CHEMISTRY COMMUNITY

WesleyWu_1C

If the coefficients in a chemical equation are doubled, the unique reaction rate would decrease by a factor of 2.

WesleyWu_1C

From your question I think Gr means Gibbs Free Energy of the entire reaction. Gr can be calculated by doing Gf(products) - Gf(reactants).

WesleyWu_1C

If there are two reactants, the order of a reaction is by adding up the two exponents in the rate law (rate = k[A]^n [B]^M, so the rate law is n + m). How do you find n and m? Usually they give you a bunch of experimental trials where they used different or same amounts of A and B to find different ...

WesleyWu_1C

You would have to use an ice table and find the concentration of H3O+ (sometimes you will have to used the quadratic equation to find it). Then you plug in the concentration of H3O+ to get the pH.

WesleyWu_1C

Sometimes you want one of the species in your equation to be 1 mol, which is why other species have fractions as coefficents.

WesleyWu_1C

Yeah, you're right.. To solve for part d, all you need to find is the rate constant and the exponents for each reactant (which you found in the previous parts already). Then you just plug everything back into the rate order equation and find the rate.

WesleyWu_1C

So the way I answered this question was by looking at all three of the rate laws we know (0 order, 1st order, and 2nd order). Rate laws usually only include the reactants, so I knew the rate law was something like this: rate = k x [CH3Br]^n x [OH-]^m. The first part of the question says when we doub...

WesleyWu_1C

An intermediate is produced and used up. The catalyst appears as a reactant in the first step (which means it must have been in the original experiment) and is then later reproduced.

WesleyWu_1C

I don't think so, but maybe you can ask him during office hours. I feel like Dr. Lavelle cares more about using the equation correctly than just memorizing an equation.

WesleyWu_1C

The anode reaction is always reversed because usually when you look at the table, you get the reduction reaction the standard reduction potential. Since the anode is where oxidation occurs, you want the oxidation reaction. Therefore you would flip the reduction reaction to get the oxidation reaction...

WesleyWu_1C

Platinum is an inert electrode which is why you add that to a cell diagram when you need an electrode. In addition, you can also use graphite (Cgraphite) because it is also an inert electrode.

WesleyWu_1C

n is the moles of electrons and can be found by looking at the overall balanced redox reaction.

WesleyWu_1C

E cell naught is calculated in standard conditions and can be calculated by the standard reduction potentials. E cell is the cell potential when it's not under standard conditions and can be calculated from the equation: Ecell = Ecell(naught) -RT/(nF)lnQ.

WesleyWu_1C

Usually they give you the reduction potential for a half reaction in the table, so if you want the oxidation potential, all you do is flip the half reaction which switches the sign for E (naught).

WesleyWu_1C

n is moles of electrons, and you find it by looking at the overall balanced redox reaction for the cell.

WesleyWu_1C

In addition, you want a galvanic cell with a positive E (naught) for the reaction. So after you see the the E (naught) of the two half reactions, you can figure out which reaction will be the reduction and which reaction will be the oxidation.

WesleyWu_1C

I know that for test 2, it will just be on the 2nd page of the thermodynamics outline page and on electrochemistry. So no kinetics.

WesleyWu_1C

No, I don't think the order of the of the two molecules of the same phase matters. As long as you have anode and then cathode, and then have the electrodes at the beginning and end of the cell notation, you should be fine.

WesleyWu_1C

"n" means moles of electrons and can easily be found by looking at your balanced redox reaction and looking at the number of electrons that were transferred.

WesleyWu_1C

Lavelle told us in class that Pt and C(gr) are both good inert conductors, but that Pt is more commonly used.

WesleyWu_1C

Another way Lavelle related work and cell potential was this equation:

w = -nFE

where w = maximum work, n = moles of electrons (which is found in the balanced redox reaction), and E = cell potential of the cell.

WesleyWu_1C

When you reverse a reaction, the voltage does change sign.

