CHEMISTRY COMMUNITY

Brianna Becerra 1B

The slow step can be found in the rate law as the slow step heavily determines the rate of the reaction as a reaction can not go any faster than its slowest step.

Brianna Becerra 1B

The Arrhenius equation can be used to calculate k as it is characterized by k = Ae^ (-Ea/RT). When manipulated, it can be also used to compare k1 and k2 at two different temperatures.

Brianna Becerra 1B

Kinetic analysis is the speed or rate of a reaction. The forward and reverse reactions can differ in their rates making it so their analysis can be separate. In 14B, we only evaluate the forward because the reverse comes with various other complications.

Brianna Becerra 1B

At this moment, there has been no update on whether the final will be during a typical 3-hour final period or if we will be given longer.

Brianna Becerra 1B

I assume by trials, you mean the problems that have different experiment charts. For a problem like this, you can use any of them as long as all of the information can be filled in except k.

Brianna Becerra 1B

Something I have noticed is that in some problems, they will give you a number to be plugged in which may already have a unit of time to it. If this is so, then this dictates what unit of time will be the outcome, or you could convert the number given to match a desired one.

Brianna Becerra 1B

Yes, this is ignored because the problem is asking for the rate law and the main concern is converting the grams given into molarity so it can be then multiplied by .063 which is then to plugged into k x2 x [H2][I2].

Brianna Becerra 1B

Yes, that is correct. This is because, at equilibrium, there is no E change. In turn, G=-nFE and since E is zero, G is as well.

Brianna Becerra 1B

A first-order reaction means that there is one reactant or molecule present in the rate law. A second-order rate law either has two of the same reactant (rate law would be squared) or two different ones (they would be multiplied by each other). Two examples of second-order reactions are rate=k[CO2]^...

Brianna Becerra 1B

The unique rate law takes into consideration the stoichiometric coefficients and divides by them. The rate law, however, is a rate function of the concentration where the reactants are considered.

Brianna Becerra 1B

This equation can also be modified and used in order to compare the rate constants at two different temperatures. The modified equation would be ln(k2/k1) = (Ea/R)(1/T2 - 1/T1).

Brianna Becerra 1B

Typically, these problems are provided via cell diagram and ask a question that involves using the Nernst equation in order to calculate a missing concentration or to calculate the cell potential. (E° would be equal to 0).

Brianna Becerra 1B

Because this is used as a comparison for the other cell potentials, the hydrogen electrode cell potential is equal to 0.

Brianna Becerra 1B

The Nernst equation is : E = E° -(RT/nF) ln Q . It changes for different redox reaction as E° is a specific scientifically calculated value which differs for each reaction. ln Q is also dependant on the concentration which is another aspect contributing to the varying outcomes when using the equation.

Brianna Becerra 1B

In our notes, we were not taught how to do calculations but focused more on understanding the concept of electrolysis. I would say to make sure you can then answer any question involving its understanding. More specific information can be found in the textbook as well!

Brianna Becerra 1B

n refers to the number of electrons being transferred which can be determined by looking at the balanced half-reactions and seeing how many electrons were added to either side of the equation. Make sure that the number of electrons in both half-reactions are equal to each other!

Brianna Becerra 1B

If partial pressure is used in both the reactant and product, then converting it using Pv=nRT would make it so the conversion would not make a difference as you would be essentially canceling the conversion out.

Brianna Becerra 1B

The Nernst equation can be derived from ∆G = ∆G° + RT ln Q by substituting ∆G with -n F E(∆G = - n F E). You then divide both sides by - n F. You can then substitute - ∆G°/nF with E°. This then leaves you with E = E° - (RT/nF) lnQ !

Brianna Becerra 1B

If a process is spontaneous, then E is a positive value. Due to the set up of the equation, this also means that if a process is spontaneous, then delta G is equal to a negative value. Both of these rules apply with the negative symbol applied to the equation.

