CHEMISTRY COMMUNITY

Brennan McGurrr 3C

In an aqueous solution, the concentration of water cannot be measured. It will not have an effect on the rate of the reaction, so it is not included in the rate law.

Brennan McGurrr 3C

Last quarter there was some curving and extra points given on the final. I would guess it depends on how hard the final is and how everyone's grades compares to that.

Brennan McGurrr 3C

Galvanic cells are solutions with electrodes inserted to measure the electric flow of a redox reaction. Concentration cells are a special type of galvanic cell in which the ions in the anode and cathode are identical, but present at different concentrations.

Brennan McGurrr 3C

Salt bridges counteract the movement of the electrons in the cell. Electrons, which have a negative charge flow towards the cathode. In order to keep the solutions neutral, cations must flow toward the cathode and anions must flow away. The same is true bit vice versa for the anode. If there was no ...

Brennan McGurrr 3C

If the half reaction does not have a conducting solid, like Cu, Zn, Fe, Al or more then a platinum conductor electrode must be inserted. An example of this would be an anode with an ion being reduced into another ion.

Brennan McGurrr 3C

Why aren't the anode and cathode separated during electrolysis?

Brennan McGurrr 3C

Delta U is zero in an isolated system because neither energy nor matter can be exchanged with the surroundings.

Brennan McGurrr 3C

The smaller concentration is with the anode, and the larger concentration is with the cathode.

Brennan McGurrr 3C

Yes. Since Q is used to compare it to K, they are calculated the same way. Each compound is raised to its stoichiometric coefficient.

Brennan McGurrr 3C

The first rule is that H is always +1 and O is always -2. The oxidation numbers of a compound must add to the total charge of it. Ions usually match with their respective charges in a compound.

Brennan McGurrr 3C

The question should tell you that the anode is on the left and the cathode is on the right. The diagram is labeled with substances in the anode in cathode. The anode is being oxidized, while the cathode is being reduced. This will allow you to fill in the missing spots in the half reactions.

Brennan McGurrr 3C

What I find easier is to treat it like an acidic solution and then covert. It is easier to balance H and O. Once you find the half reactions, balance everything except for H and O. Then add water to balance the O. Then add H+ to balance H, and this should also balance the charges. Make sure the mole...

Brennan McGurrr 3C

If you're asking about the cell diagram notation, what I do is always find out which substance is the anode and which is the cathode. The anode goes on the far left, and the cathode goes on the far right. Now start working inward. If the substances are not separated, ex. both in solution, but a comm...

Brennan McGurrr 3C

I got the same thing. Maybe double check your superscripts and subscripts when you put it into Sapling. Sometimes it is hard to control all the charges and amounts.

Brennan McGurrr 3C

In depends on whether the reaction is in an acidic or basic solution. For both cases, balance all other elements in the half reaction except for H and O. Then, add H2O to balance the oxygens while ignoring H for now. Then, add H+ to balance H, this should also balance the charges on each side. Then,...

Brennan McGurrr 3C

The Van't Hoff equations is used to find different K values at multiple temperatures if one K value is known. It relates all the thermodynamic properties to the equilibrium constant.

Brennan McGurrr 3C

Isobaric means that the pressure does not change. Certain thermodynamic equations require the pressure to be constant. This can help distinguish between the different equations.

Brennan McGurrr 3C

It's due to the equation to calculate Gibbs Free Energy. When T is very low, it will lower the term in the equation with T and delta S. This makes delta G way more dependent on delta H.

Brennan McGurrr 3C

Residual entropy is more used for comparison for questions in this class. Basically, the more complex a molecule is, the more residual entropy it has. Questions will ask you which one has more or less.

Brennan McGurrr 3C

The change in entropy is usually a lot smaller. It is more convenient to list them in joules. It just has to be converted when using them together.

Brennan McGurrr 3C

To add on to the other response, the reason the equation delta S=q/T can be used is because the temperature remains constant. During phase changes, energy is added to the system but the temperature does not change.