When you multiply or divide the reaction, the reason E naught doesn't change is because E naught in an intensive property since you're using two standard electrodes.

WesleyWu_1C

Anode and cathode are just terms used to describe parts of the galvanic cell. The anode is the part of the half-cell where oxidation occurs and the cathode is the part of the half cell where reduction occurs.

WesleyWu_1C

I believe the porous disc is just another way to keep the charges of both cells to be neutral.

WesleyWu_1C

Yeah, my TA said the same thing about how midterms will be given back to us after lecture on Wednesday.

WesleyWu_1C

The work would be zero because in this vacuum the external pressure is zero. The system is not using any energy to push the piston up.

WesleyWu_1C

So when a reaction is at equilibrium, delta G is equal to 0. The only way delta G naught is also equal to zero is if K = 1.

WesleyWu_1C

Another way of finding delta g naught is by using the equation delta G = delta G naught + RTlnQ.

WesleyWu_1C

In addition, besides canceling out species when they are present on both sides of a reaction, you can also cancel electrons if there are the same number of electrons on both sides.

WesleyWu_1C

Heat capacity is an extensive property, but specific heat capacity is an intensive property. The reason why is because specific heat capacity is defined as per 1 gram.

WesleyWu_1C

When a question tells you there s a change in pressure, you need to know more than that to see which side the reaction will shift to. If there was an increase in pressure because there was a decrease in volume, then the reaction favors the side with the fewer moles of gas. If there was an increase i...

WesleyWu_1C

An irreversible free expansion tells you that there will be constant pressure, so work = -P x delta V.

WesleyWu_1C

To calculate Gibb's free energy, you can use the same method as Hess's law. You can also use the equation: delta G = delta H - T(delta S).

WesleyWu_1C

When you increase the volume, which decreases the pressure of the gas molecules and changes the concentration of the gas molecules, the reaction will shift to the side with more moles of gas.

WesleyWu_1C

Also, to find out what delta g is and to figure out if the reaction is spontaneous, you use the equation: delta G = delta H - T(delta S).

WesleyWu_1C

Distance traveled is a great example of a nonstate property because lets say you take 20 steps forward and then 10 steps backward. How many steps did you take? If distance traveled was a state property you would do final minus initial which would be 10 - 0 = 10 (we are saying your starting point is ...

WesleyWu_1C

Just to add on the standard conditions for Delta G° are 1 atm for pressure and 25 degrees Celsius.

WesleyWu_1C

The standard enthalpy of formation is 0 when elements are in their stable form. For example, since the most stable form of oxygen is O2, then the standard enthalpy of formation is 0. Another example, is zinc(s). The standard enthalpy of formation for zinc in its solid state is 0 because zinc's most ...

WesleyWu_1C

Since enthalpy change is usually under constant pressure, maybe that's why only Cp equals enthalpy change.

WesleyWu_1C

Steam would cause more severe burns because if you look at the heating curve, you will see that steam will have more enthalpy than boiling water at 100 degrees Celsius. More enthalpy means more heat which means worse burns.

WesleyWu_1C

One of the examples that Dr. Lavelle gave for another state property is altitude. For altitude, the path doesn't matter. What matters is where the hiker ends up.

WesleyWu_1C

I think it depends on what information is given to you in the equation. For example, it the question only gives you bond enthalpies then you should use bond enthalpies for your calculations, even though bond enthalpies is the most inaccurate.

WesleyWu_1C

Temperature remains constant during these phase changes because the heat is actually breaking the intermolecular forces.

WesleyWu_1C

Because even though by adding the inert gas the pressure inside is increasing, the equilibrium constant is a ratio of the concentration of the products and reactants. The inert gas is not a product or reactant, and the moles and volume of the products and reactants are still the same. Concentration ...

WesleyWu_1C

A strong acid would have a higher Ka. For example, a strong acid could have Ka = 10^-1. The formula for pKa is pKa = -logKa. If you do -log(10^-1), you get pKa = 1. Therefore this strong acid has a low pKa. I like to first think about Ka and then work backwards. A higher Ka means 10^-x where x is a ...

