CHEMISTRY COMMUNITY

Sydney Tay 2B

Wmax is equal to delta G which is also equal to -nFEcell

Sydney Tay 2B

Lavelle said that most orders will be in whole number calculations.

Sydney Tay 2B

The half life equations are on the equation sheet

Sydney Tay 2B

All of the graphs for the ordered reactions should have linear plots. It just depends on what is on the axis that determines what is the order of the reaction.

Sydney Tay 2B

The final is cumulative, so everything we have discussed in class since the first day of the quarter is fair game for the final.

Sydney Tay 2B

The overall rate law of the reaction is dependent on the slowest reaction mechanism. So the overall rate law would be equal to the rate law of the slowest step regardless of the reaction rates of the other steps. Since the slowest step is the "bottleneck" for the whole reaction you only ne...

Sydney Tay 2B

In the example 14.8, the textbook gives the reactions AgCl(s)- --> Ag+(aq) + Cl-(aq) and they found the potential of the cell using the half reactions AgCl(s) + e- --> Ag(s) + Cl-(aq) E= +0.22 V and Ag+(aq) + e- --> Ag(s) E= +0.8 V. They reversed the last half reaction to be Ag(s) --> Ag+(aq) + e- a...

Sydney Tay 2B

To calculate the oxidation state of an element that is a transition metal. You first figure out the oxidation state of the element that it is compounded with. Based on that oxidation state and the overall charge of the compound, you can calculate the transition metal oxidation state. The sum of the ...

Sydney Tay 2B

It is easier to find the initial reaction rates so you don't have to take into account the rate of the reverse reaction.

Sydney Tay 2B

I don't think he'll curve it since the way the class is graded is out of a certain number of points :(

Sydney Tay 2B

Can someone explain what the difference is between the E value that is found when you take the log of K and Q and how can we use that number to determine which way the reaction will proceed?

Sydney Tay 2B

How do we determine which ions are moving across the salt bridge and in what direction they are moving?

Sydney Tay 2B

Write the half-reactions, the balanced equation for the cell reaction, and the cell diagram for each of the following skeletal equations: Cl2(g) + H2(g) --> HCl(aq) How are we suppose to determine which elements go on which sides of the line? I understand that inert solids are suppose to go on the o...

Sydney Tay 2B

At equilibrium deltaG is 0 when at constant temperature and pressure. The example they give in the textbook is that when the temperature is 0 C, solid water and liquid water are at an equilibrium (as seen in the heating curve because they are both present), so the deltaG is 0.

Sydney Tay 2B

The Van't Hoff equation allows people to find the new equilibrium constant (K) when temperature changes, knowing the values of enthalpy and entropy.

Sydney Tay 2B

When calculating for W when there is 1 mol of a substance does this mean that you have to raise the number of microstates available to the power of Avogadro's number?

Sydney Tay 2B

You only really need to know these when solving for entropy. They're used for monatomic ideal gases for the equation deltaS = n*C*ln(T2/T1). The heat capacity changes depending on if pressure or volume is held constant.

Sydney Tay 2B

Can someone clarify why heat capacity is extensive but specific heat and molar heat capacity is intensive.

Sydney Tay 2B

During the test of an internal combustion engine, 3.00 L of nitrogen gas at 18.5 $C was compressed suddenly (and irreversibly) to 0.500 L by driving in a piston. In the process, the temperature of the gas increased to 28.1 $C. Assume ideal behavior. What is the change in entropy of the gas? I know t...

Sydney Tay 2B

In the 6th edition textbook, the example 8.6 asks to find the heat at constant volume after finding the final temperature at constant volume and pressure. In the example to find heat they use the equation delta U = nC(v,m)deltaT. I understand why the heat capacity at constant volume was used, but in...

Sydney Tay 2B

The first law of thermodynamics is the conservation of energy, meaning that the internal energy of an isolated system is constant. This relates to the universe because the universe is an isolated system, and therefore the energy within it is constant.

Sydney Tay 2B

Can someone explain why irreversible processes are held at constant pressure?

Sydney Tay 2B

In lecture, Lavelle was explaining that when the reaction goes to completion heat will be released and and delta H will be negative since the heat is leaving the system. He used this example to show how thermodynamics is time independent and only reliant of the initial and final states of a reaction.

