CHEMISTRY COMMUNITY

Andrew Nguyen 2I

what was the name of the first electricity detective?

Sherlock Ohms

looooolllll

Andrew Nguyen 2I

How do you distinguish between a catalyst and intermediate given reaction mechanisms? Can someone give an example with both also?

Andrew Nguyen 2I

I was wondering for why in the solutions to 15.63 it says K = k'/k

I thought K = k/k' always. Can someone explain?

Andrew Nguyen 2I

Just wanted to clarify - in a multi-step reaction, if the first step is a slow step does that mean the overall reaction rate should be the rate of the slow step? And if the first step is a slow step and a latter step is the slow step we have to take into account both the first and slow step? If I'm ...

Andrew Nguyen 2I

I think the slides in class have been using indefinite integration; though there are a lot of sources which tell you how to get the same equation with definite integration. For the most part the algebra and calculus is very similar up to the last step. Nonetheless, both ways can give you the same eq...

Andrew Nguyen 2I

A lot of sources say something like this is too complex to determine if reactants and products are expressed in the rate law; however I would just use the rules we've been taught by adding the powers up as integers, where powers in the denominator are simply negative numbers.

Andrew Nguyen 2I

Use log rules if the order is not obvious from observation. For this you get something like 2.416^b = 5.8 as said by the person above. use the log power rule by taking the log of both sides; this takes b down getting b*log2.416 = log 5.8 solving for b should give a number very close to 2 indicating ...

Andrew Nguyen 2I

I've seen the precipitate and solution one like 20 times on facebook - it's not even funny anymore

Andrew Nguyen 2I

The unique rate is the specific rate for the reaction (it does not relate directly to any reactant/product's individual rate in the reaction). However, using the stoichiometric coefficients of the reactants/products, the unique rate can be used to find the specific reactants'/products' individual ra...

Andrew Nguyen 2I

Always look for 2 experiments which keep all concentrations reactant except for one reactant for the first step. After that you can find the order of another reactant where the first reactant (which you found the rate for previously) can also be changing since you already have the rate of it.

Andrew Nguyen 2I

Sometimes the order number can be seen by simple observation, though it's better to have a foolproof method for rates like this. The rate changes by a ratio of 50.8/8.7 and the concentration by 3.02/1.25 So, simply equate the concentration raised by the order number equal to rate (3.02/1.25)^x = 50....

Andrew Nguyen 2I

The solutions say that the correct statement is A. I was wondering if this was a typo?

Andrew Nguyen 2I

How are we supposed to know to use 25 degrees Celsius for the temperature?

Andrew Nguyen 2I

For 14.27 ; we are supposed to find two delta G's from the two standard reduction potentials and then add the two delta G's to find the delta G for the desired reaction; why can't we just add the standard reduction potentials - does this not work to give the standard reduction potential of the desir...

Andrew Nguyen 2I

thanks

Andrew Nguyen 2I

Since potassium permanganate and iron(II) chloride are asked to be used, how are we supposed to know which element in each compound is the electrode element; like for potassium permanganate - how do we know that potassium is not at the electrode, and also for iron(II) chloride. Also, after we find o...

Andrew Nguyen 2I

Why is the free energy related to Q while the standard free energy is related to K?

Andrew Nguyen 2I

I understand how the cell potential is intensive from the equation of the free energy and the cell potential; though I was wondering if anyone knows how this could be explained conceptually.

Andrew Nguyen 2I

Also the internal energy of an ideal gas is determined by the temperature so if there's no change in temperature there can be no change in internal energy for the gas.

Andrew Nguyen 2I

Could someone explain?

Andrew Nguyen 2I

How would I go about calculating degeneracy (W) given a molecular formula?

Andrew Nguyen 2I

Why is the total change in entropy 0 for reversible processes? Also is the total change in entropy the same thing as the change in entropy of the universe?

Andrew Nguyen 2I

Can someone explain why the half reactions are written as such based on the cell diagram - for the left side of the cell diagram it says Pt(s) ; H2(g); HCl(g) where the semicolons represent the lines in the cell diagram. I was wondering why this half-reaction was then 1/2H2 = H+ + e- I thought it wo...

Andrew Nguyen 2I

I'm still a little confused about how to find what the degeneracy (W) is. I know what the definition is though, I noticed there were several types of problems regarding such. I recall a picture of a flask example and finding the degeneracy from the formula of a compound. If anyone recalls these exam...

Andrew Nguyen 2I

I was wondering for the entropy of reaction and entropy of formation; is the entropy for formation simply a specific type of entropy of reaction - like if the reaction equation represents 1 mole of compound being formed would this make the standard reaction entropy = standard entropy of formation. A...

Andrew Nguyen 2I

Can someone explain what the molar entropy value is for products/reactants. I was wondering why for the enthalpy of formation of products/reactants it didn't mention anything like the "molar enthalpy of formation", etc. and why entropy has such a term? Also is there a difference between st...

