CHEMISTRY COMMUNITY

Stevin1H

Is the catalyst included in the rate law expression or not? I know that the catalyst isn't included in the balanced reaction so would it be in the rate law expression?

Stevin1H

Do we include OH-(aq) in the cell diagram? I know we include H+(aq) but I was wondering if it was the same for OH-(aq)

Stevin1H

How do you determine if a reaction is spontaneous or not when you're given the deltaS of the system and deltaS of the surroundings?

Stevin1H

Can someone explain the concept behind when the change in internal energy would be equal to 0?

Stevin1H

Do you have to include an inert electrode if there is a liquid phase in the cell diagram? For example would Hg(l) I Hg2^2+(aq) require an inert electrode?

Stevin1H

What is the conceptual idea for rate constant k in the equation? What does the rate constant k mean for the reaction?

Stevin1H

What is the conceptual idea for rate constant k in the equation? What does the rate constant k do?

Stevin1H

Can anyone explain the concept behind the unique rate of reaction and how it applies to the chemical equation?

Stevin1H

Are all decay problems typically referring to first order reactions? Or could there instances where it requires us to use a different order reaction?

Stevin1H

What conditions will affect the value of rate constant k and how does it change the rate constant?

Stevin1H

How were we supposed to determine that the Gibbs free energy was negative on test 2 for the examples regarding the melting snow and activating a heat pack?

Stevin1H

Typically, you would add H+ when balancing hydrogens in the reaction and H2O when balancing the oxygens in the reaction. Oxygen is usually balanced first and then Hydrogen because the H2O changes the total number of Hydrogens in the reaction as well. After balancing oxygen with H2O, you would now kn...

Stevin1H

You can memorize it, or learn how to derive it from the two delta G equations. Delta G = -RTlnK and Delta G = deltaH - T(deltaS). Set both equations to each other and you can derive the Van't Hoff equation.

Stevin1H

By looking at the reduction potential value from the table for each reaction, you would know which one is the anode or cathode by making sure that the Ecell value is a positive value because it is a galvanic cell.

Stevin1H

How do we the order of where to put the H+ and OH- in the cell diagram? For example: O3/O2,OH- and Ag+/Ag, why is the cell diagram Ag(s) | Ag+ (aq) || OH- (aq) | O3(g), O2(g) | Pt(s).

I thought it would have been O3(g) | O2(g), OH- (aq) | Pt(s)

Stevin1H

Suppose that each of the following pairs of redox couples is joined to form a galvanic cell that generates a current under standard conditions. Identify the oxidizing agent and the reducing agent, write a cell diagram, and calculate the standard cell potential. (c) H+ /H2 and Fe3+/Fe2+ For C, why do...

Stevin1H

When do we know to add an inert electrode in the cell diagram? And how do we know which half reactions to used based on the appendix for certain reactions. (Ex. AgBr(s) -><- Ag+(aq) + Br-(aq))

Stevin1H

Yes, the cell potential has to be positive because the galvanic cell is converting chemical energy to electrical energy. A positive cell potential is related to a spontaneous reaction as well.

Stevin1H

How do we determine the temperature for when a reaction is at equilibrium in order to use this value to determine the other values of temperature that would be spontaneous with a negative Gibbs Free energy value or non spontaneous with a positive Gibbs Free Energy value?

Stevin1H

Yes, Gibbs free energy is a state function because we can apply Hess's method to find delta G knot. Or another method would be calculating the Delta G knot of the reaction by subtracting the sum of the delta G knot of products by the sum of the delta G knot of the reactants.

Stevin1H

Since Entropy is a state function and we see that there are two variables changing (the volume and temperature), we can set up two different equations and add the total to find the total change in entropy. We have the equation delta S = nRln(V2/V1) for when the volume is changing and delta S = nRln(...

Stevin1H

When the value of w is positive this means work is being done on the system (ex. is compression). This is because the formula for work is w=-PdeltaV so when there is compression from work being done on the system, the negatives will cancel out and the w becomes positive. Therefore, when work is bein...