Brianna Becerra 1B

Some basic oxidation numbers which are used commonly and will help you figure out which is the reduction/oxidation is that typically, 0=2- and H=1+. Knowing these can help you figure out the oxidation number of another element being used with them when considering what value combination would make u...

Brianna Becerra 1B

If given the reductions, the one with the higher value, therefore, it wants to be reduced and serves as the reduction. This means that the other equation serves as the oxidation reaction which will then be flipped.

Brianna Becerra 1B

This is done under basic conditions. In order to balance the oxygen, you add needed H20 to the necessary side. This often result in a surplus of Hydrogen on one side causing H20 to be added to the other side, along with OH- in order to cancel out the added oxygen. It differs from acidic conditions a...

Brianna Becerra 1B

Something important to pay attention to is the difference between delta G and delta G naught. Delta G naught refers to the change in Gibb's Free Energy under standard conditions. Equations we have discussed involving delta G naught are seen through ∆G° = ∆H° - T∆S°and ∆G° = - RT ln K. Equations with...

Brianna Becerra 1B

An anode is where current flows into a polarized cell while a cathode is where a current leaves a polarized cell. We know that oxidation involves the loss of electrons while reduction involves the gaining of electrons. Because of this, we can pair oxidation with anode and reduction with cathode.

Brianna Becerra 1B

The delta G calculated last week is delta G naught or the change in Gibb's Free Energy under standard conditions. We were first taught to calculate this using Delta H naught - T x Delta S naught. This week, we learned how to calculate the same change in Gibbs Free Energy under standard conditions th...

Brianna Becerra 1B

An equation that utilizes both is when Delta G naught is used to calculate delta G through Delta G= Delta G naught + RTlnQ. Delta G naught can be calculated by using
-RTlnK.

Brianna Becerra 1B

You pay attention to the units you have already and want to cancel out to get the units desired for the type of problem. The different gas constants have different units and are on the constants and equations sheet.

Brianna Becerra 1B

A closed system is when the energy of the system can exchange with the surroundings, but it is closed so the matter can not (an example of this is a thermometer). An isolated system is when neither energy or matter can exchange with its surroundings(an example of this is a bomb calorimeter).

Brianna Becerra 1B

An isothermal reversible expansion is when the temperature of the system stays the same as the Energy does not change. This is due to it happening so slowly that heat flow can enter the system and replace the lost energy.

Brianna Becerra 1B

It is important to understand that this shift is due to a change in the concentration affecting the moles as when the volume is compressed, the concentrations will increase (C=n/v)

Brianna Becerra 1B

We can be given different molarities in the sense that one of the given can be the initial molarity, and another given can be the molarity at equilibrium. The molarity at equilibrium can be then used to help solve for x which can be used to calculate the equilibrium constant.

Brianna Becerra 1B

A reaction is reversible because the infinitely small changes allow for the energy which is being used up, to be replaced with heat that is entering the system as it changes ever so slightly. The reaction is so slow, it is able to stay at equilibrium. An irreversible reaction, however, is one which ...

Brianna Becerra 1B

To calculate the molar heat capacity, you multiply the moles by the constant volume or pressure, and then multiply this by the change in temperature.

Brianna Becerra 1B

When w is negative, it means that work is being done (expansion), while when it is positive, it is compression.

Brianna Becerra 1B

You first change torr to atm by multiplying 750(.00131). This then gets multiplied by the change in volume leaving you with the units atm L. To convert this into joules, you multiply it by 2 versions of the gas constant divided by each other so that the units cancel leaving you with Joules. (8.314k ...

Brianna Becerra 1B

a. sounds correct, the system is isolated, b. is an example of a closed system as the coolant does not exchange matter, however, the coolant shares energy in order to keep the refrigerator cold c. a bomb calorimeter is an example of an isolated system as the calorimeter is closed and made of materia...

