranges and values of K mean for the reactants and products?

Zoya Mulji 1K

you want to take the square root because you want to manipulate the K equation for part (B) and make it look like the K equation for the original given reaction.

Zoya Mulji 1K

For (B) first write out the K for this equation. When you write it out, you can see that this K looks almost similar to the K of the original given reaction. The only difference is the power to which each product and reactant is raised. If you multiplied the powers from the original K times 1/2, you...

Zoya Mulji 1K

You only want to include the product and reactant that are in the gaseous or aqueous state. Since the other products and reactants are solids and liquids you don't use them in your calculation of Q.

Zoya Mulji 1K

If you are looking for Kp then he said to write the units as atm.

Zoya Mulji 1K

because C is more electronegative, it is better at pulling and the O-H bond is easier to break. since this conjugate base is weaker/easier to break, its acid is stronger.

Zoya Mulji 1K

a strong base will come from a weaker acid so draw the conjugate bases for the given and see which one is a weaker acid.

Zoya Mulji 1K

look at regions of electron density and create orbitals based on that number.

Zoya Mulji 1K

When the conjugate base of an acid is more electronegative, it is better at pulling so the O-H bond is easier to break. This means the conjugate base is weak and it's acid is stronger.

Zoya Mulji 1K

coordination # is the # of ligand molecules attached to the transition metal ion.

Zoya Mulji 1K

Benzoic acid is also a weak acid and you can remember this because the COOH in benzoic acid is often found in biological molecules and organic acids tend to be weaker.

Zoya Mulji 1K

What steps do you go through to draw a coordination compound?

Zoya Mulji 1K

What are some examples of coordination compounds used as chemotherapy drugs?

Zoya Mulji 1K

A weak base will partially dissociate but a strong base fully dissociates to give ions in a solution. Weak bases also have pH from 7 to 10 and strong ones have pH 10 to 14.

Zoya Mulji 1K

We only really learned how to name them so I would probably just focus on/study that.

Zoya Mulji 1K

Can someone explain how to go about checking which molecules have the highest boiling points in a series? What steps do I take/ things that I check to put the molecules in the correct order?

Zoya Mulji 1K

Intermolecular forces:
ionic bonding --> H-bonding --> dipole-dipole bonding --> induced dipole/London dispersion

Zoya Mulji 1K

Since N, O, and F all have super high electronegativity and H has a low electronegativity, they can have have a dipole moment between the atoms. --> you need the H because it's low electronegativity corresponds to the N, O, and F's high electronegativity.

Zoya Mulji 1K

Yes it's because the actual atom is bigger so it's going to slightly decrease the bond angles by making the other atoms be a little closer together.

Zoya Mulji 1K

We probably don't have to deal with *exceptions* but still have to consider the changes when lone pairs are added or when different bonding atoms are changed.

Zoya Mulji 1K

I believe sometimes the bond angles can be slightly influenced if one bonding atom is significantly bigger than the other three bonding atoms, but in this context I think we only need to demonstrate a change in bond angles with the presence of a lone pair.

Zoya Mulji 1K

If you have the lewis structure, you can draw your dipole arrows considering electronegativity and if the arrows don't balance out then the molecule will be polar.

Zoya Mulji 1K

With the electron geometry, all you have to consider is the number of things attached to the central atoms (lone pairs, atoms) to determine what the shape/geometry would be. When determining the molecular shape, you build off of this and determine how many of the "attached things" are lone...

Zoya Mulji 1K

Bigger molecules do have higher boiling points but the shape of the molecule also can influence boiling point. For example, molecules with the same molecular formula but different shapes (branched vs. linear) can have different BPs.

Zoya Mulji 1K

Hydrogen bonding is easy to see because it is present in molecules with N, O, F atoms. The N, O, or F atoms have to have lone pairs available and then and H atom covalently bonded to the electronegative atom and close to another electronegative atom.

Zoya Mulji 1K

What is the relationship between polarizability and the states of atoms/molecules?

Zoya Mulji 1K

What is the relationship between electron distortion and polarizability of the electron?

Zoya Mulji 1K

Why is the interaction potential energy always negative?

Zoya Mulji 1K

Can someone explain the components of the formula for interaction potential energy and what the alpha and r means?

