CHEMISTRY COMMUNITY

annikaying

Does anyone know what it means for the final to be online? Do we have to print and scan or is it multiple choice or?

annikaying

open book pretty much allows you any resource you have

annikaying

What is the functional difference between a differential rate law and an integrated rate law?

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What kind of reaction would be zero order?

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What is the difference between an elementary rate law and an overall rate law?

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How do you tell if K >1 given a redox reaction?

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Can someone explain any or all of the parts of this problem to me in regard to finding the half reaction?
AgBr(s) <-> Ag+(aq) + Br-(aq)
H+(aq) + OH-(aq) -> H2O(l)
Cd(s) + 2Ni(OH)3(s) -> Cd(OH)2(s) + 2Ni(OH)2

annikaying

How would one write the cell diagram of reaction that is in an acidic solution? Is it any different?

annikaying

When writing a cell diagram, does it matter which order you put the two components of the half reaction? for example if one of the half reactions is 2I-(aq) -> I2(s), does it matter which is written first?

annikaying

In homework question 6L.5 part b, only one of the half reactions doesn't include a solid. However in the back of the book it says that both sides of the cell diagram include platinum and I was wondering why?

annikaying

What does it mean for a reaction if it is first order versus second order or any other order?

annikaying

How is temperature incorporated into finding rate? For example in class, one of the example problems said the temp was originally at 25 degrees celsius and then it was quickly heated to 300 degrees. How is this incorporated into the concentration vs time graph?

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What are the units for rate?

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What's the difference in finding the rate using just reactants versus both reactants and products?

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How can you tell whether kinetics or thermodynamics controls a reaction?

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What exactly is an electrode?

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What exactly is a salt bridge?

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What exactly causes the e to move? And on that how exactly are they moving?

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What does it mean for voltage to be negative verses positive?

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What exactly is voltage?

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How do constant pressures and volumes affect the calculations for entropy, enthalpy, and Gibbs free energy?

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How do constant pressure and temperature affect calculations for internal energy?

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What is most important in deciding if a reaction is spontaneous (ex enthalpy, entropy, Gibbs free energy)?

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why does delta H = q at constant pressure?

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Do we need to know about the rate of reactions for the midterm?

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How can you tell when you have to include the energy required for a phase change in a reaction?

annikaying

Is there a difference in equation used for when something is irreversible vs reversible besides the ones for calculating work?

annikaying

What exactly does it mean for a reaction to be irreversible? I know the definition with the infinitely small changes but that doesn't quite make sense to me on a conceptual basis.

annikaying

What is the relationship between work and heat when calculating enthalpy? Not just a formula but conceptually what it means.

annikaying

What exactly is the equipartition theorem and will we need to know it for the midterm?

annikaying

The conversion should be on the equation sheet.

annikaying

A state function is something that is not dependent on how you get to the end result. For enthalpy, it doesn't matter how you get to the value therefore it is a state function. This also implies that state functions are additive.

annikaying

The system is the actual reaction and the surrounding is everything else.

annikaying

What are some types of closed systems we might see that don't include a piston?

annikaying

How necessary is it to truly understand the calculus behind the work of expansion? Will there be questions on the midterm that specifcally ask to solve for this?

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kp is used when dealing with gases and is usually given with units like atm or bar. kc is for molar concentrations and will be given as aqueous solutions.

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No, test 1 only covers to last Friday's lecture which is outlines 1 and 2

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Do all reactions technically establish an equilibrium?

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How can you tell when a solvent is part of the reaction? For example self test 5G.3A on page 401 how was it decided which molecules are involved in the equilibrium constant?

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Are salt solutions and buffers the same thing? If not what's the difference?

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Can ph be above 14 or below 0? Or is there a specific cap at those values?

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Why does a reaction favor products when heated if is endothermic?

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How do you perform calculations with weak acids and weak bases?

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protonation is the addition of a proton and deprotonation is the removal of a proton. Protonation refers to bases usually and deprotonation to acids.

annikaying

I understand how to calculate concentrations when mixing a weak acid or base with water, but what happens when mixing a weak acid and a strong base or vice versa?

annikaying

What exactly is the relationship between kc and kp? Wouldn't a reaction with all its components being aqueous have a significantly lower kp than that of a reaction in the gaseous state? I guess I'm asking what is the point of calculating both?

annikaying

does pv=nrt only work for the individual components of K? For example if I wanted to convert kc to kp would I have to put all of the separate components into pv=nrt?

annikaying

K is a ratio and therefore is moreso a comparison than a value. You can also think of the units as canceling as the units on top equal that of the bottom.

annikaying

If you have a chemical equation in which one molecule is aqueous and another in the gaseous state, when writing K would you mix using concentration and partial pressure? Or would this not happen.

annikaying

Why were all of the phosphorus-oxygen bond lengths the same?

annikaying

What are the possible angular momentum quantum numbers of the highest energy electrons in magnesium ions? How did you go about figuring this out?

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On test two for number 7a why was the answer 14 hydrogen bonding sites?

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What factors affect the bond strength of an acid when going down a group?

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How are pi bonds incorporated into hybridization?

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Combustion implies that the reactant given is reacting with O2.

annikaying

You have to be given the actual bond length from previous experiments but there are general guidelines such as double bonds being shorter than single bonds.

annikaying

During lecture a lot of emphasize was placed on oxides and I was wondering what specifically oxides have to do with acids and bases?

annikaying

What exactly is the difference between Lewis acids and bases and Bronsted acids and bases?

