CHEMISTRY COMMUNITY

Morgan Gee 3B

As the concentration of a given species that has a negative order increases, the rate decreases. You can consider this to be similar to adding a product in an equilibrium reaction.

Morgan Gee 3B

The rate law is dependent on the slowest reaction. However, assuming the slowest reaction is not the first reaction, there will be some intermediate formed in a previous question and used in the slowest reaction. Therefore, you need to "cancel out" that intermediate by essentially substitu...

Morgan Gee 3B

The rate constant can be affected by temperature.

Morgan Gee 3B

Everything is held up until the slow reaction proceeds. Intermediates cannot be used up and intermediates cannot be produced until the slow step proceeds. As a result, the rate law is dependent on the slowest step.

Morgan Gee 3B

You are correct in that the rate law is dependent on the slowest reaction. However, assuming the slowest reaction is not the first reaction, there will be some intermediate formed in a previous question and used in the slowest reaction. Therefore, you need to "cancel out" that intermediate...

Morgan Gee 3B

ln(2)

Morgan Gee 3B

Order of a chemical species is the exponent over it in the rate expression. The order of a chemical reaction is the sum of all exponents in the rate expression for a chemical equation.

Morgan Gee 3B

Sometimes you may be given the rates for the forward reaction but may want to know how fast a product is produced. This would prompt you to use stoichiometric coefficients to determine the rate of formation for a certain product.

Morgan Gee 3B

If you remember from Dr. Lavelle's lecture with the graph involving the activation energy, the size of the activation energy is what determines the rate of the reaction. Changing the coefficients does not change the activation energy, thereby not changing the rate of the reaction.

Morgan Gee 3B

Q follows the same formula for K but at any given set of concentrations. On the other hand, K is the constant for equilibrium.

Morgan Gee 3B

Oxidizing reactants get reduced and reducing reactants get oxidized.

Morgan Gee 3B

E cell is the voltage of a cell at any given conditions. E cell naught is the voltage of a cell at very specific conditions. Specifically, there are at 1 atm, 298 K, and 1 M.

Morgan Gee 3B

A concentration cell is one that has the same chemical species. However, the concentration of the different solutions are different and the imbalance causes the reactions to progress. The transfer of electrons and progression of the chemical reaction allows a concentration cell to have a voltage.

Morgan Gee 3B

In general, you want the overall reaction to have a positive voltage. Remember Dr. Lavelle's jokes about not asking for a negative voltage battery? As a result, you tend to make the smaller potential negative.

Morgan Gee 3B

The purpose of the salt bridge is to balance out the concentrations and complete the circuit of ions flowing.

Morgan Gee 3B

I personally like oil rig better because it's shorter than leo goes ger but both work perfectly fine!

Morgan Gee 3B

I always try to look for single elements like H2 because they have an oxidation number of 0. If you compare it to a compound that has hydrogen such as H2O, you know that H must have an oxidation number of +1 to counter the -2 in oxygen. By becoming more positive, H2 became oxidized.

Morgan Gee 3B

Leo is an acronym used to help remember what happens during oxidation. It goes "losing electrons (is) oxidation". The idea is that if you know oxidation, you don't need to memorize reduction. Something I've seen is "leo goes ger" which is losing electrons oxidation and gaining el...

Morgan Gee 3B

The salt bridge maintains the concentrations and allows the ions to flow. Essentially, it allows the circuit of electrons to flow similar to how electronic circuits work.

Morgan Gee 3B

The cell is the term used to describe the chemical and redox reactions that occur that allow a battery to occur.

Morgan Gee 3B

There are different R constants based on the units they have. For example, 1.00 atm = 101.3 kPa. While R may be 0.082057 atm L/molK, it would be 8.31 kPa L/mol K (which if you notice is the same as 8.31 J/mol K)

Morgan Gee 3B

No it will not because the value is so small. However, the safest thing to do would be to use the constants given on our equation sheet to be the most accurate as possible.

Morgan Gee 3B

Water has such a high specific heat capacity because of the hydrogen bonds that are present. Hydrogen bonds are the strongest intermolecular force (some others would be van der waals and dipole-dipole) and require the most energy to break them. This causes water to have such a relatively high boilin...

Morgan Gee 3B

Enthalpy is represented by H and is heat. Heat is defined as energy either entering or leaving a system. When an object cools down, that object is losing energy in the form of heat, meaning that enthalpy is negative. Entropy is represented by S and can be called disorder. This has to do with degener...