WesleyWu_1C

Noble gases are very stable on their own because their outer orbital is already filled up with the max number of electrons (8). They wouldn't need or want to form covalent bonds.

WesleyWu_1C

When Ba(OH)2 is placed in water, it dissociates into Ba^2+ and 2OH-. So the reaction would be Ba(OH)2 + H2O -> H2O + Ba^2+ + 2OH- For every 1 mole of Ba(OH)2, there are 2 moles of OH-.

WesleyWu_1C

Yes, I believe so.

WesleyWu_1C

There's a possibility where you get two x values that are both positive, but when you do initial concentration of reactant minus one of the x values, you get a negative value. It's important to check to see if the equilibrium concentrations turn out positive.

WesleyWu_1C

I think your mistake is that when you were trying to change the equilibrium constant to a quadratic equation you accidentally did 85 x .0008 = .68, when the actual answer is 85 x .008 = .068. This difference of 10^-1 probably was the reason why you were getting the wrong answer.

I hope this helps.

WesleyWu_1C

No, adding an inert gas does not change the equilibrium constant or cause any side to be favored.

WesleyWu_1C

Also, if the question gives you a Ka value, then you know that the acid is weak because only weak acids have a Ka value. The same goes for bases with their Kb value.

WesleyWu_1C

The way I explain it to myself is that these stoichiometric coefficients are just telling us more than one of these species was formed. For example, in the balanced chemical equation to form water, 2H2 + O2 <-> 2H2O, the equation is telling us that two H2O species were created. Another way of writin...

WesleyWu_1C

I think the explanation is trying to say that even though you might start with an initial higher pressure of reactant, by the time the equation reaches equilibrium, the equilibrium constant K will still be the same. The only thing that changes the equilibrium constant is changing the temperature bec...

WesleyWu_1C

The way I could tell Cl2 was more stable was the fact that the K for equation for Cl2 <-> 2Cl was smaller than the K for the F2. A smaller K, means that compared to the other reaction, the reactant (Cl2) is favored more. In addition, if you compare the equilibrium concentrations of Cl2 to F2, you se...

WesleyWu_1C

The difference between Q and K is that K is the equilibrium constant which in other words is when the reaction has reached equilibrium. Q, the reaction quotient, is something you can do during anytime of the reaction. By comparing Q to K, you can see the direction of the reaction. If Q=K, then you k...

WesleyWu_1C

When K>1, that means the reaction favors the products or favors the right side. Also, if you think about the definition of K and how it's the concentration of products over the concentration of reactants, then when K is greater than 1, that means that there are more products than reactants when the ...

WesleyWu_1C

To determine the direction of an equilibrium reaction you can just compare K to 1. If K <1, than the reaction favors the reactants and if K >1 then the reaction favors the products. Dr. Lavelle uses 10^3 or 10^-3 as comparison when he uses strongly favors. For example, if K<1, the reaction favors th...

WesleyWu_1C

H2PO4- can either accept or donate an H+. It's one of the examples of an amphiprotic molecule, where it can either give or receive a proton.

WesleyWu_1C

Yeah, I also believe the answers should be 1.60 and 1.70.

WesleyWu_1C

You have to look at the cation and anion of the salt and determine if they are stable as cations and anions. If they are not stable as cations and anions, then they will probably affect the pH.

Yes, BaCl would not affect the pH because Ba+ is in group 2 and because Cl- is a stable anion.

WesleyWu_1C

I don't know if we can make that general statement that coordination number is synonymous with regions of electron density. I feel like most times that statement is true. I think the best way to calculate out the coordination number is to draw out the Lewis Diagram and count all the coordinate coval...

WesleyWu_1C

When we say that an acid is stronger, we mean that more of the products are formed. For example, the strong acid HCl dissociates into H+ and Cl-. Since we know that HCl is a strong acid, we know that Cl- is a stable anion because if it wasn't a stable anion it would want to combine back with H+ to b...

