CHEMISTRY COMMUNITY

ALegala_2I

Test 2 and the corresponding answer keys can be found here.

viewtopic.php?f=160&t=62122&p=237630&sid=fbd87ea7b2442d1db0b2bd7a14b04e68#p237630

ALegala_2I

The first step is fast and the second step is slow.

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Are zero order reactions common?

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Since the question is asking about the rate of consumption, it is already taking into account that oxygen is being used up. Therefore the answer is meant to be positive in terms of consumption rate.

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How do you derive this equation from the Arrhenius Equation?

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I also had the same question. We did not do any practice problems in class and it seems particularly complex.

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You can determine the rate limiting reaction from the rate law.

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The rate law tells you the instantaneous reaction rate in terms of the concentration. Each reaction has a unique rate law which is specific to its reactants.

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For first order reactions, it is good to know how the graph looks in terms of [A] and ln[A]. Below is general trend for first order reactions in both situations. https://saylordotorg.github.io/text_general-chemistry-principles-patterns-and-applications-v1.0/section_18/0fd0e9359ab66f04b9ee0e414d2d9a9...

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Capital K is the equilibrium constant while lower case k is the rate constant for kinetics.

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Yes, you need to use half life. Since 1/4 is (1/2)^2, to have your final concentration be a fourth of the initial, it would take two half lives. Correspondingly, it would take 3 half lives to to get 1/8 of the initial.

ALegala_2I

You can use the equation, E = Eo - RT ln Q, to find the electric potential under non standard conditions.

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Use the value that corresponds with reduction potential for the substance in a solid state.

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For the units to cancel out correctly, you have to use R = 8.314 J/(mol*K). Whenever you need to decide what R to use, always check the units of the other values given.

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In the example during class, a porous membrane separated the two sides of the cell. However, only then anion was able to pass this membrane.

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I believe that the product is supposed to be Cl- not Cl2.

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I believe it is an error in the question. It should be Cl2 --> 2Cl-. This will show the change in oxidation state.

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Here is a chart that can help with oxidation numbers.

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You can also find the charge by looking at the charge of the compound as a whole. For example if you have MnO4-. The total net charge for the compound is -1 and we know that oxygen has a oxidation number of -2. Since there are 4 oxygens we know that the total charge that comes form the oxygens are -...

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You either have to be given the standard enthalpy or find it using a table of values to solve for the delta H.

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What are oxidizing agents and reducing agents?

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From what we learned, we only distinguished our calculation for reversible and irreversible to calculate work and the total change in entropy of the universe.

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Actually, both of the c values are for monoatomic gases. Cv is used when the reaction is carried out at a constant volume and Cp is used at constant pressure.

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ALegala_2I

You have to use the deltaS = nCln(T2/T1) equation. First, you use this equation to raise the temperature of water from 85 - 100 (make sure you convert to Kelvin) and use the molar heat capacities at constant pressure of liquid water. Then, you use this equation to lower the temperature of water from...

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How many microstates does the molecule BF3 have for the B-F bond?

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The irreversible equation is only used when pressure is constant. If pressure is changing, then you use the reversible equation.

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Work is being done because there is a change in the moles of gas from reactants to products. When not specified, we assume that the reaction is being done under ideal conditions.

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R is the gas constant which is on the equation sheet. C is the specific heat capacity which is usually given in the problem.

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You use w=-PV when there is an expansion occurring at a constant external pressure. You use the other equation when there is a change in internal and external pressure for expansion work.

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In an isolated system, there is no transfer of heat or matter. In terms of internal energy (U=q+w), there is no heat exchange so q=0 and no change in matter so w=0. This means that the change in internal energy is equal to zero and that it remains constant throughout an experiment on an isolated sys...

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The question is essentially asking how much energy it takes to heat the copper kettle which has its own unique specific heat capacity and how much energy it takes to heat the water. You have to perform two calculations to get the total change in energy.

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Since we are measuring the q of the reaction and we know that heat is being released, the reaction is exothermic, making the q negative.