Zoya Mulji 1K

shielding occurs across energy levels because the electrons in the energy levels that are closer to the nucleus block the electrons higher up from receiving the full charge. electron-electron repulsion occurs within the same energy level because when there are multiple electrons, they push each othe...

Zoya Mulji 1K

to find orbitals you would use ml. the values can range from -l to +l so you would need to find l from n and then find the values for ml.

Zoya Mulji 1K

the negative is always there in the equation because if we say that as n --> infinity, that E is 0, as the electron comes back down from high energy levels and approaches the nucleus, it loses energy and the values for energy are "negative." in a review session, a good analogy used was ......

Zoya Mulji 1K

frequency determines whether or not electrons are emitted. the intensity increases the number of photons but not that actual energy.

Zoya Mulji 1K

since formal charge indicates the gain/loss of electrons while forming a covalent bond, it serves as a predictor for stability in a lewis structure. The structure with the least formal charge should be lower in energy and thereby be the better Lewis structure.

Zoya Mulji 1K

Why are anions much bigger than their parent atoms/ why are cations much smaller?

Zoya Mulji 1K

example: with oxygen (+8), the outer electrons are being blocked from the full charge by the inner electrons. the inner electrons shield the outer electrons from the electrostatic attraction of a positive nucleus. the outer electrons feel a reduced electrostatic attraction and this results in an eff...

Zoya Mulji 1K

going off the previous answer, there is a high electron affinity for elements in the top right of the periodic table so it follows a similar trend to ionization energy in that it decreases down and group and increases across a period. this does exclude noble gases though because adding an electron t...

Zoya Mulji 1K

I get that as you go down a group, the electrons get further away from the nucleus and are shielded by the inner electrons so the ionization energy decreases. Why does ionization energy increase across a period?

Zoya Mulji 1K

Something to also consider: the 1st ionization energy is easier because the atom would be neutral and when you remove an electron, the charge becomes positive and the attraction on that 2nd electron would be higher

Zoya Mulji 1K

You would need to pull from the outermost electrons so if you had 4d10 5s2 5p1 you would pull or add from 5p1 first and then if you need to pull more you would move on to 5s2. Pay attention to the numbers out in front of the orbitals and pull from the highest number first.

Zoya Mulji 1K

You would normally find the electron configuration and pretend like it does not have a + or -. After finding the normal electron configuration, you can go in and add or remove an electron. The only time you would not be able to look for the normal configuration in the periodic table is if you were l...

Zoya Mulji 1K

electrostatic potential energy is proportional to/ depends on ((q1)(q2))/ r where q1 is the charge 1, q2 is the charge 2, and r is distance. electrostatic energy goes up when the charge of the nucleus goes up and and goes down when the distance goes up because E and r are inversely proportional.

Zoya Mulji 1K

What is the arrangement of following types of photons of electromagnetic radiation in order of increasing energy: g-rays, visible light, ultraviolet radiation, microwaves, x-rays?

Zoya Mulji 1K

De Broglie suggested that the equation works for any particle with momentum, that has a rest mass, and has wavelike properties.

Zoya Mulji 1K

In lecture today, it was said that a particle with less than 10^-15m wavelength does not have detectable wavelength properties. If the mass is higher, it will have a smaller wavelength and therefore is more likely to only have particle-like behavior and not wave-like behavior.

Zoya Mulji 1K

What wavelength values from De Broglie's equation indicate whether or not a particle or electron has detectable wavelength properties?

Zoya Mulji 1K

accuracy indicates how close measurements are to the "true" or real value and precision indicates how close measurements are to each other, but not necessarily to the "true" value.

Zoya Mulji 1K

can someone elaborate on how spectroscopic analysis of light can be used to identify different elements?

Zoya Mulji 1K

^ Also remember that we will get a formula/constants sheet for every test so a lot of the information we need will be given to us. There's no harm in memorizing though!

Zoya Mulji 1K

Can someone explain how to do one of the learning outcomes in this section. It says we should know how to use the Bohr frequency condition to explain the origin of the lines in the spectrum of an element.

Zoya Mulji 1K

^^ I would recommend pulling up the Review/Outline for Fundamentals that's on the website. Just go through the key concepts and make sure you know how to do a couple of types of problems from each bullet point.

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