CHEMISTRY COMMUNITY

Amy Lefley 1J

Yes, the rate will increase by a factor of 2 if the concentration of H2 is doubled because the reaction is first order to both of the reactants, meaning they are directly proportional.

Amy Lefley 1J

Since rate=k*(concentration)^power of reaction, and we know that the units of rate are always mol.L-1.s-1, and that sometimes the concentration is to the zero, first, or second power depending on the order of the reaction, then the units of k must change.

Amy Lefley 1J

It is appropriate to use pseudo-first order rate law when all reactant concentrations are changing, making the reaction very difficult to study. In this case, we make one reactant concentration small and the others large so that the reaction rate is dependent on only one reactant.

Amy Lefley 1J

When graphing a first order reaction, with time on the x-axis and ln(A) on the y-axis, the y-intercept is the natural log of the initial concentration of the reactant, but what does the x-intercept of this graph represent?

Amy Lefley 1J

Why does a higher rate constant mean a shorter half life?

Amy Lefley 1J

How do we know that radioactive decay is a first order reaction?

Amy Lefley 1J

How does Gibb's free energy compare to other energies like potential energy, internal energy, or kinetic energy? Can it be any of these types of energies or does it differ in some way?

Amy Lefley 1J

No, just the elements or molecules are included in the cell diagrams to keep them easy to read.

Amy Lefley 1J

Usually, the problem will say that the reaction occurs in an acidic or basic solution if no H+ or OH- is already in the equation.

Amy Lefley 1J

It is also important to note that you might get slightly different answers when using the two different methods due to rounding differences since you are using a table of information for one and information given in the problem for the other.

Amy Lefley 1J

It makes sense that you do not include elements like F2 and O2 in the enthalpy of formation equation because these diatomic molecules are already in their most stable form so it does not take any energy to get them into their most stable form.

Amy Lefley 1J

To solve using Gibb's free energy, you find the Gibb's energy of formation for each molecule. If the energy is positive, then that means the elements are unstable and if the energy is negative, then that means the elements are stable.

Amy Lefley 1J

Isothermal is when the temperature stays constant and free expansion is when a gas is allowed to expand without any constraints.

Amy Lefley 1J

Yes, since deltaU is equal to 3/2nRT, if deltaU is zero then T must be zero and the pathway is isothermal.

Amy Lefley 1J

When calculating the equilibrium constant using pressure, do you have to convert to atmosphere or do units not matter?

Amy Lefley 1J

For the equation W=-nRTlnV2/V1, if the temperature stays constant, why is it included in the equation but for the other work equation W=-PdeltaV if the temperature changes along the pathway, why is temperature not included in the equation?

Amy Lefley 1J

Yes, the work is positive because work is being done on the system and not by the system, so the system gains energy.

Amy Lefley 1J

Use the equation W=-PdeltaV for a sudden irreversible expansion when work is done against a constant external pressure and temperature changes - less work is done for this pathway. Ue the other work equation for a reversible expansion, when temperature is constant, external pressure is not constant,...

Amy Lefley 1J

When calculating the change in internal energy of a system, I know you can use the equation q=C*deltaT. Why is mass or moles not included in this equation? Are there other equations that can be used?

Amy Lefley 1J

The standard enthalpy of formation of an element in its most stable form is zero because the definition of standard enthalpy of formation is how much energy it takes to form a given molecule under standard conditions. If an element already exists in its most stable form, nothing has to form, so stan...

Amy Lefley 1J

All of the energy used in a phase change is used to break or form the bonds, and none of it to speed up the kinetic energy of the molecules or increase the temperature.

Amy Lefley 1J

I have noticed that most answers tend to be in bar. Since Kp is a ratio, the units do not matter, but just make sure all the numbers in the calculation are in the same units.

Amy Lefley 1J

I think the main reason for using an ice chart would be that you are given a weak acid. If you are given a strong acid, there is no need to use one because we can assume that the acid completely dissociates. For a weak acid, on the other hand, it only partially dissociates, which is where an ice cha...

