CHEMISTRY COMMUNITY

Ally Huang- 1F

A first order reaction is a reaction whose rate depends on only the concentration of one reactant molecule. It is said to be unimolecular. A second order reaction is a reaction whose rate depends on the concentration of two reactant molecules and it is said to be bimolecular. A zero order reaction i...

Ally Huang- 1F

The value of A would be given. We would not be expected to find A in order to use the Arrhenius equation.

Ally Huang- 1F

A catalyst is inputted into the reaction as a reactant and comes out unchanged as a product. An intermediate is formed as a product in one step and then used up as a reactant in a proceeding step. Therefore, I don't think a catalyst can be an intermediate and vice versa.

Ally Huang- 1F

If there is an intermediate in the second step of a reaction, then you must use the pre equilibrium approach in order for the rate law to agree with the observed rate law. If the early step is fast and the later step is slow, then there is a build up of the intermediate and the first step is conside...

Ally Huang- 1F

k is the rate constant for the forward reaction. k' is the rate constant for the reverse reaction and K is the equilibrium constant.

Ally Huang- 1F

If it specifies that it is a galvanic cell, then the sum of the standard cell potentials must be positive and therefore spontaneous. If galvanic cell is not specified, then the sum of the standard cell potentials can be negative; it just means that the forward reaction is not spontaneous.

Ally Huang- 1F

For this problem you compare the standard reduction potential of each metal ion with the standard reduction potential of water. The one with the higher, more positive standard reduction potential will be reduced at the cathode.

Ally Huang- 1F

Yes, since water is not part of the equilibrium constant, changing the amount of water will have no effect on the equilibrium of the reaction.

Ally Huang- 1F

In order to get a negative delta G, E° must be positive. In order to get a positive E° one of the standard potentials can still be negative, as long as the sum of the standard potentials is positive.

Ally Huang- 1F

If the standard cell potential is negative, that means the forward reaction is not spontaneous. The reaction will proceed spontaneously in the reverse reaction, however.

Ally Huang- 1F

Common salts used to form a salt bridge are sodium chloride, potassium chloride, or potassium nitrate. You do not want the ions of the salt bridge to react with the solutions in each half cell to form a precipitate.

Ally Huang- 1F

The E cell of galvanic cells are positive because they are spontaneous. The E cell for electrolytic cells are negative because they are not spontaneous and an external current is needed to drive the non spontaneous reaction.

Ally Huang- 1F

Hg (l) can act as a conductor so it would be the electrode in this case. Therefore, a platinum electrode would not be necessary.

Ally Huang- 1F

The unique rate equation sets the rate of change of product concentration and reactant concentration over time equal. The equation takes into account the stoichiometric coefficients in the reaction. For example if one product has a stoichiometric coefficient of 2 and all other stoichiometric coeffic...

Ally Huang- 1F

If I understand what you are asking, there are multiple ways in finding change in enthalpy. We learned the methods of using bond enthalpies, heat of formations, and Hess's law. For entropy I believe that the only way is to do products- reactants with the standard entropy of formation values.

Ally Huang- 1F

The salts in salt bridges are commonly KCl and KNO3. It is important that the ions from the salt bridge will not react with the solution it is going into. If the ion from the salt bridge formed a precipitate with a solution of one of the half cells, the salt bridge would be ineffective.

Ally Huang- 1F

The answer is B because it is the option where the acid and base have the highest molarity. A neutralization reaction with highly concentrated acids and bases will produce a lot of heat. If you think about baking soda and vinegar mixing, a large amount of heat is released in this reaction.

Ally Huang- 1F

The salt bridge is necessary in order to keep the charges balanced in each cell when electrons are moving from the anode to the cathode. Without a salt bridge a positive charge would build up in solution on the anode side and a negative charge would build up in solution on the cathode side. The nega...

Ally Huang- 1F

Removing NO from the system would cause the reaction to shift left in order to minimize the stress on the reaction. Partial pressure can be treated as concentration of a specific compound so if the reaction shifted left, NO2 concentration and partial pressure would decrease.

Ally Huang- 1F

You use the Van't Hoff equation when trying to find K, an equilibrium constant, at a different temperature. Delta H at standard temperature and pressure must be known in order to use this equation, but this equation allows us to see temperature dependence of K.

Ally Huang- 1F

If you are referring to standard enthalpy of formation, elements in their natural state have a standard enthalpy of formation of zero because there is no change in enthalpy when elements in their standard state are formed. Everything other than elements in their standard state have a change in entha...

