CHEMISTRY COMMUNITY

Clara Hu 1G

For reversible, PV=nRT, and w=-nRTln( $\frac{V_{2}}{V_{1}}$ ). For irreversible, w=-P $\Delta$ V.

Clara Hu 1G

In this homework problem, the second K is actually 10 times smaller than the first, so you would actually divide the first K by 10 rather than how you did 10 times the first K.

Clara Hu 1G

The change in internal energy will be 0 for all isothermal expansions, whether the expansion is reversible or irreversible.

Clara Hu 1G

They can both be used because ln of any number is equal to 2.303log of the same number.

Clara Hu 1G

According to thermodynamics, the reaction from diamond to graphite is spontaneous and favorable. However, because kinetics rather than thermodynamics is controlling this reaction, it occurs extremely slowly. So, diamond is kinetically stable, but thermodynamically unstable.

Clara Hu 1G

Because the rate of the reaction should have the units of mol/L s, for zero order, rate=k, so k has the units of mol/Ls. For first order, the units of k times concentration (mol/L) needs to be mol/L s, so the units of k are s^-1. For second order, the units of k times (mol/L)squared needs to be mol/...

Clara Hu 1G

In part c it is asking for the unique rate of the reaction, so you divide the rate for the certain term by its stoichiometric coefficient.

Clara Hu 1G

Ka is the equilibrium constant for the dissociation of acids, so in this problem you would calculate it the same way you calculate regular k.

Clara Hu 1G

Also, if you plot a straight line with [A] vs t, it is zero order. ln[A] vs t means that it is first order, and 1/[A] vs t is second order.

Clara Hu 1G

Using log makes it easier to find the pH because pH= - log [H+].

Clara Hu 1G

Also, the overall reaction order is found by adding together the reaction orders of the substances whose concentrations affect the reaction rate.

Clara Hu 1G

This is what happens in a concentration cell.

Clara Hu 1G

E is cell potential, which is an intensive property, and its units are in Volts, which is J/C.

Clara Hu 1G

You would use $\Delta S = nRln(\frac{v2}{v1})$

Clara Hu 1G

Gibbs Free Energy is energy associated with chemical reactions and is equal to $\Delta H-T\Delta S$ . Standard Gibbs Free Energy is when things are occurring at a standard state, which I believe should be 25 degrees C and 1 atm.

Clara Hu 1G

I think that Delta G is the free energy change of a reaction. Delta G r is the Gibbs Free Energy of the reactants and Delta G r knot is the standard free energy for the reactants.

Clara Hu 1G

Also, the anode, oxidation half reaction, is always on the left, while the cathode, reduction half reaction, is always on the right.

Clara Hu 1G

$\Delta$ S total must be greater than zero, or positive, to be spontaneous. This is part of the Second Law of Thermodynamics.

Clara Hu 1G

For this example, at 333K when deltaG=0, Br2(l) and Br2(g) are at equilibrium or boiling point, so if the temperature increases above 333K, the forward process would be favored and Br2 would vaporize to the gas phase only.

Clara Hu 1G

When delta H is positive, it takes a very high temperature for entropy to dominate and cause delta G to become negative. So delta H + is only spontaneous at high temperatures.

Clara Hu 1G

Heat and work are not state functions because work is proportional to the distance traveled, meaning that the path taken does matter.

Clara Hu 1G

It doesn't really matter if the change in temperatures are in Kelvin or Celsius because the Kelvin is in the same scale as Celsius, just +273, just make sure that the initial and final temperatures are both either in Kelvin or Celsius.

Clara Hu 1G

You would use q=mc(delta)T if you knew the mass of a substance and had the specific heat capacity while you would use q=nc(delta)T if you knew the number of moles and had the molar heat capacity because you want the final units of q to be in Joules.

Clara Hu 1G

Entropy decreases when an ideal gas is compressed because the volume decreases and pressure increases.

Clara Hu 1G

For 8.91, I first used q=mC \Delta T to find the amount of heat needed to raise the liquid water by 5°C, which was 0.312kJ. Then, I divided it by 0.5 hours to find the amount of heat transferred per hour, which was 0.624 kJ/hr. I multiplied that by 10.5 hours which was the time it took an ice cube t...

Clara Hu 1G

When using specific heat capacity to get q, only the mass and change in temperature are needed because the equation is q=mC \Delta T. The units for q is in joules and specific heat is in J/g°C, so when you multiply the specific heat by the mass (g) and change in temperature, (°C), you are left with ...

Clara Hu 1G

Bomb Calorimeters are isolated systems as nothing exchanges with the surroundings because the bomb calorimeter is insulated and does not allow heat energy to transfer to the surroundings.

