CHEMISTRY COMMUNITY

Joanne Lee 1J

You add H+ in acidic reaction and OH- in basic reactions and then you can determine where to add it in each equation based on where the equation is unbalanced.

Joanne Lee 1J

The oxidizer has a higher oxidation number and the reducer has a lower oxidation number.

Joanne Lee 1J

I heard you have to go pick it up from Lavelle's mailbox or your TA. It would probably be best to email you TA to ask.

Joanne Lee 1J

You have to analyze the equations figure out which side needs OH- or H2O in order for the entire equation to be balanced.

Joanne Lee 1J

When you derive the half life, the initial concentration will cancel out in that equation so therefore initial concentration makes no difference in first order reactions.

Joanne Lee 1J

Factors that can affect k include cell potential and temperature.

Joanne Lee 1J

If it is a first order reaction, the graph should be linear.

Joanne Lee 1J

The syllabus says you need to know how to do so but it isn't very likely that it will actually be asked on the final.

Joanne Lee 1J

I don't think you will be asked derive the integrated rate law.

Joanne Lee 1J

Yes, rate constants are always positive because they represent concentration and concentration has to always be positive.

Joanne Lee 1J

Electrons always flow from the anode to the cathode, or from left to right.

Joanne Lee 1J

The reduction is spontaneous when the standard reduction potential is positive.

Joanne Lee 1J

It depends on the solution; if it is acidic add H+ and if basic then add OH-.

Joanne Lee 1J

A potential difference is the amount of energy required to change the electrical charge of an object.

Joanne Lee 1J

Half reactions are balanced when there are the same number of electrons on the products and reactants between two half equations.

Joanne Lee 1J

You can decide which form of R to use based on what the units of the given values are.

Joanne Lee 1J

K will always be given when solving for x or else there would be no way for us to find x.

Joanne Lee 1J

We used the quadratic equation to solve for x when we are given the starting values and want to find the equilibrium concentrations. Once we get the equation ax^2+bx+c, we can plug in the appropriate values into the quadratic equation.

Joanne Lee 1J

You can simplify a cubic equations if the K value is less than 10^-3 which might result in a quadratic equation or an easier equation to solve for x.

Joanne Lee 1J

Adding an inert gas will change the pressure of the system but not the K or Q value of the reaction.

Joanne Lee 1J

Delta U is zero for isothermal reactions because the internal energy of the system does not change.

Joanne Lee 1J

Spontaneity is determined by Gibbs free energy and whether that value is positive or negative.

Joanne Lee 1J

Yes, the standard entropy of reaction does depend on the state of the molecule.

Joanne Lee 1J

Residual entropy is the difference in entropy between a non-equilibrium state and crystal state of a substance close to absolute zero.

Joanne Lee 1J

I don't think it would be possible to have a negative entropy, it is always positive.

Joanne Lee 1J

A state function is a property where the value does not depend on the path taken to reach that specific value. Therefore, state functions can be added or subtracted to find the answer.

Joanne Lee 1J

The system is the object that is of interest and the surrounding is anything else that might be involved in the experiment.

Joanne Lee 1J

The slopes of the curves are the period of times where it is in its specific phase but the flat area of the graph is when the substance is changing from one phase to the next.

Joanne Lee 1J

The temperature of the sample remains constant even though heat is being supplied because all the energy is being used to change the substance phase, not alter the temperature of the sample.

Joanne Lee 1J

I think when we add or subtract, it's dependent on the place of the number. So, since the last significant figure it in the tens place for 340, the answer would have the last significant in the tens place.

Joanne Lee 1J

A closed system example could be a sealed beaker of water or a cold pack.

Joanne Lee 1J

Yes "U" is a state property because it does not depend on how the system got from the initial to the final state.

Joanne Lee 1J

A state function is a property that depends only on the current state of the system and is independent of how that state was prepared. Examples can include internal energy, pressure, volume, temperature, and density.

Joanne Lee 1J

In an isolated system, a reaction can still take place inside the system but it doesn't have any effect on the outside world. Therefore, changes in the system can still be observed, recorded and calculated.

Joanne Lee 1J

A closed system is any system where energy can be exchanged with its surroundings. An example of this would be a sealed beaker of water. On the other hand, an isolated system nothing can be exchanged with their surroundings and an example of this would be combustion of glucose in a bomb calorimeter.

Joanne Lee 1J

K can only be used when you know that the reaction is at equilibrium. Therefore, if the unbalanced equation is at equilibrium, simply balance the equation and then you can find K.

Joanne Lee 1J

K is used when the reaction is at equilibrium but Q is used at anytime during the experiment. Oftentimes, the Q and K values can be compared to see whether the reaction favors the reactant or the products.

Joanne Lee 1J

If the Ka or Kb is less than 10^-3, then the x on the bottom can be ignored because the x value will be so small that it won't make a big difference to the original concentration.

Joanne Lee 1J

I usually watch Khan Academy or Organic Chemistry Tutor but the Organic Chemistry Tutor videos tend to be on the longer side, so Khan Academy might be more helpful if you are short on time.