Sydney Tay 2B

Can someone explain what the difference is between a standard enthalpy and the enthalpy of formation? And in which situations they should be used in.

Sydney Tay 2B

According to the heating curve for water, the graph indicates that steam occurs when water reaches a temperature of 100 degrees Celsius or higher. This means that it contains a greater amount of heat as compared to boiling water which maxes out at 100 degrees Celsius. The more heat energy something ...

Sydney Tay 2B

A reversible process is a reaction that can be reversed by an infinitely small change in either direction.

Sydney Tay 2B

N_{2} + 3H_{2} \rightleftharpoons 2NH_{3} What happens if we increase N_{2} ? Increase NH_{3} ? Decrease H_{2} ? This was explained during lecture, but I'm still a little confused. Can someone explain this to me again? Increasing reactants will push the chemical reaction in favor of the products, a...

Sydney Tay 2B

The strength of an acid is dependent on how likely it is to fully dissociate. Strong acids tend to fully deprotonate so their Ka value is higher. Weak acids do not dissociate as easily and their Ka values will be smaller in comparison.

Sydney Tay 2B

Test 1 will cover equilibrium and acid and bases equilibrium. So we will probably be asked to calculate pH and molar concentrations after equilibrium has been reached.

Sydney Tay 2B

A reaction occurs equilibrium when both the forward reaction and the reverse reaction occur at the same rate, this can also be shown when Q=K.

Sydney Tay 2B

Kp is the equilibrium constant using partial pressure. Normally if all the compounds in a chemical reaction are in the gas phase then you don't need to change the partial pressure of a gas into concentration unless you are asked to find Kc. If a reaction has aqueous and gas compounds then you will h...

Sydney Tay 2B

Pure solids and liquids are not included in calculating the equilibrium constant, but aqueous solutions and gases are included.

Sydney Tay 2B

Yes, dissociation energy is the energy required to break a certain bond. The energy required to break a bond will increased with the number of bonds between molecules and if the length of the bond is larger.

Sydney Tay 2B

Yes, using formal charge will help to see which structure is the most stable. You want to make the most atoms end up with a formal charge of 0 in order for the molecule to be at its most stable state. This does not apply to molecules that have a charge, for those molecules, you want the formal charg...

Sydney Tay 2B

This applies to the DeBroglie equation where wavelength = planck's constant/momentum. Because of this equation as the wavelength increases the momentum decreases, thus the two are inversely proportional.

Sydney Tay 2B

For the question in the 6th edition textbook 12.17 how can you tell if a compound is amphoteric or not? Specifically looking at As2O3 and Bi2O3, how can you tell that these compounds are amphoteric?

Sydney Tay 2B

Iodine also has a greater number of electrons and therefore has the potential to create a greater dipole movement. London dispersion forces are a weaker form of dipole interactions, and as the number of electrons participating increases, the interaction between molecules will be stronger.

Sydney Tay 2B

In the formula above, why is sodium not included inside the brackets?

Sydney Tay 2B

HF is a weak acid because it does not completely dissociate in water. This is most likely due to the fact that the bond between HF is too strong for the molecule to fully dissociate.

Sydney Tay 2B

I believe we will need to know the basic angles of the more common shapes, like a tetrahedral has angles of 109.5. I don't think he will make use memorize all bond angles when there are lone pairs involved. I just think that we need to know that a lone pair causes greater repulsion and the bond angl...

Sydney Tay 2B

Lone pair bonding has the greatest electrons repulsion. That is why we take into account the lone pairs, but we do not take into consideration the number of bonds when determining VSPER shape.

Sydney Tay 2B

The number of bonds connecting 2 atoms is disregarded because they have the same electron repulsion. However, we take into consideration when there are lone pairs because lone pairs give off greater electron repulsion in comparison to bonded electrons.

Sydney Tay 2B

A lone pair has greater repulsion than bonded electrons and will cause the bond angles between the other atoms to decrease due to this repulsion. There is not a way to know how much a lone pair will decrease a bond angle, but as long as we know that a lone pair results in a bond angle that is lower ...

Sydney Tay 2B

Electronegativity is how well an atom can attract electrons towards itself. Electron affinity is the amount of energy released when an electron is added to a neutral atom to form a negative ion.

