CHEMISTRY COMMUNITY

Russell Chuang 1J

We can find the E through multiple methods. We can use Nernst equation to solve for it using Eknot and the Q or we can split the reaction into halves and add they reduction potentials.

Russell Chuang 1J

We can determine the units of k based on the order of the reaction. For first order, the units 1/s, for second order, the units 1/M*s, and for zero order, the units M/s.

Russell Chuang 1J

The instantaneous rate occurs at a specific time while the average rate is taken over a range of time.

Russell Chuang 1J

We can find the overall order of a reaction by adding together all the exponents of the rate law.

Russell Chuang 1J

The rate constant is negative because as the reaction occurs, the reactants will decrease, thereby losing concentration. That is where the negative sign comes from.

Russell Chuang 1J

If we look at the exponents on the rate law, we can find the order. The exponents summed together is the total order.

Russell Chuang 1J

Why is the slow step the rate determining step?

Russell Chuang 1J

We can simply use the half life equation of 0.693 divided by k or the reaction constant.

Russell Chuang 1J

What does the k stand for in the second order reaction equation, and how does k correlate the graph of the second order reaction?

Russell Chuang 1J

A is a constant for the frequency of collisions with the right orientation. If they do not hit at the right angle, they overcome the energy needed.

Russell Chuang 1J

The activation is the energy needed to start the reaction so it should be the start of the curve.

Russell Chuang 1J

What does the zero order reaction graph look like?

Russell Chuang 1J

Are catalysts included in the rate law?

Russell Chuang 1J

If you are subtracting the two, then you would flip the sign on the reduction potential. However, if you are adding the electrical potential of the two equations, do not flip the sign.

Russell Chuang 1J

Nernst equation is E=Einitial -RT/nF*lnQ and is used to find the potential of energy in a cell at a given point during the reaction.

Russell Chuang 1J

Work is the force that is required to move an object a set amount. We can calculate for it through a lot of equations depending on the set up of the system. For something like an irreversible isothermal reaction, w=-pv but for a reversible isothermal reaction w=-nRTln(V1/V2).

Russell Chuang 1J

In general, we only need to know the common ones like oxygen or hydrogen, and the rest will be either provided or solved for in the problem.

Russell Chuang 1J

We add H+ to balance redox reactions because we generally have to balance the amount of oxygen in the reaction by adding H2O. When we finish balancing the amount of H2O, we then balance the amount of hydrogens by adding it to the other side. This is where the H+ comes from. However, for basic soluti...

Russell Chuang 1J

You have to break this up into 3 components. The first step is finding the entropy as you heat the water up from 29 degrees to 100 degrees. Then add that entropy to the entropy at boiling point. Finally, add that sum to the entropy as the water vapor cools from 100 degrees to 29 degrees. The equatio...

Russell Chuang 1J

To solve one of them, first convert the 500W to joules. Once you have the joules, convert the difference in mass for a compound into its moles. Then to find the delta H, take the energy of 500W in joules and divide by the moles you calculated for. The delta S is simply the the delta H divided by the...

Russell Chuang 1J

You have to solve for the moles using the ideal gas equation. Once you found the moles, plug it into the equation for the entropy using specific heat and two different temperatures. Make sure to use Kelvin for the temperatures.

Russell Chuang 1J

What is the purpose of the salt bridge in the cell diagram?

Russell Chuang 1J

Do the net charges on both sides or a redox equation need to be equal? And why or why not?

Russell Chuang 1J

For question 20 on the achieve homework, I don't know why it would be spontaneous when both the Q is greater than and less than the K.

Russell Chuang 1J

The first step is to calculate the change in G using the values in the table. We take the final Gibbs free energy and subtract it by the reactant Gibbs free energy. We then plug it into the equation G=-RTlnK to solve for K.

Russell Chuang 1J

When a reaction is endothermic and heat is added, will the equilibrium constant decrease or increase?

Russell Chuang 1J

Bond enthalpies are always positive. They end up being negative when we are taking the products of them and subtracting the reactant bond enthalpy values.

Russell Chuang 1J

They are all state functions because they are extensive. Therefore, we can conduct Hess-law like calculations on with them.

Russell Chuang 1J

Heat capacity is an extensive property because it is dependent on how much of a substance there is. Another example would be entropy. Something like density is intensive property because it does not depend on how much of a substance there is.

Russell Chuang 1J

For most questions, it will specify whether a reaction is reversible or not. A sign is if that there a rapid change in volume or if there is constant external pressure, then the system behaved in an irreversible fashion.

Russell Chuang 1J

We use the first equation when there is a constant pressure and the volume expands at an irreversible rate. We use the second equation when there is not a constant pressure and the system expands at a very small rate

Russell Chuang 1J

I am slightly confused on what the difference between a closed an isolated system is. Can someone explain?

