CHEMISTRY COMMUNITY

Nina Gautam 1K

In homework problem 9.55, we are asked to write a balanced equation for the formation of molecules and calculate standard reaction Gibbs free energy, entropy, and enthalpy. In the solutions manual, fraction coefficients are used to yield exactly one mole of product. In problem 9.57, however, we are ...

Nina Gautam 1K

This is a concept question from the homework and maybe it's just the wording but I don't understand the solution... The statement reads "At equilibrium, the rate constants of the forward and reverse reactions are equal." The solutions manual says it is false, and that the rates of forward ...

Nina Gautam 1K

Chapter 20 has a lot of information on functional groups, including how to name them. This may go into much more detail and complexity than we need to know for the exam, though. I would just focus on the groups he went over in class.

Nina Gautam 1K

Le Chatelier's Principle states that when a change is imposed on a system, the equilibrium will shift to counteract the change. If temperature is increased, there is more energy available, and the reaction shifts in the direction of the endothermic reaction. If temperature is decreased, it is more e...

Nina Gautam 1K

I believe it is because they dissociate into the solution and are not being oxidized or reduced, so they are not necessary to include

Nina Gautam 1K

It's not necessarily because the first and second order equations start with ln[A] and 1/[A] instead of just [A], those are just mathematical functions that make it easier to understand the other side of the equation. The rate of reaction in first and second reactions depend on the concentration on ...

Nina Gautam 1K

As Lavelle said in class, if there are intermediate steps, he will give us the intermediate species. We don't have enough general chemistry knowledge at this point to come up with it on our own.

Nina Gautam 1K

Yes, they are always positive because they are with respect to time.

Nina Gautam 1K

The reaction rate should always be positive because even if a species is reducing in concentration, which is negative, we are describing the speed at which it is changing with respect to time

Nina Gautam 1K

It's a unique reaction rate because it is the same for all concentrations of reactants and products when it is multiplied by their stoichiometric coefficient. The species doesn't need to be specified when writing a unique rate.

Nina Gautam 1K

Are we responsible for knowing overall order of a reaction rate if the reaction has a rate law that depends on the concentrations of more than one reactant? Also will we need to know about fractional or negative orders?
Thanks!

Nina Gautam 1K

I don't believe the speed of the reaction impacts spontaneity of the reaction; since delta G is a state function, it is only based on initial and final states, not how fast or slow the reaction occurs. If the activation energy barrier is lowered, the reaction will occur more quickly but still end up...

Nina Gautam 1K

What are all the scenarios in which an inert electrode is necessary? Also, can it always be Pt(s) or are there situations where it should be a different metal?

Nina Gautam 1K

I don't think order matters, but it may be easier to see the species being reduced by keeping them next to each other and writing the proton all the way to the right of the reducing side.

Nina Gautam 1K

yes, n always refers to moles of electrons

Nina Gautam 1K

I'm not sure if this helps but my TA said to just assume acidic conditions unless otherwise stated, and if it is a basic solution, solve it as if it were acidic and then convert to basic at the end.

Nina Gautam 1K

first you write the anode oxidation with a single bar in between 2 substances in different phases, and then a double line to indicate a salt bridge, and then the cathode reduction with a single bar again in between substances that are in contact with eachother but are in different phases

Nina Gautam 1K

In question 9.31, the solutions manual states that 1-pentene will have higher standard molar entropy at 298 K than cyclopentane because of its more flexible framework. Does this have to do with the rotational motion characteristic of single bonds vs double bonds in the 1-pentene structure?

Nina Gautam 1K

The 44 kJ/mol is constant in all three calculations because it is the enthalpy of vaporization of water. Only entropy changes as the temperature changes.

Nina Gautam 1K

I believe that in a non-isolated system, delta S can be negative because work can be done on the system to decrease the entropy.

Nina Gautam 1K

We call it reversible because we are thinking about it as occurring in many small steps (infinitesimally small steps) rather than all at once, which gives us a more accurate work value. Because we are thinking about it in small steps as opposed to all at once, it can hypothetically occur in the oppo...

Nina Gautam 1K

That is the equation for the internal energy of an ideal gas. Here is a very useful video link describing it clearly: https://www.khanacademy.org/science/phy ... -u-3-2-nrt
Hope this helps!

Nina Gautam 1K

I think it will state it because we are responsible for knowing both ways.

Nina Gautam 1K

For question 8.41, I was wondering why the volume of water in the calculation wouldn't change from 400g to 450g? The question asks for the final temperature of the system, so wouldn't that imply that the ice cube completely melts into the water and increases the mass of liquid H2O?

Nina Gautam 1K

Question 8.23 asks us to calculate the heat capacity of a calorimeter given an amount of heat and a temperature change. I was wondering why the mass of the calorimeter doesn't matter/isn't taken into account when, for every other calculation involving heat capacity, there is some mass or amount (mol...

Nina Gautam 1K

Are we responsible for knowing the concepts behind reversible expansion? Will there be questions like 8.11 on the test? Thanks!

