CHEMISTRY COMMUNITY

Anna Heckler 2C

t can be in seconds, minutes, or hours, but MUST be consistent across all terms or it will mess up your calculations.

Anna Heckler 2C

If the k value is very small (i.e. less than 10^-4) then you can approximate.

Anna Heckler 2C

Used in the Arrhenius equation, the frequency factor is used to describe the rate of molecular collisions.

Anna Heckler 2C

The collision model explains why most collisions between molecules do NOT result in a chemical reaction.

Anna Heckler 2C

The slowest step in the reaction determines the overall rate law.

Anna Heckler 2C

The purpose of a salt bridge is to maintain charge balance because the electrons are moving from one half cell to the other. Without a salt bridge, the solution in the anode compartment would become positively charged and the solution in the cathode part would become negatively charged. This would c...

Anna Heckler 2C

Molecularity is the number of molecules that come together to react. It is equal to the sum of the stoichiometric coefficients. (ex. unimolecular, bimolecular, etc.)

Anna Heckler 2C

In basic solutions you won't have a higher concentration of H+, so you add OH- to counteract the acidity.

Anna Heckler 2C

A zero order reaction describes a reaction where the reaction rate is constant and independent of the concentration of reactants. The rate of reaction is proportional to the zeroeth power of the concentration of reactants.

Anna Heckler 2C

You will commonly see an inert solid added to the cell diagram when the other components are in their aqueous form. You need the inert solid when there are no other solid metals in solution.

Anna Heckler 2C

ln[A] is used in order to yield a graph with a straight line, because otherwise it would yield a graph showing exponential decay. A graph with a straight line can be used to easily find the slope, which is equal to -k, giving us the equilibrium constant.

Anna Heckler 2C

While a reaction is spontaneous, its activation energy could be so large that it occurs at an incredibly slow rate.

Anna Heckler 2C

No, redox reactions change the oxidation numbers, which does not occur in all reactions.

Anna Heckler 2C

Platinum is commonly used and can be a go-to choice in our examples, but any inert metal will suffice.

Anna Heckler 2C

Q should be used when the reaction is not at equilibrium.

Anna Heckler 2C

The order of the reaction tells us how the overall rate of reaction is affected by the concentration of the reactants, basically providing a relationship between reaction rate and reactant concentration.

Anna Heckler 2C

Platinum won't get oxidized or reduced. The reactants in the electrolyte get oxidized/reduced at the surface of the inert electrode.

Anna Heckler 2C

Using deltaH, the Van't Hoff equation relates the equilibrium constant, K, to temperature, T.

Anna Heckler 2C

The oxidation number of simple ions is equal to the charge of the ion. When calculating oxidation numbers, we can use known oxidation numbers to find the unknowns.

Anna Heckler 2C

A galvanic cell is in equilibrium and has a voltage of 0 when Ecathode=Eanode.

Anna Heckler 2C

Yes, you must add to both sides in order to form a neutral H20 that would not alter the reaction.

Anna Heckler 2C

An adiabatic process occurs without transfer of heat or mass of substances between a thermodynamic system and its surroundings.

Anna Heckler 2C

The first law of thermodynamics tells us that the internal energy of a system can be increased by adding energy to a system or doing work on a system. There are many processes through which this could be accomplished, as long as energy is conserved.

Anna Heckler 2C

When you are finding the work done in a reversible pathway, you must find the sum of a series of infinitesimal steps, which can be accomplished using an integral. The work done by an irreversible pathway involves a rapid change in volume and pressure, so a different formula is used.

Anna Heckler 2C

Extensive properties depend on your sample size. Specific heat capacity, for example, is an extensive property since it will increase with a greater sample size (requires more energy to increase the temperature of a larger sample by one degree celsius than a smaller sample size).

Anna Heckler 2C

Gibbs free energy will allow you to determine if the reaction is spontaneous or not (based on the sign). Also enthalpy can be used, as negative enthalpy means the reaction is exothermic since it is releasing heat.

Anna Heckler 2C

Determining the sign of work is based on what you decide is your system and what is your surroundings - it's relative. Positive work means that work was done on the system, so it gains energy. Negative work means that work was done by the system, and the system loses energy.

