CHEMISTRY COMMUNITY

Gabriel Nitro 1E

Hi,

At the anode oxidation occurs, while in the cathode reduction occurs.

Hope this helps! :)

Gabriel Nitro 1E

Hi,

You can think of a system having the maximum cell potential at the very instant the cell is formed where the current is just on the verge of forming between the anode and the cathode.

Hope this helps! :)

Gabriel Nitro 1E

Hi, The purpose of a salt bridge is to prevent a build up of charge. A good analogy I can think of is where the wire connecting the two cells is a road with the electrons as the cars. If too much traffic is on one side, then the cars can no longer move to the other side to do electrical work. Now, r...

Gabriel Nitro 1E

Hi,

I believe the book assumes you are using the Appendix in order to solve these type of problems.

Thus, on the exam if you were given a problem similar I think you would be given the corresponding E values.

Hope this helps! :)

Gabriel Nitro 1E

Hi, n refers to the moles of ELECTRONS transferred in a redox reaction. In order to find this amount, you would need to split the overall reaction into two half reactions (oxidation and reduction) and then balance them accordingly. However, when you're balancing you need to ensure the number of elec...

Gabriel Nitro 1E

Hi, A good rule of thumb is always use Kelvin for your thermodynamic equations. In MOST (not all) cases, we have to use Kelvins because the constants we are given (such as the ideal gas constant) are expressed in terms of Kelvin (this ensures it cancels out for your final answer). Hope this helps! :)

Gabriel Nitro 1E

Hi, A good rule of thumb is to always first find out what undergoes oxidation and what undergoes reduction. Then, in order to identify the corresponding agent, it would be the opposite. For example, assume in a hypothetical reaction nitrogen (N) is oxidized from 0 to 4+. Therefore, nitrogen would be...

Gabriel Nitro 1E

Hi,

The acronym "LEO" means "loss of electrons = oxidation."

This is just a house keeping rule we have to remember what we mean when something is oxidized.

Hope this helps! :)

Gabriel Nitro 1E

Hi, As previously said, for molar entropy we always tend to look for molecules which are more complex (i.e. those which are more disordered under similar conditions relative to whatever we are comparing). If we are comparing elements, we would look at atomic number as the inclusion of more protons (...

Gabriel Nitro 1E

Hi,

Typically, we would see that oxygen (O2) would have an oxidation number of 0 as it is in their elemental form.

Hope this helps! :)

Gabriel Nitro 1E

Hi, If an expansion is considered irreversible, you think of it as a rapid expansion. In other words, it happens so fast that you can't go back to your initial condition. If an expansion is considered reversible, you can think of it as a slower expansion. In other words, because it is happening in i...

Gabriel Nitro 1E

Hi, Yes! Recall, C refers to the heat capacity, or the amount of heat to raise the temperature of a substance by 1 unit of temperature. The subscript "P" or "V" is indicative of what variable we are assuming is constant. If it is "C_p," then it is the heat capacity at c...

Gabriel Nitro 1E

Hi,

Yes! When we discuss isothermal reactions, we assume they are reversible reactions in equilibrium where the external and internal pressure of the system is the same. Also, there is no temperature change (iso- meaning same and -thermal referring to temperature).

Hope this helps! :)

Gabriel Nitro 1E

Hi,

In order to ensure you have the proper units for entropy, you should use R = 8.314 as it has the joules (J) unit in it.

Hope this helps! :)

Gabriel Nitro 1E

Hi, A phase change is defined as any transition from one of three states of matter covered in the course (solid, liquid, gas). For instance, a block of ice (solid) melting in water (liquid) is a phase change. Water vapor (gas) condensing into water (liquid) is also a phase change. Hope this helps! :)

Gabriel Nitro 1E

Hi,

A reaction is considered spontaneous if Delta G is negative. A nonspontaneous process is where Delta G is positive.