Andrew Nguyen 2I

So in the book it mentioned something about using the molar numbers vs the pure numbers in a chemical equation (in which the pure numbers are purely the stochiometric numbers), while the molar numbers are the coefficients as moles. I was wondering if using either one mattered (like if we could choos...

Andrew Nguyen 2I

Can someone explain why a negative free energy of formation indicates a stable compound with respect to decomposition; it didn't seem to make sense intuitively since if it was negative, it would have a tendency to decompose - or is it that, the negative delta G is actually referring to the formation...

Andrew Nguyen 2I

I was wondering why in this figure on page 331 it says at the top where it says example 9.7- calculating the entropy of the system - "b)the four molecules lie in random orientations (but parallel, any of the images in Fig. 9.7)." Is it saying that all the molecules in the figure except for...

Andrew Nguyen 2I

Can someone explain how if the reaction is reversible or irreversible affects the calculations for entropy - with conceptual explanations also?

Andrew Nguyen 2I

In the book there were entropy values given for vaporization and fusion I believe. I was wondering if there were entropies for the reverse processes then such as condensation - would it just be the same value with different signs?

Andrew Nguyen 2I

Can someone explain why the entropy must be calculated both for changes in temperature/volume and also just from phase changes?

Andrew Nguyen 2I

I believe it is called irreversible because the large change in volume in a quicker process, makes it difficult to compress the gas/system back to its original volume. In a reversible process the external and system pressures are very close in value at each step, so the change in volume is so small ...

Andrew Nguyen 2I

When T is being used in an equation - is there a set rule for when to use Kelvin or Celsius, or any time it is better to use either of the two?

Andrew Nguyen 2I

Why are the bond enthalpies for H-H about 300-400 kJ/mol, but the enthalpy of formation for H-H zero kj/mol?

Andrew Nguyen 2I

Can someone explain the difference between the two - also does standard enthalpy account on a per 1 mole basis while enthalpy with a chemical equation correlate with the coefficients?

Also is there a different symbol for enthalpy and standard enthalpy?

Andrew Nguyen 2I

Why does the heat capacity depend on the volume and pressure, and if they are constant or not?

Andrew Nguyen 2I

So, I know how the enthalpy equation is derived to equal the heat added to a system. Though - why is it possible to say enthalpy = U+PV I'm a little confused about what enthalpy is I guess and why its equation makes sense. Also in H = delta U + PdeltaV what is PdeltaV symbolizing, since delta U = q ...

Andrew Nguyen 2I

Is specific heat capacity a constant - i.e. the specific heat of a substance doesn't change, while heat capacity depends on the context of the problem?

Andrew Nguyen 2I

Can someone explain why mercury in a thermometer is an open system (obviously it can transfer mass+energy), but how?

Andrew Nguyen 2I

I'm a little confused by what is and isn't a state function. Some values like enthalpy only give the value at one current state and therefore do not depend on the path taken to get to such value, while work does depend on its pathway. Essentially is what determines if a value is a state function, th...

Andrew Nguyen 2I

Can someone explain the difference between heat capacity and specific heat - I was a little confused by the book's explanation and somewhere it says the energy needed to raise "one unit mass" of a substance by 1 degree celsius. Could someone explain the difference between the two terms the...

Andrew Nguyen 2I

I remember Lyndon stating that while the explanation is more complicated, a simple way to think about it is that the molecule will tend to favor an octahedral structure (the most common structure for coordinate complexes) with a coordinate number of 6. Since the complex is currently at a coordinate ...

Andrew Nguyen 2I

For the base thymine, I was wondering, why can't the oxygens accept H+ also?

Andrew Nguyen 2I

Can someone explain how the solvent affects acid strength, specifically in the context of problem 12.115. I'm having some trouble understanding why the answer is such.

Andrew Nguyen 2I

Did Dr. Lavelle mention in lecture if using H+ in the molecular formula in lieu of H3O + was acceptable?

Andrew Nguyen 2I

Can someone explain why increasing the number of oxygens, increases acid strength? Also why does adding more electronegative atoms have the same effect?

Andrew Nguyen 2I

First step is to write the molecular equation (this is what we typically write); also net ionic equations are often written in the context of reactions where aqueous substances are present, along with solid substances (so often precipitate/double replacement reactions (the problems which involve suc...

Andrew Nguyen 2I

K is the equilibrium constant using partial pressures (this would imply a homogeneous mixture of gases alone I believe). Kc is the equilibrium constant using the concentrations/molarity (this may involve gases alone, or a mixture of gases and aqueous components). If the problem gives the partial pre...

