CHEMISTRY COMMUNITY

Joon Chang 2F

Megan_Ervin_1F wrote:do you think we have to know how to derive the nernst equation for our final?

Outline 5 says "Know how to derive the Nernst equation and use it to calculate the cell potential as a function of concentration" so I'm pretty sure.

Joon Chang 2F

You use Nernst equation $E_{cell}=E_{cell} ^{\circ}-\frac{RT}{nF}lnQ$

Joon Chang 2F

You can use the equation $ln K=\frac{nFE^{\circ}}{RT}$

Joon Chang 2F

Yes I think a reaction that involves four molecules colliding simultaneously would be called a tetramolecular reaction. Given that termolecular reactions are uncommon due to three molecules having to collide simultaneously, tetramolecular reactions would be very rare.

Joon Chang 2F

Yes for differential rate laws, the stoichiometric coefficients are written under 1.

$Rate=-\frac{1}{a}\frac{\mathrm{d[A]} }{\mathrm{d} t}$

Joon Chang 2F

$\frac{1}{[A]}=kt+\frac{1}{[A]_{0}}$
(At $t=t_{1/2}$ ) $[A]=\frac{1}{2}[A]_{0}$ so $\frac{1}{[A]}=2\frac{1}{[A]_{0}}$
$2\frac{1}{[A]_{0}}=kt_{1/2}+\frac{1}{[A]_{0}}$
$\frac{1}{[A]}=kt_{1/2}$ or $t_{1/2}=\frac{1}{k[A]_{0}}$

Joon Chang 2F

Order of reaction is the power a concentration of something is raised to in the rate law (rate law is the equation for instantaneous reaction rate at certain concentration). Overall reaction order is the sum of the powers of the concentrations in the rate law. The variables "n" and "m...

Joon Chang 2F

The equation is on the equation sheet so if you know how to use it you should be fine.

Joon Chang 2F

In acidic solution balance H by using H+. In basic solution balance H by adding H2O to the side that needs H and add OH to the other side.

Joon Chang 2F

Electrons produced by oxidation at the anode (-) travel to the cathode (+) where they cause reduction. The salt bridge is used to complete the circuit by allowing ions to flow.

Joon Chang 2F

It allows ions to flow and maintains neutrality. Negative ions move to the anode side to help keep electrons flowing to the cathode side.

Joon Chang 2F

E is electromotive force or the potential difference in charge between two points. E(nought) is E under standard conditions (all solutes present at 1 molL^-1 and all gases at 1 bar). It can also be thought of as the measure of the electron-pulling power of a single electrode.

Joon Chang 2F

MadelineHlobik wrote:How do you calculate Gibbs free energy?

$\Delta G=\Delta H-T\Delta S$

Joon Chang 2F

Gibbs free energy is the energy of a system that is free to do work at constant temperature and pressure.

Joon Chang 2F

It is sealed and insulated so it is unable to exchange matter and energy with its surroundings.

Joon Chang 2F

q= $\Delta$ H=nCp $\Delta$ T at constant pressure

Joon Chang 2F

q and w are both path functions and both represent transfers of energy between systems and their surroundings.

Joon Chang 2F

Heat is the transfer of energy as a result of a temperature difference. Enthalpy is the amount of heat released or absorbed at constant pressure. Temperature is a measure of the average heat or thermal energy of the molecules in a substance. Work is the process of achieving motion against an opposin...

Joon Chang 2F

It is on the Constants and Formulas page on the website, but it was not on the Constants and Formulas page on test 1. Then again, several constants and formulas were omitted from test 1's formula page. Its required for many of the work problems, so I think it would be best to memorize it.

Joon Chang 2F

$\Delta$ H=q at constant pressure and with no nonexpansion work.

Joon Chang 2F

$\Delta$ V=(Area of Base)(height)=A* $\Delta$ D

Joon Chang 2F

Standard enthalpy of formation is basically standard reaction enthalpy for one mole of substance formed from its standard states (most stable form).

Joon Chang 2F

Work due to a change in volume is called expansion work. The equation is w= -P_{ex}\Delta V where P is pressure, and Delta V is change in volume. For part a) you are given the pressure and the dimensions to find the volume of the pump. Volume of cylinder is \pi r^{2}h . So you find the volume of the...

Joon Chang 2F

Bond enthalpies of diatomic molecules are able to be measured because they are only between two types of atoms, whereas enthalpies of other bonds are averages from different molecules. The bond enthalpy of the diatomic molecule H2 is +436 kJ. This enthalpy is able to be measured consistently because...

Joon Chang 2F

I think they put 7N2 instead of 5N2 on mistake. However, you should always balance the equation first.

Joon Chang 2F

Changing the pressure of the reaction vessel will drive the reaction in the direction where the number of molecules will decrease. If pressure is increased by compression and there are more moles of gas on the left, the reaction will shift right.

Joon Chang 2F

The concentration of H30+ is 3.1 mmol/L. I think that is where you are getting the calculation error.

Joon Chang 2F

The outline just says know where the Ideal Gas Law can be used and how to solve for unknowns using it.

Joon Chang 2F

I know that Q is calculated in the same way as K, so does that mean conversions are done the same way using P=(conc.)RT?

Joon Chang 2F

Can someone explain what will happen if only one of the reactants is added to a chemical equation?
For example, in the equation 4NH3(g) + 5O2(g) $\rightleftharpoons$ 4NO(g) + 6H2O(g), if only NH3 is added to the equation, will equilibrium shift toward the products?