WesleyWu_1C

When a complex has an overall negative charge, then you would add -ate to the end of the transition metal. So iron would become ironate, but there is a rule where you would use the latin name for a few of the elements. Thus it would be ferrate.

WesleyWu_1C

The coordinate covalent bond is when 2 electrons, that came from one atom, are being shared between that same atom and another atom. An ionic bond is more about the attraction between the positive charge on the cation and the negative charge on the anion.

WesleyWu_1C

Besides looking at the electronegativity, you can also look at the bond strengths. Since Cl has a larger atomic radius than F, the bond between HCl would be longer than the bond between HF. A longer bond means a weaker bond, so it would be easier for the H to be broken off the HCl than HF. Since it'...

WesleyWu_1C

I think the best way to determine if a ligand is polydentate is to draw out the lewis diagram and to remember that the pattern for bonding sites is "atom - space - space - atom." For example, if you look at ligand edta, then you will see that pattern.

WesleyWu_1C

I don't think the order of the ligands matter as much when writing out the chemical formula. If you're interested, the book tells you to put the ligands in alphabetical order base off their chemical symbols and single element ligands come first before molecular ligands.

WesleyWu_1C

Yes, I believe the final will include everything we have learned this quarter.

WesleyWu_1C

The way I imagine it is that hybridization is when orbitals are combined/mixed together. So for example, sp^3 is when 1 s-orbital and 3 p-orbitals combine together and sp^2 is when 1 s-orbital and 2 p-orbitals combine together. Since in the sp^2 hybrid orbital, it is only using 2 p orbitals, then sp...

WesleyWu_1C

Pi bonds interact side to side, so when molecules rotate, the p-orbitals would no longer be side to side, which would break the pi bonds.

WesleyWu_1C

I think understanding the molecules that have a biological importance that Lavelle went over in class like cisplatin and myglobins will be good to know. In addition, during lecture, he went over a bunch of elements in the first row of the d-block and went over their biological importance.

WesleyWu_1C

Usually the Bronstead Acid in a chemical reaction is also the Lewis Acid of the same chemical equation.

WesleyWu_1C

Bent and anguler are the same shape, but a bent molecule might not have the same bond angles as another bent molecule. For example, for AX2E, it would be bent and would have bond angles a bit less than 120 degrees. For AX2E2, it would also be bent, but the bond angles would be less than 109.5 degress.

WesleyWu_1C

In addition, a great way to see if you fully understand the material is to go to Lavelle's office hours even if you don't have a question. Lavelle has his office hours where it's like a group discussion, so sometimes even sitting there and hearing other students ask questions will improve your learn...

WesleyWu_1C

If you go by the definition of a bond angle which is the angle for three consecutive atoms, then there wouldn't be a bond angle for a diatomic molecule.

WesleyWu_1C

Usually when there is at least one lone pair on the central atom, then the bond angle is slightly less than the expected bond angle.

WesleyWu_1C

An electron density can either be a lone pair or a covalent bond.

WesleyWu_1C

The reason why the molecule would not be a trigonal planar is because trigonal planar means that the bound atoms are about 120 degrees away from each other, but that would not make sense because there are 2 lone pairs which means there is very strong repulsion between the lone pairs and the lone pai...

WesleyWu_1C

Just know the basic bond angles for the shapes where there are no lone pairs attached to the central atom. The only bond angle that is a bit tricky to figure out is that for tetrahedral the bond angle is 109.5 degrees.

WesleyWu_1C

Something that might help you determine if a molecule is polar is to consider it's shape according to the VSEPR.

WesleyWu_1C

My TA told me test 2 will just be from the material after the midterm.

WesleyWu_1C

For an e-, you can find the wavelength by using the de Broglie's equation lambda = planck's constant/momentum. You can't find the frequency of an e-.