Ally Huang- 1F

Delta S total is the entropy change of the surroundings and the system. If delta S total is positive then the reaction is spontaneous. If only the delta s of the system is known then temperature and enthalpy are needed to determine if delta G is negative, and therefore spontaneous.

Ally Huang- 1F

Heat capacity is the heat required to raise the temperature of an object by 1 degrees celsius. Specific heat capacity is the heat required to raise temperature of 1 gram of a substance by 1 degrees celsius. Molar heat capacity is the heat required to raise the temperature of one mole of a substance ...

Ally Huang- 1F

A simple way to think about the first law of thermodynamics is through an isolated system. The energy of an isolated system must remain constant because no matter or heat can be transferred and the system cannot be physically changed.

Ally Huang- 1F

To calculate an isothermal irreversible expansion, use the equation W=-PDeltaV. Isothermal just indicates the process occurs at a constant temperature. For an isothermal reversible expansion, use the equation -nRTln(V2/V1).

Ally Huang- 1F

Delta U is equal to zero for an isothermal reversible system. The same amount of heat enters the system as the work that leaves the system so the temperature stays constant and delta U will also equal zero based on DeltaU=q+w.

Ally Huang- 1F

The standard enthalpy of formation for an element is always zero. Therefore, the standard enthalpy of formation value for elements have no effect on the overall reaction enthalpy. The standard enthalpy of formation for elements is zero because to form an element the reactants and products would be t...

Ally Huang- 1F

Gibbs free energy is dependent on both entropy and enthalpy. Delta G = Delta H- T(delta S), so gibbs free energy is dependent on enthalpy, entropy, and temperature. A negative gibbs free energy would mean the reaction is spontaneous and a positive gibbs free energy is a non spontaneous reaction.

Ally Huang- 1F

Since isothermal processes are at a constant temperature, pressure changes do not change internal energy. So, a constant temperature means internal energy is 0.

Ally Huang- 1F

When the pressure is constant, the heat transferred to or from the system is equal to the change in enthalpy of the system. So, q at constant pressure equals delta H.

Ally Huang- 1F

Cp is greater than Cv for ideal gasses because for constant pressures, some of the heat is transformed into work since W=PdeltaV. With constant volume, all the heat added goes to internal energy since no work is done with a constant volume.

Ally Huang- 1F

Catalysts increase the rate of a reaction. It increases the rate of the forward and reverse reaction by the same amount at equilibrium so the equilibrium constant will not change. It will also not be included in the equilibrium constant.

Ally Huang- 1F

Delta H is the change in heat energy at a constant pressure. Heat is the transfer of energy due to difference in temperature. Delta H will equal q when there is a constant pressure.

Ally Huang- 1F

At 100 degrees celsius, steam will produce a worse burn than boiling water because steam contains more heat energy than boiling water. It holds more energy than boiling water because it has the heat energy of boiling water and the heat energy that was required for the phase change from liquid to vap...

Ally Huang- 1F

Enthalpy is the amount of heat transferred during a reaction at constant pressure while heat is a form of energy that can be transferred. When no work is being done on the system, heat and enthalpy can be used interchangeably.

Ally Huang- 1F

When the volume increases, work is done by the system and work is negative. When the volume decreases, work is being done on the system and work is positive.

Ally Huang- 1F

ICE tables can be used for partial pressures as well. Given you have enough information, you can use an ICE table to find the equilibrium partial pressures and therefore Kp.

Ally Huang- 1F

pKa is the -log of an acidity constant and pH is the -log of the hydronium ion concentration.

Ally Huang- 1F

Yes, 500 cal/g is the middle point of a phase change from liquid to vapor. Half of the water would be in the liquid state and the other half would be in the vapor state. It is also important to understand that the temperature is not changing during a phase change because all of the heat is going tow...

Ally Huang- 1F

State properties are not dependent on the path taken to obtain that state. You do final minus initial with state properties because it does not matter the path taken to get to the final state, only the final and initial values matter.

Ally Huang- 1F

Yes, water is included in the K constant if it is a gas because gasses can be written as a concentration and it is not the solvent. If it is a liquid it will not be in the K constant expression.

Ally Huang- 1F

The question gives the units in terms of mmol, which is millimole. There are 1000 millimoles in 1 mol, so 1.20mmol SO2 divided by 1000 gives 1.20x10^-3 mol.

Ally Huang- 1F

The equilibrium constants of strong acids and bases and weak acids and bases are calculated in the same way. It is still products over reactants and the products and reactants are raised to the power of their stoichiometric coefficient. Strong acids and bases will have a very large K value because t...