Hope this helps! :)

Gabriel Nitro 1E

Hi, Entropy is a measure of disorder in a system. For instance, you could conceptually understand this with comparing a clean dorm room to a messy dorm room. In the clean room, the room is fairly organized with where everything should be, so the entropy is fairly low. In the messy room, clothes may ...

Gabriel Nitro 1E

Hi,

I believe according to the textbook, Delta E and Delta U are both used interchangeably for the change in internal energy.

Hope this helps! :)

Gabriel Nitro 1E

Hi, A good rule-of-thumb I have always used for these calculations is to not memorize which one to use, but to look at the units. For each problem, I always write down the units for everything I am given and see what cancels out. After that, I then choose which R to use depending if I have pressures...

Gabriel Nitro 1E

Hi, Yes, it does! You always have to make sure one portion of the chemical equation is equivalent to the other side if you were to combine two equations into an overall equation (i.e. He(g) on the left and right side for an arbitrary reaction). However, if you had He(s) on the left side and He(g) on...

Gabriel Nitro 1E

Hi, A good rule of thumb to keep in mind is to consider the equations you are using, what units you are presented with, and what units you want in the end. For instance, if you were to solve for the pressure (P) of an ideal gas with V, n, and T known, you would have to use R = 0.08206 L atm K- mol-,...

Gabriel Nitro 1E

Hi, Yes. BUT! As a bookkeeping rule it is always useful to look at what units you have presented in front of you along with the units the problem is asking you to solve for. This way, you'll be able to make sure the proper units cancel out to get what you want, whether you want atm or J. Hope this h...

Gabriel Nitro 1E

Hi, Instead of memorizing the signs, it would be useful to understand what is going on at the particle level. As we go from solid to liquid to gas, the particles are allowed higher motility and are separated at farther distances from each other. Now, this would not normally happen on its own to the ...

Gabriel Nitro 1E

Hi,

V1 would be considered as the initial volume (V_i) and V2 would be considered the final volume (V_f).

Hope this helps! :)

Gabriel Nitro 1E

Hi, Hess's Law may be thought of as a principle where, because the enthalpies of reactions are state functions (i.e. path doesn't matter), we may alter them accordingly to figure out the enthalpy of other reactions we may not know. For instance, we can reverse a reaction (flip to sign of delta H) or...

Gabriel Nitro 1E

Hi,

Recall, the conjugate seesaw is a good determinant of the magnitude of [H+] in comparison to [OH-].

If the solution is acidic overall, then [H+] > [OH-].

If the solution is basic overall, then [H+] < [OH-}.

If the solution is neutral overall, then [H+] = [OH-].

Hope this helps! :)

Gabriel Nitro 1E

Hi,

It means water can either donate a proton (acts as an acid) or it can accept a proton (acts as a base).

Hope this helps! :)

Gabriel Nitro 1E

Hi,

It would be an endothermic reaction because recall enthalpy is a state function, where the overall change in independent of the path.

Thus, if the products are above the reactants in terms of enthalpy on an energy profile diagram, it is endothermic.

Hope this helps! :)

Gabriel Nitro 1E

Hi, Sublimation is defined as a phase change from solid to gas (e.g. dry ice subliming into carbon dioxide gas). It is considered endothermic because energy is being invested into the system in order to disrupt the intermolecular forces between the particles in a solid in order to become a gas. Hope...

Gabriel Nitro 1E

Hi, If a reaction requires heat, then it is considered an endothermic reaction. While breaking bonds is considered endothermic, a chemical reaction involves BOTH breaking and forming bonds. Where we differentiate between endothermic and exothermic is the net change in heat, or in other words, compar...

Gabriel Nitro 1E

Hi,

Yes! The addition of another gas (typically an inert gas) will lead to more overall collisions with the walls of the container, making the overall pressure increase.

Hope this helps! :)

Gabriel Nitro 1E

Hi,

The only change which would change the value of K would be temperature (we'll learn why when we study kinetics).

Changes in concentrations, partial pressures, addition of catalysts, changes in volume, or addition of noble gases have no effect.

