CHEMISTRY COMMUNITY

Lumbini Chandrasekera 1B

How would you calculate work when you're not given change in volume?

Lumbini Chandrasekera 1B

What's the difference between an enzyme and a catalyst?

Lumbini Chandrasekera 1B

I know temperature can affect the constant, but what about the presence of a catalyst?

Lumbini Chandrasekera 1B

A half life is the time it takes for half of a substance to decompose or change. For radioactive elements, I believe, it is the time it takes for half of that element (let's say half of 4 g which is = 2 g) to disappear. In chemical reactions, it would be the time it takes half of the concentration o...

Lumbini Chandrasekera 1B

k is the Boltzmann rate constant while K is the equilibrium constant for a certain reaction.

Lumbini Chandrasekera 1B

Why do first and second order reactions have slopes with opposite signs?

Lumbini Chandrasekera 1B

When the slope of the tangent lines to the concentration curves of the compounds involved is equal to zero.

Lumbini Chandrasekera 1B

What are the units for a zero order reaction and why?

Lumbini Chandrasekera 1B

Can you determine the order of a reaction simply from looking at the coefficients of the balanced chemical equation or do you have to use the experimental data?

Lumbini Chandrasekera 1B

When you are given a problem in regards to a galvanic cell, can you assume that the cell potential of the reaction is always positive?

Lumbini Chandrasekera 1B

Can we add standard cell potentials together when they involve a different number of electrons? This isn't in regards to a reaction in a cell.

Lumbini Chandrasekera 1B

Do we have to know how to compare the reduction of hydrogen to other half-reactions on Test #2?

Lumbini Chandrasekera 1B

High temperature is associated with lower entropy and vice versa.

Lumbini Chandrasekera 1B

How do you determine the sign of Gibbs Free Energy given that enthalpy is positive, temperature is positive, and entropy is positive.

Lumbini Chandrasekera 1B

Given the value of Gibbs free energy, how do you know whether the reaction is spontaneous or not?

Lumbini Chandrasekera 1B

Essentially the two mean the same thing. Using the summation method is just finding the reaction enthalpy value yourself.

Lumbini Chandrasekera 1B

Do we have to know how to derive equations?

Lumbini Chandrasekera 1B

Do we have to know the enthalpy of fusion, vaporization, etc. values for water for the exam?

Lumbini Chandrasekera 1B

Step ups are really good.

Lumbini Chandrasekera 1B

The units are essentially same in the essence that the difference between two Celsius values is the same as the difference between two Kelvin values. You can easily use Celsius if you are looking for delta T and get your answer with its units in Kelvin.

Lumbini Chandrasekera 1B

The only difference is that the specific heat capacity is to define per gram of that substance.

Lumbini Chandrasekera 1B

Why isn't pKa the same as pH?

Lumbini Chandrasekera 1B

Worst case the chemical equation may not be written out for you but the problem will tell you the substance and it's molecular formula would be given if it's not a common substance. You would then have to add H2O to make a reaction, unless stated otherwise, and balance the equation yourself.

Lumbini Chandrasekera 1B

Amphoteric is a substance that can act as an acid of a base, while amphiprotic is a substance that acts as an acid or base but donates/accepts protons specifically.

Lumbini Chandrasekera 1B

Since there are equal moles of gas on both sides of the equation, there is no change to equilibrium with change in pressure/volume.

Lumbini Chandrasekera 1B

Concentration is preferable but you do molar values only if all of the numbers are consistent. You can do both ways as long as you keep them consistent throughout the problem.

Lumbini Chandrasekera 1B

Keep in mind that only the moles of gas count.

Lumbini Chandrasekera 1B

Remember that the K constant formula is the products over the reactants for a chemical equation. When combining two separate equations together, the reactants of the first equation will be the products of the next and therefore cancel out when you multiply the two K's for the two equations making th...

Lumbini Chandrasekera 1B

Q and K are different values because when you're given the problem, it is not explicitly stated whether the reaction is at equilibrium at the moment. You have to determine this by using the K formula and plugging in the concentration values to determine what state the reaction is in by comparing it ...

Lumbini Chandrasekera 1B

Q CAN be at equilibrium or it can't. It's simply meant to describe the state of the reaction to compare to K value of the reaction at equilibrium to see where that reaction is sitting.

Lumbini Chandrasekera 1B

H3O+ and H+ are similar in that they define whether something is an acid. Although H3O+ is not technically a proton like H+ is, it can be thought of as a proton bound to a water molecule.

Lumbini Chandrasekera 1B

You can tell from the chemical formula whether it is likely to produce H+ protons (acid) or OH- hydroxides (base), but for something like NH3 you would have to see what is would do when adding water. When adding water, it would form NH4+ and OH-, which is a hydroxide, making NH3 a base.

Lumbini Chandrasekera 1B

What are the strong acids which we would have to memorize?

Lumbini Chandrasekera 1B

I don't think the charge is necessary to include in the nae of the ligands, but it is important when determining the oxidation number/charge of the transition metal when providing the roman numeral of it.

Lumbini Chandrasekera 1B

I believe you just have to become acquainted with the charges of the ligands and familiarize yourself with them.

