CHEMISTRY COMMUNITY

haleyervin7

Is there any case where there must be a catalyst for a reaction to occur?

haleyervin7

Do you need the observed rate to be given for this approach?

haleyervin7

In this environmental example Dr. Lavelle explained in class today, must NO always be present for the reaction from oxygen to ozone to occur, or is it just that it makes it happen more often/easily?

haleyervin7

Is it possible to know the order based on the balanced chemical equation? What other information would you need?

haleyervin7

Celine Cheng 1H wrote:If the reaction rate is dependent on a catalyst, does that mean the substrate has to be in high concentration as well?

Dr. Lavelle said to assume the catalyst/enzyme is saturated with substrate (meaning it is already working at maximum capacity) so adding substrate doesn't change the rate.

haleyervin7

Is the purpose of the negative sign just to make sure all the rates are positive? Can you assume that all initial reactant rates are negative and therefore become positive after adding the negative sign?

haleyervin7

The reactant of the reduction half reaction is the oxidizing agent. The reactant of the oxidation half reaction is the reducing agent.

haleyervin7

Does it matter if we use Pt(s) or C(s,graphite)? Do they have the same function? Are there any cases where you could use one but not the other?

haleyervin7

Does it matter the order when they are only separated by a comma? E.g., if there are two aqueous solutions, does it matter which one we list first?

haleyervin7

How do you know when/where to add H2O or H+ to the half reactions/balanced reaction when it is not in the original reaction given?

haleyervin7

Megan_Ervin_1F wrote:Also it is just standard for the anode to appear on the left

You can remember this because it is alphabetical from left to right (anode-cathode).

haleyervin7

I think anything that will be on Test 2 is fine. He posted what would be covered on the test in his last announcement.

haleyervin7

Can deltaU ever equal deltaH?

haleyervin7

What are the requirements to be able to use q/T? Just constant temp?

haleyervin7

Does this mean in a problem that gives you the amount of liters of an ideal gas (i.e. 5 L of Ne), you’d assume the molarity is 0.2?

haleyervin7

In real life, reversible reactions are unrealistic, but we use them to approximate. Almost all real reactions are irreversible.

haleyervin7

In an open system both material and energy can be exchanged, but in a closed system only energy can. To put this in everyday terms, compare a glass of water with a sealed bottle of water. In the glass, water and heat can be added, but in the sealed bottle, only heat can be added.

haleyervin7

Since temperature doesn’t change during phase change, for steam to become water again (when it hits your skin), it has to release a lot of energy, while still at 100 degrees Celsius, and all this energy goes into burning your skin.

haleyervin7

Sometimes if you are calculating the total energy transfer, you would need to calculate heat capacity from specific heat, by multiplying by the amount of substance, so it could be useful to have the heat capacity for the amount of substance you have in the first place.

haleyervin7

What is happening physically in a system when the change of internal energy of a system is negative vs. positive?

haleyervin7

Hi, can someone please explain the units and how they cancel in the work equation?

haleyervin7

Does this mean we don't need to calculate the pKa or pKb for strong acids or bases?

haleyervin7

How can equilibrium constants be used to predict solubility?

haleyervin7

Why do solutions of weak acids have higher pH values than solutions of strong acids at the
same concentration?

haleyervin7

Is this because you are basically taking the answer you got (e.g. 10^-9) and adding it to the already existing 10^-7, so it doesn't really change from neutral?

haleyervin7

How does K differ from Kc? If there is a difference, how would you solve for K when given Kc and vice versa?

haleyervin7

How does an ICE table change when the stoichiometric coefficient isn't 1?

haleyervin7

For purposes of calculation, do we always assume it is an ideal gas?

haleyervin7

Will there be any equilibrium constants that we need to memorize for certain equations or will all the information we need be given in the problems?

haleyervin7

For the midterm and final Lavelle plans a lot of review sessions, but I would say the most helpful is Lyndon's because he goes over a review sheet that he made, but the other review sessions are more helpful if you have specific questions or topics you struggle with. The UA Karen also posts weekly r...

haleyervin7

How will we know which one to use if we aren't given the lewis structure?

haleyervin7

How do we tell which weak acid or base is strongest when given several different compounds? (Like homework problem 12.49)

haleyervin7

On one of the homework questions it asked to explain which compound was a stronger base, an it used the equilibrium constant as the justification for the answer. Does this mean there won't be a question like this on the final?

haleyervin7

How does being isoelectric affect polarizability?

haleyervin7

Since myoglobin only has one spot available, which iron binds to, how does it bind to other myoglobins to form hemoglobin?

haleyervin7

Will we be expected to memorize the names of several ligands according to the naming convention?

haleyervin7

When we are told to draw a Lewis structure that could either be cis or trans, and we are asked to determine if it is polar, doesn’t this depend on how we drew the molecule? Is there a convention that favors cis or trans when drawing Lewis structures that would help us determine if a molecule is pola...

haleyervin7

When anions or cations are isoelectric, how do we determine which has higher polarizability/polarizing power?

haleyervin7

I also had a question on this problem. On the Lewis structures for part b and c, why is there not a double bond for the oxygens?

haleyervin7

I think as long as you remember the general angles (like 109.5) then you can say how other shapes are affected by the relative repulsion strength of lone pair-lone pair, lone pair-bonding pair, and bonding pair-bonding pair.

haleyervin7

How does hybridization affect molecular shape? Does this have to do with resonance?

haleyervin7

When we are asked to estimate bond angles, such as when a lone pair causes distortion and the angle to be “slightly less than 109.5” for example, how will we know how much less it is? Will we ever be asked this on a test?

haleyervin7

The week of the 19th is Thanksgiving. I think you mean the week of Nov 26th.

haleyervin7

Do sigma and pi bonds occur in both ionic and covalent bonds or just covalent?

haleyervin7

When looking at trends, what makes more of a difference, whether an element is further to the left or right or does up and down matter more?

haleyervin7

When we draw all the resonant structures, is that just a model for how the bond is actually somewhere between a single and double, or are there actually that many different structures?

haleyervin7

When drawing Lewis structures that aren’t symmetrical, like ONF, does it matter which side the O or F go on?

haleyervin7

There is an exception with hydrogen because it will never be the central atom

haleyervin7

How will we know if something is ionically or covalently bonded?

haleyervin7

When it says we should be able to calculate the number of photons from this equation, we must have the total energy before we can do that, right?

haleyervin7

How close to the speed of light is "too close" for it to be considered realistic?

haleyervin7

I also have a question on this, how do you know how many electrons are on each orbital? Is this something that is constant between elements (i.e. the 1s orbital always has two) or does it vary from element to element?

haleyervin7

What exactly does it mean when an element is in the "p-block" or "s-block", etc?

haleyervin7

What is the relationship between number of photons and energy in the equation E=hv? Do you multiply E by number of photons?

haleyervin7

How do we know how many shells and orbitals there are for each atom?

haleyervin7

Will we have to memorize any other series besides Balmer and Lyman?

haleyervin7

Is it a good idea/necessary to memorize the electromagnetic spectrum with each type's wavelength range?

haleyervin7

What causes atoms to have a different number of neutrons?

haleyervin7

On problem G5, how do you solve part a and b where it is just asking about part of the compound?

haleyervin7

Hi, I had a similar question, except I was also wondering how you know the state of each compound when it is not given.

haleyervin7

Hi, I had a similar question, except I was also wondering how you know the state of each compound when it is not given.

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