Russell Chuang 1J

How do we find the number of moles for the work equation?

Russell Chuang 1J

When a weak acid is in water but its pKa is lower than the pH, will it break apart or not?

Russell Chuang 1J

For this question, why must we consider the enthalpy of fusion for the ice cube?

Russell Chuang 1J

Heat refers to a constant energy transfer while enthalpy refers to a net value of heat in a system.

Russell Chuang 1J

I am confused on what the difference between standard enthalpy formation and bond enthalpy.

Russell Chuang 1J

Why are bond enthalpy calculations the least accurate method of finding the enthalpy of a system?

Russell Chuang 1J

We use Cv when we want to keep volume constant, and we use Cp when we keep pressure constant. Cp will be higher than Cv because Cv does not have to lose energy to work of expansion.

Russell Chuang 1J

I am still confused on what exactly a state property is. Thank you.

Russell Chuang 1J

The reason why temperature stays the same during heating in vaporization or melting is because that extra energy of heat is used to break the bonds between the molecules.

Russell Chuang 1J

What do we do with the equilibrium constant if we flip the reaction?

Russell Chuang 1J

Why does volume need to change and not just pressure in order to affect the rate/direction of the reaction?

Russell Chuang 1J

How does heat affect the equilibrium constant?

Russell Chuang 1J

How does the ice table look for problem 5.I.35?

Russell Chuang 1J

I attempted the 5.I.29 textbook problem, but I am having issues with the answer I am getting. Aside from setting up the ICE table, are there any other tricks within this problem?

Russell Chuang 1J

K is an established constant for the equilibrium but Q is the ratio of concentration a certain point during the reaction.

Russell Chuang 1J

We use molarity for ICE charts because the constants for equilibrium are given in molarity. Molarity keeps all the units consistent.

Russell Chuang 1J

Le Chatelier essentially states by changing physical parameters or components to a chemical reaction, the reaction will try its best to minimize the effects of such changes. An example is adding more reactants, which will result in more products.

Russell Chuang 1J

How do we convert between Kp and Kc? Thanks!

Russell Chuang 1J

Why is it harder for a polyprotic acid to lose its second hydrogen?

Russell Chuang 1J

When pKa is less than pH, is a conjugate produced or does it make it a weak base?

Russell Chuang 1J

What is the difference between pKa and pH?

Russell Chuang 1J

AlCl3 is acidic because when it dissolves in water, the Cl will break off the AlCl3. The Al will then bond with OH to leave just a proton. This proton will produce hydronium or H30+

Russell Chuang 1J

What are some examples of amphoteric compounds?

Russell Chuang 1J

Why is pyridine less basic than trimethylamine?

Russell Chuang 1J

Why is hydrochloric acid stronger than carbonic acid?

Russell Chuang 1J

What are some examples of amphoteric compounds, and how are they amphoteric?

Russell Chuang 1J

why does having a resulting stable anion make an acid strong?

Russell Chuang 1J

For benzene, the three dimensional model has a circle of orbitals above and below the actual ring. Why does that occur?

Russell Chuang 1J

Hybridization is based off areas of electron density. Therefore, the number of bonds won't matter and all you count is the number of bonds and lone pairs. In this case, there are 4, therefore, it is sp3.

Russell Chuang 1J

What is the difference between a normal ligand and a chelating ligand?

Russell Chuang 1J

What's the difference between myoglobin and hemoglobin and what accounts for this difference?

Russell Chuang 1J

Ligands are elements with lone pairs that form coordinate covalent bonds with a metal ion.

Russell Chuang 1J

I am confused on where the ate for tetracyanonickelate came from?

Russell Chuang 1J

Sigma bonds should be more stable and therefore stronger than pi bonds. This due to the overlapping orbitals that sigma bonds are found in. Compared to sigma bonds, pi bonds are found in orbitals parallel to each other, therefore, they are weaker.

Russell Chuang 1J

The COFH has a larger dipole moment because it the dipole vector on the C and H bond points towards the carbon when compared to the C and F bond on the COF2. The COF2 all have dipole moments pointing away from the carbon, lowering its overall dipole moment.

Russell Chuang 1J

If a molecule with 5 bonding regions has 3 lone pair electrons, is the bonding angle still 180? I know it's labeled as linear but do the lone pair electrons affect the bonding angle?

Russell Chuang 1J

Dipole moments are differences in polarity when two atoms unequally share electrons. For instance, when a hydrogen and an oxygen bond, the oxygen holds onto the electron more tightly, thereby having a more negative charge.

Russell Chuang 1J

How does a lone pair affect the bonding angle of a linear structure?

