CHEMISTRY COMMUNITY

Naji Sarsam 1F

As my last post for chemistry community ever:

Never trust an atom...

I've heard they make up everything...

Naji Sarsam 1F

I was studying electrochemistry and saw that for a galvanic cell, liquid mercury can act as an electrode. How is this possible?

Naji Sarsam 1F

The effect of translational and rotational momentum is covered in the chemistry textbook, however it is not of extreme importance. It is mainly used to derive the equations for the energy of ideal monoatomic gasses.

Naji Sarsam 1F

I believe its because solid iodine cant be a conducting solid. It is a very brittle solid as it is not held together by ionic bonds but rather covalent bonds and intermolecular forces. Metals or Ionic solids can be electrodes, however.

Naji Sarsam 1F

Why can we ignore the rate of the reversion reaction when doing kinetics? Do the rate laws, such as rate = K [R1] [R2], give just the initial rate of the reaction or the rate of the reaction as it progresses?

Naji Sarsam 1F

As far as I understand it, Carbon Graphite is just another alternative to platinum. Whenever you can use platinum you can also use carbon graphite. But as you said, platinum is much more common.

Naji Sarsam 1F

There have been no announcements yet about a review packet. I would imagine though that it would be announced in Monday's lecture if there is one. If not, then there probably isn't.

Naji Sarsam 1F

Also, If your schedule does not align with any review sessions, reading the assigned chapters in the book helps a lot. I know it takes quite a long time; you don't have to read everything, just what you need help on. OFten the book explains concepts very clearly and gives step by step problems.

Naji Sarsam 1F

To clarify, the reaction is still considered a redox reaction. However, it is also important to note that the standard cell potential of every concentration cell equals 0.

Naji Sarsam 1F

The rate laws are instantaneous rates. Usually, the average rate won't be asked for unless the give you a chart of data.

Naji Sarsam 1F

Often, chemical reactions may be understood as a series of reactions acting in order of steps to take the original reactants to create the final products. This series of steps is called the reaction mechanism. The slowest step of the reaction mechanism often determines the order of the reaction.

Naji Sarsam 1F

Normally, the order of the reaction must be determined empirically. Often, empirical data is given in the question which you may manipulate to determine the order of the reaction.

Naji Sarsam 1F

This is because by definition, initial rates refer to the rate of the forward reaction at the moment it has started. Mathematically, this is when t approaches 0.

Naji Sarsam 1F

n represents the moles of electrons transferred in a redox reaction. To know how many electrons are transferred, you have to divide a redox reaction into its reduction and oxidation half-reactions.

Naji Sarsam 1F

This is because since technically it is the same product and reactant on both sides. Thus the reduction reaction and oxidation reaction have equal magnitude yet opposite sign values for E. Thus when you add them together, they cancel out to equal 0.

Naji Sarsam 1F

Can someone explain why platinum was used in the galvanic cell during dr. lavelle's lecture?

Naji Sarsam 1F

If cell potential is an intensive property, why does changing the molarity of reagents in a chemical reaction change the cell potential? In lecture we started using principles similar to le chatelier's principle, however, I thought cell potential does not matter on the amount of reagent present

Naji Sarsam 1F

We discussed how three concepts.

1.) how to balance a redox reaction by splitting it into its composite half-reactions and then adding them together

2.) cell diagram notation

3.) the nernst equation

Naji Sarsam 1F

Yes, delta S and delta H are assumed to not be temperature-dependent, meaning constant, when using the vant hoff equation

Naji Sarsam 1F

The Nernst is E=E^{o}-\frac{RT}{nF}ln(Q) E is the cell potential of a reaction not at equilibrium and not at standard conditions E^{o} is the cell potential at standard conditions R is the gas constant T is the temperature of the reaction n is the moles reacting F is faradays constant Q is t...

Naji Sarsam 1F

A good way to approach problems are to explicitly write down the variables that are given to you. For example, if a problem mentions 6 moles, 278.15 K temperature, and that it is an ideal gas then you should write down n = 6, T = 278.15, and R. Then write down the symbol for the variable(s) you are ...

Naji Sarsam 1F

Yes, the Vant Hoff equation can only be applied effectively under the assumption that the entropy change is independent of the temperature of the reaction. This assumption can be made unless explicitly told otherwise.

Naji Sarsam 1F

The Van't Hoff Equation is derived from two expressions for Gibbs Free Energy.

Naji Sarsam 1F

An easy way to remember all of the Cp,m values is the equation Cp,m = Cv,m + R. This equation is derived in the chemistry book chapter 4, and it lets you only have to memorize the Cv,m for monoatomic, linear, and nonlinear gasses since the Cp,m is just R plus those values.