Amy Lefley 1J

When calculating the pH of a strong acid, you assume all of it dissociates, so however many moles of acid you have is the amount of moles of H30+ is. You would use the log equation to find pH from there. If you are given a weak base, all of it does not dissociate, so you would have to use an ice tab...

Amy Lefley 1J

For the question 5I.13 part b in the 7th edition, it asks, if 2.0 mmol F2 was placed into the reaction vessel instead of chlorine, what would its equilibrium composition at 1000. K? I am assuming you use an ICE table to solve for the concentrations, yet I keep getting an answer that is slightly off ...

Amy Lefley 1J

I also think it is important to consider the fact that your solution depends on if pressure is increased by decreasing the volume of the container, or adding an inert gas.

Amy Lefley 1J

I'm pretty sure you would find Ka by doing 10^-2.12, which would give you 0.0076, a reasonable value.

Amy Lefley 1J

When you are finding the equilibrium constant of the reverse reaction, you simply take the inverse of the equilibrium constant for the forward reaction.

Amy Lefley 1J

In addition to this, a system reaches equilibrium when the forward and reverse reaction rates are equal.

Amy Lefley 1J

I know that we do not include solids and liquids when calculating the equilibrium constant because they do not have concentrations, but even if they do not have concentrations, don't they still affect the equilibrium?

Amy Lefley 1J

I was confused by this too. I think the alphabetical rule only applies when you are naming the complex, not writing its formula, so I think the ligand can be in any order. In terms of the parentheses, I am not completely sure - maybe to make the complex name easier to read?

Amy Lefley 1J

I think you are referring to problem 7 in Fundamentals J. A neutralization reaction is an acid and base reacting to form a salt and water. If we are given the salt and know that water is always produced, we just have to find the two reactants. For part A, for instance, we are given the salt KBr and ...

Amy Lefley 1J

I remember Professor Lavelle mentioning that either Bronsted or Lewis is a more general classification meaning that all acids and bases are one thing but not necessarily the other. Which term is more general, Bronsted or Lewis?

Amy Lefley 1J

For Homework problem 2F.3 7th Edition Part B we were asked to state the number of sigma and pi bonds for the molecule SO2. The answer I got was that there should be 2 sigma and 2 pi bonds. However, the first answer in the book is 2 sigma bonds and 1 pi bond. I do not understand how this would be pos...

Amy Lefley 1J

A sigma bond is formed by two orbitals, each with one electron that interacts end to end. A pi bond on the other hand, is also formed by two orbitals, each with one electron that overlap side-by-side. Therefore the difference between a sigma and pi bond is that a sigma aligns end to end, while a pi ...

Amy Lefley 1J

Question 2F15 in the 7th edition asks: do you expect the bond angle between two hybrid orbitals to increase or decrease as the s-character of the hybrids is increased? The answer is: as the s-character of hybrid orbital increases, the bond angle increases. I do not know how to approach this question...

Amy Lefley 1J

In class we were shown a diagram of s-s orbital overlap, s-p orbital overlap, and p-p orbital overlap. I am wondering if these visuals are simply conceptual to try to get us to understand the concept or if this is actually the configuration in an atom?

Amy Lefley 1J

I am aware that a pi bond, unlike a sigma bond, cannot rotate and if a pi bond does try to rotate the bond breaks. What are the biological implications of a pi bond breaking in our bodies?

Amy Lefley 1J

When finding the regions of electron density in order to determine the hybridization why do both single and double bonds count as one region of electron density? Wouldn't the single versus double bond alter the hybridization?

Amy Lefley 1J

Also it is important to note that there can be dipole induced-dipole interactions and induced dipole-induced dipole interactions. Dipole induced-dipole interactions require a dipole to be present and an induced dipole-induced dipole are always present because atoms will always have electrons that ca...

Amy Lefley 1J

Covalent radii, to my understanding, is the covalent bond length which is the sum of the two atom's radii. Isn't this assuming that there is no space between the atoms in the bond or is it just that the space is negligible?