Hope this helps! :)

Gabriel Nitro 1E

Hi, Total pressure is the sum of all the partial pressures of the all the gases in a system. For example, let's say you have a reaction vessel where the partial pressure of He is 5.0 atm and the partial pressure of Xe is 10.0 atm. Thus, the total pressure of the system would be 15.0 atm. Hope this h...

Gabriel Nitro 1E

Hi,

Assuming the initial concentrations of reactants and products are equilibrium concentrations, then the reaction should proceed to the right.

Hope this helps! :)

Gabriel Nitro 1E

Hi,

A reaction is endothermic if the delta H is positive.

A reaction is exothermic if the delta H is negative.

Hope this helps! :)

Gabriel Nitro 1E

Hi,

Yes. If the enthalpy (delta H) is negative, the reaction is exothermic. If the enthalpy (delta H) is positive, the reaction is endothermic.

Hope this helps! :)

Gabriel Nitro 1E

Hi,

Yes, temperature is the only change which affects the value of the equilibrium constant K.

Hope this helps! :)

Gabriel Nitro 1E

Hi,

You would raise those coefficients to their respective product, assuming they are in the gaseous or aqueous phase for the equilibrium constant.

Hope this helps! :)

Gabriel Nitro 1E

Hi,

Adding helium will increase the overall pressure of the system, but it will not increase the individual partial pressures of the other gases enclosed in the system.

This is why there is not shift when it is added.

Hope this helps! :)

Gabriel Nitro 1E

Hi,

We would only include H2O in the gaseous phase, as in the equilibrium constant.

We would not include H2O in the solid or liquid phase as they are pure substances.

Hope this helps! :)

Gabriel Nitro 1E

Hi,

Yes, the balanced chemical equation is required to find K.

Note, however, the stoichiometric coefficients must be to the lowest factor and must be whole numbers. For instance, don't put 0.5 as a coefficient or if the coefficients are 2 and 4, simplify to 1 and 2.

Hope this helps! :)

Gabriel Nitro 1E

Hi, Note, the equilibrium constant is just an arbitrary number. The larger K is, the more it favors the products. (K > 1) The smaller K is, the more it favors the reactants. (K < 1) However, when a reaction is at equilibrium, because the constant is just an arbitrary number the concentrations of rea...

Gabriel Nitro 1E

Hi, In order to determine the predominant direction of a reaction, it depends on how you phrase it. Whether you are talking about the relative magnitudes of the K value (1) or a response in doing something to perturb the system (2). Note, whether the reaction is a decomposition or synthesis reaction...

Gabriel Nitro 1E

Hi, It entirely depends on the context on what you are given. If you are given any information which may lead you to find concentrations ( mol, M, mmol, L, mL, g, mg ), use K_c . If you are given any information which may lead you to find partial pressures ( PV = nRT, atm, bars, mm Hg ), then use K_...

Gabriel Nitro 1E

Hi, Note, it is important to remember the equilibrium constant K is dependent only on temperature. Changes to initial conditions such as initial concentrations, initial partial pressures, or introductions of catalysts do not affect the value of K . When the temperature is increased for the system, i...

Gabriel Nitro 1E

Hi, A conjugate base is what the original acid turns into when it gives up a proton or H+. For instance, consider the following reaction: HA(aq)+H_2O(l) \leftrightharpoons A^-(aq) + H_3O^+(aq) In the context of the equation, HA(aq) represents a weak acid. When HA give...

Gabriel Nitro 1E

Hi,

In order to determine the denticity of a ligand you would need to look at the not only just the available lone pairs needed to create a coordinate covalent bond, but also the spacing.

For example, this is why H2O is monodentate even though it has two lone pairs.

Hope this helps! :)

Gabriel Nitro 1E

Hi, Na+ does not affect pH as the electrostatic interactions between Na+ and H2O are not significant enough to yield a coordination compound, which would have made the pH more acidic. Cl- does not affect pH because it is the conjugate base of a strong acid. Even if Cl- were to react with H2O to yiel...