Morgan Gee 3B

Yes that is correct. You'll notice how when there's m, the heat capacity constant is written as Cs, which actually means specific heat capacity. As for n, the heat capacity is written as Cm, which actually means molar heat capacity.

Morgan Gee 3B

The easiest way for me is to think of what we do with ice. To make ice go from its solid form to liquid form, we have to heat it up. That is essentially the same as adding energy to the ice. That tells me that solid to liquid is endothermic as it requires energy. This leads me to determine that goin...

Morgan Gee 3B

Ionic salts are formed by the neutralization of some acid or some base. The acid and base that were neutralized to form the salt affect whether the salt would be basic or acidic. For example, strong acid plus strong base is neutral. Weak acid plus strong base is basic. Strong acid plus weak base is ...

Morgan Gee 3B

pKa is the -log[ka]. This changes the relationships because of the way logs work. When you do 10^-14 = ka x kb and take the negative log of that equation, you end up with 14 = pKa + pKb

Morgan Gee 3B

For strong binary acids, it's only HCl, HI, and HBr. For acids with oxygen, if there's two more oxygens than hydrogens, it's a strong acid. For bases, it's pretty much any group 1 metal with OH- and anything past Ca(OH)2 for the group 2 metals. Different organizations have different definitions for ...

Morgan Gee 3B

The different gas constants are based on the units that make them up. As a result, determine the units that are given/desired and pick your gas constant based on that value.

Morgan Gee 3B

Something that's nice to know is that combustion reactions are always going to be exothermic. Synthesis reactions are usually going to be endothermic.

Morgan Gee 3B

Yes you can rearrange the equation. You just need to change the deltaH accordingly based on the rearrangement you did. For example, switching the equation means you need to multiply the deltaH by negative one. If you double the reaction, you need to multiply the deltaH by two.

Morgan Gee 3B

Endothermic reactions will always have a positive deltaH because they require energy. On the other hand, exothermic reactions will always have a negative deltaH because they release energy.

Morgan Gee 3B

0 degrees celsius, 273 K, 1 atm, 760 mmHg, 101.3 kPa, and 1 M

Morgan Gee 3B

HClO3 is a strong acid. When it comes to oxoacids (acids that have oxygen), if you have two more oxygens than hydrogens, it is usually considered strong. Some common examples would be HNO3, H2SO4, and HClO4. Some examples of weak oxoacids would be HNO2, H3PO4, HClO, HClO2.

Morgan Gee 3B

Energy is required to break bonds, while energy is released when bonds are formed. We consider heat in energy to be the same as energy (as it is after all a form of energy).

Morgan Gee 3B

Ka is acidity constant and is calculated with Ka = [A-][H3O+]/[HA]. A high Ka value is correlated with a strong acid, while a low Ka value is correlated with a weak acid. Kb is basicity constant and is calculated with Kb = [BH+][OH-]/[B]. A high kb value is correlated with a strong base, while a low...

Morgan Gee 3B

Ka is calculated with the general equation, Ka = [A-][H3O+]/[HA]. [] represents concentration, A- is the conjugate base of an acid, H3O+ is a hydronium ion, and HA is the acid. As an acid dissociates and gives off an H+ to an H2O, the concentration of A- and H3O+ both increase. We determine how stro...

Morgan Gee 3B

An inert gas is one that won't react. By adding inert gas to a closed container, the pressure would increase. However, because there is now inert gas inside, some of the collisions between the reactants and the products would also be with the inert gas. This means that while there is an overall incr...

Morgan Gee 3B

PV=nRT is used primarily to convert between mols/concentration into pressure and vice-versa, assuming that the gases are ideal. This can be helpful when you're given Kp and concentration or you're given Kc and pressure. Because the equilibrium constants are of different units, you would have to conv...

Morgan Gee 3B

Q is the reaction quotient which is the concentration of products to the concentration of reactants raised to their coefficients. Q can be less than K, greater than K, and equal to K. When Q is less than K, that means there are more reactants than products and the forward reaction needs to occur at ...

Morgan Gee 3B

When we take the log of something, we consider anything in front of the decimal place in the answer to be from the exponent. For example -log(1.0 x 10^-5) = 5.00. The 5 is from the exponent and all the numbers after the decimal are considered to be significant. Because 1.0 has two sig figs, we need ...

Morgan Gee 3B

Heat (energy) is required for the forward reaction to occur and an increase in the temperature is equivalent to an increase in energy. As a result, the forward reaction will occur at a greater rate. This can be used to help indicate that Q < K as we know that in that scenario the reaction "shif...