Anna Heckler 2C

The biggest concern with units is just making sure that everything you are calculating is in consistent units. A given question may ask for different units, so just pay attention to that and make sure that you use the correct constants.

Anna Heckler 2C

ΔHfusion and vaporization are given values, so you do not need to worry about memorizing them!

Anna Heckler 2C

A gas will expand to fill any volume. Therefore, if the volume increases, the pressure of the gas will decrease as the gas fills the entire container.

Anna Heckler 2C

Gas molecules "occupy more space" since they have a higher entropy, meaning higher disorder, so their location at a given time is less known.

Anna Heckler 2C

Intensive properties don't depend on sample size, whereas an EXtensive property does depend on sample size. We can conclude that entropy is an extensive property because entropy increases when there is more of a sample present.

Anna Heckler 2C

It will be obvious which method to use since each one has different steps and requirements. So the problem will provide multiple equations for Hess' Law, and a table of standard enthalpies of formation for this method.

Anna Heckler 2C

The work equation has a negative sign to represent the loss of energy from the system when it does work on the surroundings. But, the sign of the equation is relative. If compression is occuring (i.e. work is being done on the system) then the work equation has a positive sign.

Anna Heckler 2C

The SI unit for enthalpy is joule per kilogram. However, it can be expressed in different units (not SI).

Anna Heckler 2C

A molecule can only be canceled if it occurs in the same number of moles on the reactant and product side. This means they are balanced and can cancel.

Anna Heckler 2C

The standard form of a molecule has given values associated with it. The standard form is observed at 25 degrees Celsius, 1 atm.

Anna Heckler 2C

If the reaction is endothermic, the reaction requires heat and the surroundings cool down. Adding heat to an endothermic reaction means that the forward reaction will be favored.

Anna Heckler 2C

The standard enthalpies of formation is a value that is given for molecules and used to calculate the overall standard enthalpy of formation of a reaction.

Anna Heckler 2C

If the temperature is increased in an endothermic reaction, the reverse reaction is favored. Adding heat to a system that overall released heat in the forward direction does not favor the formation of more product.

Anna Heckler 2C

Heat capacity is a given value.

Anna Heckler 2C

Work is not considered a state function because the amount of work done is dependent on more than just the initial and final values - it depends on the path taken to get from the initial to final values.

Anna Heckler 2C

Water is not included if it's in its liquid state because it is considered a solvent. If it is in its gaseous form, then it is included in calculations.

Anna Heckler 2C

If X is smaller than 10^-3, then the affect of subtracting this value from the denominator is negligible.

Anna Heckler 2C

Enthalpy is a state property because the "path" taken to get from the initial to final value is not important.

Anna Heckler 2C

Use the gas constant that has the same units as the other values you are using in the calculation. For example, if your pressure is in atm, then use the gas constant that has the unit with atm (so they match and cancel).

Anna Heckler 2C

N is determined by the moles of gas, or put more simply, the concentration.

Anna Heckler 2C

These all mean effectively the same thing.

Anna Heckler 2C

Changing the pressure does not affect K, as K is a constant and all of the pressures would change by the same factor. Temperature DOES change K.

Anna Heckler 2C

Changing the concentrations of R or P does not affect K because K is a constant. It changes Q, and so you can calculate Q to tell you know the reaction will proceed to return to the given ratio of K.

Anna Heckler 2C

You can convert between Kp and Kc using the ideal gas law. Kp is used for partial pressures of gases, whereas Kc is used for concentrations.

Anna Heckler 2C

Q can be thought of as a snapshot of the reaction concentrations at a moment in time. K is a value that does not change, remaining the same throughout the whole reaction. If Q is greater than K, there is more product than would be found when the reaction is at equilibrium, so the reaction will proce...

Anna Heckler 2C

You add the -ate when the complex is negatively charged. When it is neutral or positively charged, you leave the name as it normally is.

Anna Heckler 2C

pH = -log[H+]
pOH = -log[OH-]

Anna Heckler 2C

Hydrogen bonds are, in essence, the strongest type of dipole-dipole interaction. Ionic bonds will always be stronger than dipole-dipole/H bond interactions.

