CHEMISTRY COMMUNITY

Tracy Tolentino_2E

Second order has a negative slope because it is 1/[A] over time. As [A] is the reactant concentration, by decreasing over time, the second order graph increases because 1/[A] becomes bigger over time.

Tracy Tolentino_2E

I say stick to Kelvin because that is typically what we use. Plus in most equations, the gas constant is in the equation which is 8.314 J/(K * mol).

Tracy Tolentino_2E

When a bond is broken, energy is required because it takes energy to break bonds. Similarly, energy is released when bonds are formed.

Tracy Tolentino_2E

They are not the same precisely because of the y-axis. Because they are the integrated rate laws, they are supposed to be linear. They have to follow the y = mx+b format. As a result, the slope = -k, but the y axis are different: first order is ln[A] and zero order [A]. You could tell which order re...

Tracy Tolentino_2E

What is this pre-equilibrium approach? How does this affect the rate law of a reaction?

Tracy Tolentino_2E

I know we had to use Nernst equation, but what was the point of mention "3 moles of A(s)"? Was that supposed to trick us?

Tracy Tolentino_2E

If given the reaction mechanisms, how can you identify if a catalyst was involved?

Tracy Tolentino_2E

In Test 2, there was a problem that asked me what happens to the E(cell) if the mass of the anode is halved. What does happen to E(cell) if you change the mass or concentration of the electrode?

Tracy Tolentino_2E

The Arrhenius equation is used to find the rate constant at a different temperature. It shows the rate constant’s dependence on temperature.

Tracy Tolentino_2E

Rate constant is the comparative rates of reaction and product while rate is the measurement of how fast or slow a reaction occurs. A rate constant only changes with temperature but rate is affected by change in k or concentration.

Tracy Tolentino_2E

If states are the same, you use a comma to separate the elements. If the elements are in different states use a vertical line.

Tracy Tolentino_2E

Because all the E potentials are given as reduction values. You have to flip this value to get the oxidation value.

Tracy Tolentino_2E

(knot) just means that the E or Gibbs free energy are at standard conditions. So 25 degrees C, 1 atm, and 1.0 M.

Tracy Tolentino_2E

Generally, that's what we assume the cathode and anode to be. If not, you would need to see the oxidation numbers to figure out which reaction is which.

Tracy Tolentino_2E

We know pH as the -log[H+].
Since Q is [products]/[reactants], we assume H+ to be a product.
For the Nernst equation, instead of E(knot) - (RT/nF)lnQ, we would use E(knot) - (0.0592/n)logQ.

Tracy Tolentino_2E

Yes, reducing agents are the ones that causes another substances to reduce (the substance oxidizes) and oxidizing agents are the ones that causes substances to be oxidized (the substance reduces).

Tracy Tolentino_2E

He is probably going to give us a list of half reactions and make us use only some of them. So yes, we would probably need to search for them on a table.

Tracy Tolentino_2E

Can we use half lives to determine the time at which concentrations decreased by 1/4 instead of 1/2? Subsequently, what about decreasing to only 1/4 or 1/8 concentration? If so for the latter, do we take the half life, then take it once more? or do we multiply the half life by something?

Tracy Tolentino_2E

What do we use the differential rate laws for? I know integrated rate laws are for concentration vs time, but when do we use the differential ones?

Tracy Tolentino_2E

The following redox reaction is used in acidic solution in the Breathalyzer test to determine the level of alcohol in blood: H+ (aq) + Cr2O7^2- (aq) + C2H5OH(aq) ---> Cr^3+ (aq) + C2H4O(aq) + H2O(l) Identify the elements undergoing oxidation or reduction and indicate their initial and final oxidatio...

Tracy Tolentino_2E

In the equation deltaG = -nFE, how do we figure out the n (if its moles of electrons).
For example, in part a 2Ce^+4(aq) + 3I^-(aq) + 2Ce^3+(aq) + I3^-(aq), Ecell° 5 11.08 V
How do I find the n in the equation?

Tracy Tolentino_2E

The Van't Hoff equation relates the change in equilibrium constant (K) and to a change in temperature, given that deltaH and deltaS are constant.

Tracy Tolentino_2E

We had Pt because a metal is needed as an electrode for the cell diagram to proceed. As it is a solid conductor, Pt is chosen because it is inert (not changed in reaction but helps with reduction or oxidation).