Joanne Lee 1J

In addition to leaving out water, you should also leave out solids and liquids in the ICE table.

Joanne Lee 1J

The reaction quotient is the ratio of products to reactants at any time during the experiment but K is the ratio of products to reactants at equilibrium only. The reaction quotient will often tell you if the reaction is at equilibrium or which side (left or right) it favors.

Joanne Lee 1J

When you look at the balanced equation, the number of moles of each compound will tell you the change. For example if there is two moles of water the change would be 2x. The positive and negative depends on what compound you start out with. If you are given the amount of reactant and water is a prod...

Joanne Lee 1J

We include aqueous solutions because Q is calculate the same way as K and K includes aqueous solutions.

Joanne Lee 1J

Yes, when a reaction shifts to the left, it favors the reactants and when it shifts to the right it favors the products.

Joanne Lee 1J

If there is an equation with liquids and gases in either the products or reactants side, only the gases are included in the Kc equation.

Joanne Lee 1J

Solids and liquids are not counted in the equilibrium constant because the concentration does not change in between the products or reactants.

Joanne Lee 1J

Yes, the equilibrium constant should be the same regardless if we calculate it using the equilibrium concentrations or the equilibrium pressures.

Joanne Lee 1J

Solids and liquids are not counted in the equilibrium constant because the concentration does not change in either the products or reactants. Therefore, yes only gases and aqueous solutions are included when trying to find K.

Joanne Lee 1J

When you are finding the K, the units of the products and reactants are either all molarity, partial pressure, etc so all the units will cancel out when K is found.

Joanne Lee 1J

If the K value is between 10⁻³ and 10³ then it SLIGHTLY favors either the product or reactant, depending on if it is bigger or smaller than one.

Joanne Lee 1J

When a pH is less than one, that means the concentration of H+ ions is greater than one.

Joanne Lee 1J

Yes, for pH sig figs, only the values after the decimal place count.

Joanne Lee 1J

For any strong acid, you can just take the negative log of the molarity of the HCL to find the pH.

Joanne Lee 1J

Weak acids don't completely ionize in a solution. All the H+ ions will not separate from the molecules whereas in a strong acid they will.

Joanne Lee 1J

A negative pH doesn't happen to often but if you run into a problem with a negative pH then it means that the concentration of hydrogen ions is more than one.

Joanne Lee 1J

The more electronegative an element is, the less acidic it will be when bonded with a hydrogen. Higher acidity molecules will be more likely to give off hydrogen atoms and less electronegative elements are less likely to do so. Therefore, since CL is less electronegative than F, it is more acidic an...

Joanne Lee 1J

Strong acids and bases will completely dissociate in water whereas weak bases and acids only partially dissociate in water. However, it might be easier to just memorize strong acids and bases in order to identify between the two.

Joanne Lee 1J

Proton acceptors are known as bases and proton donors are acids.

Joanne Lee 1J

Adding the charge is helpful because then you can identify when a molecule has given up an electron/ hydrogen molecule or received one.

Joanne Lee 1J

I would try to remember all the strong acids, just in case, seeing as there isn't too many to memorize.

Joanne Lee 1J

For the VSEPR formula XA2E2 it would be called bent.

Joanne Lee 1J

I think it would still be considered polar because the two Cl and the two H have different electronegativity values so the charges don't all cancel each other out.

Joanne Lee 1J

I believe you can just say the structure is bent.

Joanne Lee 1J

No tetraderal and trigonal pyramidal are not the same. Tetradral has four bonding pair and zero lone pairs whereas trigonal pyramidal has three bonding pairs and one lone pair.

Joanne Lee 1J

The bond angle of bent should be about 104.5 degrees.

Joanne Lee 1J

I don't think you need to know the specific boiling and melting points of each type of interaction but just know how the interaction affect the boiling and melting points and which ones might have higher or lower boiling and melting points.

Joanne Lee 1J

Even though the structures we draw don't exist, finding the Lewis structure most similar to the actual molecule allows us to better see what the molecule might look like and how strong and how long the bonds are between each element.

Joanne Lee 1J

I think if you need to express resonance, the teacher is asking you to draw out all possible resonance structures.

Joanne Lee 1J

Any element in period 3 or beyond has access to their respective d orbital so they are able to have/ accept extra electrons and put it in their empty d orbital.

Joanne Lee 1J

Dipole-dipole interactions are only important for CH3Cl, CH2Cl2, and CHCl3 because these molecules are polar whereas CH4 and CCl4 are nonpolar. Only polar molecules have dipole-dipole moments so it is only significant for those three molecules.

Joanne Lee 1J

The bond lengths are the same value because the actual structure is a mixture of all the different versions of the resonance structure. Therefore, it isn't just one that has a double bond and the rest a single bond but all the bonds are a mixture of both, making the bond length in between the value ...

Joanne Lee 1J

Double bonds are shorter than single bonds because double bonds are stronger and therefore pull the electrons closer together in the two elements which decreases the length of the bond.

