CHEMISTRY COMMUNITY

IScarvie 1E

For a simpler example, ice melting to water at room temperature is favorable (low enthalpy high entropy), but water freezing into ice is not.

IScarvie 1E

This confused me too, but the thing to remember is that the equation is solving for the change in entropy, not entropy itself, and the temperature in the equation is a constant, not change in temperature. If a system is already at high temperature and the molecules are excited, it's change is entrop...

IScarvie 1E

Temperature is a number directly proportional to the energy of a system (at least when you're working with ideal gasses, which we are). So when there is no change in T, there also cannot be any change in U.

IScarvie 1E

A closed system can exchange energy with its environment, but an isolated system cannot.

IScarvie 1E

Everything on outlines 1-4 will be covered.

IScarvie 1E

In lecture today we learned that most biochemical reactions are very irreversible and that few reactions are truly reversible, but we assume that they are when we want to solve for the maximum entropy.

IScarvie 1E

A normal calorimeter is an open system, while a bomb calorimeter is a closed system, so you can assume volume is constant

IScarvie 1E

If we need to use these values they will be provided to us on the test.

IScarvie 1E

If the temperature raises from 25 to 27 C, by converting to K it is being raised from 298 to 300 K. However, the change in temperature for both is still 2. Therefore doesn't matter if you use kelvin or Celcius to measure delta T (unless you need to cancel out units later in the problem).

IScarvie 1E

Both are acceptable, however Standard Enthalpy of Formation is required to be in kJ/mol.

IScarvie 1E

If delta H is noted to be at STP, then you can assume it is at 25 degrees C. If not, the temperature should be stated

IScarvie 1E

Typically when you are solving for x from an ICE table and x is not less than 10^-3, it will be easiest to solve with the quadratic formula

IScarvie 1E

Yes, when a reaction proceeds to the right, it forms products

IScarvie 1E

Every K value correlates to a temperature. When you are given a table of k values, make sure you pick the one that correlates to the temperature you are given

IScarvie 1E

H2O is in excess, so the change in concentration is negligible

IScarvie 1E

1.8x10^-5 expanded is the same thing as .000018. .1-.000018 = .09999 something, which is very very close to .1. So when x is very small, it will not affect the constant in any significant way

IScarvie 1E

This is why every time we are given a K value we are also given a temperature at which the reaction took place. At different temperatures, the K value will be different.

IScarvie 1E

The brackets are strictly used to show that we are dealing with molar concentrations, and are used to solve for kc. Parenthesis and kp are used to deal with pressure

IScarvie 1E

When a reaction reaches equilibrium, no matter how many products or reactants you start with, you will always have the same ratio of products to reactants, K. So if you were to take a sample of the reaction before it reached equilibrium, measure the concentrations of reactants and products, and foun...

IScarvie 1E

No, because they are pure substances and therefore don't have concentrations to use in the ratio

IScarvie 1E

Chemical equilibrium means that the net change of the forwards and reverse reactions cancel out, so there is a constant, k, that expresses the ratio of the products and the reactants at equilibrium. This doesn't mean they have equal concentrations (it's very rare for k to be 1), but it does mean tha...

IScarvie 1E

I believe yes, because not all acids and bases lose or accept protons.

IScarvie 1E

Acids donate protons, bases accept them

IScarvie 1E

So far, yes

IScarvie 1E

A chelate is a ring structure of ligands around a central metal ion

IScarvie 1E

An acid or base must dissociate completely to be strong. Otherwise, it is weak

IScarvie 1E

A lewis acid/base accepts/donates electron pairs, while a bronsted acid/base donates/accepts protons

IScarvie 1E

The bonds they would form are stronger than the ones the H2O are forming, so they force the H2O out of the way

IScarvie 1E

It confused me too, I tend to remember it by thinking that bases usually go from a relatively negative charge to a relatively positive one (by donating a lone pair or accepting a proton) and acids do the opposite

IScarvie 1E

When an acid is dissolved in water, the hydrogen will dissociate and bond with a water molecule, forming H3O

IScarvie 1E

A chelate is a complex containing at least one ligand that forms a ring of atoms that includes the central atom.

IScarvie 1E

A chelate is a complex containing at least one ligand that forms a ring of atoms that includes the central atom.

IScarvie 1E

When the molecule is a long chain, you determine the shape of each portion of the chain around each central molecule separately

IScarvie 1E

The names are mostly pretty intuitive, it's usually most helpful to envision the molecule in a three-dimensional space. I also use flashcards for some of the harder ones like seesaw.

IScarvie 1E

Instantaneous dipoles are momentary moments where one side of the molecule will be more electronegative than the other as electrons move around the nuclei. When two nonpolar molecules are next to each other, these instantaneous dipoles form induced dipoles, as the temporarily negative side of one is...

IScarvie 1E

No, the shape doesn't vary

IScarvie 1E

If you can remember what the shape looks like three-dimensionally, most of the angles (except 109.5) are pretty intuitive. For example, for the trigonal bipyramidal shape in a 3d space, you can see visually where the 90 and 180-degree angles are.

