CHEMISTRY COMMUNITY

Faith Fredlund 1H

The above work shows 2pH because they are showing that in a neutral solution, pH=7 and pOH=7, so because they have the same value, you can take the equation

pH + pOH = 14

and substitute pH for the pOH and get,

pH + pH = 14 or 2pH = 14

Faith Fredlund 1H

Increasing reducing power is associated with a less positive, more negative reduction cell potential (found in a half cell reduction potential table). Increasing oxidizing power is associate with a more positive, less negative reduction cell potential.

Faith Fredlund 1H

They catalyst does change the reaction mechanism. It is in this way that it is able to lower the activation energy and speed up the reaction. thus, new intermediates are formed.

Faith Fredlund 1H

Increasing reducing power is associated with a more negative (less positive) reduction half reaction potential. Increasing oxidation power is associated with a more positive (less negative) reduction half reaction potential. You would find the reduction half reaction potentials in a given table of v...

Faith Fredlund 1H

On test two its states: Circle the one that best decsribes the change in Gibbs Free Energy (ΔG) for the process described below: a) The melting of snow caused by a sunny day ΔG<0 ΔG=0 ΔG>0 I put ΔG>0, but that is not the answer and I was wondering why. I thought melting was an endothermic process an...

Faith Fredlund 1H

First order reactions have a slope of -k, the reaction is dependent on initial concentrations of reactants. Second order reactions have a slope of k, the reaction is dependent on initial concentrations of reactants. Zero order reactions have a slope of -k, the reaction in independent of the concentr...

Faith Fredlund 1H

This is because the battery is doing non expansion work, and ΔG is the energy available to do such work; so, the maximum amount of work a battery can do is ΔG at a constant temperature and pressure.

Faith Fredlund 1H

Yes, the anode should always be written on the left and the cathode on the right, as this is the normal convention.

Faith Fredlund 1H

As the element's reduction half-cell potential becomes more negative (less positive), its reducing power increases.

Faith Fredlund 1H

I am confused how to find the number of electrons transferred during cell reactions.

For example, the number of electrons transferred in
2Ce(4+)(aq) + 3I(-)(aq) --> 2Ce(3+)(aq) + I(3)(-)(aq)
is 2 and I don't understand why.

Faith Fredlund 1H

How do you know when to give ΔG in kJ or kJ/mol?

Faith Fredlund 1H

Yes, and when you are finding the maximum amount of work a battery can do at a constant temperature and pressure, which is equal to ΔG, you will be multiplying the cell potential E, which is in volts, by Faraday's constant which is 96,485 Coulomb/mol, so your answer will be reported in Joules.

Faith Fredlund 1H

When the questions states that the electrode component of the cell diagram uses Platinum. In the cell diagram it is generally written as the outermost component of the electrode in the diagram. Example: Hydrogen electrode constructed with Platinum Right electrode: H+(aq)|H2(g)|Pt(s) Left electrode: ...

Faith Fredlund 1H

Constant pressure:
w=-p* Δv

This one is used in the derivation of the last equation:
w= - v1∫v2 Pdv

During an isolated and reversible reaction:
w=-nRT ln (v2/v1)

Faith Fredlund 1H

For systems that undergo a temperature change and a volume change, it is difficult to calculate a change in entropy when those two actions are occurring simultaneously, so we consider these problems in two parts. You first calculate the change in entropy due to the change in volume ΔS= nRln(V2/V1) a...

Faith Fredlund 1H

Also, in cases where ΔH is not positive and ΔS is not negative, but ΔS is still negative, you must look at the temperature of the reaction to determine if it is spontaneous or not because S is dependent of certain conditions including temperature.

Faith Fredlund 1H

Generally when you are supposed to find the degeneracy of a system you are ultimately trying to find the entropy of a system. S= (Kb)ln(W) entropy= (Boltzman's constant)ln(degeneracy) Systems with higher degeneracy have higher entropy because the atoms or molecules can possess more disorder in the w...

Faith Fredlund 1H

Generally the question will deliberately state whether a system is reversible or irreversible.