Nina Gautam 1K

I believe the metal forms the system and the water forms the surroundings, because q(sys)=-q(surroundings) and we calculate q(sys) by observing changes to temperature in q(surr).

Nina Gautam 1K

The most stable form of solid sulfur at room temperature is rhombic sulfur. Once it is heated about 95ºC, it is transformed into monoclinic sulfur, which is just a different arrangement of molecules.

Nina Gautam 1K

Are we responsible for knowing and being able to apply the equations in ch 8.10? This section gives the molar heat capacity at constant volume for monatomic gases and linear molecules, as well as knowledge of rotation and the equipartition theorem. Thanks!

Nina Gautam 1K

A state property is a value that is calculated purely by the final value - initial value. I think the only non-state properties we need to be concerned about at this point are work and heat, which Lavelle mentioned in class.

Nina Gautam 1K

I believe that in a coffee cup calorimeter, the pressure is constant whereas in a bomb calorimeter, the volume is constant

Nina Gautam 1K

First, find the energy required to melt the ice, ΔH°fus. For water in the it is 6.01 kJ/mol. Then find the specific heat capacity of water in liquid state, which is 4.184 J/°C*g. Then convert both values to kJ; for ΔH°fus, multiply by the amount in grams and divide by molar mass, which is 80g H2O/18...

Nina Gautam 1K

I have seen it written both ways in the textbook and think it is fine to write it either way

Nina Gautam 1K

Correct, Bronsted acids are proton donors and Bronsted bases are proton acceptors while Lewis acids are electron acceptors and Lewis bases are electron donors. From what I understand about strength of acids/bases, a strong Bronsted acid isn't necessarily a strong Lewis acid as well, but I'm not 100%...

Nina Gautam 1K

CO is carbonyl, NO is nitrosyl, and (C204)^-2 is oxalate

Nina Gautam 1K

Will we have to be able to convert between equilibrium constant in terms of partial pressures to equilibrium constant in terms of molar concentrations?

Nina Gautam 1K

Only molecule B can form a chelating complex because the two amine groups on the molecule are close enough that they are able to coordinate to the same metal atom at the same time. A chelate is just a complex containing a ligand that forms a ring of atoms that includes the central atom. Hope this he...

Nina Gautam 1K

Do single electrons on a central atom have the same effect on the shape of the molecule as a regular lone pair?

Nina Gautam 1K

I had the same question, this website helped me a lot with explaining what a hybrid orbital is in simple terms: https://www.chem.fsu.edu/chemlab/chm104 ... ation.html
Hope this helps!

Nina Gautam 1K

A double bond is always comprised of one sigma bond and one pi bond. Sigma bonds are single bonds, and one of the other multiple bonds in higher order bonds.

Nina Gautam 1K

When writing the chemical formula for hydrogen telluride, why is it H2Te and not TeH2?

Nina Gautam 1K

If the electronegativity difference between the two atoms is greater than 2, the bond is considered ionic. If the electronegativity difference between the two atoms is less than 1.5, the bond is considered covalent

Nina Gautam 1K

The larger an atomic radius, presumably the more shells of electrons the atom has. Therefore, there are also more electrons on the inner shells that shield the electrons in the outer shells from the full electrostatic charge of the nucleus, so the effective charge (Zeff) on them is reduced. If there...

Nina Gautam 1K

Yes, ionic Lewis structures are surrounded by brackets and then the charge is indicated on the outside. Also to determine if a structure should be in brackets, I would use the electronegativity trend as you suggested

Nina Gautam 1K

Carbon has a greater electron affinity because a half-filled p subshell is more stable than one that is 2/3 full. The overall trend that electron affinity increases across a period is not absolute; there are exceptions

Nina Gautam 1K

The 4s^2 would be above the 3d^2, following the electron configuration. Also the 4s^2 electrons would be the primary valence electrons and would get removed first before the 3d^2 electrons.

Nina Gautam 1K

When electrons are filling up the p-orbitals, is it implicit that 2px gets occupied before 2py and that 2py gets occupied before 2pz (in that order) before a second electron occupies 2px? I understand Hund's rule that electrons will fill orbitals that are empty before pairing with another one, but i...

Nina Gautam 1K

There are also modules for Heisenberg's Uncertainty Principle on the website. The post-module questions are also a good resource to prepare.

Nina Gautam 1K

You first need to convert the work function from kJ to J, which you did in your original post, but then since it is the energy required per mole, you then also need to divide by Avogadro's constant. Hope this helps!

Nina Gautam 1K

A condensed/combined equation relating energy and wavelength is E= hc/λ. You would use it when given the wavelength and asked to find energy or vice versa.

Nina Gautam 1K

In ionic equations, how do you know when to split up molecules (as Kourtney did for both reactant molecules) vs keeping molecules together? (Such as keeping Cu(OH)2 together in the products but splitting up 2NaNO3 to 2Na+ + 2NO3-?

Nina Gautam 1K

Another way a question could be implicitly asking about limiting reagents is by asking what the maximum or theoretical yield is from a given set of masses (of reactants), or by providing masses of reactants and the actual yield of an experiment and requiring us to find the percent yield.

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