CHEMISTRY COMMUNITY

Kyra Dingle 1B

What is the chemical formula for the molecules in candy?

Carbon-Holmium-Cobalt-Lanthanum-Tellurium

or CHoCoLaTe

Kyra Dingle 1B

In irreversible expansion, external pressure is held constant, while for reversible expansion, external pressure is changing. You can tell by the equations that are used under each condition as irreversible expansion uses -P(deltaV) and reversible expansion uses -nRTln(V2/V1).

Kyra Dingle 1B

How many state functions should we have gotten as an answer for the question on the final?

Kyra Dingle 1B

What is connection between a zero order reaction and the presence of a catalyst?

Kyra Dingle 1B

On Friday, Lavelle explained a bit about substitution reactions and nucleophiles. Do we need to understand this concept for the final? If so can someone explain how these reactions connect to reaction profiles that are based on Gibbs Free Energy rather than Activation energy?

Kyra Dingle 1B

Can someone explain the difference between the steady-state and the pre-equilibrium approach?

Kyra Dingle 1B

Will we need to derive each of the different order reactions from the differential rate law for any future tests?

Kyra Dingle 1B

What is the difference between a rate constant and an equilibrium constant?

Kyra Dingle 1B

For this question, we are meant to calculate the time needed for a concentration to decrease to a) 1/16th b) 1/4th c) 1/5th the original value. We are given the half-life of the second-order reaction and the initial concentration. In the solution manual we use the second-order half life equation to ...

Kyra Dingle 1B

How do you know when to use $ln\frac{[A]_{t}}{[A]_{0}}=-kt$
or when to use $ln\frac{[A]_{0}}{[A]_{t}}=kt$ ?
Are there specific instances when we use each?

Kyra Dingle 1B

Why does a directly proportional relationship between the rate of the reaction and the concentration of the reactants indicate a first order?

Kyra Dingle 1B

What is the unique rate of reactions? How would you calculate it?

Kyra Dingle 1B

The rate of the reaction can be found as the change in concentration of product or reactant over the change in time. The rate law (aka differential rate law) is found using the equation k[R]^n in which n is the order of the reactant, [R] represents the concentration of the reactant, and k is the rat...

Kyra Dingle 1B

How come the standard reduction potentials stay the same when half reactions are balanced?

Kyra Dingle 1B

I believe you can determine how many electrons to add to a half reaction based on the change in oxidation number of the element being reduced or oxidized. The number of electrons added would then make up for the difference to make both sides of the reaction balanced

Kyra Dingle 1B

When giving a full redox reaction and asked to write either the oxidation or reduction half-reactions, can we use the elements alone with an oxidation number for each half reaction? or are we expected to utilize the full compound when writing the half reaction? For example, in 14.1 we are asked to w...

Kyra Dingle 1B

What is the difference between molar entropies and standard entropy of formation? Why do we use molar entropies to find the standard reaction entropies and not standard entropies of formation?

Kyra Dingle 1B

Why can we look at the Gibbs Free Energies of Formation to determine stability? Why would a positive free energy of formation indicate an unstable compound while negative ones indicate stable compounds?

Kyra Dingle 1B

When asked to calculate Gibbs Free Energy when should you use the equation deltaH - T*deltaS compared to using the standard formation values and subtract the sum of the products from the sum of the reactants?

Kyra Dingle 1B

For future exams will we be required to know the states of substances like in 9.31 in which we needed to know the states of ethene and polyethylene to determine which has the higher molar entropy?

Kyra Dingle 1B

How would you define molar entropy? What are some good ways to determine if a substance or compound has a higher or lower molar entropy?

Kyra Dingle 1B

Can someone explain further why when determining the standard entropy of water at 85 degrees C you need to find the entropy change when heating the reactants to boiling point and the change when cooling the products back down to 85 and then finally add those changes with the standard entropy at 100 ...

Kyra Dingle 1B

How would you derive the equation you would use for entropy changes due to changes in pressure?

Kyra Dingle 1B

When a problem mentions that an entropy change occurred isothermally do we assume that the process was also reversible? Why or why not?

Kyra Dingle 1B

When using the Second Law of Thermodynamics, how do we know when q will be negative? Does it depends on whether q is referring to the system or surroundings? or when q is referring to heat lost or gain?

Kyra Dingle 1B

Why is part c, q<0, always false in adiabatic processes, in which no energy is transferred as heat? Is this because in these processes, q is simply 0 and would not be negative for the situation? What is an example of a situation in which q would be negative?

Kyra Dingle 1B

For our test would we be provided with the standard enthalpies of formation, if given a question asking to calculate the standard reaction enthalpy for a reaction?

Kyra Dingle 1B

What is the difference between an extensive and an intensive property, and how do they relate to heat capacity?

Kyra Dingle 1B

What is the difference between internal energy and enthalpy?

Kyra Dingle 1B

Yes as the molecule becomes more complex the heat capacity will increase as a result. Homework problem #29 in the textbook deals with this concept as NO2 is seen to have a higher molar heat capacity compared to NO due to the additional oxygen allowing for a greater absorption of added energy.

Kyra Dingle 1B

Can someone give again the explanation Lavelle shared last Monday about why steam burns a lot more and how that relates to phase changes?