Naji Sarsam 1F

Moreover, chemical reactions are not known to just spontaneously release electrons. First, it is favorable for electrons to be bound to a nucleus since the positive nucleus attracts the negative electron. Second, the products of a chemical reaction require the same amount of electrons as the reactants

Naji Sarsam 1F

It does matter as the reaction is not in equilibrium yet, so you must know which side is the reactants and which side is the products because only the reactants will decrease and only the products will increase. The language of the question should inform you which side of the reaction is reactants o...

Naji Sarsam 1F

The units for entropy and enthalpy may be joules or kilojoules, it is just whatever is most useful for the number of joules there are. However, when doing calculations that include entropy and enthalpy in an equation, of course, you must match up their units--most of the time to joules.

Naji Sarsam 1F

There is no difference between the terms spontaneous and favorable in terms of chemical reactions. The formal term is actually spontaneous, but modern connotations of that word may make it seem that spontaneous reactions happen very quickly. Rather, the term means that the reaction is favorable and ...

Naji Sarsam 1F

Dr. Lavelle's lecture pertained specifically to isothermic reversible expansion. In this type of expansion, the delta U equals 0. This is because isothermal reactions mean that once energy is used in the form of work, the system gains that energy back as heat to maintain the same temperature--thus t...

Naji Sarsam 1F

A phase change affects the entropy of a molecule because intermolecular bonds are either being broken or formed, which affect how ordered the system is. In cases where intermolecular bonds are being broken--melting and boiling--the entropy increases as atoms are freer to move and occupy more energy ...

Naji Sarsam 1F

If there are two possible options for a microstate, then W = 2^N where N is the number of atoms

Naji Sarsam 1F

If there are two possible options for a microstate, then W = 2^N where N is the number of atoms

Naji Sarsam 1F

An easy way to conceptualize it is as follows. When you heat up a substance, you give the atoms of that substance more energy. That means those atoms have more positions to be in as well as more energy states to be in. Thus, when you heat up a substance, you increase the Degeneracy W of the substanc...

Naji Sarsam 1F

Thermodynamics is the study of heat exchange, work, and energy in general. Thermochemistry is a branch of thermodynamics that applies those concepts to specific chemical reactions. For example, bond-enthalpy is a thermochemistry concept as it applies the thermodynamic concept of energy to chemical b...

Naji Sarsam 1F

Understanding this reaction is difficult because of vague terminology. The set up of this reaction is such that the system does not lose any net energy, meaning there is no net change in temperature. What happens is when the gas expands it does work. This work, of course, requires energy, which is d...

Naji Sarsam 1F

As far as Dr. Lavelle has used it in lecture, he only used it in a theoretical sense--not in actual application. Lavelle used this equation to prove that the internal energy U of an isothermal reversible reaction is 0. This is because the temperature is constant for this reaction, and as the equatio...

Naji Sarsam 1F

Standard enthalpies of formation are given for certain molecules in the tables of the textbook. The standard enthalpy of a reaction though should be calculated.

Naji Sarsam 1F

We discussed section 4C i believe

Naji Sarsam 1F

Bond Enthalpies refer to the energy stored in a certain type of bond--whether it be single, double, or triple--and the specific atoms that are being bonded Standard Enthalpies of Formation refer to the energy stored in a molecule calculated from the reaction of its formation from the most stable for...

Naji Sarsam 1F

The standard enthalpy of formation by definition refers to the energy of the reaction required to produce a molecule from the most stable states of its constituent atoms. For example, the reaction for the stand enthalpy of formation for Hydrogen Iodide is: H_{2} + I_{2} \rightarrow 2HI The standard ...

Naji Sarsam 1F

To understand how temperature affects a reaction, one must know whether the reaction is endothermic or exothermic. For temperature increases: Products are favored in endothermic reactions Reactants are favored in exothermic reactions For temperature decreases: Reactants are favored in endothermic re...

Naji Sarsam 1F

Yes. Moreover, it is important to understand that chemical equilibria and acid-base equilibria are the same exact process. We just have different terms for the Ks of each as acid-base reactions usually involve just proton disassociation. Thus, almost everything you would do for chemical equilibria a...

Naji Sarsam 1F

Dr. Lavelle said that Delta G will not be on this exam. He was referencing future material for those who may remember enthalpy from highschool chemistry.

Naji Sarsam 1F

Yes, this material will be on Test 1

Naji Sarsam 1F

Halogen anions in solution do not affect the ph as they are weak conjugate bases of their corresponding strong acids: HCl, HBr, Hi, and so on. The only exception to this would be F- anion, as it is a strong conjugate base since HF is a weak acid.