Anna Heckler 2C

We will be given the ionization constants (Ka and Kb) if needed

Anna Heckler 2C

In the cis-molecule, the chlorines are on the same side. They bond to adjacent guanines by kicking off a nitrogen on a DNA molecule. The trans-platin version of the molecule has Cl's oriented on opposite sides, so when one of the Cl's binds to a guanine, the DNA Polymerase can easily kick off the Cl...

Anna Heckler 2C

Basically the only time it will be neutral is when all four atoms in a tetrahedral molecule are the same atom. Lone pairs and varying atoms creates dipoles that affect the net dipole, and therefore polarity, of the molecule.

Anna Heckler 2C

I would just know the general trends, we likely won't have to do calculations based off this quation. Polarizability refers to an atom's ability to form instantaneous dipoles, and is based on how large an atom's electron cloud is. Know that the bigger an atom is, the more polarizable it is.

Anna Heckler 2C

Yes, porphyrin is tetradentate! It forms a "ring" (chelating ligand) that gives blood its red color.

Anna Heckler 2C

Schrodinger's equation describes the wave function. Solving the equation give you the position and momentum of the wave.

Anna Heckler 2C

While it is helpful to memorize the strong acids, strong bases can be identified by all cations (bound to OH-) in group 1 and some of group 2.

Anna Heckler 2C

Ferrate is the anion with chemical formula [FeO4]2−

Anna Heckler 2C

When drawing resonance structures, you still only want the lewis structures with the most "well balanced" formal charges. Note that the negative charge should always go on the most electronegative atom.

Anna Heckler 2C

Amphiprotic means that something can act as both a proton donor and proton acceptor. The example that Lavelle used in class was water, as it serves both functions in aqueous solutions

Anna Heckler 2C

acid = proton donor
base = proton acceptor

Anna Heckler 2C

It is most convenient to memorize the list of strong acids since there aren't that many. However, in more conceptual terms, strong acids completely dissociate in water whereas weak acids only partially dissociate. We see the presence of an equilibrium arrow because some of the compound still remains...

Anna Heckler 2C

The roman numeral indicates the charge of the ion. They are used for elements that can have ions with multiple different charges as a way to specify.

Anna Heckler 2C

Ground state refers to the lowest energy state regardless of whether it's an atom or an ion. Ions are not considered to be in "excited states".

Anna Heckler 2C

While you may have to draw a Lewis Structure, you will not need to draw the molecule's VSEPR model. You will just need to know the shape and electron geometry.

Anna Heckler 2C

Lone pairs occupy more space than a bonded pair of electrons, therefore causing greater repulsion from other bonded pairs.

Anna Heckler 2C

In a molecule, dipole moments cancel when there are two equal dipoles oriented in the opposite direction.

Anna Heckler 2C

Hybridization occurs when atomic orbitals fuse together to form new hybridized orbitals.

Anna Heckler 2C

The bonds with the most ionic character exist between atoms with the greatest differences in electronegativity.

Anna Heckler 2C

Oxygen most commonly forms a double bond within a molecule because it results in a formal charge of zero. But, it can also form single or triple bonds.

Anna Heckler 2C

Lone pairs refers to a pair of valence electrons that are shared with another atoms when covalently bonded.

Anna Heckler 2C

Lone pairs on bonded atoms weaken the bond because of repulsion. Electrons are negatively charged - like charges repel each other, so the repulsion of these clustered electrons weakens the bond.

Anna Heckler 2C

Transition metals in the d-block can exist in a wide variety of oxidation states due to their electron configurations. Problems will specify what charge that cation has.

Anna Heckler 2C

Cations are significantly smaller than anions because they have lost the electrons in their outermost shell. The protons in the nucleus pull the remaining electrons very tightly towards the nucleus, decreasing the atomic radius. Anions, on the other hand, gain electrons to complete their outer shell...

Anna Heckler 2C

Noble gases have a full octet of electrons in their outermost shell, making them stable and virtually unreactive. Since valence electrons determine the chemistry of the atom, noble gases do not exhibit the trends of ionization energy/electron affinity/etc. that we see with atoms with incomplete oute...

Anna Heckler 2C

Ionic bonds are stronger than covalent bonds. A covalent bond involves overlapping of orbitals while an ionic bond involves charge separation.

Anna Heckler 2C

Both of those are correct, however, the way Lavelle taught us in class emphasizes the fact that subshells have different energies.