For reversible systems:
w= -nRTln(V2/V1)
ΔS= q(rev)/ T @ a constant temperature
ΔS (where T1 --> T2) = nCln(T2/T1)

For irreversible systems:
w=-PΔV
ΔS= nRln(V2/V1)

Faith Fredlund 1H

The 3/2R part of this equation comes from the fact that the molar internal energy of a monatomic ideal gas as a temperature T is the molar heat capacity of that gas at a constant volume (C˅(V,m)). So, you would use this equation when you are finding the internal energy of a monatomic ideal gas at a ...

Faith Fredlund 1H

101.325J= 1L*atm

This value is given in the constant and equations sheet on the left hand side.

Faith Fredlund 1H

For irreversible expansion against a constant external pressure, you use the equation w= -PΔV. Temperature is not constant along the pathway in this case. For reversible expansion of an ideal gas you use the equation w= -nRTln(V2/V1) Temperature would be constant along the pathway in this case. If t...

Faith Fredlund 1H

A reversible process is the form of discrete expansion such that the system does the maximum amount of work possible on its surroundings. It expands in such small steps that the system is, in effect, almost always at equilibrium or just near it. This means that because the system is expanding minute...

Faith Fredlund 1H

J/C.mol

Faith Fredlund 1H

Hess's Law: the overall reaction enthalpy is the sum of the reaction enthalpies of the steps into which the reaction can be divided (it is a state function). For problems dealing with Hess's Law I would assume constant temperature considering you would will be using various chemical equations and th...

Faith Fredlund 1H

^^^ Yes, you will get the same answer because in effect, the other bonds in the chemical equation will cancel out such that they are broken and reformed (they are the same bond), so leaving them out when calculating the enthalpy of formation does not matter. We are only interested in the bonds that ...

Faith Fredlund 1H

w is positive when the system does work , and w is negative when work is being done on the system. The same goes for heat; Q is positive when heat is added, and Q is negative when heat is taken out or absorbed by the surroundings. Both of these can be seen in the equation
ΔU= w + Q

Faith Fredlund 1H

"A constant-volume calorimeter was calibrated by carrying out a reaction that released 3.50kJ of heat in a 0.200L solution in the calorimeter (q= -3.50kJ), resulting in a temperature rise of 7.32°C. In a subsequent experient, 100.0mL of 0.200M HBr (aq) and 100.0mL od 0.200M KOH (aq) were mixed ...

Faith Fredlund 1H

Steam causes more severe burns than water because for liquid water to become steam, it has to undergo a phase change during which there is a large absorption of energy (the phase change is an endothermic reaction). When water burns skin, it simply releases the amount of heat/ energy contained in the...

Faith Fredlund 1H

Exothermic reactions give off heat into the surrounding area.
They will result in a -ΔH.
Endothermic reactions absorb heat from the surrounding area.
They will result in a +ΔH

ΔH = Hp° - Hr°
(change in enthalpy) = (enthalpy of products) - (enthalpy of reactants)

Faith Fredlund 1H

I believe, based on what the textbook states, that K is another notation for Kp, or the equilibrium constant for partial pressure; the lack of a subscript p in this table was simply a choice made by the author. K is given in terms of partial pressures (bar; the unit). Kc on the other hand is the equ...

Faith Fredlund 1H

In my notes I have it written that if [H3O+]<10^(-7), then the solution is considered to be neutral because we know that autoprotolysis generates 10^(-7) mol/L H3O+ Therefore, when [H3O+]<10^(-7) it would indicate that a basic solution is produced from the weak acid, which we know is not true. So, w...

Faith Fredlund 1H

This is called the Conjugate Seesaw. For every acid, there is a conjugate base; and for every base there is a conjugate acid. If you start with a strong base or acid, its conjugate will be weak; the reverse is also true for if you start with a weak base or acid, then it will have a strong conjugate....

Faith Fredlund 1H

Yes. When Q<K, the forward reaction is favored, so this means reactants will be used up to form more products. Taking product out of a solution such that it never reaches equilibrium is a method many chemical/ drug manufacturing companies will utilize so that they will obtain higher total outputs of...

Faith Fredlund 1H

Weak acids do not completely dissociate in chemical reactions involving a solvent, while strong acids do. Generally if you are given a problem that includes a value of Ka (the acidity constant), then you will be dealing with a weak acid because strong acids do not have these constants. An acid is de...

Faith Fredlund 1H

At 25°C, K=3.2X10^(-34) for the reaction 2HCl(g) --> <-- H2(g) + Cl2(g). If a reaction vessel of volume 1.0L is filled with HCl at 0.22 bar, what are the equilibrium partial pressures of HCl, H2, Cl2? I understand how to fill out the ICE table, but am unsure of how to complete the calculation. The s...