Brennan McGurrr 3C

What I do is look at the equation sheet that we are allowed to use on the midterms and final. I use it during the homework so I can get used to what I have to remember and what I don't. The biggest thing for this unit would be reading the problem to determine the situation for each equation.

Brennan McGurrr 3C

Residual entropy does not take movement of molecules due to temperature into consideration. The residual entropy is based solely on if possible positioning of the atoms in the molecule. For example, CO has two possible microstates, C-O and O-C. Cl2 only has one possible microstate, Cl-Cl. The more p...

Brennan McGurrr 3C

A particular container holds 3.24 mol of neon gas. The volume of this container can be altered by sliding a piston in or out. The volume is changed from 7.70 L to 2.50 L while at the same time the temperature is changed from 311 K to 227 K. The molar heat capacity, CV,m, for neon is 12.47 J/(mol · K...

Brennan McGurrr 3C

There are two main types of phase changes. One is the phase changes that take condensed molecules and spread them out. This requires energy, but increases the number of possible states, so there is a positive delta H and a positive delta S. An example of this would be melting ice. The other type of ...

Brennan McGurrr 3C

Dr. Lavelle explained a lot of applications of entropy in lecture, but I was a little confused on what does entropy actually measure or mean?

Brennan McGurrr 3C

Combustion refers to an exothermic reaction of a compound reacting with oxygen. It does not have to be a hydrocarbon but that is the most common, for example cellular metabolism.

Brennan McGurrr 3C

The molecules in liquids and solids are so close together due to intermolecular forces that they cannot expand their volume. If you heat a glass of water the volume of water will not change.

Brennan McGurrr 3C

For Kelvin and Celsius, the scale is different by only adding 273 to kelvin. Since there is no multiplication involved in the conversion, a change in 25 degrees Celsius to 26 degrees Celsius is the same as a change from 298K to 299K.

Brennan McGurrr 3C

For me I use the phrase "Brickle no so clo perclo." It stands for Br I Cl NO3 SO4 2- ClO3- ClO4-.

Brennan McGurrr 3C

Water can form a hydrogen bond using every atom in the molecule, making water have a large number of hydrogen bonds compared to other molecules. In order for water to be in the vapor state, the molecules need to be moving fast enough so the attractive forces of the hydrogen bonds cannot condense the...

Brennan McGurrr 3C

The heat capacity is stated in the form of how much heat per one mole of substance. If you convert the per one mole to per however many moles of substance you have, it will give the change in heat for that amount.

Brennan McGurrr 3C

For bond enthalpies, they are always listed in the gas phase. If any of the compounds in the chemical reaction are in the liquid or gas phase, the enthalpy of the phase change to convert it to a gas must be added.

Brennan McGurrr 3C

This problem combines two methods of solving for enthalpy. The two methods used are the standard enthalpy of formation and bond enthalpies. Graphite and H2 are the most stable forms of carbon and hydrogen, so those two compounds reacting would result in the enthalpy of formation of their product. Th...

Brennan McGurrr 3C

Hess's Law states that the enthalpy of a reaction is fixed at a certain conditions and not dependent on the intermediate pathways or reactions. In short, Hess's Law states that enthalpy is a state function.

Brennan McGurrr 3C

I think it all depends on the stoichiometric coefficients of the chemical equation. If the acid or base is polyprotic, [A-] and [H30+] will not be the same. The same goes for [HB] and [OH-]. The the stoichiometric coefficients are the same, then the concentrations will be the same.

Brennan McGurrr 3C

I would write the equilibrium expression for NH4Cl in water because that is the substance being put in the solution. The problem gives you the concentration of NH4Cl in solution. The Kb for NH3 can be used to find the Ka for NH4Cl, which then can be used in a ice box to find [H3O+] and then pH.