Joanne Lee 1J

It should take about a week for the midterm to be graded.

Joanne Lee 1J

Bond length is dependent on the type of bond, whether it is a single bond, double bond, or triple bond. Then if each molecule has resonance the bond lengths will be in between the lengths of the two different bonds. We have not been taught how to specifically find the exact value of the bond length.

Joanne Lee 1J

There are supposed to be eight questions on the midterm but there are multiple parts to each question.

Joanne Lee 1J

In order to identify if a species is a radical, just count the total number of valence electrons in that molecule and if it is an odd number, it is a radical.

Joanne Lee 1J

Each bond line is two electrons shared between elements.

Joanne Lee 1J

Usually P, S, and Cl don't have less than eight electrons because they are not stable until they complete their octet or exceed it. Therefore, while it is unstable, it will always be trying to react with other elements until it becomes stable.

Joanne Lee 1J

Like our first test, I'm pretty sure the test will all be free response because the practice midterm given to us by the UA's is also all free responses.

Joanne Lee 1J

The most likely charge for an atom to form is based on the number of valence electrons of each element. For example, Na has one valence electron so it would be more likely to give that one electron up than try and collect seven more. Therefore it has a likely charge of +1. On the other hand, P has f...

Joanne Lee 1J

Adding x, y, or z states specifically the orientation of the orbital and where it lies on a 3D (x,y,z) graph.

Joanne Lee 1J

When you are filling out an orbital, know that each orbital must have one electron before the electrons are paired. This is because electrons prefer to be in different orbitals due to their negative charge that repels other electrons. So for example, if four electrons are in the p orbital there woul...

Joanne Lee 1J

You should write the plus sign just to signify specifically which way the electron is spinning.

Joanne Lee 1J

So because you know it is the d orbital, you know l= 2. To determine the ml value, know that ml equals the range of value from -l to l. Therefore, in this case, the values of ml would be -2, -1, 0, 1, and 2.

Joanne Lee 1J

In this equation, q1 and q2 is the value of the charge of the two electrons.

Joanne Lee 1J

Yes, you will still receive full credit, as long as they are all problems that were assigned based on the syllabus.

Joanne Lee 1J

Both the midterms and finals will be administered at a different time than lecture and discussion times. For example, the midterm is from 6PM - 8PM on Novemebr 6.

Joanne Lee 1J

The E represents the amount of energy of a photon but you can always compare that E value to the work function value to determine whether the E amount is enough to remove the electron from one shell to another.

Joanne Lee 1J

Yes, there can be cases where the photons do not have enough energy to eject an electron. If there is not enough energy, then the electron will stay in whatever orbital it is currently in and will not jump to the other orbitals.

Joanne Lee 1J

For questions that require you to use Heisenberg equation, the question will have the words uncertainty in position, velocity, or momentum. If these words are not stated in the question, then you should not use Heisenberg's equation.

Joanne Lee 1J

A greater energy difference implies greater frequency because energy and frequency are proportional to each other. As one increases, the other does as well and vice versa based on the equation E = hv.

Joanne Lee 1J

You also need to remember that you are dividing Planck's constant by the momentum and the units for Plank's constant is J(s) where Joules is kg⋅m2⋅s−2. So, in order for the two masses units to cancel out, you have to use kg in the denominator as well. It's always about using the same units as the co...

Joanne Lee 1J

I think that's something you should get familiar with. Especially the Balmer and Lyman series since Lavelle specifically went over those two in class.

Joanne Lee 1J

The extent of the change in the electrical field is referring to the slope of the waves and so as the frequency decreases, the waves of would be broader and more spread out, therefore meaning that the slopes of the waves would be less steep. This decrease in the slope means that the extent of the ch...

Joanne Lee 1J

For number 25, it states that the photoelectric experiments gave rise to a new equation relating the energy of light to its frequency. Select the right equation.
A. c = λ x v
B. Ek = 1/2(MV²)
C. MV²/2 = hv - φ
D. E = hv
E. None of the above

Which one is the correct answer? Thank you!

Joanne Lee 1J

Hey everyone! I heard that there would be a lecture that includes sig figs, does anyone know if this is true or should I just go ahead and review it on my own?

Joanne Lee 1J

According to the law of conservation of mass, during a chemical reaction, mass is neither created or destroyed so the equation must be balanced in order to follow this law.

Joanne Lee 1J

I think you can leave the textbook at home since often times during lecture we are taking notes off of Dr. Lavelle's powerpoints. The textbook is probably just helpful for the homework or for supplementary knowledge if something in the lecture was confusing for you.

Joanne Lee 1J

If I am not mistaken, you use Avogadro's Number to find the number of atoms, molecules, or formula units when you are given the number of moles of any substance.

Joanne Lee 1J

I personally round it to the hundredth place of the decimal place and it usually gets me the same answer as the answer in the solutions manual so that should work but I guess the safest option would be using all the values in the periodic table.

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