Gabriel Nitro 1E

Hi,

The central atom in a coordination compound is always the transition metal.

Hope this helps! :)

Gabriel Nitro 1E

Hi, Oxoacids are acids containing an oxygen. (i.e. HNO3 for example). They are most commonly found in organic acids, such as a acetic acid. (i.e. HC2H3O2) In the scope of this course, one of the main things you'll need to know is the effect of the additional number of oxygen atoms on an acid in term...

Gabriel Nitro 1E

Hi,

Whenever we term a dipole as "cancelling out," we mean that the polar bonds are oriented in such a way that the molecule is symmetric (I.e. tetrahedral). This effectively removes the dipole from the molecule, making it nonpolar.

Hope this helps! :)

Gabriel Nitro 1E

Hi,

The reason the list of LDFs are listed as it is, is because the size of I2 is far larger than that of the other diatomic molecules with the most number of electrons. This results in a greater polarizability and in turn, leads to stronger LDFs.

Hope this helps! :)

Gabriel Nitro 1E

Hi,

Polar molecules tend to have polar bonds which are in an asymmetric molecule, while nonpolar molecules either have only nonpolar bonds or have polar bonds which cancel out.

Hope this helps! :)

Gabriel Nitro 1E

Hi,

You should also take into account the shape of the molecule as the asymmetry/symmetry may cancel out polar bonds.

Hope this helps! :)

Gabriel Nitro 1E

Hi,

Yes! More bounded atoms imply more electrons, increasing the polarizability of the particle or the strength of the LDFs.

Hope this helps! :)

Gabriel Nitro 1E

Hi,

I like the think of the axial atoms as those "pointing upward" in the vertical direction, while equatorial atoms are those "pointing to the side" as with the equator of the Earth.

Hope this helps! :)

Gabriel Nitro 1E

Hi, This is because the atomic radius of the iodine atom is far larger than that of the fluorine atom. This leads to increased polarizability, increased LDFs, and increased strength of intermolecular attractions. The more energy required to disrupt these interactions, the higher the temperature need...

Gabriel Nitro 1E

Hi,

Yes! That is correct! The additional hydrogen bond makes the GC attractions stronger!

Hope this helps! :)

Gabriel Nitro 1E

Hi,

Yes! LDFs are based on the polarizability of a given particle, which are determined by electrons. Due to how every molecule has electrons, LDFs are exhibited everywhere!

Hope this helps! :)

Gabriel Nitro 1E

Hi, Before we can deduce which element has a higher melting point, we need to understand what determines the melting point. As the melting point is the temperature at which a substance transitions from a solid into a liquid, you can think of the temperature as an amount of energy (i.e. higher temper...

Gabriel Nitro 1E

Hi, It is important to note that London Dispersion Forces arise from electrons. As the delocalized electrons of a given particle are moving around at any given moment in time, if you were to take a snapshot over a given interval you would see that at some point the electrons would be dispersed in su...

Gabriel Nitro 1E

Hi,

The relationship is that bond length is inversely proportional to bond strength. Therefore, if you are comparing two bonds and one is shorter than the prior, the latter has a higher bond energy.

Hope this helps! :)

Gabriel Nitro 1E

Hi, This is because since the electronegativities of nitrogen (N), oxygen (O), and fluorine (F) are so large in magnitude, they are often singled out from the typical dipole-dipole classification when covalently bonded to hydrogen as a hydrogen bond. However, because carbon's (C) electronegativity i...

Gabriel Nitro 1E

Hi,

Yes! Those are all considered intermolecular forces as they are "between" two species!

Hope this helps! :)

Gabriel Nitro 1E

Hi,

A Lewis acid accepts an electron pair, while a Lewis base donates an electron pair.

Hope this helps! :)

Gabriel Nitro 1E

Hi, Well, before we can understand why attractive interactions yield negative energies we need to first answer one question: Why do atoms form these interactions? In nature, you can think of most particles as being "unstable." Generally, when atoms or molecules are in an unstable state the...