Ally Huang- 1F

If K is less than 1 x10^-3, then the x can be considered negligible when it is being added or subtracted. For example, 0.09-x can be written as 0.09 since x is such a small number, subtracting x would pretty much have no effect.

Ally Huang- 1F

At equilibrium the reaction quotient, Q, equals the equilibrium constant, K. When the concentration of the reactants and products change, Q no longer equals K and the reaction will shift in a way to keep K constant. Only temperature changes the equilibrium constant.

Ally Huang- 1F

When the pressure of the system decreases the reaction goes toward the side with more moles to restore equilibrium in the system. If the pressure of the system increases the reaction will favor the direction with fewer moles. Any inert gas will not change the reactant and product concentrations and ...

Ally Huang- 1F

I believe the equilibrium constant of water is so small because a very small concentration of ions will actually form in water. There is a very small concentration of Hydronium and Hydroxide ions relative to non- ionized water.

Ally Huang- 1F

It does not matter which ratio you use. Either 2:1 or 1:.5 will work and you will get the same answer for both ratios.

Ally Huang- 1F

The reaction quotient can be calculated for partial pressures and concentrations, but when comparing Q to K it is important to compare the reaction quotient for partial pressures to the equilibrium constant to partial pressures, not the equilibrium constant for concentration.

Ally Huang- 1F

K is the constant you get for the ratio of the concentration of products at equilibrium to the concentration of reactants at equilibrium. Q is the ratio of products to reactants at any time. Q is used as a point of comparison to K to determine which direction the reaction will proceed to reach equil...

Ally Huang- 1F

If K and Q are equal that means the system is at equilibrium because the ratio of the products to reactants is the same for K and Q and therefore, the system has the correct ratio of products to reactants needed for equilibrium. Since Q is equal to K the reaction will not favor one direction but wil...

Ally Huang- 1F

I believe Dr. Lavelle said we would never have to solve cubic equations in this class. So, if you ever end up with a cubic equation, you should just use the initial concentrations given because the change in concentration is so small and negligible.

Ally Huang- 1F

In addition to the important points of equilibrium constants listed above, equilibrium constants also show if the forward or reverse reaction is favored or if there is a greater concentration of reactants or products at equilibrium. If K is greater than 1x10^3, there is more products at equilibrium ...

Ally Huang- 1F

Bronsted acid and bases refer to the transfer of protons. Bronsted acids donate a proton while bronsted bases accept a proton. Lewis acids and bases refer to the transfer of electrons. A lewis acid accepts a pair of electrons while a lewis base donates a pair of electrons.

Ally Huang- 1F

It would be helpful to draw lewis structures to determine if the ligand is a polydentate. Polydentates are when the lone pairs of electrons are on different atoms on a ligand. Drawing the lewis structure will make it easier to see if lone pairs are available on more than one atom.

Ally Huang- 1F

Intermolecular bonding is interactions between molecules like dipole- dipole forces, hydrogen bonding, ion- dipole, and london dispersion forces. Intramolecular bonding is bonding within molecules between atoms like covalent and ionic bonding.

Ally Huang- 1F

It would be good to know them. Common strong acids are HCl, HBr, HI, HNO3, H2SO4, and HClO4. Common strong bases are LiOH, NaOH, KOH, RbOH, CsOH, Ca(OH)2, Sr(OH)2, and Ba(OH)2.

Ally Huang- 1F

The inductive effect is when electron density of the molecule is affected due to an electron withdrawing atom or portion of a molecule. The inductive effect creates a more stable conjugate base of an acid. An electronegative atom helps pull negative charge away from oxygen; it delocalizes the electr...

Ally Huang- 1F

Stronger acids have delocalized electrons that can move around and occupy other atom's octets. This makes the anion less reactive which is therefore more stable and can more easily lose a proton. Delocalized electrons always makes a molecule more stable and contributes to higher acidity.

Ally Huang- 1F

Ligands are lewis bases because they donate a pair of electrons. I am pretty sure molecules must donate a pair of electrons to count as a lewis base, so a molecule that donated one electron would not be considered a lewis base.

Ally Huang- 1F

A very general way of writing acid/base reactions is to have the acid donate a hydrogen and the base accept a hydrogen. The base will gain a hydrogen and the acid will lose a hydrogen in the reaction.

Ally Huang- 1F

I believe they are pretty much the same thing. Lewis base is a more general term for a Bronsted base. Bronsted base must donate a pair of electrons to an acidic hydrogen and a lewis base is anything that donates a pair of electrons anywhere to another molecule. For your second question, it is possib...