Faith Fredlund 1H

Looking at the moles in an equation to determine the direction the reaction will favor due to a change in pressure at a constant temperature implies that there is a change in volume, unless it is states that an inert gas is added to a container with a constant volume. The reaction will favor the sid...

Faith Fredlund 1H

In addition to this question, I was wondering how I would know when to use an ICE table. Are there any key words or given information that would help indicate when I should use this tool? Thanks!

Faith Fredlund 1H

PV=nRT where P= pressure, V=volume, n= moles, R= gas constant, T=temperature, shows that pressure and volume do indeed have an inverse relationship. Assuming moles, the gas constant, and the temperature do not change (let's call their collective product 1 for simplicity), you now get the equation PV...

Faith Fredlund 1H

The equilibrium would shift to the side containing more moles because it is the favored reaction. With less pressure inhibiting the reaction, it is then allowed to occur.

Faith Fredlund 1H

When comparing molecules containing bonds between the same types of atoms, you can determine which one has a higher boiling point based on the strength of its bond. Generally single bonds< double bonds< triple bonds. You can also take the size of the atoms into account when determining boiling point...

Faith Fredlund 1H

You can tell that period 3 allows for an expanded octet when forming bond because of its angular momentum quantum number (l). Because it has a principle quantum number of n=3, this means that possible values for l include l= 0, 1, 2 which correspond to s=0, p=1, and d=2 orbitals. d-orbitals allow fo...

Faith Fredlund 1H

Bronsted acids are actually characterized as donating protons, not accepting them, so in the case of H2SO4, the molecule would become deprotonated and lose one of its H atoms to become HSO4^(1-). This is a case in which an anion can act as an acid because HSO4^(1-) can donate another H+ to become SO...

Faith Fredlund 1H

On page 448 of the 7th edition of the textbook it states, "in the Lewis theory, the proton is the acid; in the Bronsted theory, the species that supplies the proton is the acid. In both the Lewis and the Bronsted theories, the species that accepts the proton is a base; in the Arrhenius theory, ...

Faith Fredlund 1H

Intermolecular forces occur between two molecules and do not generally affect a single molecule's shape. Usually, the shape of molecules in combination with their atom components will determine the intermolecular forces they possess. This is because shape must be known in order to determine if a mol...

Faith Fredlund 1H

The oxidation number is the charge on the central transition metal of the coordination compound. It can be determined by looking at the charges of the coordination complexes ligands, and then the overall charge of the complex. The oxidation number of the metal will be the charge of the coordination ...

Faith Fredlund 1H

Use di, tri, tetra, etc. to indicate the number of each type of ligand in the complex ion; if there were two NH3 ligands in the complex, this portion would be called diammine. Use bis, tris, tetrakis, etc. when the ligand you are naming already contains a Greek prefix such as those listed above (di,...

Faith Fredlund 1H

I believe the book states that the best way to tell if a compound is amphoteric (having both qualities of an acid and a base), is to look at the atoms that compose it; the presence of a metalloid being an indicator that it is likely to be amphoteric. Otherwise, to be sure you would need to see how t...

Faith Fredlund 1H

Some times you can determine if a molecule is polar or not by its Lewis Structure; however the VSEPR model is the most accurate to help determine the polarity of a molecule. By looking at the shape and determining the arrangement of the atoms in the molecule, you can then tell if it is polar or not....

Faith Fredlund 1H

Elements with an octet expansion exception begin in the 3rd row because in this row n=3, therefore l=0,1,2 : meaning that electrons of an element in the 3rd row can lie in a l=0 s orbital, a l=1 p orbital, or a l=2 d orbital. Because the 3rd row elements have access to bonding with d-orbitals, they ...

Faith Fredlund 1H

The 7th edition of the textbook states on page 725 that "some ligands are polydentate ("many toothed") and can occupy more than one binding site simultaneously," This is because they have one or more extra lone pairs of electrons that can be used to bind to the central metal atom...

Faith Fredlund 1H

To obtain the oxidation number of the coordination compound [Fe(CN)6]^-4, you first have to determine the charge of the compound CN, which is -1. because there are 6 of the CN compounds, we know there is a -6 charge on that part of the coordination compound. If the overall charge of the compound is ...