Morgan Gee 3B

Kc is the equilibrium constant based on the concentration of the species. As a result, we need to work with concentration for our ICE tables.

Morgan Gee 3B

Temperature is given as the K value is different based on what temperature is used. This just keeps the questions consistent and as accurate as possible. For our purposes, we don't really care about temperature unless using PV=nRT

Morgan Gee 3B

Depending on the state/phase of water, we either include or don't include it in the equilibrium constant or reaction quotient. If it is considered a liquid or solid, we would not consider it, similar to other liquids and solids. However, if it is gaseous, we would include it. It would not be aqueous...

Morgan Gee 3B

Q is the general way for writing reaction quotient. To be more descriptive, we use Qc or Qp depending on the phase/state of the chemicals. We use Qc for reaction quotient of concentration. This happens when the chemical species are aqueous (aq) and are given in concentration (mol/L). We use Qp for r...

Morgan Gee 3B

P = pressure V = volume (usually in liters) n = moles R = gas constant T = temperature (usually in kelvin) Make sure to be extra careful with units as there are different gas constants based on the different units used for the pressure. For example, there is a different gas constant depending on if ...

Morgan Gee 3B

All constants are given and on the equation/formula sheet that Professor Lavelle allows us to use. Just be careful to use the right constant based on the unit of the pressure. There are different constants depending on if the pressure is measured in bars, atm, etc.

Morgan Gee 3B

In lecture today (1/6/2020), Professor Lavelle said that we can approximate 1 bar to be 1 atm. In case you're curious, the conversion is 1 atm is about 1.013 bars. If you ever worked with kPa and atm, you might remember that 1.00 atm is about 101.3 kPa. Because 1 pascal (Pa) = 1 x 10^-5 bar, we can ...

Morgan Gee 3B

Using the equation E - hv, you get joules/photon. This allows us to calculate the amount of joules per mol and other similar units using dimensional analysis.

Morgan Gee 3B

Wavelength is typically converted to meters for calculations because the meter is the base unit for length. This results in most other units (such as Joules) using meters.

Morgan Gee 3B

Solve for the moles present in the reactants by using molar mass and dimensional analysis. Then, divide all mols of reactants by the molecule that is the least present. This gives the ratio of reactants present all in relation to one chemical. Using this information, look at the balanced chemical re...

Morgan Gee 3B

Whenever I do conversions, I personally always write out the units, which helps me deal with the different magnitudes of size. I do this with scientific notation. For example, if I were to convert 357 nm to m, I would do 357 nm (1 m/1 x 10^9 nm).

Morgan Gee 3B

Avogadro's number is used to describe the quantity of some object in one mol. As a result, you use Avogadro's number during some form of dimensional analysis relating to a mol. As for when you would divide or multiply by Avogadro's number, that can be determined by looking at the units of the previo...

Morgan Gee 3B

Professor Lavelle discusses the placement of lone pairs in one of his lectures where he uses the models to demonstrate positions with the most space for the lone pairs. This explains some of the more odd placements of lone pairs in some geometries such as AX2E2 (bent/tetrahedral) and AX2E3 (linear/t...

Morgan Gee 3B

Benzene has a total of 9 single bonds and 3 double bonds. There are 6 hydrogens bonded to each carbon (6 single bonds) and 3 single bonds between carbons (3 more single bonds) for a total of 9 single bonds. There are also 3 double bonds between carbons for a total of 3 double bonds. This means that ...

Morgan Gee 3B

All bonds have one sigma bond. A double bond has one sigma bond and one pi bond. A triple bond has one sigma bond and two pi bonds.

Morgan Gee 3B

Understanding the 3D model of the lewis structure is important too, as 2D images may be misleading. A common example is the linear molecular geometry from a trigonal bipyramidal electron geometry (AX2E3). While it may appear to be polar because of the asymmetrical lone pairs, it is still considered ...

Morgan Gee 3B

Understanding the units for this question is extremely important. M is the unit mol/liter and is often referred to as concentration. We are given grams and concentration, but we still need mols and liters. To find the mols, we use the molar mass of CuNO3 which is 125.55 g/mol (from the periodic tabl...

Morgan Gee 3B

All ionically bonded compounds have some covalent character. The strength of the covalent character is different when looking at the cation or anion of the ionic compound. For cations, small, uncharged cations such as Al+3 have a greater covalent character as it can distort electrons to a greater de...

Morgan Gee 3B

C and H have very similar electronegativities, causing their bond to be considered a nonpolar covalent bond. The reason why they are so far apart is because of their difference in electrons in the valence shell. It makes more sense for H to be in group 1 because it was 1 electron in the valence shel...

