CHEMISTRY COMMUNITY

Aiden Metzner 2C

Are voltaic cells the same as galvanic cells?

Aiden Metzner 2C

If the reaction is endothermic, increasing the temperature lowers the activation energy because it adds energy to the system. For the endothermic reaction this makes it easier for the reactants to form products, this is the opposite for an exothermic reaction.

Aiden Metzner 2C

The initial rate is the rate when there are only reactants, and it is the rate that the reactants are used up in a reaction. The unique rate is the rate a molecule is used up divided by its stoichiometric coefficient, all molecules in a reaction will have the same unique rate.

Aiden Metzner 2C

Count the oxygens and hydrogens in the molecule. The oxygens are -2 and the hydrogens are +1, the other element in the molecule will add to these elements to get the molecule to whatever charge it is.

Aiden Metzner 2C

If you look at the units and liters and seconds are in the denominator then it is second order.

Aiden Metzner 2C

If you are given the K for the forward reaction and the overall K then you can determine the K for the backwards reaction and thus determine the rate for the backwards reaction

Aiden Metzner 2C

Depending on what you are given you can tell. If you are just given the reaction, then you can tell what order it is by looking at how each reactant affects the rate. If you are given a certain unit for the k value, then you can also tell the order.

Aiden Metzner 2C

The higher Ecell value is usually reduced because the E cell values are the standard values of reduction. One that produces a higher value that is reduced is more likely to be reduced in a reaction.

Aiden Metzner 2C

Why is the standard cell potential of a concentration cell always equal to 0?

Aiden Metzner 2C

Because the only thing that is making the cell have a potential is the difference in concentration between the cathode and the anode, so changing the concentration of one or both will affect the cell potential.

Aiden Metzner 2C

I believe Dr. Lavelle mentioned in lecture that W = -nfe and G = -nfe. Is this true for all reactions? Or is it only for standard conditions?

Aiden Metzner 2C

No the Downs Process was never really gone over in lecture and isn't covered in the homework so it likely won't be on the final exam.

Aiden Metzner 2C

We only use reactant rate for initial rate because we assume there are only reactants and no products when just starting the reaction, this is why it is known as initial rate. This is used for all reactions

Aiden Metzner 2C

I'm pretty sure we just need to know the final equations associated with each of the derived equations. A lot of the time equations are derived for us in class so we can understand them better but we don't need to fully apply all the derivations

Aiden Metzner 2C

I like doing all the homework problems in the textbook because Lavelle loves putting problems like those on the test. I also like to review past midterms and exams.

Aiden Metzner 2C

Each different ordered reactions involve having the concentrations be increased to certain powers. ^2 for second order. Therefore the units are changed by that order as well.

Aiden Metzner 2C

In lecture it seemed like professor said that k is always the slope of the graph of the rate. Is this true for zero order, first order, and second order reactions. Or is it only true for zero order?

Aiden Metzner 2C

I'm pretty sure that at least for test 2 we will not have to do any calculations involving electrolysis.

Aiden Metzner 2C

Yes for Q the anode is always over the cathode. It is very confusing because you would think it would be cathode over anode but in the case of the nernst equation it is the opposite

Aiden Metzner 2C

When using the equation G= -nFe how do we determine what n is?

Aiden Metzner 2C

An electrolytic cell converts electrical energy into chemical energy, a galvanic cell converts chemical energy to electrical energy.

Aiden Metzner 2C

You can also calculate G in standard states using the Gfinal-Ginitial, and you can do the same with G in non standard states, since G is a state function

Aiden Metzner 2C

I'm pretty sure since you are subtracting electric potential, a negative electric potential means that delta G is positive. So whatever the sign of the electric potential, delta G will always be the opposite

Aiden Metzner 2C

You include water in the half reaction when you need to balance O2 in the reaction. Then if there are left over H+ ions you include water in the reaction as well as OH- ions

Aiden Metzner 2C

Yeah it is everything we've learned after the midterm until the end of electrochemistry I think

Aiden Metzner 2C

I'm not sure when we apply this equation. Can someone explain to me what types of problems we use this equation for?

Aiden Metzner 2C

Instead of using the sign of delta G to determine which way a reaction can proceed. Could we also just figure out if Q is less then or more then K and decide that way?