Gabriel Nitro 1E

Hi, So, recall the delta negative the delta positive symbols are used to denote a separation of charge in an atom. This separation of charge is based on the electronegativities or "pulling power" of an atom's nuclei for electrons. So, if an atom has a high electronegativity, it really want...

Gabriel Nitro 1E

Hi,

Yes! Recall, London Dispersion Forces (LDFs) originate due to the temporary displacement of electrons, resulting in a separation of charge in the overall molecule as a result of delocalized electrons. Therefore, LDFs are present in all particles due to the presence of electrons.

Hope this helps!

Gabriel Nitro 1E

Hi,

Bond length is inversely proportional to bond strength. So, let's say you were given two bonds of two arbitrary molecules for "X-X" and "X=X." Because the double bond in the second molecule is stronger, the bond length must be shorter.

Hope this helps! :)

Gabriel Nitro 1E

Hi, Yes! Hydrogen bonding does originate from a separation of charge (i.e. partial positives and partial negatives) within the molecules in question, as does the case of dipole-dipole interactions. Hydrogen bonding, however, is simply a more perturbed separation of charge (or a stronger variant) due...

Gabriel Nitro 1E

Hi, Typically, when we are doing electron configurations, we number the electrons in order of lowest energy to highest energy. You can think of it as having the principal quantum number be listed in order of consequence (n=1, 2, 3... => 1s 2s 3s 4s) and in order of the subshells (s then p then d the...

Gabriel Nitro 1E

Hi, There are multiple ways to think about this concept, but I'm going to answer it in terms of electron configurations. This is due to how nonmetals (i.e. the elements near the right-most end of the periodic table), as with other elements, have a tendency to reach a noble gas configuration in order...

Gabriel Nitro 1E

Hi, A common tip I would use is to first write down what equations you will be working with right in front of you. From there, I would be sure to write out each step in the process without skipping any details as I am plugging in equations. Finally, I would check at the end to see if the units of bo...

Gabriel Nitro 1E

Hi,

Generally, we consider ionic bonds to be stronger than covalent bonds.

Hope this helps! :)

Gabriel Nitro 1E

Hi, Whenever we are constructing Lewis Structures, often times we arrive at situations where there is more than one valid structure. Note, I am not referring to resonance, I am referring to a scenario of whether or not you should have all singles bonds or include a double bond here and there as with...

Gabriel Nitro 1E

Hi, In the context of electron configuration and orbitals, let's break down what "px, py, and pz" means. The "p" in front of each portion of the question indicates the subshell/state the electron is occupying. Thus, the electron is begin associated with the p-subshell/state. The ...

Gabriel Nitro 1E

Hi, Whenever you are doing empirical formula problems and simplifying the ratios of the moles of its components, always be sure (for the sake of ease) to use moles of just the atom, not it's elemental state. For instance, use moles of N instead of moles of N2 or use moles of O instead of moles of O2...

Gabriel Nitro 1E

Hi, In the context of the chapter, recall that we are studying electromagnetic radiation. By the name, it implies the radiation were are studying exhibits an electric field ("electro-") and a magnetic field ("-magnetic). Now, you can think of an electric field as an array of an infini...

Gabriel Nitro 1E

Hi, With regards to uncertainty in position, if you are not solving for it, the problem will most likely give you the value. However, they could give it to you in a variety of ways. For instance, in terms of the "atom in a box" model, they could give you a statement such as "The uncer...

Gabriel Nitro 1E

Hi, Yes that is correct! Recall in the context of hydrogen (H) atoms, electrons may leave the ground state (n=1) by getting excited by an incoming photon from a source of electromagnetic radiation. Now, in our discussion of Lyman and Balmer series we are interested in which energy level the excited ...

Gabriel Nitro 1E

Hi,

Yes! That is correct! The Rydberg equation is only appropriate for working with electron transitions in the hydrogen (H) atom. In systems differing from hydrogen (H), as with carbon (C) or nitrogen (N), an alternate equation must be used.