Stevin1H

What is the concept behind why deltaG is 0 for molecules such as H2(g) and N2(g)?

Stevin1H

To solve this problem you would have to know that W = (# of positions)^#of molecules. And since the molecule has 6 different positions for the atoms and 1 mol for SO2F2, W would be 6^6.022x10^-23. Then you substitute this W into the equation S=KblnW and find the entropy.

Stevin1H

In order to avoid the calculator over flow, you would have to manipulate the equation using math. Since S=KblnW(#)^N, you can bring the N down and the equation would be N*Kb*In(#)

Stevin1H

The specific heat capacity for copper and water are two different values. According to the table in the textbook, the specific heat capacity of copper is 0.38 J/g.C and the specific heat capacity of water is 4.184 J/g.C

Stevin1H

This is not saying that the pressure is negative. The negative is in this equation because if the volume of the system is compressed, delta V (which is Vf-Vi) will be a negative value. This negative value of delta V and the negative value in the equation will become positive since two negatives beco...

Stevin1H

The enthalpy of vaporization refers to asking the amount of energy to vaporize 1 mole of the substance because the units of enthalpy is kJ/mol. So for this problem, you would do 4.76kJ/0.579mol to find that 8.22kJ of energy is required to vaporize 1 mole of CH4.

Stevin1H

For this problem, you would need to use the formula q=mCdeltat twice. This is because the specific heat capacity for copper and H2O are different. And after calculating both values of heat for copper and H2O, add the two values together to find total heat required.

Stevin1H

Oxygen di uoride is a colorless, very poisonous gas that reacts rapidly with water vapor to produce O2, HF, and heat: OF2(g) + H2O(g) ---> O2(g) + 2HF(g) deltaH=-318 kJ What is the change in internal energy for the reaction of 1.00 mol OF2? How do we know that the temperature for PV=nRT is 298K give...

Stevin1H

The bond enthalpy values depend on whether there is a bond breaking or bond forming. Since breaking a bond requires energy, this is an endothermic process (positive). And for the formation of bonds, energy is released when this occurs, making it an exothermic process (negative).

Stevin1H

Bond enthalpies between atoms will be positive when bonds are being broken because energy is required in order to break the bond (this is an endothermic process). However, when bonds are being formed, energy is released (exothermic process) and we account for this by including a negative in front of...

Stevin1H

For bond enthalpies, it would be the total energy to break the bonds of the reactants - the total energy released by products from bonds forming. Remember, to break a bond, energy is required (+) and to form a bond, energy is released (-). For bond enthalpies, you would draw the lewis structures of ...

Stevin1H

Can anyone explain the concept behind why steam at 100 degrees Celsius causes a worse burn than boiling water at 100 degrees Celsius? I know it involves the phase change chart but I would like a more precise definition

Stevin1H

For a closed system, only heat can be transferred in and out the system (so matter is not included). But for isolated systems, energy and matter both cannot leave or enter the system, therefore making the energy and mass fixed in an isolated system.

Stevin1H

Q is calculated the same was as K with products/reactants, but Q is the value not at equilibrium. In respect to the equilibrium constant K, if Q<K, this means the concentration of reactants is greater than the concentration of products, so forward reaction is favored to reach equilibrium. If Q>K, th...

Stevin1H

We can only ignore x in an ice table when the equilibrium constant, K, is less than 10^-4. Also, we are not necessarily saying x is 0. We can neglect the x because the value of x is so small that it makes very minimal difference when subtracting from the initial concentration. For example, if the in...

Stevin1H

If there is an insertion of inert gas into a reaction to increase the pressure, this will have no effect on changing the concentrations in the reaction. This is because only volume changes concentration when moles are constant as shown in (M=n/V) and the inert gases do not react with the reactants i...

Stevin1H

Can someone explain the concept of how a decrease in Pressure will favor the production of the side with more moles of gas in a reaction and how an increase in pressure will favor the side with fewer moles of gas?