Faith Fredlund 1H

A Lewis Base is an electron pair donor, and a Lewis Acid is an electron pair acceptor. This classification of acid or base is not determined by a resonance structure of a molecule, but rather is based upon atoms compose the molecule, cation, or anion, and their likelihood to keep or donate electrons...

Faith Fredlund 1H

Determining whether a molecule is polar or nonpolar requires a combination of knowledge of an element's electronegativity (which can be seen through trends on the periodic table) and an understanding of the shape of the molecule. For a molecule to be polar, is must have dipole moments-- at which ato...

Faith Fredlund 1H

No it cannot be named this. I'm not sure there is a reason why, but Dr. Lavelle said in class to a boy that asked this name question that it may never be called square bipyramidal. It will always be octahedral; named for its eight faces.

Faith Fredlund 1H

A molecule's geometric shape is not always determined by its bond angle. For example, if a molecule contains a lone pair of electrons, like in H2O, the bond angle would be 120, but the geometry would be bent or angular. For NF3, the bond angle would also be 120, but the geometry would be trigonal pl...

Faith Fredlund 1H

Polarity is also largely in part due to the shape of the electron. When an electrons has lone pairs of electrons amidst other atoms, it is likely to be polar. Similarly, a bond between three atoms all of which include different electronegativity, is likely to results in a polar molecule.

Faith Fredlund 1H

When you draw the Lewis structures of H2O and CO2 you should see that the O in the H20 has two lone pairs of electrons, which somewhat clump together due to the repulsion of the H atoms. These electrons, in effect, cause the bent shape of the atoms. Meanwhile, the Lewis structure of CO2 shows the C ...

Faith Fredlund 1H

As Dr. Lavelle implied in class, electron affinity increases across each period (row) and decreases down each column. Because He is at the top right corner (the furthest right and the highest in its column) , it has the highest electron affinity.

Faith Fredlund 1H

Yes, ionic bond are always between metals and non-metals. This is because metals have low ionization energies (which make them good conductors) and non-metals have high ionization energies. This makes it easy for metals to give their electrons to non-metals to form the chemical bond between them.

Faith Fredlund 1H

Elements with low ionization energies lose electrons more easily, leading them to have a positive net charge; whereas elements with high ionization energy are more likely to take electrons to complete their octet causing their net charge to become negative with the increase in electrons.

Faith Fredlund 1H

As electromagnetic radiation decreases, the wavelength becomes shorter and therefore the distance between each crest grows. Because the distance between each peak is longer, the over slope of the wavelength becomes less severe and disturbs less of the magnetic field. There are less changes of peak t...

Faith Fredlund 1H

Since you know the two equations ΔP=(m)(ΔV) uncertainty in momentum=(mass in kg)(uncertainty in velocity in m/s) (ΔP)(Δx)> or = h/4π (uncertainty in momentum)(uncertainty in distance)=(plank's constant)/4π you can put them together to create the equation Δx=(6.626X10^-34)/4π(m)(ΔV) you set the equat...

Faith Fredlund 1H

There should be no energy left in the atom when an electron is removed from an atom, but if there is extra kinetic energy absorbed by the electron in the process of removal it will result in the release of a photon or the loss of energy through movement.

Faith Fredlund 1H

Positive and negative spins are merely to indicate that the spin of the electrons are different and does not necessarily reflect their motion up and down or side to side. It just shows that they are opposite and therefore interfere with the magnetic fields around them differently.

Faith Fredlund 1H

I believe that s orbitals have symmetric electron density because the s orbital itself is spherical in shape; whereas the p and d orbitals are not and contain nodal planes. Electrons cannot exist in nodal planes and this exception shows that electrons do not have an equal probability of being at any...

Faith Fredlund 1H

When giving our responses, when do we have to use SI units?

Faith Fredlund 1H

We have to determine the ratio of moles between the reactants and the products to ensure that there is a preservation of mass before and after the reaction. The balanced equation reflects this conservation of mass and provides information that allows us to determine how much product can be produced ...

Faith Fredlund 1H

Technically, a limiting reactant is the reactant that is completely consumed during the reaction. If there are three reactants and two of the three are totally consumed, it would make sense for them both to be limiting reactants, while the third is i n excess. I could be wrong, but that is my interp...

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