Tracy Tolentino_2E

G(not) is the standard Gibbs Free energy. So it's the energy in standard conditions. (1 M, 1atm, 25 degrees Celsius)
G is Gibbs Free energy in other conditions

Tracy Tolentino_2E

From a cell diagram, how can you reverse back to the half reactions if both reactants and products are same states? And to that end, can we also figure out voltage from the diagram?

Tracy Tolentino_2E

In the salt bridge of the cell diagram, does the salt have to have the same charge as the electrodes for the ions to flow continuously? And would the E(not) of the diagram change if we change the conductors (the alligator clips and which they connect to)?

Tracy Tolentino_2E

In a basic solution, bases dissolve into OH- ions, so balancing these reactions require OH-. We would add OH- ions to whichever side that has H+ ions, so that water can form. 1. Separate half reactions. 2. Balance elements that aren't O or H 3. Balance O by adding H2O 4. Balance H by adding H+ 5. Ba...

Tracy Tolentino_2E

Concentration affects cell potential because of Le Chatelier's principle. An increase in concentration in one of the reactants causes the reaction to proceed right to make more products. This means a higher positive voltage being produced.

Tracy Tolentino_2E

In the Nernst equation, E = E(not) - (RT/nF)lnQ.
E(not) is the standard cell potential
R is the gas constant (8.314 J/K mol)
T is temperature (in Kelvin)
n is the moles of electrons transferred
F is Faraday's constant . (96485 C/mol)
Q is the concentration of products over concentration of reactants

Tracy Tolentino_2E

Why is it that chemical energy and electrical energy can turn into one another?

Tracy Tolentino_2E

Can someone explain the part about K being less than or equal to 1? I understand that when deltaG is positive, it's spontaneous and if negative, nonspontaneous, but does that have anything to do with the sign of deltaS and deltaH?

Tracy Tolentino_2E

If we are given deltaS and deltaH in nonstandard conditions, can we still use the Van't Hoff equation?

Tracy Tolentino_2E

For the Van't Hoff equation, I know we use it to find K at different temperature, but does pressure matter or affect this equation?

Tracy Tolentino_2E

Can someone explain how to figure out oxidation numbers? Like with the example Professor Lavelle used during class on Friday.

Tracy Tolentino_2E

Hi guys, I know this is not a chemistry question but has anyone seen my calculator? It’s a Casio. I accidentally left it today at the 1 pm lecture. I sat in the middle row, around the 3rd seat to the front. Please tell me if you guys found it.

Tracy Tolentino_2E

Entropy is actually an extensive property, where the value depends on size or mass. Intensive means the value does not depend on the size.

Tracy Tolentino_2E

Gases have a higher entropy than liquids because they have a higher number of microstates. They occupy a greater volume than liquids and can move at greater speeds. As a result, they can occupy different positions and arrangements.

Tracy Tolentino_2E

Under what conditions would we use q=mCdeltaT? and for q=-q, does the phase of the substance matter? Or do we have to calculate both the change in temperature and the phase change?

Tracy Tolentino_2E

When do we use specific heat capacity? And what equations would use this instead of molar heat capacity or even heat capacity in general?

Tracy Tolentino_2E

At constant pressure, q (heat) equals delta H (the change in enthalpy).

Tracy Tolentino_2E

No, transfer of mass isn't allowed because mass is conserved within the boundaries of the system. Since heat or light aren't physical, they are allowed to transfer outside the system.

Tracy Tolentino_2E

internal energy of a system refers to the sum of potential energy of the system along with kinetic energy.

Tracy Tolentino_2E

isothermal expansion is where there is no change in temperature, temperature stays constant. In an ideal gas, the internal energy equal (3/2)nRT. From that, the change in internal energy is (3/2)nR(deltaT) because n and R are both constants. With deltaU also being q+w, we can say q+w=(3/2)nR(deltaT)...

Tracy Tolentino_2E

Molar heat capacity is affected by molar mass. NO2 has a higher molar heat capacity because it is a larger molecule due to being bonded with 2 oxygen molecules instead of 1 like NO. Along with that, NO2 has a higher molar mass than NO.

Tracy Tolentino_2E

Microstates are a part of the Boltzmann equation. Microstates (W) is the number of ways in a system for energy of molecules to be arranged. In the example given, there are two atoms with two same energy states. Therefore, there are 4 different ways (micro states) of arranging the energy of the atoms...