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Bomb calorimeters are more sophisticated versions of regular calorimeters. The reaction takes place in a metal vessel with a constant volume. This metal vessel is in water and the temperature change is monitored.

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Heat capacity is an extensive property because it varies by the amount of the substance in the situation. Specific heat capacity measures the amount of heat to raise one mole or one gram of a substance by one degree celsius. Since it is per mole or per gram, it can be applied to a variety of situati...

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Why is the standard enthalpy of diatomic gases (O2) equal to zero?

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How does the delta H of water when it is melting compare to the delta H of water when it is vaporizing?

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You can however determine the relative stability of the reactants and products by looking at the Ka value. If it is very large, the products are more stable and if it is very small, the reactants are more stable.

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The approximation is also acceptable if the Ka value is less than 10^-3.

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Does this mean that cooling an exothermic reaction will favor the products?

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When you increase pressure, you are decreasing the volume. This relationship is seen in the PV=nRT equation. A decrease in volume means an increase in concentration. To balance out the increase in concentration, the equilibrium will go toward the side with fewer moles.

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When pressure increases, there is a decrease in volume. This inverse relationship can be seen through the PV=nRT equation. When the volume decreases, this means that the concentration (n/V) of all products and reactants increases. Due to the increase in concentration, the reaction will proceed towar...

ALegala_2I

Why do changes in concentration, pressure, and volume have no effect on the K value?

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A lower pKa value means that the acid is stronger. This value can be useful when comparing relative strength of acids between two weak acids.

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Does this removal of x in the expression depend on the value of K?

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When the pressure decreases, the volume increases as they are inversely proportional. This means that the concentration also decreases and to bring the system back to equilibrium, the reaction which creates more moles will be favored.

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How does the increasing the pressure of a gas like Helium, which is not active in the chemical equation, affect equilibrium?

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I believe it is referring to this chart.
[img]Screen%20Shot%202020-01-03%20at%207.53.41%20PM[/img]

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Solids and liquids are not included because there is generally a large amount of it. This generally does not affect the reactants or products which is why it is left out of the ICE table calculations.

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When do you use Kc vs Kp?

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K tells you the proportion of products to reactants present in the reaction and whether there are more products or reactants. When a certain reaction is strongly favored, it means that the K value is greater than 1000.

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The OH- in both compounds with accept a proton to create water. Since it is accepting protons, these compounds conform to the definition of a Bronsted base.

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What does the term polyprotic mean? Can a molecule be both polyprotic and amphiprotic?

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For a conjugate base, you remove a hydrogen and add a 1- charge.

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Water can only be labeled as an acid or a base depending on the reaction. In some cases, it may act as an acid and donate a hydrogen, In other cases, it may act as a base and accept protons. Water has a set constant, Kw, which is 1.01 × 10^-14 at 25 °C.

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For binary acids, the atom with a greater radius will be more acidic because it can easily give off an H+ ion. For example, HI is a stronger acid than HF. For oxoacids, the molecule with the greatest amount of oxygens is the most acidic. This is due to the fact the it increases electronegativity, ma...

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HCO3- and HPO4 2- can both accept and donate protons. In this way, they are considered amphiprotic and can be used as an acid or a base in the reaction. If they are an acid, they lose the hydrogen in the reaction. If they are basic, they gain a hydrogen in the reaction.

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This coordinate compound is bisethylenediamine dinitro iron (IV) sulfate.

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Lewis and Bronsted Acids and Bases are simply different because of how they define and acid and a base. In Bronsted's definition, an acid is a proton donor and a base is a proton acceptor. In the Lewis definition, an acid is an electron pair acceptor and a base is an electron pair donor. The Lewis t...

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When do you add the suffix -ate to the metal name in a coordination compound?

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I believe that the parentheses are present to be able to identify the molecules in the coordination compound. It is just for ease of reading not a special purpose.

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For a seesaw shaped molecule, how do you know that the lone pair should be on the equatorial plane and not the axial plane?

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In the seesaw shape, the bond angles will be <90, <120, and <180.

