CHEMISTRY COMMUNITY

Karishma_1G

The one exception to this that Dr. Lavelle mentioned was mercury since it is a liquid at room temperature. Though it is a liquid, it can still conduct electrons and act as an electrode.

Karishma_1G

A cell always has to have a conducting metal. If the reactants and products of the redox reaction are all aqueous, the electrons will not be transferred. In these scenarios you have to have an inert (one that does not take part in the reaction) electrode to attract the electrons/create a current.

Karishma_1G

In a cell diagram, a comma is used to separate two species of the same state. Vertical lines are used to separate species if they are in different phases. Additionally, it is convention to put a vertical line after the electrode on the anode side and before the electrode on the cathode side; the ele...

Karishma_1G

Yes, higher oxidation power means more likely to gain electrons/be reduced. Therefore, the higher the standard reduction potential, which can be said to represent a substance's affinity for electrons, the greater the oxidizing power.

Karishma_1G

You will be given this information.

Karishma_1G

Delta U for an isothermal reversible expansion is zero. These types of reactions usually take place in a heat reservoir. The energy that is lost when the system does work is replaced by heat energy from the surroundings. Therefore q and w are equal in magnitude and opposite in sign; q is positive si...

Karishma_1G

The units of k are different depending on reaction orders because the units for rate are always the same (mol x L -1 x s -1 ). Since the concentration of the reactants are raised to a power based on their particular order, the units may go up in exponents. For example since concentration is squared ...

Karishma_1G

Delta U for an isothermal reversible expansion is zero. These types of reactions usually take place in a heat reservoir. The energy that is lost when the system does work is replaced by heat energy from the surroundings. Therefore q and w are equal in magnitude and opposite in sign; q is positive si...

Karishma_1G

You have to find the two half-reactions in the standard potentials table. Then you would use the formula E(cell) = E(cathode) - E(anode). The cathode is the site of reduction and the anode is the site of oxidation.

Karishma_1G

Like others have said above, water can either be a solid, liquid or gas. However, it will never be aqueous since an aqueous solution is, by definition, one where the solvent is water. Water cannot be dissolved in itself (it cannot be both the solvent and the solute).

Karishma_1G

Electrolysis uses a current supplied by an external power source to force oxidation and reduction for a non-spontaneous reaction.

Karishma_1G

The Nernst equation is most often used to find the cell potential at a certain point during the reaction. The equation uses the standard cell potential and Q. If two out of these three variables (cell potential, standard cell potential, reaction quotient/concentrations) are given in a problem, I wou...

Karishma_1G

A concentration cell is a cell in which the two half cells are identical except for their concentrations. Therefore, the overall reaction's standard cell potential is zero and the reaction is driven by the difference in concentration. For the reaction to be spontaneous, usually the anode (site of ox...

Karishma_1G

I also usually balance the half reactions in order to see how many electrons need to be exchanged in order for them to cancel when you add the two half reactions together.

Karishma_1G

He reversed it because copper was being oxidized in the reaction.

Karishma_1G

No, cell potentials do not change based on stoichiometric coefficients. This is because a standard reduction potential is an intensive property, meaning that its value does not change based upon on the quantity of electrons/species reacting.

Karishma_1G

Yes just like Joanna said above, you add an inert metal to act as an electrode when there isn't already a metal on both sides.

Karishma_1G

The salt bridge isn't actually made out of salt. It is a tube with ions inside to prevent the charge build-up during the redox reaction. I believe that without a salt bridge, a positive charge would build up on the anode side and a negative charge on the cathode side which would preventing the react...

Karishma_1G

For all spontaneous reactions delta G is negative. Therefore, using the Delta G = -nFE equation, we find that E has to be positive for Delta G to be negative. This is because F (Faraday's Constant) is a positive number and n (moles of electrons transferred during the reaction) will also be positive....

Karishma_1G

Correct, Dr. Lavelle said this in lecture today.

Karishma_1G

I believe so since there are HW assignments on this topic.

Karishma_1G

The C in the equation from the textbook is most likely referring to the heat capacity, whereas the C in Dr. Lavelle's equation is the molar heat capacity (that's why you have to multiply by the number of moles)

Karishma_1G

Like stated below, an extensive property is one that depends on the amount of matter present. Volume, mass and length are all examples of extensive properties. Intensive properties, on the other hand, are those that do no matter on the amount of matter present. Examples include density.