Brennan McGurrr 3C

The total pressure is the sum of all the partial pressures of a system. The problem gives you the Kp and the initial concentration of PCl5, so you can set up an ICE box to find an equation for x, and then plug in x to find each of the partial pressures of PCl5, PCl3, and Cl2. Add them all together a...

Brennan McGurrr 3C

You would have to FOIL the denominator then multiply that expression to the other side. This will allow you to set the equation equal to 0 and use the quadratic formula. If you have a graphing calculator, you can graph both sides of the equation and find where they intersect to solve this. I find th...

Brennan McGurrr 3C

pKa and pH are used to find whether the predominant species in a solution is charged or neutral. pKa is the -log of the equilibrium constant, while pH measures the hydronium concentration is solution. pKa is specific to a reaction, while the pH is just a state of a solution. There does not necessari...

Brennan McGurrr 3C

For this type of question K would also change, so either the K value would need to be given or the equilibrium concentrations at each temperature. If the question stated whether the reaction was endothermic or exothermic, the direction of the change in K could be predicted.

Brennan McGurrr 3C

In one of the lectures from last week, Dr. Lavelle said we can use this general guideline: If the Ka or Kb is greater than 10^3, it is considered a strong acid or base. If Ka or Kb is less than 10^-3, it is considered a weak acid or base. If the Ka or Kb value is in between 10^-3 and 10^3, the acid ...

Brennan McGurrr 3C

Gases are always part of the equilibrium expression because if it is not a pure gas, it is a mixture of gases with measurable concentrations. If it is a pure gas, the pressure can still be measured.

Brennan McGurrr 3C

Pure substances cannot have a concentration because there is only one substance present. In order for something to have a concentration, there must be a solute and a solvent. It is like trying to say how concentrated or dilute a glass of water is. Since the concentrations of pure substances do not e...

Brennan McGurrr 3C

The question says that 18.3 percent of the BrCl remains after the reaction reaches equilibrium. This means that if you multiply the moles of BrCl given in the question by 0.183, it will give you the amount of moles of BrCl at equilibrium. Divide this by 1.00L and it will give you the concentration. ...

Brennan McGurrr 3C

The only things that are graded in terms of weekly homework are the weekly 5 chemistry community posts and the sapling problems posted on CCLE. Dr. Lavelle has all recommended textbook readings and problems on the syllabus, but they are not graded or required. Also the Audio-Visual Focus Topics post...

Brennan McGurrr 3C

The way I learned it in high school is to visualize a see saw. If the see saw in balanced, the reactants and products are at equilibrium. If one of these is changed, the see saw will tip one way. The only way to get it back to balanced (or equilibrium) is to convert some of what was increased into t...

Brennan McGurrr 3C

Initial, change, equilibrium. It is just a way to organize what happens to reactions to reach equilibrium.

Brennan McGurrr 3C

The question is asking what will the new concentrations of these compounds be after more NO is added to the system. Initially, the question gives you concentrations and equilibrium, which can be used to find K. Then the question says the NO concentration increased to 0.700M, making the system no lon...

Brennan McGurrr 3C

The bond angles are slightly less than 90 degrees because the two lone pairs have more electrostatic repulsion than the bonded atoms.

Brennan McGurrr 3C

pKa is the -log of Ka, which is the equilirbrium constant for an acid dissociation reaction in solution. The higher the Ka, the stronger the acid. Therefore if you take the -log of a large Ka, the pKa will be very low. Lower pKa means the acid is stronger. If the pKa of an acid is higher than the pH...

Brennan McGurrr 3C

It would depend on this number of lone pairs and bonded atoms. For example, in an octahedral e- density arrangement with 4 bonded atoms and 2 lone pairs, the orientation that allows the regions to be furthest apart is square planar, with both of the lone pairs on opposite ends. In a trigonal bipyram...

Brennan McGurrr 3C

Reducing CO2 emissions would lower the CO2 concentration in the atmosphere. This would make rain less likely to be acidic. It is similar to the physiological example he gave of CO2 decreasing the pH of blood. The body has to increase respiration rate to maintain blood pH as CO2 concentrations rise. ...