Tracy Tolentino_2E

The main difference between irreversible and reversible expansion work is that the irreversible doesn't remain in thermodynamic equilibrium while reversible does. In reversible, the external and internal pressures of the system are equal throughout the process. In irreversible, there's a difference ...

Tracy Tolentino_2E

If the volume is constant, q (heat/enthalpy) equals the change in internal energy of the system (deltaU). Despite that, change in enthalpy equals deltaU + V(deltaP), because no work is being done on the system due to that constant volume.

Tracy Tolentino_2E

How is it that at 100C, both liquid and gas can exist at the same time? And why does steam require more energy to be converted?

Tracy Tolentino_2E

Bond enthalpies can be used to calculate the net enthalpy change.
For the reactants, bond energies are positive because it takes energy for bonds to break. For products, energy is negative because when bonds form, energy is released. We then add all the energy values to gain the net enthalpy change.

Tracy Tolentino_2E

Are bond enthalpies always given to us or do we have to figure them out? Also, does the amount of bonds being formed or broken matter when calculating the overall enthalpy change? For example, if 2 bonds of C-H were formed in a reaction, do we multiply its’ bond enthalpy by 2? And do coefficients ma...

Tracy Tolentino_2E

Do solids and liquids have standard enthalpies of formations?

Tracy Tolentino_2E

So in lecture, Professor Lavelle describes why steam causes severe burns compared to boiling water using a chart. Can someone explain the reasoning?

Tracy Tolentino_2E

Ka and Kb relate to pH and pOH from Kw.
Kw = Ka * Kb
With that, Kw = [H30+][OH-]
pH = -log[H30+] while pOH=-log[OH-]

Tracy Tolentino_2E

When do we use the Kw value?

Tracy Tolentino_2E

Q is the reaction quotient and is calculated at any time during a reaction. Q will change as time passes. Q and K are similar except that K is the value when the reaction is at equilibrium. If Q>K, the reverse reaction is favored, and if Q<K, the forward reaction is favored. IF Q=K, the both reverse...

Tracy Tolentino_2E

If the change value, x, divided over the initial concentration is less than 5% of that initial, it's safe to assume that the change was negligible. This is to affirm that when we have a quadratic equation, we don't have to do the quadratic formula to solve for x.

Tracy Tolentino_2E

If both of those reactions are combined and form the third reaction, then we can add them. As a result, the K values can be multiplied together to find the K value of the third reaction.

Tracy Tolentino_2E

When do we use ICE tables? I assumed it was when we had to find concentrations of the products, given K and the initial concentration(s).

Tracy Tolentino_2E

Why does only a change in temperature affect K and not pressure or concentration? How does Le Chatelier principle apply to this if the principle sees the direction of the reaction due to changes?

Tracy Tolentino_2E

Is there a relationship between pKa and pH? If so, what is it?

Tracy Tolentino_2E

Do we not have to calculate anything?

Tracy Tolentino_2E

A gaseous mixture consisting of 2.23 mmol N2 and 6.69 mmol H2 in a 500.-mL container was heated to 600. K and allowed to reach equilibrium. Will more ammonia be formed if that equilibrium mixture is then heated to 700. K? For N2(g) + 3H2(g) <---> 2NH3(g), K=1.7x10^-3 at 600.K and 7.8x10^-5 at 700. K...

Tracy Tolentino_2E

When doing the ICE tables, do we only use concentration of the reactions? What if we are given partial pressures?

Tracy Tolentino_2E

Write the expression for K for each of the following reactions: (A) 2C2H4(g) + O2(g) + 4HCl(g) <—> 2C2H4Cl2(g) + 2H2O(g) Why is it that we write K for this problem using pressure yet for 5G.7 where we essentially do the same thing after balancing the reaction, they use Kc for the problem. Which is c...

Tracy Tolentino_2E

Why are liquids not included in the equilibrium constant? Do we only included gases within K?

Tracy Tolentino_2E

What does the value of K supposed to tell us about the reaction? And what does strongly favor mean within equilibrium?

Tracy Tolentino_2E

The name is Ammonium amminetrichloridoplatinate(II). Why is it platinate and not platinum?

Tracy Tolentino_2E

So the name for [Fe(OH)(OH2)5]Cl2 is pentaaquahydroxidoiron(III) chloride. But how did they get the charge on iron? And why is it chloride if there are two chloride, shouldn't it be dichloride?

Tracy Tolentino_2E

How can you tell a ligand is a polydentate? And what are examples of anionic ligands, how are they different from anions?