Naji Sarsam 1F

A polyprotic acid is an acid that can disassociate more than once. An example of this is phosphoric acid. However, it requires much less energy for this acid to disassociate the first time in comparison to the energy required to disassociate the second or third time. Thus, regarding the Ka of each d...

Naji Sarsam 1F

That is correct. Reactions at equilibrium do not naturally stray from equilibrium. That does not only mean that Q would ever increase to higher than K once at equilibrium, but also that it would never decrease lower than K.

Naji Sarsam 1F

Can someone please explain how Le Chatelier’s Principle works? especially with changes in pressure?

Naji Sarsam 1F

To understand how a reaction will proceed to reach equilibrium, it is important to understand what K and Q represent symbolically. Both represent the ratio of products to reactants in the reaction. However, K represents that ratio at equilibrium, while Q represents that ratio while not at equilibriu...

Naji Sarsam 1F

For heterogeneous equilibrium problems, it may be confusing as to use either concentrations or pressure. But recognize, if there are any reactants which are aqueous, it does not make sense to use their partial pressure. Thus, you’d have to use concentration for all reagents in the equilibrium. If th...

Naji Sarsam 1F

Peer Learning Sessions are opportunities Dr. Lavelle Provides for students who are either confused on a subject or just need extra help. There are three types of sessions: drop-in sessions, workshops, and step-up sessions.

Naji Sarsam 1F

Yes, an example is ammonia NH3

All bronsted acids are also lewis acids, but not all lewis acids are bronsted acids.

Naji Sarsam 1F

Yes, all ligands in coordinate compounds are lewis bases because they donate electrons. The central metal atom then is a lewis acid

Naji Sarsam 1F

The difference between amphoteric and amphiprotic lies in understanding the difference between lewis acids and bronsted acids. Bronsted acids require a proton to be donated or accepted. The lewis acid definition encompasses all bronsted acids, but also acids which do not donate protons but rather ju...

Naji Sarsam 1F

I believe you are misundestanind what the conjugate see saw is. The conjugate seesaw refers to the foloowing four concepts 1.) if an acid is strong, the conjugate base is weak 2.) if an acid is weak, the conjugate base is strong 3.) if an base is strong, the conjugate acid is weak 4.) if an base is ...

Naji Sarsam 1F

The hydrogen bonding od DNA Base pairs, heme as a coordination compound, cisplatin for chemotherapy, vitamins as acceptors of dangerous radicals, the role of carbon dioxide in blood ph

These are the examples i can think of

Naji Sarsam 1F

Hybridization is when a central atom's orbitals average in their energy levels, creating hybrid orbitals to free up all of their electrons. I think the simplest example demonstrating this is Carbon. Carbon has an electron ground state of [He] 2s^{2} 2p^{2} This means that carbon only has two unpaire...

Naji Sarsam 1F

It is possible to have positively charged ligands, although they are rare because ligands are lewis bases. The charge of the ligand does not matter in naming, but the charge of the central transition metal does matter. So if the positively charged ligand means that the central transition metal has a...

Naji Sarsam 1F

Yes the Iron is bonded to the carbon on each side of the "sandwhich"

Naji Sarsam 1F

There are different naming conventions for different types of molecules. Here are the very basic rules Ions: "Cation Name" "Anion Name + ide" ex.) NaCl : Sodium Cholride Covalently Bonded Molecules: "Central Atom's Name" "Greek Suffix + Peripheral Atom's Name + ide...

Naji Sarsam 1F

You do not need to do any mathematical calculations to determine angles. Rather you have to memorize the angles present in each molecular geometry, and that every time a bonding pair of electrons is replaced by a lone pair, those angles decrease. Linear molecules have an angle of 180 Tetrahedral mol...

Naji Sarsam 1F

The molecular geometry of carbon dioxide is linear. This is because there are only two electron density regions: the two double bonds between carbon and each atom.

Naji Sarsam 1F

Sigma bonds are stronger than pi bonds because the electron clouds between atoms that have a sigma bond overlap more than those electron clouds would overlap in a pi bond. The more overlap between electron clouds in sigma bonds allows for a stronger electronegative attraction between shared electron...

Naji Sarsam 1F

There are two characteristics of bonds that we need to know: the number of bonds and the type of bonds. The number of bonds refers to whether it is a single, double, or triple bond. The type of bond refers to whether the bond is a sigma or pi bond. A sigma bond is one where the electron clouds overl...

Naji Sarsam 1F

It can stay a p orbital, as there is the hybridization sp2 which is used in molecular geometries with three regions of electron density--such as trigonal planar geometries.