Brennan McGurrr 3C

A pi bond restricts rotation due to having two regions of electron density overlap. The orbitals involved in the pi bond overlap side to side, so there are two overlapping regions in addition to the end to end overlap of the sigma bond. The bond cannot rotate without the pi bond breaking. It's like ...

Brennan McGurrr 3C

Oxidation number means the charge that an ion forms during bonding. For example in NaCl, Na has an oxidation number of +1 and Cl has an oxidation number of -1. However, transition metals often have several possible oxidation numbers. Using a roman numeral after its name indicates which one. Anions c...

Brennan McGurrr 3C

Determining conjugate acid/base pairs involved looking at the donation and receiving of protons, or H+ ions. An acid will donate a proton when it reacts with water, forming its conjugate base. Similarly a base will accept a proton from water, leaving a conjugate acid. For example in the reaction HCl...

Brennan McGurrr 3C

Since the problem is asking for a difference in pH, the initial concentration you use does not matter. The second concentration must be 12% of the first one. For instance if we used 0.01M H+ as the initial concentration, the second concentration would be 0.0012M. The difference would be: Change in p...

Brennan McGurrr 3C

Since chlorine is inside the brackets it is a ligand and not a separate ion. So it would be triaminetrichlorocobalt(III).

Brennan McGurrr 3C

The notations for hybrid orbitals denotes how many orbitals are involved in the hybridization. If one s orbital and three p orbitals are mixed, the notation would be s^1p^3. The 1 is implied so its just sp^3. There are 4 orbitals in total being mixed, so the superscripts must add to 4. In the exampl...

Brennan McGurrr 3C

I think the best way to learn these is memorization by looking at the name. Synthesis means putting to things together, so its A+B->AB. Decomposition means taking things apart, so its AB->A+B. Combustion makes me think of explosions or fire, which means it must have gases involved. It's A+O2->CO2+H2...

Brennan McGurrr 3C

The orbitals of an atom hybridize in order to form bonds with other atoms. In a normal Aufbau diagram, carbon has a pair of valence electrons in the 2s subshell, and two unpaired electrons in 2p. Carbon can form 4 bonds though, so there must be a way for all 4 of these valence electrons to be unpair...

Brennan McGurrr 3C

Can cisplatin bond to any other nitrogenous bases other than guanine, or do there have to be two guanines in a row for it to bond to the DNA strand?

Brennan McGurrr 3C

The way to determine this is to look at the VSEPR shape and drawing the dipole moments over each bond. If the shape is asymmetrical, like bent or seesaw, and the molecule has polar bonds, it will most likely be polar. The only way for a molecule to be polar when al the bonded atoms are the same is i...

Brennan McGurrr 3C

Coordination compounds are formed between metals and ligands which are held together by a coordinate covalent bond. The metal is a cation which accepts the lone pair, and the ligand has a lone pair to donate. This is similar to Lewis Acids and Bases. In terms of naming these compounds, the ligands a...

Brennan McGurrr 3C

The shape is different because sulfite has a lone pair on the central atom while carbonate does not. The lone pair on sulfite makes it trigonal pyramidal. Carbonate has 3 bonded atoms and no lone pairs on the central atom, so it is trigonal planar.

Brennan McGurrr 3C

The name of the shapes in the VSEPR model are based solely off of the position of the bonded atoms in the molecule. Even though H2O was four electron density regions in a tetrahedral shape, only 2 of these regions have bonded atoms. This forms a bent or angular shape.

Brennan McGurrr 3C

I think since Cl is larger than F, it would push the two F atoms together, making the angle between the two smaller and the angle between Cl and F larger. This force would be stronger than the repulsive force between the F atoms since they are smaller, so they would not return to their original posi...

Brennan McGurrr 3C

The best way I have found is to memorize the shapes and the number of regions of electron density they correspond to. Then if there are lone pairs, remove atoms that would make the atoms as far away as possible, which would reveal the shape.