Amy Lefley 1J

Why does a tetrahedral have bond angles of 109.5 degrees while a trigonal pyramidal have bond angles of less than 109.5 degrees. Is it because the lone pair on the trigonal pyramidal is closer to the central atom and pushes the other atoms closer together?

Amy Lefley 1J

How does the attractive force related to hydrogen bonding compare to that of other intermolecular forces (ion-ion, ion-dipole, dipole-dipole, dipole induced dipole) and why?

Amy Lefley 1J

Although I agree with the point mentioned above, it is also important to think about the size of the atom. The larger the atom or the more energy levels it has, the farther the atom will be from the atom it is bonded to. Since the distance between the two atoms will be larger, the bond will be weaker.

Amy Lefley 1J

In addition to this, I believe that the more polarizable an atom is, the stronger the bond it will form with another atom.

Amy Lefley 1J

The question is: Which bond is longer: the NF bond in NF3 or the PF bond in PF3? The PF bond is longer, but why? Is it because P has a larger atomic radius?

Amy Lefley 1J

I believe that to find the bond length you add the atomic radii of each atom that is part of the bond. The atomic radii will usually be provided to you.

Amy Lefley 1J

To find the formal charge of an element, you use the equation V - (L+S/2) where V is the valence electrons, L is the lone electrons, and S is shared electrons.

Amy Lefley 1J

I think when you reference quantized energy you are thinking about energy levels in an atom. When the electron absorbs the energy of a photon, it can only jump up to an integer amount of energy levels. If the electron absorbs enough energy to be ejected from the atom, the left over energy (photon en...

Amy Lefley 1J

I do not think we are required to know whether an electron spin is up or down. I think the only thing to note here is that if two electrons are paired, they have opposite spin. If two electrons are parallel, on the other hand, they have the same spin.

Amy Lefley 1J

I am aware that Schrondinger's equation is used to precisely describe the location of an electron within an atom, but why is a wave function used to do this?

Amy Lefley 1J

Black body objects are simply theoretical-in other words, in the real world there does not exist an object that is truly a black body, or absorbs all wavelengths of light.

Amy Lefley 1J

This is simply a convention. A free electron or one that is no longer attracted to the nucleus of an atom can be said to have zero energy. As an electron goes down in energy levels, the energy becomes more negative. That is why there is a negative sign in the Rydberg equation.

Amy Lefley 1J

The question is : Give the notation for the valence shell configuration (including the outermost d-electrons) of (a) alkali metals (b) group 15 elements (c) group 5 transition metals (d) the coinage metals (Cu, Ag, Au). I do not understand the format they used for the answers. The answers are: ns^1,...

Amy Lefley 1J

A bound electron is one that is still considered part of the atom and is attracted to the nucleus whereas a free electron is one that absorbed enough energy from photons to completely leave the atom.

Amy Lefley 1J

The threshold energy differs with each metal used. So for different problems using the same metal, the work function or threshold energy would remain the same.

Amy Lefley 1J

Although I do not think we need to know much detail on black body radiation, I think it is helpful to know that it is an object that absorbs all wavelengths of light. This is a conceptual idea, and I do not think there actually exists an object that can absorb all wavelengths, just the majority.

Amy Lefley 1J

Yes, that would be your final answer! When finding mass composition of a compound the main steps are to: 1. find the molar mass of the entire compound 2. find the molar mass of each element within the compound 3. divide the molar mass of each element you found in step 2 by the molar mass you found i...

Amy Lefley 1J

This is how I approached the problem: 1. You are given the molarity (0.10 mol/L) and the starting volume (0.010 L). You can also find the ending volume by using a doubling equation. For this equation you do: 0.010(2^90) which equals 1.24 x 10^25. 2. Now, we can use the equation MV=MV that we used in...

Amy Lefley 1J

Also keep in mind the rules for significant figures are different for adding and subtracting versus multiplying and dividing. When you are adding and subtracting, you use the value with the least amount of decimal places (so if you have 14.23+2.9 the answer would have one decimal place). For multipl...

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