Ally Huang- 1F

If there are 6 ligands at the corners of an octahedron, it is considered an octahedral complex. 4 ligands at corners of a tetrahedron is considered tetrahedral complex and 4 ligands at the corners of a square is considered square-planar. Dr. Lavelle said we will not have to differentiate between the...

Ally Huang- 1F

Hybridization is based on the number of electron density regions around the central atom. If there is one region of electron density, it will have s orbitals. If there are two regions, it will have sp orbitals. If there are 3 electron density regions there is sp2 orbitals... and so on. CH4 has 4 reg...

Ally Huang- 1F

Another thing to remember when determining polarity is that many of these structures are 3 dimensional. For example, with CH2Cl2, placing the Cl atoms opposite each other and placing the H atoms opposite each other may seem like the dipoles would cancel, however due to the 3 dimensional shape the di...

Ally Huang- 1F

While a ligand is an ion or molecule that attaches to a central atom, ligands can also be described as electron donors. A ligand will usually donate one or two pairs of electrons to form the bond. If the ligand donates one of its lone pairs it is said to form a coordinate covalent bond.

Ally Huang- 1F

A coordination sphere is also shown by the atoms bound by square brackets in the coordination complex formula. Ligands link to a central atom to form a complex.

Ally Huang- 1F

The strength of an acid is dependent on the amount of dissociation. A strong acid dissociates completely and there will only be the dissociated products in the solution. A weak acid only partially dissociates and there will be both dissociated and undissociated products in solution.

Ally Huang- 1F

The answer to a) is [Ar] because when two electrons are added to sulfur, it has the same number of electrons as argon. [Ar] is the noble gas configuration for S2- because S2- is isoelectronic with argon.

Ally Huang- 1F

Since there is a lone pair on the central atom, it is usually polar. Usually an odd number of lone pairs on the central atom makes it polar. Also, since SF4 shape is see saw, two of the SF bond dipoles cancel each other out because they are 180 degrees from each other. The other two SF bonds point d...

Ally Huang- 1F

"Ground-state" electron configurations are the same as "electron configurations". They are both assumed to be at the lowest energy point. The question would specify an excited electron configuration if it didn't want the ground state configuration.

Ally Huang- 1F

I don't think polarizability has any connection to polarity. Polarizability is based on the size of the atom and how easily an electron cloud can distort. Everything has a polarizability even if it is non polar.

Ally Huang- 1F

Double bonds are equally weighted as single ones when doing VSEPR models because it is just considering electron density. Whether it is one bond or two bonds, it is still one area of electron density.

Ally Huang- 1F

Instantaneous dipoles last for only an instant. Electrons are constantly moving and electron distributions are constantly changing. Therefore, the instantaneous dipoles created by the uneven electron distributions are constantly changing as well.

Ally Huang- 1F

Due to fluctuating electrons, electron distributions within the atom are constantly changing. The uneven electron distribution that occurs creates instantaneous dipoles. It is said fluctuating electrons create fluctuating dipoles because of the instantaneous dipoles that are constantly created from ...

Ally Huang- 1F

Fluctuating electron distribution occurs because of the constant movement of electrons. The uneven electron distribution creates instantaneous dipoles, which are constantly changing due to constant movement of electrons.

Ally Huang- 1F

If you draw the lewis structure for each compound, it makes this problem a little easier to understand. AsF3 has a lone pair on As, so it is polar and has dipole moments. Therefore, it will experience dipole- dipole interactions between molecules. AsF5 has no lone pairs on As and the dipole moments ...

Ally Huang- 1F

Ion- ion interactions would be the attractive force between two ions like Na+ and Cl-. It is the attraction between a positively charged cation and a negatively charged anion.

Ally Huang- 1F

What is the best way to know how to draw lewis structures and where to put double bonds or single bonds? For example, how do you know where to put double bonds in ClO4-?

Ally Huang- 1F

The definition of the work function is the energy required to remove one electron from the metal surface. The unit for this is often Joules per mole because that is a more standard way of writing energy. Even though the energy is reported in those units, work function refers to just one electron so ...

Ally Huang- 1F

When atoms are going from a higher energy level to a lower energy level you would use the equation E(photon)=-deltaE, which always makes energy of the photon positive. When you have a negative change in energy it means light is emitted and the energy of the light emitted is always a positive number.

Ally Huang- 1F

I believe any electrons that are able to move locations between resonance structures are considered delocalized. Either lone pairs or bonds can change positions from one structure to the next and are therefore delocalized.

