CHEMISTRY COMMUNITY

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The combustion reaction is $CH_{4}+2O_{2}\rightarrow CO_{2}+ 2H_{2}O$ . Combustion reactions are typically writing as the organic molecule and oxygen as the reactants and water and carbon domioxide as the products. Combustion is typically an exothermic reaction.

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I would know them just in case. Adiabatic means q=0, isothermal means constant temperature and isobaric means constant pressure. It’s also helpful to know that isochoric means constant volume.

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I think we have to decide on our own. If the K value is less than 10^-3 than I would assume to use the approximation. However, the safe bet is to use the quadratic formula.

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While thermodynamics tells us why a chemical reaction occurs, kinetics tells us how a reaction occurs. The quantity related to kinetics is the rate constant and the thermodynamic quantity is correlated to delta G as it is the free energy associated given off during a a chemical reaction.

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To determine the units of the rate constant, a formula you could use to determine this is $1/M^{Overall Order-1}s$ .

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Yes. For a zero-order reaction, the rate of the reaction is independent of reactant. The integrated rate law will help us determine is the reaction is zero-order is the plot of time (x-axis) vs. concentration of the reactant (y-axis) gives us a negative linear regression.

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Cell potential is an intensive property and is not a state function. Thus, we cannot just simply add the values together and apply a method similar to that of Hess's Law for cell potential. Therefore, since, delta G is a state function, we can use the equation \Delta G=-nFE to find the change in Gib...

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The cell potential is the potential difference associated with a galvanic cell that is working reversibly. A cell works reversibly when its pushing power is balanced against an external matching source of potential difference. The formal term for "voltage" os "potential difference,&qu...

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Yes. For $\Delta G=-nFE$ , n is the number of electrons that are transferred in the reaction

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The subscript r is an abbreviation of "reaction." Thus delta H "r" would imply the change in enthalpy of the reaction and delta S "r" would signify the entropy change of the reaction.

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The change in entropy formula has final over the initial in that property because we are observing a change from an initial state to a final state. Pressure and volume are inversely proportional due to Boyle's Law and thus, pressure is an exception where it would be initial pressure over final press...

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The higher the temperature, the more thermal energy the system has and thus, the system has more ways to distribute that energy. The more ways there are to distribute energy, the higher the entropy. The larger the volume, the more ways to distribute the molecules in that volume. The more ways there ...

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Delta G is equal to max work under constant temperature and pressure. G is defined as the maximum non-expansion work under constant T and P.

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Not necessarily. Since entropy is a state function, finding the change in entropy irreversibly is the same as the change in entropy for a reversible reaction. Therefore, the change in entropy for a irreversible reaction is not immediately the negative of the reversible reaction.

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Can someone explain how to get the answer for question #6 part d?

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Due to the third law of thermodynamics, all substances have an absolute amount of entropy. Standard molar entropy is the total (minimal) amount of entropy that one mole of a substance gains as it is brought from 0 K to the standard conditions and thus, it is always positive (greater than zero) becau...

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In the sixth edition, the Gibbs Free Energy Problems are 9.51 through 9.68.

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I don’t think we need to use derivatives and integrals on the midterm but don’t quote me on this. I think we derived these equations in lecture/notes to understand where these variables and equations come from.

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Reactions that have a constant P and involves a solid and/or liquid will result in P $\Delta$ V as insignificant. Because the volume of the reactants equals the volume of the products, there is no expansion work.

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U is a state property and is the internal energy of a system. Changes in internal energy are a function of work. The energy of a closed system can be changed by heating/cooling or compression/expansion. \Delta U=q + w. If \Delta V is zero (constant volume), delta U= q_{v} . If \Delta P=0 (constant p...

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The reversible expansion does the maximum amount of work because the gas is pushing against the maximum possible external pressure.

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A reversible process is a process that can be reversed in order to obtain the initial state of a system. There is also an equilibrium between the initial state and the final state of the system. An irreversible process is a thermodynamic process that cannot be reversed in order to obtain the initial...