Brianna Becerra 1B

I believe that the conversion between celcius and kelvin is listed on the constants and equations page which Lavelle provides during tests.

Brianna Becerra 1B

I believe the calorimeters discussed in the class were both made of materials/in such a way that the heat could not be transferred to the calorimeter itself making it have no effect on the change in temperature.

Brianna Becerra 1B

The specific bond enthalpy values to use in calculating the net change is either given or can be found on a table by locating the specific bond formation or breakage and taking this number and applying it as a positive for reactants and a positive for reactants and then adding them all together.

Brianna Becerra 1B

I believe that a bomb calorimeter is an isolated system because it is enclosed and the materials used in it do not allow for the reaction inside to affect the surroundings. This fits the definition of an isolated system as matter can not be exchanged due to the reaction being fully enclosed and the ...

Brianna Becerra 1B

I believe you are referring to how would we know the phase change value as this needs to be added to the change in bond enthalpies to correctly calculate the change in enthalpy if there is a phase change present. We were not taught how to calculate it in the lecture thus far so I would assume that i...

Brianna Becerra 1B

You can see from the graph that there is a moment where the water begins to boil and the temperature stays the same while heat is still being supplied. This is the phase change occurring but the vaporization is not seen until the temperature on the graph begins to rise.

Brianna Becerra 1B

The least accurate of the methods is using bond enthalpies as the bonds which are not diatomic are just averages from many different molecules causing it to be a less accurate method. In lecture, it was not specified whether Hess's or the standard reaction enthalpies are more accurate however I assu...

Brianna Becerra 1B

No, because solids can not have a concentration due to their form and for liquids, the change in concentration is so minute, it also does not affect the overall concentrations.

Brianna Becerra 1B

In class, we have been applying the concepts which we first learned of reactions at equilibrium, and now we are applying them to acids and bases. That is why we have been now calculating for Kb AND Ka.

Brianna Becerra 1B

The examples we have covered in lectures are an application of the rules we have learned for calculating k, but for different situations such as to acids and bases.

Brianna Becerra 1B

When K is less than 10^-3, then it means that at equilibrium, there are more reactants or that the equilibrium sits to the left.

Brianna Becerra 1B

An increase in pressure according to Le Chatelier's principle will cause there to be a shift in the equilibrium towards the direction that would cause fro the pressure to reduce. This change in pressure, however, does not change K.

Brianna Becerra 1B

An increase in pressure according to Le Chatelier's principle will cause there to be a shift in the equilibrium towards the direction that would cause fro the pressure to reduce. This change in pressure, however, does not change K.

Brianna Becerra 1B

If there is a strong acid, then the conjugate base will be weaker. Similarly if you are presented with a weak acid, then the conjugate base will be stronger. This trend is also true when evaluating the conjugate bases of weak/strong acids.

Brianna Becerra 1B

Aqueous solutions are included in the calculation as they affect the concentration and would then affect the calculation of K/Q.

Brianna Becerra 1B

Units are not used when calculating for K because instead of using the molarity, it would be more accurate to use the chemical activity of the compound which is typically equal to the concentration. Activities do not have units resulting in K not using units either.

Brianna Becerra 1B

They are similar to each other as the calculation of products divided by reactants is the same. The main difference is that k occurs at equilibrium while q occurs before equilibrium is reached. By calculating Q and comparing it to K, we can tell which way the reaction is going more towards.

Brianna Becerra 1B

The equilibrium constant is when the concentrations of the reactants and products at equilibrium are calculated such that product concentration at equilibrium is divided by the reactant concentration at equilibrium. The k rate constant is referring to the rates in which the product is turning to rea...

Brianna Becerra 1B

Liquids are omitted when calculating the equilibrium constant because when there is a solvent, the concentration does not change since there is such a large excess making it insignificant to the calculation. Solids are not used because they do not have molar concentrations.