Andrew Nguyen 2I

Can someone explain when to use di vs. bis, or tri vs tris, with examples of both used

Andrew Nguyen 2I

I forgot if Dr. Lavelle mentioned this, though did he say it was ok to use the old method of naming ligands instead of the new IUPAC method. Like writing cyano instead of cyanido.

Andrew Nguyen 2I

This is more of a Lewis structure question however I was wondering why Sn-Cl2 only has 6 valence electrons around it in the molecule; obviously this is an exception to the octet rule, though I was wondering if anyone could explain this.

Andrew Nguyen 2I

b) asks to give the formula for : pentaammine-sulfato-colbalt (III)- chloride

In the formula and bracket colbalt goes first, however I was wondering if it mattered if the amine group or sulfate was written first in the formula; so if it matters if (NH3)5 goes before (SO4) or vice versa.

Andrew Nguyen 2I

What exactly does it mean when a ligand is described as "attaching directly" to the central metal atom. It seems like the word "directly" is emphasized. Is there a conceptual idea behind this, or am I looking too much into this - is there a reason it is said to attach "direc...

Andrew Nguyen 2I

What exactly is the relation of promotion to hybridization - my thought process had seen promotion as a means for carbon to form 4 bonds; then hybridization would be used to adjust the VSEPR theory to account for carbon's tetrahedral shape (4 hybrid orbitals instead of 3, 90 degree 2p orbitals). Not...

Andrew Nguyen 2I

Yes, the bond length does decrease if it is a single, double, or triple bond - its multiplicity. This can be sorted out intuitively, knowing that the higher the multiplicity, the stronger the bond and the pull, resulting in a shorter length between the connected atoms (the bond length).

Andrew Nguyen 2I

The VSEPR formula is denoted as AXE where X may have "A" represents the central atom (you write it as A) and X may have a subscript with a number to represent the number of bonded atoms are bonded to the central atom; if it is 1, then it is simply written as X with no subscript. E would be...

Andrew Nguyen 2I

For number 23 It gives the uncertainty in position as "+-5 m" We then use 10 as the uncertainty in position to account for the +- range of 5m however in number 1.45 in the textbook A ball is described as rolling down at 5m/s with +-5m/s; the solutions manual uses 5 then as the uncertainty ...

Andrew Nguyen 2I

I'm a little confused about how CH2Cl2 is polar. In terms of its shape it creates a tetrahedral, yet it seems like the vectors for identical atoms would cancel out in any form if we look at a 3D picture of a tetrahedral. Can someone explain why I'm going about it wrong; perhaps with a picture of the...

Andrew Nguyen 2I

This type of notation is to emphasize which ion lost the electron(s) (cation) and which atom gained the electron(s) (anion). This notation just creates emphasis and decreases confusion in which atoms the electrons belong to. From what I've seen you can do this one bracket method or simply put both t...

Andrew Nguyen 2I

For ionic compounds, I saw a lot of lewis structures drawn with one ion in a bracket and the other ion outside of the bracket. For example in the solutions manual, for K3P it shows phosphorus in a bracket with the three potassiums on the outside. How do we know which ion belongs outside or inside a ...

Andrew Nguyen 2I

The Lewis Structure for HOCO is asked to be drawn. My question pertains to many other examples, but this molecule is just one example of my question. For HOCO, how do we know if the hydrogen is attached to the oxygen or the carbon. Or for something like XeOF2, knowing Xe is the central atom, how do ...

Andrew Nguyen 2I

Zeff talks about electrons penetrating the nucleus while other electrons are less able to penetrate such making it less susceptible to the pull of the nucleus. Electron shielding talks about how certain electrons are closer to the nucleus due to a lower shell, while other electrons are in a higher s...

Andrew Nguyen 2I

I've noticed after doing some of the problems that the d-block elements fill up the orbitals in the d-block before the previous s-block, which goes against certain patterns from before. Is this a correct observation and if so, could someone explain why this occurs?

Andrew Nguyen 2I

The answer saying that the absorption lines have the same principal quantum number mean the lines in each series (so all the similarly placed lines in the Balmer seires, Lyman, etc. , not lines from different series). The quantum number determines the energy state of the atom's electron. As the elec...

Andrew Nguyen 2I

Can someone explain the relationship between photons and electrons. When E=hv is used, the energy of the photon is discussed, but is the electron involved in this equation at all?

Andrew Nguyen 2I

So Dr. Lavelle stated that we should begin balancing the equation by balancing the element present in the least number of reactants/products. For example P4O10 + H2O = H3PO4 ; we should start by balancing either phosphorus or hydrogen since both are in two reactants/products. Next, both phosphorus a...

Andrew Nguyen 2I

So for this problem, it's saying that from the calcium carbonate's decomposition, a certain amount of CO2 is produced. I know that the percentage yield should be the actual yield over the theoretical yield. But just to confirm, do I assume that the theoretical yield in this case is 42.73 g (100% for...

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