Morgan Gee 3B

Ionic character occurs between two covalently bonded molecules. The greater the difference in electronegativities, the greater the ionic character is. While we are not given specific values, we can use periodic trends to predict differences in electronegativity.

Morgan Gee 3B

Trigonal planar has the VSEPR formula of AX3, while trigonal pyramidal has the VSEPR formula of AX3E. Trigonal planar has three regions of electrons, while trigonal pyramidal has four regions of electrons. However with trigonal pyramidal, there are 3 bonded atoms and 1 lone pair.

Morgan Gee 3B

All single bonds are sigma bonds. Any additional bonds would be considered pi bonds. Therefore, a double bond has one sigma bond and one pi bond, and a triple bond has one sigma bond and two pi bonds.

Morgan Gee 3B

All bonds have at least one sigma bond. A double bond would have a sigma bond and a pi bond. A triple bond would have a sigma bond and two pi bonds.

Morgan Gee 3B

A general rule of thumb is that covalent molecules are two nonmetals bonded and ionic compounds are a nonmetal and a metal bonded together. While H is on the left side of the table, it is still considered a nonmetal (think H2 gas). This explains why NaCl (a metal and nonmetal) is ionically bonded wh...

Morgan Gee 3B

When there are two lone pairs and two bonded atoms, it is called bent.

Morgan Gee 3B

If you look at the fluorines in the lewis structure, you notice that they actually form a straight line, similar to other linear molecules. While there are 3 lone pairs on the central atom along with the fluorines, they would still maintain the linear shape.

Morgan Gee 3B

Using periodic trends, you can determine whether a molecule is polar covalently bonded or nonpolar covalently bonded. Typically, two different elements are a large enough difference in electronegativity to be polar covalently bonded. A common exception would be C-H bonds where they are typically con...

Morgan Gee 3B

Elements that are large enough and have access to the d sublevel have the ability to hybridize. This means that they can access the d sublevel to create more bonds. This is why we consider elements in the 3p sublevel to be able to have expanded octets. They are both sufficiently large enough and hav...

Morgan Gee 3B

The formal charge of carbon should be -2. There are 4 bonds and 4 lone pairs so (4/2 + 4) = 6. The valence electrons of carbon is 4 so 4-6 = -2.

Morgan Gee 3B

As Dr. Lavelle has said, always put the least electronegative element as the central atom. When comparing carbon and nitrogen, you'll see that carbon is less electronegative than nitrogen. Just using periodic trends, nitrogen is further up and right than carbon. Also, nitrogen has a greater effectiv...

Morgan Gee 3B

Water (H2O) has a partial positive charge on hydrogen and partial negative charge on oxygen. This means that we need to look for atoms that have a partial positive or partial negative. This can be determined through comparing the electronegativity of the different bonded atoms in urea. For example, ...

Morgan Gee 3B

Any zero after decimal points are counted as a significant figure.

Morgan Gee 3B

Polarity is commonly used in context of the distribution of electrons due to a difference in electronegativity between two elements. For example, nonpolar covalent bonds and polar covalent bonds describe the distribution of electrons between two bonded nonmetals.

Morgan Gee 3B

Electron affinity, electronegativity, and ionization energy all follow the same trend in that as you go up and to the right in the periodic table, they increase. The reasoning for the same trend is very similar but the actual definitions are quite different. Electron affinity is the energy in kJ rel...

Morgan Gee 3B

While electrons increase and the repulsion causes the radius to increase slightly, protons are also increasing. The positivity of the protons cause the electron cloud to shrink, resulting in a decrease in atomic radius as you move across a period.

Morgan Gee 3B

I personally found that not combining equations is easier for me to understand. I don't have to convert between equations and makes my work seem much more methodical.

Morgan Gee 3B

If you wanted to consider how many bonds an atom would form, you could draw the orbital configuration/electron configuration of the element. Those indicate how many electrons are available in the valence shell which gives an indication of how many bonds can be formed. In terms of aluminum, the elect...

Morgan Gee 3B

Intermolecular bonds are between (inter) molecules. This means that these bonds are interactions that hold many molecules together and can include hydrogen bonds, van der Waals, dipole-dipole, etc. Intramolecular bonds are within (intra) bonds. These are the bonds that actually hold the atoms in a m...

Morgan Gee 3B

Ionic bonds tend to be stronger than covalent bonds as solids but weaker than covalent bonds when in solution. In chemistry, ionics bonds are usually considered stronger as we work with ionic bonds in the solid state more often while in biology, ionic bonds are considered weaker as molecules tend to...