Stevin1H

The relationship between the forward reaction and the reverse reaction for K is that the equilibrium constant for the reverse reaction is the inverse of the forward reaction. Here is an example: N2(g) + 3H2(g) ⇌ 2NH3(g) For the forward reaction: Kc=(NH3)^2/((N2)(H2)^3) For the reverse reaction: Kc=(...

Stevin1H

Only temperature will change the K value. Temperature changes the value of K depending on if the reaction is endothermic or exothermic. For a change in the concentration and pressure in the products or reactants, the system will eventually come back to equilibrium over time so the ratio of the produ...

Stevin1H

This question is asking for the equilibrium constant, K, expression. This question requires an ice box and I believe the ice box can be applied to both concentration and partial pressure. For the ice box, the initial value of NO would be 1.0 bar (given) and the initial values of N2 and O2 are 0. The...

Stevin1H

Can someone explain the concept behind how temperature affects the equilibrium constant value in terms of endothermic and exothermic? What changes in the system when the forward reaction is endothermic rather than exothermic, and vice versa?

Stevin1H

Increasing the pressure using inert gas has no effect on the equilibrium composition because the inert gas does not react with the molecules in the system. It is important to remember that the system does not respond to a change in pressure, rather it responds to a change in concentration. Increasin...

Stevin1H

When we are calculating the equilibrium constant, K, we would use the equilibrium concentrations. If we were to use the initial concentrations, the molar concentration ratio of products over reactants would not be equal to the correct value for the equilibrium constant. Using the initial concentrati...

Stevin1H

K can be used to determine the equilibrium constant using either concentration (Kc) or partial pressure (Kp). K determines the ratio of product over reactant at equilibrium and the value should be the same for each reaction under the same conditions and temperature. Q is very similar to K as they ar...

Stevin1H

The simple definition for Lewis is Lewis acids are electron pair acceptors and Lewis bases are electron pair donors. For Bronsted acids, these are proton donors (H+ donor) and a Bronsted base is a proton acceptor (H+ acceptor). Lewis acids and bases are more general terms since every Bronsted acid/b...

Stevin1H

How can a compound be both monodentate and bidentate? For example, in the book problem for 17.33 (6th edition), (CO3)2- can be either a monodentate or a bidentate.

Stevin1H

Why is it that if the coordination compound has a net overall negative charge that we would have to add the suffix "-ate" at the end of the metal name. For example, Co(Cn)5(OH2)]^2- would be aquapentacyanidocobaltate(III)

Stevin1H

The VSEPR formula of AX2E2 suggests that the molecular shape will be bent, though it has 4 electron density regions. And for 4 electron density regions, it suggests the electron pair geometry would be tetrahedral, which has bond angles of 109.5. But for AX2E2, it has lone pairs so the bond angles wi...

Stevin1H

The bond angles for see saw would be slightly less than 90 from the atom on the axial axis and equatorial axis. And for the atoms on the equatorial axis, the angle would be slightly less than 120. This is due to the lonep pair that is present in the see saw structure.

Stevin1H

Since the Iodine atom is fairly large since it is near the bottom of the group, the larger atoms do not like to form double bonds which resulted in having 2 single bonds and 3 lone pairs for the lewis structure of I3-.

Stevin1H

For determining the ionic character, we only look at the electronegativity for the individual atom. So for H2S, we would only consider the electronegativity of a single H and a single S atom to determine the ionic character of the compound.

Stevin1H

Polarizable refers to atoms or ions with electron clouds experience distortions. Polarizability is usually associated with anions. Large anions are highly polarizable since the nucleus has weaker control over the outermost electrons due to a larger orbital. Ions with a higher negative charge (a high...

Stevin1H

How is the strength of bonds affected by the presence of lone pairs? Is the strength of a bond stronger or weaker with or without the presence of lone pairs?