Kyra Dingle 1B

Do we need to know the conversion of liter-atmospheres to joules?

Kyra Dingle 1B

If a solid is added, it should have not effect since it is not included in the equilibrium constant. May I ask which specific problem you are referring to in his practice test?

Kyra Dingle 1B

One way to determine is through what the problem gives you. If only the amount of the initial reactant is given, then the initial concentration of the products would be 0. This then means that the reactants will be consumed to make products until the reaction reaches equilibrium. Since the reactants...

Kyra Dingle 1B

NO2 cannot be drawn with two double bonds and one lone pair on the N central atom because it violates the octet rule. N cannot have exceed the octet rule because it does not have empty d orbitals unlike many of the third period elements, which uses their empty d orbitals to accommodate more electrons.

Kyra Dingle 1B

The value of Kc can change when stoichiometric coefficients are halved because when calculating Kc itself it requires the stoichiometric coefficients used in the chemical equation as exponents of the reactants or products. To demonstrate using an equation that had A + 2B = 4C and assuming they are a...

Kyra Dingle 1B

I believe the term "sits to the left" means there are more reactants at equilibrium, which can be seen through determining if K is small (K<10^-3). The term "sits to the right" then refers to a larger amount of products, which can be seen through determining that K is large (K> 1...

Kyra Dingle 1B

Can someone explain how to find the pKa of NH3OH and (CH3)2NH2? I understand the need to subtract the pKb from 14 to find the pKa, but how do you find the pKb in the first place?

Kyra Dingle 1B

Do we need to know the conductivity of certain acids and bases for the final?

Kyra Dingle 1B

XeO2F2 is polar and it helps to identify this through drawing out the lewis structure. In doing so, you can see that Xe has 5 electron densities with 4 bonded pairs and one lone pair. The single lone pair gives the compound a seesaw shape which then would be polar

Kyra Dingle 1B

The molecular shape can be used to determine polarity through observing the lone pairs and the resulting shape of the compound. If there are no lone pairs the compound should be nonpolar, but once there are lone pairs it is important to observe the shape to see if any dipole moments exists and if th...

Kyra Dingle 1B

Can someone explain again the concept behind why the fact that electron withdrawing atoms can stabilize anions by delocalizing the negative charge is true?

Kyra Dingle 1B

What are some important things we need to know regarding the biological aspects/importance of coordination complexes? For example, we need to know 4 myoglobins form hemoglobins.

Kyra Dingle 1B

For writing the reaction quotient, Q, or equilibrium expression, K, when do we write it as partial pressure with the capital P then the molecule as a subscript in contrast to as a concentration with the molecule surrounded in brackets? For example in 11.3, it asks to write the equilibrium expression...

Kyra Dingle 1B

Can someone elaborate why the pi bonds for the structure in 4.95 have only the 2p hybridization in contrast to the sigma bonds with the sp2 hybridization and perhaps how you would come to this conclusion through observing the lewis structure?

Kyra Dingle 1B

There is a table in the book that includes a list of common ligands and their corresponding formulas. Are we required to know all of these for the test or final?

Kyra Dingle 1B

In the problem 4.25, why is CH2CL2 polar? I understand the Cl is more electronegative and thus there is a stronger pull of the electrons/negative charge towards the Cl. However, when drawing the lewis structure couldn't the Cl be draw opposite to each other to make these charges cancel?

Kyra Dingle 1B

When drawing lewis structures, do we need to draw them in a way that reflect the molecular shape? For example in sulfur tetrafluoride (SF4), during lecture we drew it with the lone pair on the left side of the sulfur (the equatorial plane). I believe this reflects the most stable shape with the leas...

Kyra Dingle 1B

When asked to find the lewis structure, do you automatically write the structure with the lowest energy?

Kyra Dingle 1B

Would someone be able to explain why the lewis structures for the compounds are written separately and not with any connecting bonds? For example in part a, the chlorine anion is not bonded to the NH3 and stands alone with 4 lone pairs. How would you also be able to recognize that you need do this f...

Kyra Dingle 1B

Can someone elaborate further on the effective nuclear charge and how it relates to electron shielding in multiple electron atoms?

Kyra Dingle 1B

Both values are correct. However, the specific value you would use for a problem is all dependent on the number of significant figures required for the problem. For example if only 2 sig figs are required, 3.0* 10^8 m*s^-1 would be used in the problem.

Kyra Dingle 1B

I believe to determine which has a higher electron affinity, you would need to refer to the periodic table. Electron affinities tend to be the highest towards the right of the periodic table. You would apply this electron affinity trend by comparing where each element is locating in relation to each...

Kyra Dingle 1B

The main difference between the Lyman and Balmer series is the energy level in which electrons come to rest. For the Lyman series n=1, while for the Balmer series n=2. Another important characteristic to note is that the Lyman series is found within the ultraviolet spectrum, while the Balmer series ...

Kyra Dingle 1B

Before doing anything it is important to check that all the equations are balanced! 1. Convert the 2.50 t to grams. This is best done by converting first to kilograms and then converting that value to grams. 2. Convert the g of NaBr to moles by dividing by the molar mass of NaBr. 3. Once you found t...

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