Brennan McGurrr 3C

Yes they are opposite. Polarizing power measures a cation's ability to distort electron clouds, while polarizability measures an anion's ability to have its electron clouds distorted.

Brennan McGurrr 3C

In a trigonal bipyramidal arrangement, the axial atoms form a 90 degree angle with the equatorial atoms, and the equatorial atoms form a 120 degree angle with each other. It is most stable for atoms to be as far apart as possible, when the central atom has one lone pair instead of an atom, one of th...

Brennan McGurrr 3C

Dr. Lavelle has not gone over the rules for nomenclature or the names of polyatomic ions, so I would say if you needed to know the molecular formula of a specific compound, it would be given in the problem or you would be required to find it out.

Brennan McGurrr 3C

For group 13 elements to fulfill the octet rule, they would have to gain 5 electrons, which would take a large amount of energy. This is why it is often more stable for these elements not fill their valence shell, or from 3- ions, like aluminium does.

Brennan McGurrr 3C

Both are about the same process, but polarizability for London dispersion forces is used to determine the strength of these forces, while polarizability for ionic bonds is used to determine its covalent character.

Brennan McGurrr 3C

The biggest factor when determining BP and MP are the type of intermolecular forces present. If there are two different types, the one with the stronger type will have a higher BP and MP. For example, water forms hydrogen bonds, so it has a higher BP than methane, which only has London Dispersion fo...

Brennan McGurrr 3C

If there are two different elements involved in a bond, than that bond as a dipole moment pointing in the direction of the more electronegative atom. By looking at the molecular shape, a molecule's polarity can be determined. For example, in a trigonal planar shape, let's say all of the bonds have a...

Brennan McGurrr 3C

The strength of an acid or base is determined by how soluble they are in water. Strong acids like HCl and HBr are completely soluble due to their high ionic character. Weak acids like CH3COOH are not completely soluble and remain partially as molecules in solution. We don't need to know this right n...

Brennan McGurrr 3C

A general rule is to put the least electronegative atom in the middle. It can never be hydrogen. Electronegativity increases across a period and decreases down a group.

Brennan McGurrr 3C

The polarizing power is less for bigger cations due to Coulomb's Law. A bigger ionic radius means the nucleus of the cation is further away from the electrons in the bonding region. The electrostatic attraction decreases as two opposite charges are separated by an increasing distance. In smaller cat...

Brennan McGurrr 3C

P-block elements with a principal quantum number (n) of 3 or more have electrons in d orbitals. In normal octet bonding, only the s and p orbitals are being shared, which is why each element is most stable with 8 valence electrons. However, to accomodate formal charge, electrons in the d orbitals ca...

Brennan McGurrr 3C

I am pretty sure the noble gas configuration is acceptable unless the question specifically asks for the complete electron configuration. Creating an Aufbau diagram would also require the full electron configuration.

Brennan McGurrr 3C

I remember hearing that for the longer multiple choice questions there would be some incorrect choices that would show only an error in a part of the question, like the empirical formula one you mentioned. I think there will be partial credit if you chose one of these answers.

Brennan McGurrr 3C

I got confused about the wording of this question too. The question is basically asking how many possible electrons could be represented by the following quantum numbers. I think it is easiest to just look at the periodic table. The first one only gives you the principal quantum number, which is 2. ...

Brennan McGurrr 3C

This question asks to solve for energy in two different ways. The first part asks for the energy of the photon, which moves at the speed of light. In this case you can use the formulas E=hv and c=(lambda)v. Combined its E=(hc)/(lambda). The second part asks for the energy that the electron gives off...

Brennan McGurrr 3C

When we went over the atomic spectrum, Dr. Lavelle showed us how as the energy levels (n) increase in an atom, the differences in energy between adjacent levels decrease. For instance, the energy difference between n=1 and =2 is larger than the difference between n=3 and n=4. The energy of a shell i...