Brianna Becerra 1B

You can identify when you should be using Kp as the reactants/products will be in the gas phase. Kc is used when the problem is given in the form of concentration or moles per liter. They seem interchangeable when solving for the equilibrium constant because the process is the same of dividing the p...

Brianna Becerra 1B

Cisplatin is used as a chemotherapy drug as the Cl binds to DNA as it is substituting two adjacent guanines.

Brianna Becerra 1B

For instance, the melting points of something with an H-bond would be higher than that of London dispersion because it is stronger.

Brianna Becerra 1B

I believe that the final grade will be available anytime after it is graded so maybe a week or two for now. When you get the copy, it is only to see what specifically you got wrong.

Brianna Becerra 1B

For example, if you were drawing the Lewis structure of NH3, there would be a lone pair on the N. This would then be sp3 and shown with 4 _ _ _ _. The first space would have an arrow going up and down representing the lone pair and the last 3 would only have an upwards arrow showing binding sites.

Brianna Becerra 1B

They dissociate 100% because they are so strong.

Brianna Becerra 1B

A bronsted acid is a proton donor and a bronsted base is a proton acceptor.

Brianna Becerra 1B

The longer the bond, the weaker it is making it easier to be broken. The easier it is broken the stronger the acid. The higher the electronegativity, the shorter the bond. This is seen in HF having a stronger bond than HI.

Brianna Becerra 1B

Stong acids are almost completely ionized in a solution whereas for strong bases they are completely ionized in water. A weak acid will be incompletely ionized in a solution whereas a base would be incompletely ionized in water.

Brianna Becerra 1B

We covered reactions between acids and bases, how to figure out pH from logarithms and properties which make an acid stronger or weaker.

Brianna Becerra 1B

Anionic ligands are ligands that dissociate from the metal as an anion.

Brianna Becerra 1B

Something that really helped me was going to the review sessions as well as doing different practice questions to test what I knew and what I needed to work more on.

Brianna Becerra 1B

This has to do with the bond length as the longer the bond, the more easily it is broken. This means that if the bond is longer, then it would be considered a stronger acid in comparisons such as HF and HI as in this case HI bond is longer making it easier to lose the H+.

Brianna Becerra 1B

If there is a single bond, it is sigma, if it is a double, it is sigma and pi and if there is a triple bond then it is considered one sigma two pi.

Brianna Becerra 1B

It is negative as it is always an attractive force.

Brianna Becerra 1B

This is the difference between the number of bonds and anti-bonds.

Brianna Becerra 1B

^ Steric numbers are used when determining VSEPR models and means the number of lone pairs as well as atoms bonded to a central atom.

Brianna Becerra 1B

We discussed transition metals, coordinate compounds, ligands, naming coordinate compounds as well as acids and bases.

Brianna Becerra 1B

It is also important to note that sigma bonds allow the atom to rotate while pi bonds do not.

Brianna Becerra 1B

Ion dipole occurs when there is a charged atom and a molecule such as cl- H20. Dipole Dipole is when there there are two molecules being compared. This can be see through HF and HF.

Brianna Becerra 1B

Induced dipole forces occur when one molecule is charged and then reacts with another which was nonpolar and then causing this new molecule to have a new charge which has just been induced by the original charged molecule.

Brianna Becerra 1B

Polarizability increases as the atoms become larger as this causes the electronegativity or electron pulling power to decrease allowing for the electrons to be more easily moved.

Brianna Becerra 1B

An example where the charges "cancel out" can be seen through the example BeCl2. Here, there is a negative charge on both of the cl which is on opposite ends meaning the arrows drawn will go away from each other making it so that the charges cancel out and it is now considered to be non-po...

Brianna Becerra 1B

An example where the charges "cancel out" can be seen through the example BeCl2. Here, there is a negative charge on both of the cl which is on opposite ends meaning the arrows drawn will go away from each other making it so that the charges cancel out and it is now considered to be non-po...