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When delta H is positive, the positive sign indicates that the reaction is endothermic, meaning that it requires heat.

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A state function depends only on the current state of the system, any change inits value is independent of how the change in state was brought about. Heat is not a state function because the energy transferred as heat during a change in the state of system depends on how the change is brought about....

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The value of K_{w} for water at body temperature (37 degrees Celsius) is 2.1x10^{-14} . How would you calculate the concentration of the hydronium ion and the hydroxide ion given only this information? Would you assume that the concentration of the hydronium ion is equivalent to the concentration to...

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You would typically use an ICE table when the reaction involves a weak acid or weak base. You would use molar ratios when the reaction involves a strong acid or strong base as these types of reactants completely dissociate. Weak acids and weak bases do not completely dissociate and thus, we would ha...

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When there is an increase in temperature of the system, Le Chatelier’s Principle states that the reaction will shift away from the heat and the energy of the exothermic reaction is favored. On the other hand, a decrease in temperature shifts the reaction toward the heat and the energy of the endothe...

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In regards to amount/number of moles, I like to visualize Le Chatelier's Principle like a seesaw. Let's say the left of the seesaw are the reactants and the right of the seesaw are the products. Increasing the amount of reactant leaves the seesaw tilted, having more weight on the left side. In order...

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You would commonly use torr or atmosphere as the units for partial pressure. I would stick with atmospheres to be safe. A bar is atmospheric pressure at sea level and equals 100 kilopascals.

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Can someone please explain and clarify the following question: The following flasks (picture not included) show the dissociation of a diatomic molecule, $X_{2}$ , over time.
C)Assuming that the initial pressure of $X_{2}$ was 0.10 bar, calculate the value of K for the decomposition.

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I would know this formula and how to apply it just in case. $K_{a}= ([H^{^{+}}] [A^{^{-}}])/[HA])$ . $pK_{a}=-log_{}1_{0}K_{}a$

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If given the molarity of the strong acid solution, you would take the -log[H+] to calculate the pH. Since it is a strong acid, it completely dissociates and the molarity of the strong acid is equivalent to the concentration of H+ ions.

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All Bronsted-Lowry bases must have a lone pair to accept a hydrogen, and all Lewis bases have lone pairs. However, Lewis bases may act as nucleophiles (a chemical species that donates an electron pair to form a chemical bond in a reaction) for any number of atoms and not just for H.

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Hybridization is the mixing of two non equivalent atomic orbitals. The result of hybridization is the hybrid orbital. Different types and numbers of atomic orbitals are participating in making hybrid orbitals. Different atomic orbitals have different shapes and number of electrons. But all the hybri...

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Here are some basic rules for assigning oxidation numbers: -The cation is written first in a formula, followed by the anion. -The oxidation number of a free element is always 0. -The oxidation number of a monoatomic ion equals the charge of the ion. -The usual oxidation number of hydrogen is +1. Exc...

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Electron transfers are essentially redox reactions, where the oxidation state of the reactant and product change as the process of an electron moves from one atom or molecule to another. Transition metals can exist in more than one oxidation state and thus electron transfer reactions commonly involv...

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Part b) of question 2E. 29), is asking us to identify which of the three isomers of dichlorobenzene has the largest dipole moment. Can someone explain to me why the first structure has the largest dipole moment in comparison to the second isomer?

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When predicting the molecular shape, I understand that the first step is to draw the lewis structure for the molecule; however do we account for formal charges in this situation? In other words, do we use the most stable form of the lewis structure to determine the shape?

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Electron geometry teaches us about the arrangement of different electron groups and we consider both the lone electron pairs and bond electron pairs. Through electron geometry we get the spatial arrangement of lone pairs and bond in the molecule. Molecular geometry helps us understand the entire ato...

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BaO is more soluble in water than MgO because its atomic size gives the molecule a more iconic nature and less lattice energy. The MgO molecule has a cation with a smaller radius, indicating that there is strong attraction between the cation and anion in the lattice.