Naji Sarsam 1F

Molecular geometries depend on the number of atoms bonded to the central atom, and the number of lone pairs that central atom has. Molecules which have 5 atoms bonded to the central atom, and 0 lone pairs, are of the geometry trigonal bipyramidal. Molecules which have 4 atoms bonded to the central a...

Naji Sarsam 1F

Yes, sigma and pi bonds will be on the exam. Dr. Lavelle discussed them very shortly at the end of Friday's lecture on 11/15/19. He will discuss them more on the upcoming Monday lecture on 11/18/19. Briefly: single bonds have a sigma bond; double bonds have one sigma bond and one pi bond; triple bon...

Naji Sarsam 1F

This is the same as tetrahedrals. They are not called tetrahedrals because the molecule has four atoms, rather it is the mathematical term for the shape with 4 equal faces. It just happens that 4 atoms arrange themselves into the vertices of the tetrahedral

Naji Sarsam 1F

The name octahedral refers to the shape that a six atom molecule makes. This is because the term is a geometric one, as octahedral refers to the geometric shape hacing 8 faces, thus octa. However, the shape only has 6 vertices, which in a molecule is the 6 atoms.

Naji Sarsam 1F

Yes, this exam should also include intermolecular forces as well as the VSEPR model. Moreover, the first slide of Dr. Lavelle's lecture on Monday 11/18/19 will be on the exam. However, Dr. Lavelle noted that hybridization will not be on the exam.

Naji Sarsam 1F

This is because lone pair electrons take up more volume with their electron clouds as they are only being held by one atom's nucleus. Bonding electrons are confined to a smaller volume as they feel the influence of two atoms' nuclei, confining them to a smaller space. Thus, it is not that lone pair ...

Naji Sarsam 1F

Yes, that is the correct order of interaction strength, except that it is missing the ion-ion interaction which is the strongest interaction of all. And yes, Van Der Waal Forces also are called London Forces. However, Dr. Lavelle prefers if you call the interaction induced dipole-induced dipole inte...

Naji Sarsam 1F

dipole - induced dipole interaction: One molecule has a permanent dipole This permanent dipole molecule is near another molecule that doesn't have a permanent dipole However, the molecule with a permanent dipole polarizes the other molecule, inducing a dipole in it, and forming an intermolecular int...

Naji Sarsam 1F

It is important to distinguish between polarizing power and polarizability. Polarizing power is the ability of an atom to polarize another. Polarizability is the opposite: the ability of an atom to be polarized. Polarizability is similar to the trend of electronegativity. An atom is more polarizable...

Naji Sarsam 1F

Interaction potential energy is always negative because atoms always lose energy when forming bonds; they never gain energy. In other words, the energy of an atom without a bond is higher than that of the same atom with a bond. So, if you take the final energy of the atom with the bond and subtract ...

Naji Sarsam 1F

The length and shape of a hydrocarbon often affect its state of matter when at room temperature. When hydrocarbons have the same shape--particularly the rod shape--the longer hydrocarbons are those that are more solid while the shorter ones are more liquid and gaseous. When hydrocarbons have the sam...

Naji Sarsam 1F

Interaction potential energy is always negative because atoms always lose energy when forming bonds; they never gain energy. In other words, the energy of an atom without a bond is higher than that of the same atom with a bond. So, if you take the final energy of the atom with the bond and subtract ...

Naji Sarsam 1F

It is important to distinguish between polarizing power and polarizability. Polarizing power is the ability of an atom to polarize another. Polarizability is the opposite: the ability of an atom to be polarized. Polarizability is similar to the trend of electronegativity. An atom is more polarizable...

Naji Sarsam 1F

Fluctuating dipoles becomes important when discussing induced dipole - induced dipole interactions. A simplification of the premise is that electrons in an atom are always moving; they are not static. Thus, in molecules, electrons are still moving around their atoms in, essentially, random motion. T...

Naji Sarsam 1F

Here it is important to understand the difference between formal charge and charge. The charge relates to the entire molecule. For example the charge of H_{2}O is 0; the charge of the sulfate polyatomic ion is 2-. The formal charge then is a calculation tool used for single atoms in particular withi...

Naji Sarsam 1F

The square of the atomic orbital function gives the probability of where the electron will be in that orbital.

So the orbital function describes the shape of the volume the electron can reside; the square of that function tells you how likely it is to be in each location within that volume.

Naji Sarsam 1F

There are two kinds of octet exceptions: atoms which exceed the octet and those which fall short of an octet. The atoms which exceed the octet are those in columns 15 through 17 and in rows 3 or below. The most common we will use are Phosphorus, Sulfur, and Chlorine. This is because these atoms can ...