Anna Heckler 2C

One reason that a double bond may exist between two atoms is because it is the most stable, energetically. We sometimes add double bonds when drawing lewis structures because it decreases the number of lone pairs of electrons in the molecule.

Anna Heckler 2C

An anion is indicated in a Lewis structure by drawing brackets around the molecule with the overall charge written out next to it. When determining how to draw this Lewis structure, you sum the valence electrons of all atoms in the molecule. Then, you add the number of electrons indicated by the cha...

Anna Heckler 2C

Yes. Experimentally, we can see that the bond length is an average of single and double bond lengths. This is the resonance hybrid structure of the molecule.

Anna Heckler 2C

Wave-particle duality asserts that all objects exhibit both wave-like and particle-like properties. Particles with a very small mass, such as electrons, exhibit this wave-particle duality, whereas something that has a very large mass, like a car, will only really show particle-like properties.

Anna Heckler 2C

A good rule of thumb for determining the probability of finding an electron at a certain location is the orbital diagrams. For the p-orbitals, for example, the probability of finding an electron where the nodes intersect is 0, whereas the probability of finding one within the nodes is fairly equal a...

Anna Heckler 2C

All calculations should be done while keeping as many sig figs as possible (or as many as your calculator allows). Then, when you round at the end, you can be confident that your final rounded answer is as accurate as possible.

Anna Heckler 2C

Parallel spins are not impossible according to Pauli Exclusion Principle. Conceptually, this is because electrons repel each other and their spins cannot be oriented in the same direction. It is considered most common to have the first spin up and the second one down.

Anna Heckler 2C

Pauli Exclusion Principle and Hund's Principle both come into play when determining how to fill electron orbitals. We can use PEP to ensure that two electrons do not have the same spin within the same orbital. We use Hund's Principle to ensure that orbitals are filled from lowest energy level to hig...

Anna Heckler 2C

For the intents and purposes of this class, the constant for the speed of light, c, always equals 3.00 x 10^8. However, it is important to note that the speed of light is not constant as it moves from medium to medium. When light enters a denser material, the speed and wavelength of light decrease w...

Anna Heckler 2C

Constructive interference describes when the waves are in phase (peaks are overlapping). When this occurs, the amplitudes of the peaks are added to create one larger wave. Destructive interference describes when the waves are out of phase. The peaks do not overlap, and the amplitudes are subtracted.

Anna Heckler 2C

The energy change from n=2 to n=1 is the greatest because of the electron's attraction to the positively charged protons in the nucleus. When the electron makes this energy change, it is actually releasing energy because it wants to be pulled in towards the nucleus. The attraction is greatest when i...

Anna Heckler 2C

As stated above, one photon can never eject multiple electrons. You may be referring to the energy level of the incoming photon in comparison to the threshold energy of the ejected electron. If the incoming photon has an excess of energy compared to the threshold energy needed to eject an electron, ...

Anna Heckler 2C

The mass of a neutron is 1.674929 x 10-27 kg.

Anna Heckler 2C

Electrons can released quantized amounts of energy (in the form of a photon) to "jump" down energy levels. Electrons are attracted to the nucleus because the negative charge of the electron is attracted to the positive charge of the protons. So, when it is decreasing energy levels, it is a...

Anna Heckler 2C

When it comes to precision, its always best to do all of the calculations using as many decimal places and sig figs as possible. Then, you can round your final answer to the correct number of sig figs and know it will be as precise as possible.

Anna Heckler 2C

I find it helpful to circle all of the relevant parts of the equation and then rewrite it in an abbreviated version. So, for example, if the problem is talking about compounds reacting with each other, I prefer writing all of them in their chemical symbols and writing out the actual equation.

Anna Heckler 2C

In past chemistry classes, we have converted the fraction to a decimal and rounded to the correct number of sig figs. I assume Lavelle will prefer we do this since that is typically how figures are reported on lab reports and other experimental documents.

Anna Heckler 2C

The fact that 3000 has 1 sig fig but 3000. has 4 sig figs has to do with the accuracy of a measurement. If you reported a measurement as 3000 lbs, someone could infer that the scale you were using was accurate to the nearest thousand. However, if you reported a measurement as 3000. lbs, someone can ...

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