Hope this helps! :)

Gabriel Nitro 1E

Hi,

It depends on the problem, but in most cases we will be working with energy in terms of one particle (i.e. photons or electrons as in the photoelectric experiment).

Hope this helps! :)

Gabriel Nitro 1E

Hi, Yes! As the intensity of the light increases, we associate that property as increasing in brightness! However, don't forget increasing intensity increases the number of photons! For example, let's say we have two intensities I_1 and I_2 , where I_1 > I_2 . Thus, I_1 would have more photons than ...

Gabriel Nitro 1E

Hi, The main difference between the Lyman Series and the Balmer Series during electron excitation in the hydrogen (H) atom is based on the wavelength of light (and subsequent energy) when the excited electron returns to the ground state. For the Lyman Series, electrons return to the principal energy...

Gabriel Nitro 1E

Hi,

Personally, I would approach with caution in the context of the problem. Depending on if the ejected electron has 0 kinetic energy (KE) or an excess amount, the energy of the incoming light may be exactly the same as the work function or be greater.

Hope this helps!

Gabriel Nitro 1E

Hi, When I was in high school, a good tip I used when balancing equations was to first rewrite the equation on a separate piece of paper and ensure I wrote it down correctly. Next, I would start balancing whatever was the most convenient first (i.e. the atom in least amount) and then proceed from th...

Gabriel Nitro 1E

Hi, With regards to the law of conservation of mass, we only factor in portions of the problem which are considered mass (kg, mg, ng, &c.). Heat, however, is not considered as mass, but as energy as when butane is combusted. Thus, the law of conservation of mass in a closed system still takes in...

Gabriel Nitro 1E

Hi, The reason he had to multiply the ratio to get the empirical formula is because when we write out a chemical formula in general, it is not preferred to have fractional numbers (i.e. N_1.5 is not appropriate, while N_2 is). Thus, we need to ensure that 1.33 is multiplied accordingly to get a numb...

Gabriel Nitro 1E

Hi, The mass of a proton and a neutron are approximately the same, which is about 1 amu (atomic mass unit). The mass of an electron is far less than that of a proton or neutron, which is about 0.0005 amu (atomic mass unit). This is why when we do stoichiometry problems, we approximate the molar mass...

Gabriel Nitro 1E

Hi, Honestly, it depends on the situation. If you were provided a problem which gives you a specific variation of the molar mass of an atom, I would use that. If during the exam you were given an entire periodic table for the length of the test, I would use that. However, despite the variation, as l...

Gabriel Nitro 1E

Hi, When dealing with a chemical equation, the stoichiometric coefficient refers to the number in front of the elements/compounds/ions/&c in the balanced chemical equation. With regards to balancing, sometimes it may be useful to use fractional numbers (i.e. 13/2) in the process of balancing, bu...

Gabriel Nitro 1E

Hi, With regards to your question on SI Units, it entirely depends on the problem. For instance, if the problem was a dilution equation and it gave you all of the quantities in terms of molarity (M or mol/L) and liters (L), but asked for an answer in milliliters (mL), use mL in your final answer. Or...

Gabriel Nitro 1E

Hi,

Yes, I believe that is true. In the example the professor provided, it is termed as a "combustion reaction." This implies the substance which undergoes combustion (in this case butane) reacts with oxygen (O2) to form carbon dioxide (CO2) and water vapor (H2O).

Gabriel Nitro 1E

Hi, When using the dilution equation "M1V1 = M2V2" it is ensured to be used with the units of moles (mol) per liters of solution (L) as in "mol/L" for Molarity and liters (L) for Volume. With regards to mL, if the question asks for milliliters (mL) for an answer, be sure to use l...

Gabriel Nitro 1E

Hi, I agree. Typically, with the periodic table when doing calculations (i.e. stoichiometry, empirical formulas, molecular formulas) I would use the periodic table with 4 significant figures. On the one hand it offers an apt number when dealing with numerical calculations, such as the ease with mist...

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