Ally Huang- 1F

When ionic bonds form, an electron cloud forms between the two atoms. When opposite charged atoms approach each other, the attraction and repulsion of opposite and alike charges leads to polarization in the anion. A large amount of polarization increases the covalent character, while less polarizati...

Ally Huang- 1F

The element with the lowest ionization energy goes in the middle because it is the element that can share its electrons easiest. You can also think of it as the least electronegative element goes in the middle because it is able to share more of its electrons. Atoms with high ionization energies are...

Ally Huang- 1F

Can someone explain why electron affinity is the highest in the top right corner of the periodic table. I understand it is the energy released when an electron is added, but why is that highest in the top right corner?

Ally Huang- 1F

The diffraction patterns that electrons create does show electron wave like properties. In the double slit experiment it was shown that electrons behave as waves. When electrons passed through slits and hit a screen, dark and bright lines showed up. The bright spots were formed from electrons having...

Ally Huang- 1F

At this point in the class we don't need to worry about the angles of the atoms in the lewis dot structure. We will learn later on the correct angles that should be drawn in lewis dot structures. I believe Lavelle said to just draw the atoms as symmetrically as possible for now.

Ally Huang- 1F

The main difference between ionic and covalent bonds are the types of atoms that form the bonds. Ionic bonds are bonds between a metal and a non metal. For ionic bonds one atom will donate an electron to the other atom. Covalent bonds are bonds between two non metals. In covalent bonds the atoms are...

Ally Huang- 1F

The Rydberg equation works for the hydrogen emission spectrum and other one electron systems. It only works for systems with one electron because when there are multiple electrons, there is shielding, repulsion, and changing attractions of the electrons to the nucleus. Therefore, for systems with mo...

Ally Huang- 1F

Can someone explain why 3d has a lower energy than 4s if you are technically filling the 3d orbitals after the 4s orbitals?

Ally Huang- 1F

Particles have wavelike properties and particle properties. When particles behave like waves, increasing intensity increases the amplitude and frequency of light. In the photoelectric effect it was proved that light acts as particles or photons. It was shown when intensity increased, no electron was...

Ally Huang- 1F

The value of l corresponds to a specific subshell. l= 0 is the s subshell, l=1 is the p subshell, and l=2 is the d subshell. The s subshell has one orbital, the p subshell has 3 orbitals, and the d subshell has 5 orbitals. So, the value of l corresponds to a specific subshell which corresponds to a ...

Ally Huang- 1F

The uncertainty principle is mostly used for the uncertainty of position and momentum of objects with a mass. It states that if we know with a high certainty the momentum of an object, we cannot know with high certainty the position of an object. More specifically the Heisenberg uncertainty principl...

Ally Huang- 1F

Atoms can absorb only certain wavelengths based on the energy differences between energy levels in the atom. Many wavelengths may shine on the sample, but only a few are absorbed as electrons only have certain energies. In order for the atom to absorb the light coming in, the photon energy must matc...

Ally Huang- 1F

There is a potential difference between the metal surface and the detector. Therefore, the detector has a slight positive charge and the electron would be attracted to the positive charge on the detector. The electron is drawn up to the detector because of the attraction between the detector and the...

Ally Huang- 1F

Do you only use the DeBroglie Equation to solve for wavelength of an electron or can you use this equation to solve for the wavelength of light too? The light equation was part of the derivation for the equation so I am not sure if the wavelength of light can also be found from this equation.

Ally Huang- 1F

The transition from n=4 and n=5 is still considered part of the infrared region. The infrared region includes transitions to n=3, n=4, and n=5. More specifically, they are called the Paschen, Brackett, and Pfund series.

Ally Huang- 1F

The spectra of light emitted is not continuous; atoms can only absorb and emit specific energy levels. When an atom emits light, it doesn't emit a smooth band of light, but many specific lines of light. These specific lines of light emitted are unique to only one element, which is how spectroscopy i...

Ally Huang- 1F

First you must balance these equations. Fe+Br2->FeBr2 3FeBr2+Br2->Fe3Br8 Fe3Br8+4Na2CO3->8NaBr + 4CO2+ Fe3O4 Then, convert the 2.50 tons to grams. (2.5t)(1000kg)(1000g)/(1ton)/(1kg). You get 2.5E6g NaBr Then, convert to moles NaBr- (2.5E6)(1mol)/(102.9gNaBr)= 24295 mol NaBr. Then, you will use stoic...

Ally Huang- 1F

Another way I find that is helpful in finding the limiting reactant is to divide the moles of each reactant by the stoichiometric coefficient in the balanced chemical reaction. You then compare the numbers you get and the smallest number calculated is the limiting reactant. You will not use that val...

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