Stevin1H

Since lone pairs and bonds are both considered when determining the shape of a molecule, lone pairs affect the shape of the molecule because the repulsion of the lone pairs is stronger. And in order to get the atoms as far as possible for least repulsion in order to determine the shape of the molecu...

Stevin1H

In order to predict whether a molecule is polar or non polar, we would need to draw the best 3D structure of the molecule to determine the dipole moment. When we draw the best 3D structure, we would also need to know the electronegativity of each atom to draw the bond dipoles. If the bond dipoles do...

Stevin1H

Since the structure of nitrate has both a double and single bond, we have to understand that their is resonance involved. Also, remember that double bonds have shorter bond lengths than single bonds because double bonds are stronger. Resonance affects the strength of bonds because it spreads multipl...

Stevin1H

Can someone please explain the difference in molecular geometry vs electron-pair geometry? What defines the molecular geometry and what defines the electron-pair geometry?

Stevin1H

Polarizing power is referred to atoms and ions that can cause distortions. Polarizing power is usually associated with cations as cations with a small atomic radius and highly charged have highly polarizing power. This is because as these small and highly charged cations get near an anion, the catio...

Stevin1H

In order to determine which molecule is more soluble in water, we would have to look at the electronegativity of both. Since Mg has an EN of 1.2 and Oxygen has an EN of 3.5, the difference in EN is 3.5-1.2 = 2.3. For BaO, the EN of Ba is 0.9 and for Oxygen it is 3.5. The difference in EN for BaO is ...

Stevin1H

A molecule is considered to be polar when there is an unequal sharing of electrons between the two atoms. This is shown through the unequal sharing of electrons due to the difference in the Electronegativity of the two atoms. The more electronegative atom will pull the shared electrons more toward i...

Stevin1H

Are molecular shapes and the bond angle only determined by the number of bonding pairs associated with the central atom of the lewis structure?

Stevin1H

We do use De Broglie's equation here. To 3 sig figs, both protons and neutrons have a mass of 1.67x10^-27. And since de Broglie's equation is lambda=planck's constant/momentum (or mass * velocity), given that the question states both the proton and neutron are traveling at the same velocity, both wi...

Stevin1H

Covalent bonds are associated with the sharing of electrons between two nonmetals while Ionic bonds involve the transfer of electrons between a metal and nonmetal, which involves lattice energy. Ionic bonds are extremely stronger than covalent bonds because of the smaller distance between Ionic bond...

Stevin1H

Can someone explain why certain elements like Boron or Aluminum can still form a stable structure with only 6 electrons? Why does this exception to the octet rule work/make sense?

Stevin1H

I don't think you would have to write the formal charges for each atom, but it is certainly helpful to do so when determining which lewis structure is the most stable. A formal charge of 0 is the most stable.

Stevin1H

Elements in period 3, 4, ... and so on can have an expanded acted with more than 8 electrons because the electrons will be filled into the d orbital.

Stevin1H

How do you determine which atom is in the center for Lewis structures? For example, for N2O, why is nitrogen in the center of the Lewis structure if the ionization energy of oxygen is lower than nitrogen. And for [ClO4]-, how do you determine whether Chlorine or Oxygen has a lower ionization energy ...

Stevin1H

Why is it that a Ca^2+ ion is smaller than a Na+ ion?

Stevin1H

I believe it is only the elements on the periodic table with an energy level of 3 or greater that can have more than an octet due to having the space of a d orbital.

Stevin1H

I'm having a hard time understanding why the trends are the way they are for Electron Affinity and Ionization energy. Can someone please explain this?

Also, what is effective nuclear charge and how is that represented in the periodic table?

Stevin1H

Since the 4s orbital is filled before the 3d orbital, does this same idea apply to the 5s orbital being filled before the 4d orbital? And how does the filling of electron work with the addition of the f orbital?

Stevin1H

Is the s orbital degenerate? Meaning, is the degeneracy of the s orbital equal to 0 or 1?

Stevin1H

E=hv represents the energy of the photon. However, it could also be equal to the energy required to remove an electron if the kinetic energy is 0. This is shown in the formula E(photon) - work function = Kinetic energy. If the Kinetic energy is 0, then the energy of the photon is equal to the work f...