Clara Hu 1G

Also, a Bomb Calorimeter is used during dconstant Volume calorimetry because the reaction chamber is a fixed volume.

Clara Hu 1G

You would use the specific heat capacity when you have the mass, while you would use molar heat capacity when you know the amount of moles because specific heat capacity measures the joules of heat needed to raise one gram of a substance by one degree C, while molar heat capacity measure the joules ...

Clara Hu 1G

An example of when the enthalpy of formation is 0 is when two Oxygen atoms form O2. This is because O2 is the natural form of oxygen.

Clara Hu 1G

In the example given in class, hypochlorous acid was the most acidic out of HClO, HBrO, and HIO because CL has the highest electronegativity which stabilizes the negatively charged O by withdrawing electron density.

Clara Hu 1G

Also, on the periodic table, there is a diagonal band of amphoteric oxides found between the metal oxides (bases) and nonmetal oxides (acids) that form amphoteric compounds.

Clara Hu 1G

For SOCl2, the oxygen atom and two chlorine atoms are each bonded to sulfur by a single bond, and sulfur also has a lone pair to complete the octet. Then, because there are four areas of electron density with one lone pair, the shape is trigonal pyramidal.

Clara Hu 1G

Iodine has d-orbitals so it has an expanded octet and can accommodate more than 8 valence electrons. ICl3 is T-shaped because it has 5 areas of electron density with 2 lone pairs, and the Cl-I-Cl bond angle is less than 90 degrees because of the repulsion from the lone pairs.

Clara Hu 1G

T-shaped structures have 5 regions of electron density with 2 lone pairs, while Trigonal Pyramidal structures have 4 regions of election density with 1 lone pair.

Clara Hu 1G

For ICl3, there are 5 regions of electron density, but only 3 are occupied by atoms, so there are two lone pairs, which means that it is T shaped.

Clara Hu 1G

The biological function of cobalt is that it is found in vitamin B12.

Clara Hu 1G

Like in the example that was done in class with C2H4, the unhybridized 2p orbitals on each C atom overlapped side-to-side to form the pi bond.

Clara Hu 1G

The Boron in BF3 does not have a full octet because BF3 is a Lewis Acid, and the empty p-orbital on B can accept an electron lone pair from a Lewis Base.

Clara Hu 1G

When the VSEPR formula is AX4E, the shape is always seesaw. The 5 pairs of electrons are arranged in trigonal bipyramidal, with 4 bonding pairs and 1 lone pair. Since only 4 of the 5 positions are occupied by atoms, they form the seesaw shape.

Clara Hu 1G

Common examples of molecules with covalent bonds are HI, HBr, and HCl, whereas salts like KCL, KF, and LiF have ionic bonds.

Clara Hu 1G

To add on, large, electron rich anions, can be highly distorted, so they have more covalent character, and are described as being highly polarizable. Small, highly charged cations, which have high polarizing power, cause large distortions and also lead to more covalent character.

Clara Hu 1G

So just to add on, in the case of KCl, K becomes a cation with a charge of +1 while Cl forms an anion with charge -1, so the attraction between the positive and negative charges causes them to form an ionic bond.

Clara Hu 1G

It is true because non-metals do not form cations because their ionization energies are too high, so they share electrons to form covalent bonds.

Clara Hu 1G

Also, an electron that spins up and an electron that spins down can be paired in an orbital, while electrons with the same spin avoid each other and cannot be in the same orbital because no two electrons can have the same set of four quantum numbers.

Clara Hu 1G

Also, at a node, the wavefunction is zero, so the electron density at the node is also zero, and the probability of finding an electron there is zero.

Clara Hu 1G

Yes, you would use the equation E= $\frac{1}{2}$ mv² and plug in $\Delta$ v,which is the uncertainty for velocity, to get the uncertainty in kinetic energy.

Clara Hu 1G

For part b, use $E=\frac{1}{2}mv^{2}=h\nu -\phi$ . Because you know the velocity of the ejected electron and the frequency of the radiation, you can solve for the work function, which is the energy required to remove the electron, and get 1.66 x 10^-17 J.

Clara Hu 1G

After converting the amount of oxygen to moles (0.025mol), also convert the 1.50g of tin to moles, which is 0.0126 mol. Then because you have the amount of oxygen and tin in moles you can get the empirical formula because you know the ratio of tin to oxygen. You have Sn0.0126O0.025, and because 0.01...

Clara Hu 1G

For finding the concentration of potassium ions, first find the amount in moles of KCl, K2S, and K3PO4 in the solution. Then, split each compound and calculate the total amount in moles of potassium ions, which is 0.0229 moles. Then find the concentration of the potassium ions by dividing the number...

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