Lumbini Chandrasekera 1B

Conjugate bases and acids are pretty much the products which a reactant becomes after going through a reaction. If a substance is an acid as a reactant and accepts an electron pair in a reaction, it becomes a base on the product side of a chemical equation, making it a conjugate base. Generally the ...

Lumbini Chandrasekera 1B

When do you use the suffixes bis-, tris-, etc. instead of bi-, tri-, etc.?

Lumbini Chandrasekera 1B

What factors/characteristics help you determine whether a bond is strong or not in a molecule?

Lumbini Chandrasekera 1B

Since each carbon atom only bonds with three atoms each, it must make sp^2 hybrids (3 orbitals) and since when you combine the s and p orbitals together you get a total of 4 orbitals. Therefore, there is one p orbital left for the carbon atoms to maintain.

Lumbini Chandrasekera 1B

S-character is technically the percentage the s orbital in a hybridization takes up. For instance, it is 50% in an sp hybrid but it is about 33% in an sp^2 and so on. Therefore, when this s-character increases (meaning higher percentage) it means that the hybridization involves less atoms and theref...

Lumbini Chandrasekera 1B

If they had really similar electronegativities, I believe they would technically cancel out and could be considered nonpolar there would still be a slight net dipole moment just to account for the fact that they are different elements.

Lumbini Chandrasekera 1B

The major difference between the two is how polarizability is more in regards to anions and how they pull an electron to itself while polarizing power is in regards to cations and how they pull electrons towards themselves in bonds.

Lumbini Chandrasekera 1B

When naming the hybridization, do you also include lone pairs? Like is it supposed to take into account ALL electron densities?

Lumbini Chandrasekera 1B

It does not have a net dipole moment since it's "symmetrical" in the sense that it is a trigonal planar shape.

Lumbini Chandrasekera 1B

You would have to decide based on the electronegative trends and see which elements in the molecule are farther apart (therefore, more electronegative).

Lumbini Chandrasekera 1B

Do hydrogen bonds only happen between molecules or can they happen within a molecule?

Lumbini Chandrasekera 1B

In a linear shaped structure, if the two atoms on either side of the central atom are of different elements, but have the same number of valence electrons, will a 180 degree angle still be made?

Lumbini Chandrasekera 1B

For a shape to be linear (bond angle 180), do the two atoms on either side of the central atom have to be of the same element?

Lumbini Chandrasekera 1B

I think it [Ar] 3d^8 because lower principle energy levels should be filled with electrons first before the next energy level (n=4) is filled which is why it wouldn't be [Ar] 3d^6 4s^2.

Lumbini Chandrasekera 1B

What is degeneracy exactly? I remember it being on Test #2 and I got the answer wrong and was just confused on what it was asking for.

Lumbini Chandrasekera 1B

The definition mainly just surrounds the idea of whether it donates/accepts electrons or not.

Lumbini Chandrasekera 1B

The inner energy level electrons "shield" the outer shell electrons to prevent their attraction to the nucleus as they have opposite charges. I assume this happens because the inner electrons are closer and more attracted to the positively charged nucleus, therefore, the attraction is weak...

Lumbini Chandrasekera 1B

I believe when it comes to the elements on the periodic table, the orbitals go up to 5p even though energy levels can hypothetically reach up to infinity. I think whatever's on the periodic table will be relevant for life science majors.

Lumbini Chandrasekera 1B

You convert the baseball (5.15 oz) to kilograms and the speed of 92 mi/h to m/s and then you use the equation wavelength = h (planck's)/(mass)(velocity) to solve for the wavelength.

Lumbini Chandrasekera 1B

It's some circuitry device that measures the current between it's wire and metal plate to tell when electrons are being removed.

Lumbini Chandrasekera 1B

For that problem in the lecture, it was to find the frequency of the light being released and since the energy it contained must be positive, you solve for frequency by plugging in a positive energy value. You just have to know that you make the energy positive before solving for frequency because a...

Lumbini Chandrasekera 1B

I think we should have an idea of where the colors are just in case using ROYGBIV, but I'm not sure if we have to know the exact ranges.

Lumbini Chandrasekera 1B

You should show as much work as necessary to get points. It says that work must be shown to get credit, but it doesn't say how many steps.

Lumbini Chandrasekera 1B

Nope! We didn't use a blue book.

Lumbini Chandrasekera 1B

The sig figs should be based on the given values in the question, not in the periodic table. So even though there are more sig figs in the values provided in the question, you would still use that instead.

Lumbini Chandrasekera 1B

So you don't have to balance the equation because it's already balanced and you also don't need to solve for the limiting reactant because we're not given the amount of H2SO4 there is so you can't even choose which one is limiting. you pretty much just use the 1 kg of CaCO3 in the question and use s...

Lumbini Chandrasekera 1B

Dilution is where you reduce the concentration of a substance by adding distilled water, for instance. Titration is the process of finding the concentration of a substance (like an acid or base) by adding a solution of known concentration.

Lumbini Chandrasekera 1B

I think it's ok to use whichever number you get from the periodic table (but the more specific the better), but your final answer should have the same number of significant figures as that of the given (that is, the numbers you're provided in the question to do the problem).

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