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How do double bonds affect hybridization?

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Intermolecular forces are the only thing that determine melting and boiling points. Therefore having a double bond doesn't affect the melting point.

annikaying

How do you determine if the shape formed will be polar or non polar? For example if a molecule can be either cis or trans(CCl2H2) how do you tell if you are asked to determine if the molecule is polar or non polar?

annikaying

Which intermolecular force is strongest? I though it was hydrogen bonding, but now I'm wondering if intermolecular forces involving ions are stronger.

annikaying

Are induced dipole forces the same as London dispersion forces? Also does induced dipole only occur between a polar and non polar molecule?

annikaying

The more bonds there are (triple versus single) the shorter the bond is. This is because there are more e being shared and thus both atoms are pulled in closer together.

annikaying

I would convert it to an integer as the TAs always change it and they are the ones that grade the tests and homework.

annikaying

formal charge = V - (L + B/2)
V - valence e
L - e in lone pairs
B - e in bonded pairs
This will give you the formal charge of one atom in a molecule. To find the formal charge add of the formal charges of all the individual atoms.

annikaying

If the molar mass given is equal to that of the empirical formula then the chemical formula found is both the empirical and molecular formula.

annikaying

Everything that is needed should be provided. However, knowing the conversions definitely helps with exams.

annikaying

H2O is bent. I'm assuming we will cover molecular shapes with lone pairs sometime in the next week.

annikaying

A resonance structure only has a difference in the placement of double and triple bonds. I think formal charges would determine which of the resonance structures is most likely, but you only need to look at bonds to see if there is resonance.

annikaying

Does anyone know if Lewis acids and bases will be on the first midterm? And which topics are going to be covered?

annikaying

Which elements can break the octet rule when forming lewis dot structures and is it likely or just when necessary?

annikaying

How do you determine the lowest energy lewis structure? For example some structures break the octet rule to get the lowest energy structure. Does that mean formal charges are more important than the octet rule in determining the lowest energy?

annikaying

What are some of the exceptions to periodic trends? For example O has a lower ionization energy than N.

annikaying

You can look at the electronegativity difference to determine if the bond is ionic or covalent but typically you can just go off of whether or not the two atoms are both nonmetal (which gives a covalent bond) or if they are a nonmetal with a metal (which gives an ionic bond).

annikaying

What is the max number of valence e an atom can have? I know there is the octet rule but is that just where the atom is most stable?

annikaying

When drawing a lewis dot structure does it matter where in the molecule you put the added e ? For example when you have BrO- does it matter where that extra electron is added into the structure?

annikaying

Are ionic compounds actually bonded and if so how? I understand e are being transferred but how does this transfer differ from a covalent bond in which they are shared?

annikaying

How do you count the valence e in the d block? For example how many valence e does Zn have and why?

annikaying

You can cheat if you have a graphing calculator as you can store equations and notes in it.

annikaying

Molarity is the ratio of the moles of a solute to the liters of the entire solution. This is used to measure the concentration of a specific amount of a substance to the entire solution.

annikaying

Does anyone know if the midterm/final is going to be more about concepts or calculations? For example which is more likely an essay question or a calculation?

annikaying

An angstrom is equivalent to 1 x 10^-10 m. I personally compare the values of 10^x to see which way the decimal point needs to move to be in angstroms.

annikaying

Are there any tricks to memorizing which orbital electrons fill up first?

annikaying

The threshold energy depends on the type of element as different elements have different properties.

annikaying

Polar molecules have an uneven hold on the electrons whereas in non polar molecules the electrons are shared equally or mostly equally. You can tell just by looking at the electronegativity differences of the certain elements.

annikaying

Why is the line spectrum grouped in specific parts? I know it has to do with the specific releases of energy but how exactly to the two correlate?

annikaying

Can an atom only take in energy in quanta amounts? I know it is released as such but if struck with light will it only move up an energy level if that specific energy requirement is met? And if so does that mean it would need a second energy requirement to move up another level?

annikaying

I was wondering if when an electron drops two energy levels does that mean that two photons are released or is it just a photon with more energy?

annikaying

The products always include CO2 and H2O but there can also be additional products depending on what is being combusted. For example the combustion of caffeine (C8H10N4O2) also produces the product NO2 alongside CO2 and H2O.

annikaying

If you are given a formula and a given mass you can calculate the molar mass of the compound and see if the two masses are equal. If they are equal then the given formula is empirical. If not, then it is a molecular formula. You also may be able to tell by checking if the ratios are all in their sma...

annikaying

I know in some of the hw problems there are examples in which the masses of the products are given and from there you have to find out the empirical and molecular formulas of the reactant. To solve this you eventually have to take a ratio from the atoms in the product to the reactant (ex. 1 mol H/2 ...

annikaying

Doing practice problems usually helps me for tests. I will also say that jitters before the first test are definitely worse than following tests as you have less of an idea of what to expect. I would just prepare as best as you can and use your experience with the first test to help you study for fo...

annikaying

Is it necessary to imagine that you have 100g of a molecule when trying to figure out the empirical and molecular formulas? You are trying to convert everything to moles, so if you are originally given grams of the different chemicals in the molecule, could you not skip the conversion to mass percen...

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