Karishma_1G

Delta U is equal to zero for an isothermal reversible reaction because the heat that is entering the system is equal in magnitude to the work that the system is doing. For example, if -1000 J of work is being done during an isothermal reversible reaction, then 1000 J of heat is entering the system. ...

Karishma_1G

I usually always try to use atm since the most common gas constant is in terms of atm. Additionally, you can use 101.325 J = 1 L x atm to convert between energy and pressure/volume.

Karishma_1G

There are two conversions you can use to get your answer in terms of energy (Joules). 1cm³ = 1L and 1 L x atm = 101.325 J. Hope this helps!

Karishma_1G

I feel that the HW and Review Sessions are the best ways to prepare!

Karishma_1G

Strong acids do not have equilibrium constants because they dissociate completely.

Karishma_1G

The units of the partial pressures of the gasses in K_p can be in bars or atm. However, it is important to remember that K_p as a whole does not have any units.

Karishma_1G

Bond enthalpies are the least accurate way of measuring reaction enthalpies since they are an average of the different types of a specific bond.

Karishma_1G

K>Q and K<Q is significant because it helps us understand whether the reaction has reached equilibrium or not. Since Q (the reaction quotient) is calculated at a specific time during the span of a reaction, by comparing it to K we can see if the reaction has to form more products or reactants to rea...

Karishma_1G

You are able to approximate the value of x when the equilibrium constant is less than 10^-3. We can approximate because x is extremely small relative to the initial value of the acid/base, so it will not substantially effect the equilibrium concentration of the acid/base.

Karishma_1G

Yes, like Gavin said above, if the value of K_a or K_b is less than 10^-3, then the acid/base is weak.

Karishma_1G

Essentially K c represents the equilibrium constant in terms of concentration (mol/L). You can use K c with aqueous solutions and gases since both aqueous solutions and gases have concentration. K p represents the equilibrium constant in terms of partial pressure and can only be used with gases sinc...

Karishma_1G

When calculating the equilibrium constant, the products are in the numerator and the reactants are in the denominator. Therefore, the greater the concentrations/partial pressures of the products, the larger the equilibrium constant. When the equilibrium constant is greater than 10^3, we say that the...

Karishma_1G

The reaction quotient and equilibrium constant are calculated in the same way. The reaction quotient (Q) represents a value at a random point during a reaction where as the equilibrium constant (K) represents a value at exactly equilibrium (when the rate of the forward reaction is equal to rate of t...

Karishma_1G

On Worksheet 9, question #6, why would acid 2 be stronger than acid 4?

Karishma_1G

You only add the suffix -ate to the end of the metal if the overall compound has a negative charge (in your question, the compound has a 4 - charge). I believe that the latin root of iron is ferr- so you would add -ate to the end of that. However, for other transition metals, the root isn't differen...

Karishma_1G

The central atom for a coordinate covalent compound is the transition metal/ion. The ligands are usually covalent molecules (water) or negatively charged ions (F^-) that have a pair of electrons to donate.

Karishma_1G

A triple bond has one sigma bond and two pi bonds.

Karishma_1G

The general trend in electronegativity is that it increases diagonally from the bottom left corner of the periodic table up to fluorine (the most electronegative). In terms of this general trend, hydrogen can be considered an exception since it is on the left side of the periodic table but has an el...

Karishma_1G

Pi bonds are formed between two p orbitals that are perpendicular to the internuclear axis. For this reason, the two p orbitals overlap above and below the internuclear axis and cannot rotate. If you have the 7th edition of the textbook, Figure 2F.4 on page 118 is helpful for visualizing this bond.

Karishma_1G

In addition to VSEPR and Hybridization, I believe it'll also cover intermolecular forces and polarity.

Karishma_1G

Based on what we've learned so far, the homework questions, and the outline, I don't think so.

Karishma_1G

I said that we balance them because of the law of conservation of mass which states that matter cannot be created nor destroyed.