Brianna Becerra 1B

In a covalent bond, the electrons are not equally shared causing there to be a negative charge in the atom with the closer e- pair and then the other atom having a positive charge induced by the negative charge. The bond is polar if the charges of the molecules to not cancel out (H20). A bond is non...

Brianna Becerra 1B

An example of this can be seen with BeCl2. When drawing the structure, there are negative dipole charges on boh pf the Cl molecules. Because of this, the charges go away from each other and cancel out so the molecule is now nonpolar. This should not be confused with a molecule such as H20. In this L...

Brianna Becerra 1B

Even if a molecule is nonpolar, this does not change the dipole charges that the molecule still has which may have been canceled out to establish the nonpolarity. Because of this, the charges still exist meaning yes it still can have dipole dipole interactions.

Brianna Becerra 1B

In class, my TA said its basically anything that was covered after the midterm up until the new test.

Brianna Becerra 1B

Another way to remember it is that electronegativity follows the general increasing trend of ionization energy on the periodic table. That is except for the part in ionization energy where O is less than N. This dip in Ionization Energy is not present in Electronegativity.

Brianna Becerra 1B

When there are three bonding pairs, it is called Trigonal Planar. Here none of them are lone pairs. When there are four regions of e- density however one is a lone pair, this is Trigonal Pyramidal.

Brianna Becerra 1B

Resonant structures occur when there are multiple ways to draw a Lewis structure. This results in a hybrid or blend of its resonance structures. The electrons are then delocalized.

Brianna Becerra 1B

A lone pair refers to the dots surrounding the elements in a lewis structure. If it was shared, it would be represented by a line connecting the two elements. To find the number of lone pairs, simply count the number of dots.

Brianna Becerra 1B

I'm pretty sure that it is all of the elements in or past the third period can have expanded valence shells.

Brianna Becerra 1B

In ionic bonds, one of the elements gives it electrons to the other in order to complete it. In covalent, however, the electrons are shared between the two elements.

Brianna Becerra 1B

The formal charge is used to find which is the best way to draw Lewis structures. It does not correlate to energy.

Brianna Becerra 1B

One of the T.A.s said that it is more important that we understand the concept behind the equation. Make sure that you also understand what each of the terms in the equation represents as well.

Brianna Becerra 1B

I believe choosing any of the structures works but if you are being questioned about resonance, it would probably be formatted in the instructions on how to go about drawing the lewis structure.

Brianna Becerra 1B

In a) n = 2 so l can only be equal to 0 or 1 (s or p). It can therefore not be 2D as the rule for l is 0,1....n-1. The same thought process applies to C in where n = 4 therefore l can only go up to 3 meaning we can only get s,p,d, or f as subshells, but never g.

Brianna Becerra 1B

Penetration is when an electron of a certain shell is able to move through inner shells in order to be closer to the nucleus. This can be seen in an s electron of any shell that can be found close to the nucleus as it penetrates other shells to get there.

Brianna Becerra 1B

The ground state refers to the lowest possible energy of an atom.

Brianna Becerra 1B

Resonance in terms of structure of a model has to do with when drawing lewis structures. Some lewis structures have multiple bonds in different equivalent equations making it so there are multiple ways to draw some in certain cases. This is due to resonance existing however resonance does not place ...

Brianna Becerra 1B

The guideline for the octet rule is that atoms share valence electrons until a noble-gas configuration is reached. The exceptions mentioned in lecture to the octet rule are H, He, Li and Be.

Brianna Becerra 1B

n1 and n2 refer to initial and final. It can correlate to either the higher or lower levels as it is representing the initial and final levels and either can be the higher or the lower level.

Brianna Becerra 1B

Yes, this specific equation can only be used when calculating for Hydrogen atoms.

Brianna Becerra 1B

Combining equations happens when there is a shared variable in the equations which can be replaced and manipulated to make a new equation. This often occurs because in order to solve the problem, there is a two step process using two different equations. The combining of equations changes the proces...

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