Russell Chuang 1J

The plus symbolizes a positive charge that an atom has. The negative symbolizes a negative charge that an atom has. They have positive charge if they share less of an electron than the other atom its bonded to. They have a negative charge if they share more of an electron than the other atom its bon...

Russell Chuang 1J

How does the oxidation number correlate to the bond strength between atoms? Also, how do we find oxidation numbers?

Russell Chuang 1J

Can free radicals be Lewis bases?

Russell Chuang 1J

Similarly, as you move down the periodic table, the less pull the nucleus has on the outer valence electrons. Therefore, the ionization energy as you move down decreases. The electronegativity also decreases as you move down seeing as the atom or nucleus is not pulling electrons in well because of h...

Russell Chuang 1J

For the textbook problem, it said that NO2- was a radical. Can someone explain how NO2- is a radical?

Russell Chuang 1J

If the value for the electronegativity difference is between 1.5 and 2, how would the molecule be categorized, as an ionic bond or covalent bond?

Russell Chuang 1J

I think the same general rule applies to resonance structures, where a formal charge closer to zero is more stable. I also think that a full octet on each atom helps stabilize it.

Russell Chuang 1J

Formal charge is important in the matter of finding the most stable lewis dot structure. The further the formal charge is from zero, the more unstable a molecule is, and is therefore more improbable as the correct structure. Formal charge also helps indicate the dipole moments of a molecule.

Russell Chuang 1J

Typically, you can determine whether a molecule is polar or nonpolar by checking whether its dipole moments cancel out. Specifically, if a molecule is asymmetrical, that molecule will most likely be polar because its charge will be uneven across the molecule.

Russell Chuang 1J

A simple way to determine how many valence electrons an element has is by looking at the group number or it's relation to the end of the periodic table. For instance, calcium is in group 2, and therefore has 2 valence electrons.

Russell Chuang 1J

mL stands for the magnetic quantum number and specifies the orientation in space of the orbital or the projection of the angular momentum orbital.

Russell Chuang 1J

I think it is written d before s in situations like 3d then 4s because 3d has a lower energy level. 4s has a higher energy level, meaning that it should be placed after.

Russell Chuang 1J

Why is a covalent bond stronger than an ionic bond?

Russell Chuang 1J

The energy level for 4s is higher than 3d, therefore, you remove the electron from the 4s orbital first. This concept applies for all other elements when losing electrons, excluding copper and chromium.

Russell Chuang 1J

The shielding effect is when electrons closer to the nucleus block further electrons and thereby decrease attraction. Because of this, valence shell electrons are further away from the nucleus and the larger the atomic radius is. Nuclear charge is the said attraction between the nucleus and the elec...

Russell Chuang 1J

I don't think it's essential for the test, but just as a general benchmark for comparing answers, know the wavelengths would help for checking.

Russell Chuang 1J

I believe the p orbital does have a nodal plane passing through the nucleus. That way, electron density is forced away. And for the p orbital specifically, the nodal planes just happen to be the x y and z planes.

Russell Chuang 1J

Why is the DeBroglie Equation not applicable to photons?

Russell Chuang 1J

Why is it that the ultraviolet energy level is n = 1 and the energy level for visible in n=2, but the ultraviolet has higher energy? Is it because when transitioning to n=1, more energy is released?

Russell Chuang 1J

What is the purpose of heisenberg indeterminacy equation, as in what value does delta momentum represent?

Russell Chuang 1J

Like mentioned above, E represents energy while delta E represents change in energy. In the context of what we are learning, I think they are interchangeable, but variables like delta v in heisenberg's equation represent the how much the variation is.

Russell Chuang 1J

The two equations essentially are the same equation. As long as v and f represent the frequency and v doesn't represent velocity, they are interchangeable.

Russell Chuang 1J

Yes, the amplitude in a light wave represents the height of a wave but it also correlates to our perception of how bright the light source is.

Russell Chuang 1J

Why is DeBroglie equation not applicable to photons? Sorry got confused on it.

Russell Chuang 1J

The unexpected effect of the experiment was that increasing the intensity of light, without changing the frequency, did not eject more electrons. However, if the wavelength of the light corresponded correctly, then increasing the intensity of light would help eject more electrons that matched with t...

Russell Chuang 1J

Can an empirical formula be the same as the molecular formula? If so, how can you tell?

Russell Chuang 1J

Examples of intensive properties are things like state of matter or temperature and examples of extensive properties are mass and volume.

Russell Chuang 1J

The theoretical yield should usually be greater than the actual yield unless there is a side reaction that helps produce the desired product.

Russell Chuang 1J

From the archery example in class, if there are cluster of tight shots near the bullseye, is that considered both accurate and precise or just precise?

Russell Chuang 1J

If the coefficient of both reactants are the same in a balanced equation, how do we find the limiting reactant if we are given the grams?

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