Stevin1H

To solve this problem, we need to know that each orbital holds 2 electrons and that ml= -l -> l So, in this problem we are focusing on the magnetic quantum number. For example a) n=2, l=1 so ml = -1,0,1. Given that there are three orbitals in example a and that each orbital holds 2 electrons, there ...

Stevin1H

To calculate the energy per mole, you would have to multiply by Avogadro's number. The kinetic energy that you calculate was the kinetic energy for one photon. So, by multiplying by 6.022E23, this will give you the total energy for 1 mole of electrons. Here is the conversion: Joules/electron (6.022E...

Stevin1H

Can someone explain the Balmer and Lyman series and how to determine if a transition is in the Balmer or Lyman series? For example, in problem 1.15 in the 6th edition, the question is: In the ultraviolet spectrum of atomic hydrogen, a line is observed at 102.6 nm. Determine the values of n for the i...

Stevin1H

The energy required to remove an electron is equal to the work function. The work function here is equal to 150.6kJ.mol-1. So to find the amount of energy to remove an electron, we would do conversions since the answer choices are only in joules. We first convert 150.6kJ.mol-1 to joules by multiplyi...

Stevin1H

In order to solve this problem, you would also need the answer from part A. Part A asks for the the amount of energy to emit an electron with a frequency of 1.09E15 1/s. Given this frequency, use the equation c=(lambda)(frequency) and solve for lambda. lambda=(speed of light)/(frequency) = 2.75 E-7m...

Stevin1H

E(photon) - work function >= Kinetic Energy of electron. The work function (also known as the threshold energy) is the amount of energy that is required in order to eject an electron from the metal surface. Any excess energy from the photon after ejecting an electron becomes kinetic energy, as shown...

Stevin1H

Can someone please explain the difference between light acting as a wave or as a particle?

Stevin1H

Yes, the shorter wavelengths have higher frequency and longer wavelengths have shorter frequency. This can be proven from the equation c=(lambda)(frequency) where c is a constant and equals 3.00x10^8 m/s. As wavelength increases, the frequency would have to decrease and vice versa in order to mainta...

Stevin1H

For L.5 Part B, I converted the 3.5x10^3 to grams by multiplying by 1000g. With the value of Aluminum in grams, I divided by 26.98g to get the amount of moles of Al. And given the chemical equation 6NH4ClO4 + 10Al(s) --> 5Al2O3(s) + 3N2(g) + 6HCl(g) + 9H20, I used stoichiometry/mole conversions to c...

Stevin1H

For this problem, I just found the mass composition of each element of L-carritine. I found the mass percent composition of Carbon, Hydrogen, Nitrogen, and Oxygen of L-carritine. Also, make sure the total % of each element adds up to 100%.

Stevin1H

For this problem, we need to know that Avogadro's # = 6.022x10^23. And given that the radius is 144pm, the radius is only half the distance, so we would multiply it by 2 in order to get the full length. 2(144) = 288pm. Given that we have 1.00 mol Ag, we convert the mol to atoms by multiplying it by ...

Stevin1H

For this problem, I approached it seeing the information that I was given in the problem. Given 55.1g KCl in approximately 75ml (0.075L) of water then adding water to a final volume of 125ml (0.125L), the formula M(initial)V(initial)=M(final)V(final) was needed to solve this problem. First, I conver...

Stevin1H

Since the rule for multiplying and dividing significant figures is to have as many sig figs in your answer relative to the lowest amount of sig figs in your calculations, I would agree that the answer 4.56 is sufficient because the lowest number of sig figs in the calculations, as you said, was 3.

Stevin1H

In order to find the total number of atoms within a given sample in grams, it would require conversions from grams to moles to atoms. Given the mass of the sample in grams, divide the mass of the sample (g) by its molar mass (g/mol). By doing so, this gives you the number of moles in the given sampl...

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