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What are the differences between a hybrid and molecular orbital?

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Can someone distinguish the difference between axial lone pairs and equatorial lone pairs and explain how they contribute to molecular structure?

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Dispersion forces tend to be stronger between molecules that are easily polarized and weaker between molecules that are not easily polarized.

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A single bind is a sigma bond. A sigma bond is cylindrically symmetrical with no nodal planes containing to the internuclear axis. All single covalent bonds are sigma bonds. A pi bond has a single nodal plane containing to the internuclear axis. A double bond is typically considered a pi bond.

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The dipole-induced-dipole interaction is when a polar molecule interacts with a non polar molecule. This interaction arises from the ability of one molecule to induce a dipole moment in the other. However, in this case, the molecule that induces the dipole moment has a permanent dipole moment. The p...

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Resonance is the blending of structures; some lewis structures have multiple bonds in different locations and a resonance hybrid is a structure of the contributing Lewis structures.

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Atomic and Molecular Spectroscopy present more similarities than differences. Electrons in atoms can be excited to higher energy states and electrons in molecules can also be excited to high energy states. As a result, both atoms and molecules give rise to spectra.

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The most stable resonance nitrous oxide lewis structure would have the formal charges of +1 for N, -1 for O, and 0 for N. The lowest energy/best structure would have the overall formal charge minimized; in this case, the resonance structure of 0 for N, +1 for O, and +1 for N has an overall formal ch...

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Cations are positively charged ions; they are generally smaller than their parent atoms. On the other hand, anions are negatively charged ions; they are generally larger than their parent atoms.

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Think of a covalent radius as a subdivision of atomic radii. The atomic radius of an element is defined as half the distance between the centers of neighboring atoms. The covalent radius of an element, specifically nonmetals and metalloids, is half the distance between the nuclei of atoms joined by ...

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De Broglie proposed that all particles should be regarded as having wavelike properties. He went on to suggest that the wavelength associated with the "matter wave" is inversely proportional to the particles mass and speed. Photons are indeed massless; however, you must take under consider...

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The energy per photon is E=hv. h is Planck's constant (6.626 x 10^-34) and v is the frequency. One photon interacts with one electron. Each photon must have enough energy to eject one electron. Increasing light intensity increases the number of photons. If the energy per photon is greater or equal t...

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$\Delta p$ represents the uncertainty in momentum. Linear momentum is the product of mass and speed. Therefore, $\Delta p= m\Delta v$ , where $\Delta v$ is the uncertainty in the speed and m is the mass.

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Yes. For the week three homework, turn in another seven problems from the quantum world section. Chapter 1 in the book concentrates on what we are learning in class.

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No, the homework due in your discussion for week two should be the quantum world problem set. Choose seven problems that you can do based on what we already learned in class.

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Consider memorizing the Lyman (n=1), Balmer (n=2), Paschen (n=3), and Brackett (n=4) series.

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Spectroscopic analysis of light given off by excited atoms shows only photons of particular energy (v) are given off. The energy of the photon coming in corresponds to the difference in energy levels. You use the results of the light experiment to figure out what the structure is of your sample. Thu...

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In the case in which $H{_{2}}$ is presented as a diatomic molecule, the molar mass of H would be multiplied by two. Therefore, the molar mass of $H{_{2}}$ is 2.016 $g\cdot mol^{^{-1}}$ .

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There is no typo. The correct answer is D) $CH_{4}(g)+2O{_{2}}(g)\rightarrow CO{_{2}}(g)+2H{_{2}}O(g)$ . Answer choice D is the best answer choice for the balanced equation as the ratio of moles (the stoichiometric coefficients) are presented in the lowest terms.

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After balancing the equation for the reaction, calculate the molar masses for each of the reactants and products. Then convert the known masses of the reactant and products to moles. In order to identify the limiting and excess reagents, compare the calculated moles to required moles to determine th...

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