Brennan McGurrr 3C

Magnetism is the movement of electric charges. In the Stern and Gerlach experiment, the silver atoms separated after passing through the magnet due to the electrons having different spins. The spinning of the electrons is this movement of electric charges, making some silver atoms attracted to one o...

Brennan McGurrr 3C

The l symbol represents angular momentum, which tells what subshell the electron would be in. s=0, p=1, d=2, and f=3. So for 2s, n=2 and l=0.

Brennan McGurrr 3C

I think any unit conversion that is not the metric system will be given to us. It might be helpful just to know so common ones, like 1in=2.54cm and 1kg=2.2lbs, but I bet they will be given to us if we need them.

Brennan McGurrr 3C

If you don't like that notation, another way to write 350 using 2 sig figs is using scientific notation. It would be 3.5x10^2.

Brennan McGurrr 3C

I think I understand your question. Atoms are visible to the eye because they reflect all frequencies of light except those that increase the quantum level of their electrons. These frequencies are absorbed and are later emitted after the electron returns to the ground state. This process has more t...

Brennan McGurrr 3C

Electrons in p orbitals are further away from the nucleus than electrons in the s orbital. Therefore, they have higher energy. Single electron atoms do not have any electrons in the p orbitals, because s fills before p. These atoms only have one electron in the s orbital.

Brennan McGurrr 3C

The difference between the two has to do with what kind of substance in question. Covalently bonded groups of atoms are called molecules (ex. H2O, CO2). Molecules have weaker intermolecular forces than ionic compounds do. Ionic compounds are often arranged in a lattice structure, with each ion bonde...

Brennan McGurrr 3C

The difference in energy has to do with the electrostatic attraction between the protons in the nucleus and the electrons. Protons are positively charged, and electrons are negatively charged. The closer the distance between the two, the stronger the attraction, or in other words, the more energy it...

Brennan McGurrr 3C

Delta E refers to the energy of the excited level minus the energy of the ground state. This difference is the exact amount of energy needed to excite an electron between these energy levels. Only a photon with this exact energy will be absorbed and cause it to be excited.

Brennan McGurrr 3C

The difference is there are two different experiments that result in each. Electrons are ejected in a Photoelectric Effect experiment when light causes the pool electrons of metals to be ejected. In an atomic spectroscopy experiment, the light causes the electrons in a particular atom to become exci...

Brennan McGurrr 3C

I don't think its necessary to memorize every single part of the spectrum. I think having an understanding of how microwaves and radio waves have a lower frequency, larger wavelength, and less energy than UV light and gamma radiation will help clarify how the spectrum works. Also how red light has a...

Brennan McGurrr 3C

I think I understand your question. Theoretical yield has to do with calculations and is like a best case scenario. The actual yield would be equal to the theoretical yield if all of the limiting reactant perfectly underwent the reaction. This never happens in the lab, so the actual yield is always ...

Brennan McGurrr 3C

For empirical/molecular formula calculations it isn't as important since you'll be rounding to the nearest whole number, but for other calculations I would try to avoid rounding until the final answer.

Brennan McGurrr 3C

This confused me too. What I realized is that the carbons are balanced, which led me to believe there is a 1:1 molar ratio between 2-butanone and 3-methyl-3-hexanol. Other than the molar masses, that is all the information you need to do the stoichiometry, but I am definitely going to ask about it i...

Brennan McGurrr 3C

Think of it like scooping a cup of flour into a bowl and then adding two cups of water. At this point, there is one cup (mole) of flour and 2 cups of water. If I add 2 more cups of water to the bowl, there will still be only one cup of flour. The only thing that changes is its concentration (molarit...

Brennan McGurrr 3C

I asked this question in my discussion section. My TA said to basically follow the values given in the problem. Let's say you were given a value of 4.06 g, then going to 2 decimal places would be fine. But if it was 4.061 g, I would use 3 decimal places.

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