IScarvie 1E

Another important thing to remember is that CH4 does not form hydrogen bonds because C is not electronegative enough. It follows the normal dispersion rules, and Cl has more electrons than H

IScarvie 1E

Another way to think about it is that O is more electronegative than S, so its dipole moments are more dramatic than H2S's. The positive and negative ends form stronger bonds because of it.

IScarvie 1E

since F, O, and N are the three most electronegative elements, and H is very positive, hydrogen bonds are very strong and hard to break apart

IScarvie 1E

You can tell if a molecule is polar if one side is more electronegative than the other. I like to think of dipole-dipole bonds like magnets; if two things with positive and negative sides are close together, the positive will bind with the negative.

IScarvie 1E

When you have a Lewis dot structure where a double bond could be placed with a different atom of the same element and the formal charges would not change, you draw the structure each way it is possible for it to form and draw arrows between the structures, showing that they are interchangeable

IScarvie 1E

The arrow point should point towards the negative dipole, the + should point towards the positive.

IScarvie 1E

There is a biological theory of aging that revolves around free radicals. Basically, it’s thought that as the radicals bind to parts of the cell they wear it down over time, especially DNA.

IScarvie 1E

A Lewis acid is a lone pair acceptor, and a Lewis pair is a lone pair donor. I believe they are similar to covalent bonds, except they typically form as separate molecules and join to fulfill their individual needs

IScarvie 1E

Some elements are more electronegative than others; for example, Fluorine has more protons in its nucleus than Carbon, so it will pull on electrons in a covalent bond more strongly.

IScarvie 1E

I typically give each atom around the center an octet first and adjust from there with double bonds and single pairs in the center, but I think both ways work

IScarvie 1E

In general, hydrogen likes to have one bond, oxygen likes two, nitrogen likes three, and carbon likes four. When you decide where to put double bonds or triple bonds, arrange them so that the most atoms have 0 formal charge and all the electrons are used, which usually follows the rules above.

IScarvie 1E

I think it depends on the element but in general, I think I remember size and shielding being more influential on atomic radius than electrostatic interactions between the protons and the nucleus. However, both are important to consider, and I don't think there were any questions in the homework whe...

IScarvie 1E

I believe he said in our lecture on Friday that we don't need to know how to find the bond lengths in this class, just that double bonds are shorter than single bonds between the same two elements, and bonds in resonant structures are between those two lengths.

IScarvie 1E

I believe in this class you have to draw them in order to ensure that each atom gets the right number of electrons in the structure

IScarvie 1E

Yes, they do overlap, especially in electrons with more shells further from the nucleus. Like the last responder said, the probability isn't necessarily doubled, but it is influenced by the extra shell

IScarvie 1E

Inner electrons feel more electrostatic attraction from the positively charged nucleus. This charge is stronger the further down the periodic table you go, so the inner electrons in those atoms are closer to the nucleus. Outer electrons are shielded from this pull by the inner electrons, so they are...

IScarvie 1E

Nodal planes are planes in the p, d, and f orbitals with zero electron density probability. In other words, there is no likelihood of finding an electron in that spot.

IScarvie 1E

You use Hund's rule and the Pauli Exclusion Principle together to write the ground-state electron configuration of an atom. Hund's rule tells you to fill in orbitals with one electron each with parallel spin before doubling up, and the Pauli Exclusion Principle tells you to give the paired electrons...

IScarvie 1E

An orbital has three quantum numbers, while a shell is only defined by n

IScarvie 1E

It's nice to have them memorized because they are used often, but they will be given to us on tests

IScarvie 1E

Black bodies are an idealization; an actual black body that emits and absorbs all frequencies does not exist. Stars are approximately like black bodies, but not exactly

IScarvie 1E

If an electron is removed with zero kinetic energy or the energy of the light is the same as the energy required to remove an electron, you can use the energy of that light to calculate the minimum frequency

IScarvie 1E

Yes, it only applies in a vacuum, but unless the question specifies otherwise, I think you can assume it applies

IScarvie 1E

In a photoelectric experiment, the kinetic energy is also measured by a detector

IScarvie 1E

This came up in our discussion today, and generally if it's within .1 of the whole integer you want to round to it's ok. You could round 2.9 to 3, for example.

IScarvie 1E

My TA said in discussion today that we will be provided with a periodic table and an equation sheet. Hope that helps!

IScarvie 1E

It's a good idea to start writing the state symbols now so it becomes a habit. They are very useful for understanding what is physically happening in the reaction, and they may be required later on.

IScarvie 1E

I believe when you are told to write an equation for a combustion reaction, you assume the products will be CO2 and H2O. However, sometimes you will be given other products, like in homework problem M19.

IScarvie 1E

The empirical formula is not used in chemical equations because it only shows the simplest ratio of the atoms in the molecule, not the actual number of atoms present. It can be used, along with the molar mass of the molecule, to find the molecular formula, which does tell you the number of atoms pre...

Search found 66 matches