Aiden Metzner 2C

He curves the class based on the total overall scores. Don't expect your midterm score to be curved but likely if everyones final class scores are lower then expected he will curve the class

Aiden Metzner 2C

On the midterm we were asked how entropy is different based on irreversible expansion or reversible expansion. Is it true that entropy is the same for both since it is a state function?

Aiden Metzner 2C

What is the salt bridges function in a galvanic cell/battery?

Aiden Metzner 2C

We need to know heat capacity for calorimeters, which is just the heat capacity required to raise a substance 1 degree celcius. But also specific and molar heat capacities are important to know. Specific being the amount of heat required to raise 1 gram of a substance 1 degree celcius, and molar bei...

Aiden Metzner 2C

Is test 2 next week? And if so what subject areas is it covering?

Aiden Metzner 2C

Normally you are given the bond enthalpy when trying to solve the problem. I don't think we have to learn how to calculate the enthalpy of a broken bond.

Aiden Metzner 2C

What is the difference between entropy and heat gained/lost? I'm still very unclear on this.

Aiden Metzner 2C

You know the most essential parts. Just know that for acidic reactions you should apply pKa. If you are only given pKb then you can calculate pKa because their products are equal to 14.

Aiden Metzner 2C

They might have different units associated with them, or maybe one is for higher pressure and one is for lower pressure. If they are associated with the same units then you may be able to use them interchangeably.

Aiden Metzner 2C

Because it gives off heat to its surroundings and also mass is inputed into the system from gasoline

Aiden Metzner 2C

Is there any benefit to using one strategy for calculating bond enthalpies over another? Or will we be asked to use certain strategies based on what the question is asking?

Aiden Metzner 2C

Anyone know what week the midterm is? Is it week 6?

Aiden Metzner 2C

It is because there is energy required to break bonds between water molecules. The hydrogen bonds in water are strong so it takes a lot of energy, therefore more energy is stored in gas at the same temperature than at liquid.

Aiden Metzner 2C

If they are based on the same material then they likely use similar if not the same worksheets. I doubt you will miss much if you attend one session over the other.

Aiden Metzner 2C

I doubt we will have to memorize any formulas as in most Lavelle classes the formulas are all provided on the test.

Aiden Metzner 2C

Because certain molecules are more stable then others so those are favored in reactions over unstable molecules.

Aiden Metzner 2C

How do you no whether to use Pa or Pb in an acid base calculation?

Aiden Metzner 2C

Because more energy is provided to the system so in an endothermic reaction that requires heat to make products, it is easier for the reactants to become products if they are provided with heat, and vise versa for exothermic reactions

Aiden Metzner 2C

It fails at low temperatures and higher pressures because intermolecular forces become important, it also fails with heavy gases.

Aiden Metzner 2C

The one that I have been to worked out of the book as I came and asked about specific problems in the textbook.

Aiden Metzner 2C

Do you always have to use ice tables when determining equilibrium concentrations, or is it possible to do calculations without the ice tables?

Aiden Metzner 2C

He said in his outlines you have to be able to calculate a certain variable of pv=nrt given all four of the others. So just simple algebraic calculations I think.

Aiden Metzner 2C

You aren't supposed to round until the end, the answer will be the most accurate if the exact numbers are used until the final answer.

Aiden Metzner 2C

Is test 1 this week like it was in 14A or do we have more time before this test.

Aiden Metzner 2C

We use Kp when calculating partial pressure of gases and Kc when calculating concentration of aqueous solutions.

Aiden Metzner 2C

If you determine the coordination number you can determine how many molecules bond to it, if you find this out you can find the molecular shape.

Aiden Metzner 2C

Does hybridization of orbitals change depending on if the bonds are sigma or pi?

Aiden Metzner 2C

I don't think so, just remember that if it is an acid with a center molecule with oxygens and hydrogens around it. The oxygens bond to the center molecule and the hydrogens bond to the oxygens.

Aiden Metzner 2C

Electrons are never found in the nucleus even if the uncertainty in velocity is less than the speed of light. That being said I don't think there is a case where this is ever possible because heisenbergs uncertainty principle would likely always show that an electrons velocity uncertainty is more th...

Aiden Metzner 2C

I find it more helpful to look at the lewis structure and not the electron configuration when looking at hybridization. Use the regions of electron density to figure out what the hybridization is. PCL3 is sp^3 because it has 4 regions of electron density because it has three bonds and one lone pair....