Joon Chang 2F

Lewis Acid - Electron Acceptor, Brønsted acid - Proton Donor
Lewis Base - Electron Donor, Brønsted Base - Proton Acceptor

Joon Chang 2F

pH of 8-14 would have an H30+ concentration of (10^-8) mol/L to (10^-14) mol/L. This shows that larger pH numbers mean there are less H30+ due to the negative power of 10.

Joon Chang 2F

Sophia Ding 1D wrote:Just to clarify then, is the sum of pH + pOH always equal 14 then?

For all aqueous solutions at 25 degrees Celsius

Joon Chang 2F

"Describe coordination compounds for the transition metal ions in terms of coordination number,
oxidation number, and types of ligands." This is under Outline 6 and it is in the syllabus so I think it could be on the finals.

Joon Chang 2F

You can draw the lewis structure and determine what the structure is and where the lone pairs are located. See if the lone pairs are pointing in the same direction then determine if they can both bond to the cental metal ion.

Joon Chang 2F

Long A-H bonds are more acidic than shorter bonds because the longer bond is easier to break and easier to remove the H+.

Joon Chang 2F

No CH4 is nonpolar because the dipole moments between C and H cancel out evenly.

Joon Chang 2F

VSEPR is the Valence Shell Electron Pair Repulsion theory and it basically is a way to describe molecular shapes using rules of electron repulsion. Memorizing the rules will certainly help in drawing and naming the structures.

Joon Chang 2F

The compound is CH4O. The bond angles about the carbon and oxygen are 109.5 degrees because the carbon, 3 hydrogens, and oxygen form a tetrahedral shape with carbon in the center. The hybridization of the carbon and oxygen atoms are both sp3 because they each have 4 regions of electron density. The ...

Joon Chang 2F

Formaldehyde is trigonal planar so it has angles of 120 degrees. It has a hybridization of sp2 and has 3 sigma and 1 pi bonds.

Joon Chang 2F

First draw the Lewis structure. Then determine what bonds there are according to the types of bonds. A single bond is a sigma, double bond has one sigma and one pi, triple bond has one sigma and two pi.

Joon Chang 2F

Yes the formal charge for Cl in ClO2+ should be +1 because it has a lone pair.

Joon Chang 2F

First draw the Lewis Structures for the molecules. Then determine how many areas of electron density are on the central atom. Choose the shape that pertains to that number of areas of electron density and draw.

Joon Chang 2F

a) Must have lone pairs of electrons because in order to have the bent shape, there must be one or more lone pairs contributing to the repulsion of the other atoms.
b) May have lone pairs. The linear shape could have zero lone pairs or multiple lone pairs all in the same axial plane.

Joon Chang 2F

A) CF4 would have the strongest CX bond. Larger atoms mean there will be a larger distance between the atoms (longer bond length) which means the bonds will be weaker. The size of the atoms increases as you go from CF4 to CCl4 and CBr4, therefore the ones with the smallest size, CF4, would have the ...

Joon Chang 2F

I believe Sapling Learning is the online practice problem system that has practice problems with solutions. It was included in the package for the textbook at the UCLA bookstore.

Joon Chang 2F

No it is not an SI prefix. The closest SI prefix is the nanometer (10^-9m).

Joon Chang 2F

Electron Affinity is the energy released when an electron is added to a gas phase atom. A positive electron affinity means energy is released when an electron is added and a negative electron affinity means energy is needed to add an electron. Electronegativity is the electron pulling-power of an at...

Joon Chang 2F

In the p-block, the metals form cations by losing their valence electrons and the nonmetals form anions by gaining enough valence electrons to fill their p-orbital.

Joon Chang 2F

The different trends are atomic radius (Increase down a group, decrease across period), ionic radius (increase down a group, decrease across period), ionization energy (decrease down a group, increase across a period), and electron affinity (generally highest for elements in the top right of periodi...

Joon Chang 2F

Can anyone clarify the meaning/concept of quantum number m? Quantum number m s is the spin magnetic quantum number . It represents the spin state of the electron, which can be thought of as the electron spinning either clockwise or counterclockwise. It basically indicates what direction the electro...

Joon Chang 2F

According to the lecture, all moving particles with momentum have wavelike properties, but the wavelike properties are only noticed for objects with small mass and high velocity. Professor Lavelle also stated a baseball has wavelike properties but the wavelength is so small it is smaller than what i...

Joon Chang 2F

The test is on Outline 2: The Quantum World. Black body radiation is not one of the topics listed on Outline 2 so I believe it will not be on the test.

Joon Chang 2F

The answer is in the book is in g. Other than your final step of converting g to kg, your steps are correct. 3.500x10^3 kg * (1000g/1kg) = 3.500x10^6 g 3.500x10^6 g * (1mol Al/26.982g) = 129716.107 mol Al 129716.107 mol Al *(5mol Al2O3 / 10mol Al) = 64858.054 mol Al2O3 64858.054 mol Al2O3 * (101.961...

Joon Chang 2F

1keV=1,000 eV = 1.60218x10^-19 J. Use this to convert the units and solve using $\lambda = \frac{hc}{E}$ .

Joon Chang 2F

The mass of an electron is 9.10938 × 10^-31 kilograms. This will probably be given on the constants page of the tests.

Joon Chang 2F

I was confused about this problem as well. I just left the answer with the number of significant figures given in the problem.

Joon Chang 2F

Ya just do the calculations first and determine sig figs at the end using the fewest amount of "given" sig figs.

Joon Chang 2F

First you find molar mass of both reactants and calculate the number of moles of both reactants using this molar mass. Molar Mass of NH3= 17.031gmol-1. Molar Mass of O2=31.998gmol-1. Moles of NH3= 21.4g/17.031gmol-1 = 1.2565mol NH3. Moles of O2= 42.5g/31.998gmol-1 = 1.3282mol O2. Now you use the bal...

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