Tracy Tolentino_2E

How can you tell if an acid is a Bronsted acid or a lewis acid? Can an acid be considered both or does it have to be or the other?

Tracy Tolentino_2E

Why are oxoacids more readily lose H+ ions? And what are "oxoacids"?

Tracy Tolentino_2E

Can we calculate the pOH from pH? What is their relationship?

Tracy Tolentino_2E

What are amphoteric compounds? What does it mean "amphoteric oxides"?

Tracy Tolentino_2E

How do we know if an anion is stable? And what is Ka value?

Tracy Tolentino_2E

When do we need to find pOH and why would be beneficial to find it?

Tracy Tolentino_2E

Yes, it is essentially a complex that contains the ligand and forms a ring of atoms that includes the central metal atom.

Tracy Tolentino_2E

Polydentates refers to a ligand molecule with more than one donor atom.
Bidentates have two atoms that can bond to a central atom or ion.
Ambidentate are like monodentates where they have one atom that can bond to a central atom or ion, but can do it at two possible locations.

Tracy Tolentino_2E

It is linear as it has 16 valence electrons. The carbon does not have lone pairs and forms double bonds with the oxygens. So it would be AX2.

Tracy Tolentino_2E

Why is NH3 considered a neutral atom?

Tracy Tolentino_2E

Seesaw shape occurs when you have 4 atoms surrounding the central atom along with a lone pair. It would occur because during the trigonal bipyramidal, we would have three atoms in the planar, 120 degrees apart, and then an atom on the top and bottom of the central atom, making them 90 degrees from t...

Tracy Tolentino_2E

It means that the orbitals are not completely an s,p,d orbital. It is a mix of them, with a different energy and shape.

Tracy Tolentino_2E

a) sp
b) sp2
c) sp3
d) sp3

Tracy Tolentino_2E

When does a dipole-dipole intermolecular force occur?

Tracy Tolentino_2E

How does Cisplatin stop cell division? Why doesn't Transplatin have the same effect when forming a coordinate compound with DNA?

Tracy Tolentino_2E

Molecular shape excludes the electron lone pairs while electron geometry involves them.

Tracy Tolentino_2E

We got to memorize the basic angles like 90, 120, and 180 and we should be able to predict if they are greater than or less than these angles. We don’t need to know the unique ones. I just imagine what the molecule looks like in a 3D setting based on the name of the shape.

Tracy Tolentino_2E

Lone pairs aren’t considered in identifying a molecules’ shape because they are not bonded to the atom. When lone pairs are around the central atom, the atoms bonded to it are forced to move due to the electron repulsion from the lone pairs.

Tracy Tolentino_2E

Ion- dipole is between an ion and a polar molecule while dipole-dipole is between polar molecules.

Tracy Tolentino_2E

Why is the electron repulsion strength stronger for lone-lone PR> lone-bonding PR> bonding-bonding PR?

Tracy Tolentino_2E

Can someone re-explain how to write VSEPR notation? I did not write the notation at all during my notes.

Tracy Tolentino_2E

London dispersion forces are the weakest of the intermolecular forces. I think they take priority in larger atoms because of more surface area to distort the electrons.

Tracy Tolentino_2E

Polarizability is the tendency by the anion to be polarized by the cation and polarizing refers to the power of the cations to distort the electrons of the anion.

Tracy Tolentino_2E

There are bonds within a molecule like covalent and ionic bonds and bonds between molecules like london dispersion forces and hydrogen bonding. The intramolecular (covalent/ionic) are stronger than the latter (intermolecular).

Tracy Tolentino_2E

How does a dipole moment differ from a dipole interaction? Is it possible for a molecule to have both? And also, what is ion-ion dipole?

Tracy Tolentino_2E

Does H bonding only work with Fluorine, Oxygen, and Nitrogen? Why only them and not other elements? Why is this type of bonding not as strong as covalent bonding?

Tracy Tolentino_2E

You can't really tell. You can say it's positive or negative but the other electrons in the other subshells have to have the same spin.

Tracy Tolentino_2E

How does the shape of the molecule affect the strength of the dipole interactions? And why would it matter?

Tracy Tolentino_2E

How do we know if a molecule has a dipole moment? And why does the arrow have to point to the lowercase delta positive?

Tracy Tolentino_2E

Can someone explain the concept of a molecule having both ionic and covalent characters. How do we determine which is more?

Tracy Tolentino_2E

We have to indicate that it is the hybrid of all the resonance structures.

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