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Sigma bonds are also more flexible than pi bonds because of their orientation to the atom. Pi bonds do not allow rotation and they are usually the first bonds broken down in a chemical reaction.

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The VSEPR model gives you the electron geometry and molecular shape. The electron geometry of a molecule is the naming convention based on the number of electron regions. Molecules with 2 electron regions are linear, 3 electron regions are trigonal planar, 4 electron regions are tetrahedral, 5 elect...

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The AXE notation is useful to organize the types of electron regions in a molecule. For example, SF4 has a seesaw shape. This means it has four bonds and 1 lone pair. This can be described as AX4E in the notation.

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Dipoles occur when there is an unequal sharing of electrons. Each atom in a molecule has a partial charge which is either negative or positive. When one charge is significantly larger than another, or the electronegativity difference is great, a dipole is produced. Lone pairs on the central atom als...

ALegala_2I

London Dispersion forces act on all molecules and atoms. This includes nonpolar molecules, monoatomic gases, and in molecules that also exhibit dipole-dipole interactions.

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According to the problem, the boiling point of AsF3 is 68C and AsF5 is -53. You can first approach this problem by drawing the Lewis structures for both molecules to find out the intermolecular forces that each molecule has. AsF3 has a lewis structure in which a lone pair on the Arsenic atom. This m...

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Hydrogen bonds form when hydrogen interacts with nitrogen, oxygen, or fluorine. In this problem, only d can create hydrogen bonds because it has nitrogen and oxygen.

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London Dispersion forces are known as induced-dipole–induced-dipole interaction. Interactions that are proportional to 1/r6 are commonly regarded as van der Waals interactions. So London Dispersion forces are a type of van der Waals interaction.

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Electronegativity is the electron pulling power of an atom. The atoms that are more electronegative will want the electron more in real life. The negative formal charge indicates an excess of an electron. Since more electronegative atoms will have a greater power to pull this electron, they will gen...

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Sulfur is one of the exceptions that Dr. Lavelle mentioned in terms of being able to have an expanded octet. It can bond to 6 atoms and have an expanded octet with 12 electrons.

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The Question for 2.D.9: Arrange the cations Rb+1, Be+2, and Sr+2 in order of increasing polarizing power. Explain your reasoning. The cations with the smallest radius and largest charge have the greatest polarizing power. Of the three, beryllium has the smallest radius, so it would have the greatest...

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Electronegativity is the electron pulling power of an atom. As you move to the right of the periodic table, the electronegativity increases because atoms get closer and closer to having a full octet. As you move up the periodic table, electronegativity also increases because there is less shielding ...

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Cations with a smaller radius and a more positive charge have greater polarizing power. For example, K+ > K in polarizing power. Anions with a larger radius and a more negative charge have greater polarizability because they have more electrons. So I->Br-, in polarizability.

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How do we know when the hydrogen will be attached to the central atom vs other atoms? Like in the case of HClO2, why is the hydrogen attached to the oxygen and not the chlorine? https://img1.daumcdn.net/thumb/R720x0.q80/?scode=mtistory2&fname=http%3A%2F%2Fcfile7.uf.tistory.com%2Fimage%2F999FF54C...

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Radicals are fairly uncommon because they are highly unstable and reactive. They will generally only stay in that form for a short period of time before interacting with other molecules to get a pair.

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Professor Lavelle said that phosphorus, sulfur, and chlorine can have expanded octets. This is due to the fact that they have empty p orbitals which can accommodate additional electrons.

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Ag is one of the exceptions to the build up principle. It would normally have a configuration of [Kr]4d10 5s1 because the atom would be most stable when the d shell is completely full rather than the s shell. When you remove an electron from Ag, it will be removed from the outermost shell which is 5...

ALegala_2I

As of right now, I believe that we do not need to memorize the molecular formula for these molecules since we did not cover it in class. On a test, I think it would be given to us and we would just have to draw the lewis structure.

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Chlorine has the ground state electron configuration of [Ne]3s1 3p5. An electron is always removed from the outermost subshell present. In this case, the outermost subshell is 3p.