Naji Sarsam 1F

It may just be helpful to quickly show the addition of valence electrons to show the calculation for the total number of valence electrons. It will help you keep track and also make it easier for the grader.

Naji Sarsam 1F

When the question asks to draw the "most favorable" lewis structure, it generally means just the correct one if it doesn't have resonance. However, in some cases, a molecule can have resonance where one structure is preferred over another. This has to do with the formal charge. With some m...

Naji Sarsam 1F

The relationship between bond strength and electronegativity is an indirect one to understand: 1.) Electronegativity refers to the tendency of an atom to attract and accept an electron. 2.) A bond is when two atoms share at least a pair of electrons. Bond strength is affected by two principles: the ...

Naji Sarsam 1F

There are four quantum numbers: n, l, m_{l} , and m_{s} These four quantum numbers explain the individual properties of every electron possible in an atom. Moreover, in one atom, two electrons cannot have the same values for all four quantum numbers. Pertaining to the quantum number "m", t...

Naji Sarsam 1F

Electron affinity and electronegativity describe similar processes in different ways. Electron affinity is the energy released when an atom--in the gaseous phase--gains an electron This energy can be directly measured Electronegativity is the "ability" of an atom to attract electrons This ...

Naji Sarsam 1F

There are two exceptions: Chromium: Which should be [Ar] 3d^{4} 4d^{2} according to the systematic pattern normally used However, it is actually [Ar] 3d^{5} 4d^{1} Copper Which should be [Ar] 3d^{9} 4d^{2} according to the systematic pattern normally used However, it is actually [Ar] 3d^{10} 4d^{1} ...

Naji Sarsam 1F

We will be discussing the shape of molecules (the VSEPR model) in a future lecture. As of week 4, we have not discussed this and thus you should not be worried about the three-dimensional structure of molecules.

Naji Sarsam 1F

The Rydberg Formula Dr. Lavelle taught us is E_{n}=-\frac{hR}{n^{2}} This equation gives us the energy of an electron at a particular energy level ( E_{n} ) given that we know the energy level the electron is at (n), the plank constant (h) and the Rydberg constant (R). Thus, the solution of this equ...

Naji Sarsam 1F

The reason for Tungsten not following the exception rule that Chromium does is not needed for our course. We only need to know the electron configurations for the first row of the d block, since this is a life science chemistry course.

Naji Sarsam 1F

Dr. Lavelle mentioned two exceptions in class to the Aufbau principle: Chromium and Copper. Could someone please explain what those exceptions are and why they are there?

Naji Sarsam 1F

In all of the equations used for the Quantum Mechanics unit, distance must be converted to meters. After a calculation is done, the problem may ask for a unit different than meters, such as Angstrom or nanometers. Only convert to these units after the calculation is complete, never before.

Naji Sarsam 1F

In an uncertainty problem where they give a "variable" ± "a value", the uncertainty is twice that "value". This is easier to understand by example: If a problem describes the velocity of an object as 5.00 m/s ± 1.00, the uncertainty would be double the value of 1.00, eq...

Naji Sarsam 1F

An extra note which is important to keep in mind is that the "Wave Function" is a mathematical equation. That is why it is also called the Schrodinger Equation. Once you think of it in that way, it becomes very easy to contextualize all of the chemistry terms related to it. We will not lea...

Naji Sarsam 1F

Aa Dr. Lavelle discussed in class, traditionally, wavelengths smaller than 10 ^ -15 meters are considered to have unmeasurable wave-like properties. Instead, they would only have particle-like properties.

Naji Sarsam 1F

The wave model of electrons properly predicts energy levels if electrons are modeled as circular standing waves around the nucleus. This is because all waves--circular or not--have differing energies. However, for a circular standing wave to exist, it must be continuous and have no discontinuities s...

Naji Sarsam 1F

To understand diffraction patterns, one must first recognize that there are two models possible for understanding the motion of an object relevant to chemistry: the particle model and the wave model. The particle model interprets objects as solid objects which have a defined location in space. The w...

Naji Sarsam 1F

Yes, this energy is called by two names: "threshold energy" and the "work function". The reason for this energy being called the "threshold energy" is because that is the exact energy that marks the boundary for an atom to eject its electron or not. At the threshold ene...

Naji Sarsam 1F

Formula units are different from molecules in that all atoms in an ionic compound have formed atomic bonds with other atoms, to form a lattice. In this way, ionic compounds are not groups of moleculas which are associeated with one another through intermolecular bonds. Rather, they are one coherent ...

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