Karishma_1G

The textbook on page 110 (7th edition) says that for an AX 3 E 2 molecule, the lone pairs occupy two of the three equatorial positions where as the lone pairs for an AX 4 E 2 occupy the two axial positions. Why wouldn't the two lone pairs on AX 3 E 2 occupy the two axial positions like the AX 4 E 2 ...

Karishma_1G

Yes, Helium has the highest ionization energy! This is because the electrons in helium are very close to the nucleus and so the electrostatic attraction is very high. This makes it difficult to remove an electron.

Karishma_1G

VSEPR stands for Valence Shell Electron Pair Repulsion and it is used to help determine the geometrical shape of a particular molecule. Since electrons repel each other, VSEPR assumes that a molecule will have a shape that minimizes these repulsions. In class Dr. Lavelle said that lone pair-lone pai...

Karishma_1G

I don't think we've learned how to calculate it so we just have to estimate it based off of the periodic trend for electronegativity (Fluorine is the most electronegative).

Karishma_1G

Do electrons in d orbitals count as valence electrons? I'm confused because d orbitals are written after the noble gas configuration but they're not the highest energy level (s & p will always be higher). For example how many valence electrons does Manganese (Mn) have and how many valence electr...

Karishma_1G

You would use however many sig figs you used for your constants (h,c, etc.).

Karishma_1G

Hi, I was wondering how you know which element the unpaired electron goes on for Radicals. For example, how do you know whether the unpaired goes on the Cl or O in the molecule ClO (question 2C.5 part (a) in the 7th edition)? Thanks in advance!

Karishma_1G

Hi, I was wondering why copper can lose two electrons when it only has one electron in its outermost shell (4s). Wouldn't the ionization energy be extremely high to remove an electron from the 3d subshell?

Karishma_1G

Hi, I was wondering what the difference/relationship was between the effective nuclear charge experienced by an electron and the energies of the different shells (E_n) that the electrons are in (n=1, n=2, etc.). Thank you in advance!

Karishma_1G

Yes, I have the same question! If someone could explain, that would be great!

Karishma_1G

Hi! I know in lecture on Friday that Dr. Lavelle said that we only need to know what was covered in lecture up until Friday for the test. Does that mean we do not need to know electron configurations and periodic trends for the test even though it is on the syllabus for the Quantum World? Just want ...

Karishma_1G

Yes, like Michelle said above, a superscript indicates the number of electrons in that subshell.

Karishma_1G

Yes, Dr. Lavelle said that -1 is P x , 0 is P y , and 1 is p z . He also said that some books use the opposite convention and -1 is P z , 0 is P y , and 1 is p x . However, in either scenario, 0 is always P y . Determining which axes for P orbitals may appear on the test but not for D orbitals. Hope...

Karishma_1G

The formulas and constants will be given to us on test day!

Karishma_1G

It is better to use meters during calculations so that you can ensure that your units cancel out properly (ex: 1 joule is kg x m^2 x s^-2). However, when writing your final answer, it is better to use nanometers so that you don't need scientific notation. Hope this helps!

Karishma_1G

I am working on the pre-assessment for the Photoelectric Module. On question #27, it says that the work function for sodium is 150.6 KJ.mol^-1. However, I thought that the units for the work function is supposed to be just J. Do I need to convert KJ to J and then convert the mol^-1 to per Na atom? I...

Karishma_1G

Hertz and s^-1 can be used interchangeably. Hertz is the unit for frequency which can be written and thought of as cycles/second. Thus Hertz and 1/second are the same.

Karishma_1G

I've been looking for more practice!! Thank you so much for posting this - it's very helpful!

Karishma_1G

120. definitely has 3 significant figures. 120 (without the decimal point) however is ambiguous and therefore it is better to use scientific notation: 1.20 x 10^2 (this would definitely have 3 significant figures).

Karishma_1G

I think that in a recent lecture Dr. Lavelle said that he would like us to put the states of each compound in the chemical equation.

Karishma_1G

These are the rules that I learned and use when determining how many significant figures are in a value: 1. All nonzero digits are significant (ex: 345.23 has 5 significant figures) 2. Zeroes between between two nonzero digits are significant (ex: 103.106 has six significant figures) 3. Zeroes to th...

Karishma_1G

Hi Ashley!

Thank you so much for posting this! I will definitely take your advice.

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