Morgan Gee 3B

For the most part, different biological elements have a large enough electronegativity to be polar. A notable exception is that a C-H bond is nonpolar. When there are larger molecules with more than just two elements, it becomes much more tricky and requires you to see if the molecule is "balan...

Morgan Gee 3B

Ionic bonds occur when there is a very large electronegativity between two atoms. Typically this occurs between a nonmetal and a metal, with a common example being NaCl. In these cases, the electron from Na (less electronegative) is transferred to Cl (very electronegative), creating an ionic bond. C...

Morgan Gee 3B

The l value cannot be determined solely from the n value as there is simply not enough information. However, the n value provides the possible ranges for the l value. The minimum value is always 0 and the maximum value is always n - 1. The different subshells will provide you with the information ne...

Morgan Gee 3B

Personally, I prefer to use E = -hR/n^2 to solve these questions, but I can explain both. From the lecture, change in energy equals energy (final) - energy (initial). In order to find energy, we must use the given frequency and the equation E = hv. Plugging in appropriate values and maintaining sign...

Morgan Gee 3B

Something I personally ask myself is what happens when something else either increase or decreases. In the case of your question, I would be asking myself what happens when frequency increases/decreases. Because of the equation E=hv where E is energy, h is Plank's constant, and v is frequency, I wou...

Morgan Gee 3B

The important thing to remember about Lyman and Balmer is where they fall to. Lyman series falls to n=1 and Balmer falls to n=2. Lyman is ultraviolet radiation and Balmer is visible light. This makes sense because ultraviolet radiation has greater energy than visible light. As electrons fall to lowe...

Morgan Gee 3B

If you remember, this is where the confusion came in when the photoelectric effect was still being researched. The scientists initially believed that by increasing intensity (making brighter), electrons would eventually be ejected off. However, they came to realize that a higher frequency would be n...

Morgan Gee 3B

Because our midterm is going to be multiple choice, it probably does not matter too much how many significant figures you use. However, I personally plan on using as many as possible to be as accurate as possible.

Morgan Gee 3B

As you go in the top right direction, the electronegativity and electron affinity of the elements increase up until the noble gases. This means that fluorine has the greatest electronegativity out of all elements! As a result, oxygen and chlorine have slightly less electronegativity than fluorine. T...

Morgan Gee 3B

In regards to chemistry, ionic bonds tend to be stronger than covalent bonds. In biology, covalent bonds tend to be stronger than ionic bonds because biologists consider ionic bonds in solution. If ionic bonds are in solution, they are weaker than ionic bonds not in solution.

Morgan Gee 3B

Something to note is that while it may be simpler to combine the equations into one equation, you can still use the separate equations and you would still get the same answer. This may make it easier for you to understand and go from step to step.

Morgan Gee 3B

Rather than memorizing all the different types of electromagnetic waves and their associated wavelengths and frequencies, I think it's more important to know their relative position and understand the interaction between frequency and wavelength. For example, it is good knowledge to know the approxi...

Morgan Gee 3B

Doctor Lavelle used substitution to make one equation in order for the steps to be easier to solve for the answer. However, doing what he did wasn't necessary as you could have done each step individually to get the same answer.

Morgan Gee 3B

Dr. Lavelle uses 100 grams because the questions very rarely gives the mass of the unknown compound provided. That means we are at liberty to come up with any arbitrary mass of compound to work with. Because the values are given as percentages, it's a lot easier to just use 100 grams. This is becaus...

Morgan Gee 3B

I usually include units in my steps when I'm solving because it makes the solving process for me a lot easier. Personally, I use units to somewhat guide my steps and figure out what I need to multiply in order to get to the desired solution. For example, starting with mols and multiplying by molar m...

Morgan Gee 3B

Another thing that I think is important to take note of, is that you actually know that the missing metal has to be in group 2. This is because in M(OH)2, hydroxide or OH- has a negative charge, so two hydroxides has a negative charge of -2 (received two electrons total). This means the metal has to...

Morgan Gee 3B

Something interesting that I noticed with combustion reactions is that with normal combustion reactions (just carbon and hydrogen), the number of hydrogens needs to be divisible by four. For example, there needed to be two butane (C4H10) mols from the example done in class today. This effectively ma...

Morgan Gee 3B

I noticed that sapling didn't specify the units for the answer for any of the fundamental questions that Dr. Lavelle gave us. I personally tend to just write the answer with the units that were given in the question. I'm sure that Dr. Lavelle will be more specific on the exams however or he just won...

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