Aiden Metzner 2C

Yes, hybridization is solely based on regions of electron density. An atom with two bonds and one lone pair would have the same hybridization (sp^2) as something with three bonds and no lone pair.

Aiden Metzner 2C

The inductive effect is when conjugate acids and bases are stabilized by a strong electronegative atom. These atoms pull the electrons in more which makes them more stable in solution.

Aiden Metzner 2C

Is anyone elses test grade in myUCLA for test 2 a zero? I'm a little concerned as I never got my test back and am still not seeing a grade in myUCLA.

Aiden Metzner 2C

An acid or base is strong if they completely disassociate in solution. I'm pretty sure for the final we just need to know a few strong acids and a few strong bases, the bases being, KOH, NaOH, Ba(OH)2, Cs(OH), Sr(OH)2, Ca(OH)2, Li(OH), and Rb(OH) these are all group one and two elements with OH on t...

Aiden Metzner 2C

Some of the general rules for naming are as follows. Use the prefixes di, tri, tetra, penta, hexa, octa, if there are two or more of certain molecules. For ligands, name them in alphabetical order remembering to replace ammonia with ammine, or anything ending in ide with an o. Also cations go first ...

Aiden Metzner 2C

Why is the pH scale from 0-14 if it can be negative and go beyond 14?

Aiden Metzner 2C

I'm still not exactly sure what a conjugate acid is. If a molecule gives off a proton in a reaction, in the reverse reaction is it then the conjugate base since it receives a proton?

Aiden Metzner 2C

A larger constant means it is a stronger base. Keep in mind the Ka value tends to be close to zero, so a 10^-2 value will be a stronger base then a 10^-6 value. However the pKa value is on a logarithmic scale and therefore a smaller pKa value means a stronger acid/base so a lower pH if it's an acid ...

Aiden Metzner 2C

Even though in De Broglies wave equation yes it would technically have a wavelength. I think that De Broglies equation only applies to objects with relatively fast velocity. Something with an extremely low velocity would essentially just not be moving. The best example I could think of is a tectonic...

Aiden Metzner 2C

There will definitely be review sessions. I'm almost positive on Friday of week 10 lavelle does a comprehensive review of important topics in class.

Aiden Metzner 2C

What is the difference between a Bronsted acid/base and a lewis acid/base?

Aiden Metzner 2C

Transition metals have different oxidation numbers depending on their environment. They can have different oxidation numbers because they are good for electron transfer so electrons can pass through them very easily. Certain oxidation numbers allow for a certain number of ligands to bind to these tr...

Aiden Metzner 2C

If there is a molecule with an -ide at the end drop the ide and add an o. Another tip is cations go first and anions go second. Also if it is an anion you add ate to the end. There are a bunch of other strategies and I think there are also some exceptions to these rules.

Aiden Metzner 2C

Dipole moments cancel when the dipoles in a molecule are facing opposite directions. However they also cancel in a trigonal planar because they are all 120 degrees apart and each dipole faces out, causing them all to cancel.

Aiden Metzner 2C

Will Sigma and Pi bonds be on test 2? And if so what is the difference between a sigma and a pi bond, I don't recall going over this in class.

Aiden Metzner 2C

I think it is because of the fact that it is a 3-D shape. So if it were in 2D it would be hexagonal, but due to the fact that it has molecules all of bond angle 90 degrees on the xyz plane it is an octahedral. Lavelle explained something about how the shape when drawn in geometric patterns relates t...

Aiden Metzner 2C

I'm almost positive we don't have to know vapor pressure for this test. However if we do it is defined as the pressure exerted by a vapor when in thermodynamic equilibrium.

Aiden Metzner 2C

Will the test this week just be on VSEPR model of atoms or will it also include interionic and intermolecular forces?

Aiden Metzner 2C

Boiling points are dependent on the strength of force. The boiling point of a molecule is higher if the bonds are stronger because it takes more energy to break the bonds. So a molecule with shorter bonds will tend to have a higher boiling point.

Aiden Metzner 2C

Lone pairs have a stronger repulsion because they are two negatively charged electrons. So they push repulse each-other a lot more then an electron and an atom would repulse because atoms don't have as strong of a negative charge if they are even charged at all. Just remember that lone-pairs are two...

Aiden Metzner 2C

Yes to both questions, ion-dipole interactions are the strongest because ions tend to have a strong charge which attracts the charged dipoles of other molecules.