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For b and d, you would go off of the ml number. In a 4p atom in which l=1, there are 3 possibly orbitals orientations as stated above. This means that an electron in the 4p orbital could have the following configurations: n=4, l=1, ml = 1; n=4, l=1, ml = 0, and n=4, l=1, ml = -1. When you are given ...

ALegala_2I

Aufbau principle is just rules for how electrons fill atomic orbitals. It states that electrons will always fill the lowest energy state first. For example, an electron will be in the 1s orbital before the 2s orbital. It also states that electrons will be added to different orbitals with parallel sp...

ALegala_2I

This filling of the d orbital over the s orbital will also occur for elements such as chromium. Instead of being [Ar]3d44s2, the electron configuration will be [Ar]3d54s1.

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Do all the elements in group 6 and 11 have electron configurations similar to copper and chromium?

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The principal quantum number (n) specifies the shell of the electrons in an atom. For example, 4p corresponds to 4 shells of electrons in the atom. The angular momentum number (l) signifies the sub-shells. The magnetic quantum number describes the amount of orbitals in a sub shell. There are 3 orbit...

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Hi, In the textbook, a modified equation for the uncertainty principle is used with the variable h bar (see below). What does this variable signify? Which equation should we use: the one from the textbook or the one that is taught in class? https://scitechdaily.com/images/heisenberg-uncertainty-prin...

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To add on, the Heisenberg equation is specifically used in regards to uncertainty. The questions will usually ask you what the uncertainty in the velocity is or it will give you a range of values for velocity. This is your main indicator to use the Heisenberg equation over the deBroglie equation.

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DeBroglie's proposed that all particles should be considered to have wave like properties. So he devised the equation: wavelength(lambda) = Planck's constant(h)/ momentum(p). In this equation, we are treating light like a wave and finding the wavelength based on the mass and velocity of the particle.

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You use the equation E=hv when you are trying to find out the energy of a photon of light. If you know the frequency of this photon, then you can multiply it by Planck's constant to find the total energy of the photon.

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The values of c (speed), Planck's constant, and Rydberg's constant are on the formula sheet, which will be given to you for every exam.

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I think it will be helpful to know which types of light have the largest wavelengths and the shortest. For example, radio waves have the greatest wavelength while gamma rays of the shortest. It will essentially be beneficial to know the order. https://www.radio2space.com/wp-content/uploads/2013/07/c...

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To clarify, when you divide by the least number of moles. The answer you are getting is a molar ratio of atoms in the molecule. This is relative to the other atoms in the molecule. We want this ratio to be a whole number because we can only have a whole number of atoms. To find the molecular formula...

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In terms of wave properties, higher intensity means a greater wave amplitude and therefore a greater amount of energy. In the photoelectric experiment, it was found that increasing the intensity of light did not increase the energy of light. So this experiment supported the idea that light did not h...

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An angstrom is not a SI unit. It is used and recognized by many scientists but it is not part of the International System. An angstrom represents 10^-10m. This can be converted to other SI units like nanometers or picometers.

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To clarify the statement above, a molar ratio refers to BOTH the stoichemetric coefficients in a chemical equation and the moles of atoms in a molecule. For example, the chemical equation C2H4 + 3O2 → 2CO2 + 2H2O. There is a molar ratio of 2 water molecules to 2 carbon dioxide molecules. Within the ...

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There are several polyatomic ions which are good to memorize. There is a list of nomenclature in the beginning of the book which can be useful for future problems.

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I would first write down the number of atoms of each element that is present for the reactant side and the product side. I would then begin to balance my equation and typically leave hydrogen and oxygen for the end. As I balance, I would readjust the initial numbers that were written at the beginnin...

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Both 9.87 mL and 9.87 x 10^-3 L have the same value. Regardless of how it is written, the amount that would be measured for the actual experiment would be the same. If the question asks you for the volume in a specific measurement then you would have to choose one or the other.

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While the empirical and molecular formulas can be different, there are situations in which the two formulas are the same. This can be determined by dividing the molar mass of the molecular formula by the molar mass of the empirical formula. If the ratio is 1, the empirical and molecular formulas for...

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