Sydney Tay 2B

When predicting molecular shape we have to take into account the number of electron densities that the molecule has. Nitrogen is the central atom and it bonds to oxygen with a double bond and fluorine with a single bond. Since that only give nitrogen 6 shared electrons, nitrogen also has a lone pair...

Sydney Tay 2B

Electronegativity refers to the ability for an atom to gain an electron. Since noble gases already have a filled valence shell they do not require any extra electrons and do not have electronegativity (their electronegativity is zero).

Sydney Tay 2B

Halogens don't form double bonds because they don't need to share any more electrons since their valence shell is filled from the one bond.

Sydney Tay 2B

Covalent bonds are intramolecular bonds (bonds within a molecule) whereas hydrogen bonds are intermolecular bonds (bonds between molecules). In H2O the bonds between the different H2O molecules are hydrogen bonded, but in H2S the H2S molecules are bonded with a dipole dipole interaction because hydr...

Sydney Tay 2B

I'm not entirely sure that there's a shortcut to the equation, but what we learned in lecture was that the formal charge = v - (l- b/2) where v is the number of valence electrons that the element has, l is the number of lone pair electrons that the atom has in the molecule, and b is the number of bo...

Sydney Tay 2B

I would show all the possible resonance structures because a resonance is the blend of all of them together, so the most accurate way to depict the bonds of the molecule would be to show all of the blended possibilities. The different resonances of a molecule doesn't vary too much, only the position...

Sydney Tay 2B

BF4- undergoes a coordinate covalent bond which means that 2 electrons come from one atom which in this case would be the extra fluorine atom. The reason why in BF3 boron is stable with an incomplete octet is because fluorine has such a high ionization energy that it is unlikely to exist with a posi...

Sydney Tay 2B

Where you place the dots doesn’t matter, but I think you have to make sure each side of the element has a dot before pairing up electrons.

Sydney Tay 2B

I think we will need to know this because it relates to the s,p,d,f orbitals and how the electrons interact with each other.

Sydney Tay 2B

In my last discussion we went over equations that described the energy of a photon, de Broglie's equation, the uncertainty principle equation, photoelectric effect, and the rydberg equation. It would probably help to learn these equations for the test, but according to the link that someone posted a...

Sydney Tay 2B

If he didn't say to skip those readings in the syllabus I think we need to know those concepts. However, for the upcoming test (test 2) we only need to know the concepts up until orbitals and quantum numbers.

Sydney Tay 2B

He said we will not be asked to draw the orbitals ourselves, but I don't know if he'll ask us to name them from a picture that he provides.

Sydney Tay 2B

I would know the general order of the atomic spectra, but I don't think we will be asked to know what the exact wavelength ranges are for each type of radiation.

Sydney Tay 2B

Never trust atoms, they make up everything.

Sydney Tay 2B

First you have to calculate the energy from the lamp, which is 32J/s *2s = 64J. Then you can calculate the energy corresponding to the wavelength (using E=hc/wavelength), which would give the the energy per photon of light. Once you have that, you can divide 64J by your answer which is in J/photon t...

Sydney Tay 2B

I generally like to read the textbook after lectures because once it is discussed in class the content in the textbook seems like a review and a way to dive into more specifics. I also find that it is less intimidating once you have a basic knowledge over the subject beforehand. I really find it hel...

Sydney Tay 2B

He will most likely give you constants and other basic equations in order to help you like on the first test, but if you struggled with the time limit on the first test memorizing certain basic equations might help to cut time when taking the next test.

Sydney Tay 2B

I find it best to take notes by hand because it is easier to draw diagrams and other visuals to help understand key concepts. Taking notes by hand also makes it easier to go back and add little comments if the professor adds any extra information. However, if your handwriting is bad I recommend taki...

Sydney Tay 2B

Since the electron is decreasing in energy levels, it is losing energy and therefore would have a negative value. However, as it decreases in energy level it releases a photon which has a positive value in order to offset the previous negative values since energy can neither be created nor destroyed.

Sydney Tay 2B

In equations, wavelength is typically in the form of meters usually because of the other SI units given in other variables. For example, energy is given as Joules = kgm/s so the wavelength would be in meters.

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