WesleyWu_1C

A simple way I think about the results of the photoelectric experiment is that increasing the intensity only increase the number of photons while increasing the frequency increases the strength/energy per photon.

WesleyWu_1C

The easier way to calculate which atom has the partial positive charge and which atom has the partial negative charge is by looking at the eletronegativity for each atom. If the atom has a higher electronegativity then the other atom, then it will have the partial negative charge.

WesleyWu_1C

Between any two different molecules, there is a dipole moment, so there will be dipole moment for H in CH3Br. But sometimes, the dipole moments are canceled out by equal dipole moments from the opposite direction.

WesleyWu_1C

The two main exceptions to reading the periodic table for the electronic configuration are Chromium and Copper. Chromium will have a lower energy from a half filled d subshell so it's e- configuration is [Ar] 3d^5 4s^1. In addition, copper will have a lower energy with a full d subshell so it's e- c...

WesleyWu_1C

The reason why you can only use c = λv for light is because pretty much everything else you need to find the wavelength for, has mass. For example, an electron has mass and mass is not considered in the c = λv. That's why if you want to find the wavelength (λ) for an electron you use the equation λ ...

WesleyWu_1C

S = shared electrons. For example, if there is one bond between 2 atoms, then the s=2 (2 shared electrons).

WesleyWu_1C

You unfortunately did it wrong. Always remove electrons in the outermost energy level, which in this case is the 4s orbital. We know the original e- configruation is [Ar] 3d^10 4s^1, so when it become Cu^1+, the one electron in the 4s is removed, leaving behind an e- configuration of [Ar] 3d^10. I t...

WesleyWu_1C

The only exception to the ionization trend that was listed in the book (I think) was oxygen because the electron electron repulsion in one of 3p orbitals increases the energy and causes one of the two electrons to be removed from the atom a bit easier.

WesleyWu_1C

Another great example of a lewis structure bent is H20. The reason for this bending is because the lone pair of electrons have little more repulsion and cause the bonded electrons to get a bit closer together.

WesleyWu_1C

If you remember in class, Cu is an exception for telling the electron configuration from the periodic table. From reading the periodic table, we would expect the configuration to be [Ar]3d^9 4s^2, BUT through experiments, scientists have found that the e- configuration is actually [Ar]3d^10 4s^1 bec...

WesleyWu_1C

Write the order of the electron configuration from increasing energy level (n=1, 2, 3, etc.). So that's why if you remember in class we put for element Sc's electron configuration the 3d shell before the 4s shell even though, if you read it based off the periodic table 3d comes after the 4s shell.

WesleyWu_1C

The thing that is common to the lines within a series is that the lines in the same series all have to do with an electron falling down to the same energy level. For example, in the Balmer Series, those lines all have the electron fall down to n=2 energy level. In the Lyman Series, those lines have ...

WesleyWu_1C

The electron configuration in the periodic table is when the atom is in its ground state, which means that any other electronic configuration of that atom would be its excited state. So the ground state of Li is [Ar] 1s^2 2s^1, which means the example you gave in your post would be in the excited st...

WesleyWu_1C

For a photon's energy to be absorbed by an electron, the photon's energy must equal the energy difference between two energy levels. If the photon's energy is higher or lower than the energy difference between any two energy levels, then that the photon's energy is not absorbed and the photon just p...

WesleyWu_1C

Since n=3, the electron is in the third energy level, which means the electron can be in the s orbital (l=0), p orbital (l=1), or d orbital (l=2).

WesleyWu_1C

Electromagnetic radiation will only be emitted if the electrons move down from a higher transition level to a lower transition level (ground state). The reason why the energy for this electromagnetic radiation emitted is always positive is because there is a conservation of energy . So when an elect...

WesleyWu_1C

In today's lecture, the reason why the electron was in 2p-base x state was because he was using the picture in his slides that showed the breakdown of l and m-base l for the first few energy levels. If you recall, in that specific picture, it labeled the 2p orbitals from left to right x, y, and z an...

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