Aiden Metzner 2C

What is the rule for converting SI units on the test. Will we be penalised if we get the sig figs wrong?

Aiden Metzner 2C

From left to right I think that it is 6, 10 = 5, 9, 6, 3.

Aiden Metzner 2C

There is an inverse relationship because h/4 pi is a constant. So since uncertainty in momentum and uncertainty in position multiply to be greater than that number, then as one gets bigger the other one will get smaller.

Aiden Metzner 2C

Remember that chlorine is one of the three elements that regularly violates the octet rule. So it is likely that oxygen might double bond with chlorine in order to keep its octet, while chlorine would violate the rule since it doesn't need to be in octet to be stable.

Aiden Metzner 2C

Look at the periods and the groups, the farther right an element is in a group the more electronegative it is, and the farther up it is in a group the more electronegative it is.

Aiden Metzner 2C

Even though the bond lengths are represented as different, with double bonds, single bonds, etc. In resonance structures the electrons are delocalized, so the lewis structures aren't necessarily a good representation of how the molecule looks. In reality resonance structures share all the electrons ...

Aiden Metzner 2C

Are phosphorus, sulfur and chlorine the only three elements with expanded valence shells?

Aiden Metzner 2C

Does the formal charge of a molecule always equal its ionic charge? In class for the SO4 2- ion the charge was for the whole molecule. Was that just a coincidence or do the formal charges of each individual atom always add up to the formal charge of the molecule?

Aiden Metzner 2C

Atoms always want to get to a their lowest possible energy. So it makes sense that electron affinity increases as you go towards the top right of the periodic table. Atoms like halogens have high electron affinities because they will release the most energy by getting to the stable noble gas state

Aiden Metzner 2C

You somewhat answered your own question. Linear momentum relates to the de broglie equation in that it has an inverse relationship with wavelength. So yes a larger momentum means a smaller wavelength. For example a car moving 60 mph has a much larger momentum then an electron, so it has a much small...

Aiden Metzner 2C

How do we calculate the uncertainty in speed if the speed is 5+- 5 m/s? Is the uncertainty 5m/s or 10?

Aiden Metzner 2C

Yes, with more uncertainty in position comes less in position and vise versa because they multiply to a constant.

Aiden Metzner 2C

It essentially just means that you use the diameter of the atom to use as the uncertainty in position of the electron. The model of the one dimensional box is a line where the position of the electron in uncertain, it just means you don't have to find the area of the atom.

Aiden Metzner 2C

The work function is the energy it takes to expel an electron from a certain metal. The energy of the photon is E=hv and if you subtract the work function from that energy then the difference is the kinetic energy of the electron which is E=MV.

Aiden Metzner 2C

Electrons have to be outside of the atoms nucleus. Photons are in the nucleus, but if electrons were there, according to heisenbergs principle the uncertainty in the position would be too small and would therefore make the indeterminacy in the speed of the electron faster then the speed of light, wh...

Aiden Metzner 2C

You would first balance the equations and then convert the grams of each compound into moles. Then you would see which reactant would yield less of the product. By doing this you will see which reactant is limiting the mass of the product.

Aiden Metzner 2C

I was just curious the rule that we were supposed to used for answering with signifigant figures on test 1? I was also wondering if the T.A's will be grading with sig figs in mind on this test?

Aiden Metzner 2C

Black body radiation is not at all prevalent in our daily lives. Although it does exist in black holes to the extent of my knowledge there is no black body radiation present on Earth.

Aiden Metzner 2C

As illustrated in Professor Lavelle's standing wave diagram, energy levels can be seen through the electrons patterns of constructive and destructive interference patterns. You can visualize an electrons wave pattern by looking at the standing wave motion and how it switches from peaks to valleys, i...

Aiden Metzner 2C

Not sure the exact setup but in lecture Professor Lavelle spoke of pointing a light source at whatever metal you are testing. If electrons are ejected from that metal then the light source has a high enough frequency/energy to raise the electron to its second energy level (n=2).

Aiden Metzner 2C

How is it possible that the mass of water in the products is so much larger than the mass of the fat that is given in the reactants side? Isn't it impossible for mass to be created during a reaction?

Aiden Metzner 2C

I'm confused how to use the equation M1V1 = M2V2 when they only give us two molarities. Is there another equation we are supposed to be given?

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