CHEMISTRY COMMUNITY

Suchita 2I

Do you know why they gave the cell potential in the question where they were asking for [Zn2+] as a function of cell potential?

Suchita 2I

An electrolyte is basically a solution with ions (that is, a salt in its aqueous state). While electrons conduct electricity in the circuit, the ions in the electrolyte conduct electricity in solution and allow a complete circuit, making them integral to any cell.

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If the number of moles of gas are the same, you can look at phase changes during the reaction. If there are solids on the reactants' side and liquids on the products' side, the sign of delta S will be positive. Similarly, if there are solids on the reactants' side and aqueous ions on the products' s...

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If the rate law is given it is possible to determine the mechanism for the rate determining step. However, I do not think we will be asked to propose a mechanism and know the intermediates. I believe the question is more likely to focus on disproving a given mechanism or choosing the possible mechan...

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Although the negative ion present in the solution is the SO4 2- ion, which will thus move towards the positive anode, the sulfate ion cannot be oxidized so the oxidation of water takes place, leading to oxygen gas being evolved. However, the reduction half reactions and their standard potentials are...

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Nucleophiles are species that are 'attracted to the nucleus' as they have an electron pair that can be donated to an electrophile. In other words, they are Lewis bases. Since they are involved in the unimolecular and bimolecular substitution nucleophilic reactions (SN1 and SN2), questions could invo...

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Temperature is known to affect the rate of a reaction because at higher temperatures, there is an increase in the frequency of successful collisions. This is graphically represented by the Maxwell-Boltzmann curve which shows that the number of particles with energy greater than the activation energy...

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Yes, considering the time Dr Lavelle devoted to the derivations, I'm guessing they important for the test/finals.

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In a single step reaction mechanism, the equilibrium constant is equal to the forward rate constant divided by the reverse rate constant based on the fact that at equilibrium, these rates are equal. If each step in the multi-step mechanism is a reversible reaction, then I would guess that the same r...

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However, the number of steps will not always equal the number of reactants as the number of steps depends on the rate law. For instance, a reaction with two reactants can have the concentration of both reactants in the rate law, which would mean that both reactants occur in the rate-determining step...

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If the gas leaves the solution, it is no longer available to react with the other product (H20) to form the reactant. Therefore, the reverse reaction is less likely.

Suchita 2I

Reactions are controlled by both thermodynamics and kinetics. While thermodynamics determine the relative stability of the products with respect to the reactants (and therefore, the spontaneity of the reaction), the kinetics determine the rate of product formation.

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Suchita 2I

Since the question refers to a hydrogen acceptor I would assume that it means that all the hydrogen produced would be accepted by the ethene. Since 3 moles are produced, the equation for the hydrogenation of ethene is multiplied by 3 to cancel out the hydrogen produced. I would think of this as a He...

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Microstates are basically different configurations with the same energy. So when referring to the different arrangements of a molecule as in 9.25 or of a coordination compound as in 9.75, I found it easiest to actually draw out all the possible structures and then count them rather than trying to vi...

Suchita 2I

The standard entropy would be calculated through a three-step process: 1) The first step involves calculating the change in entropy with the change in temperature from 85 to 100 C using deltaS= nCln(T2/T1). The temperatures you would use in this calculation would be in Kelvin so T1=85+273=358K and T...

Suchita 2I

When using molar heat capacity to calculate q, you do not have to convert to Kelvin as the formula uses deltaT and the temperature difference in the same in both the Celsius and Kelvin scale. However, it is a good habit to always convert to Kelvin as the other formulas use this.

Suchita 2I

When finding the change in entropy with a change in temperature always use deltaS= nCln(T2/T1). In q 9.13, the formula deltaS= nRln(V2/V1) is being used since there is a change in volume from 3 to 0.5, not temperature.

Suchita 2I

You can either use deltaS= nR ln(V2/V1) or deltaS= nR ln(P1/P2) depending on whether the initial and final volume or initial and final pressure is given. This follows from Boyle's Law P1V1=P2V2. Isothermal expansion uses this equation as a change in volume leads to a change in entropy even though te...

Suchita 2I

It would depend on the units you use in your calculation. The different values of R based on the units are given in the constants and formulas sheet so you can use that to figure it out. So if you take volume in liter, pressure in atm and temperature in kelvin it would be 8.206x10^-2. Make sure all ...

Suchita 2I

The units would depend on the number of moles in the calculation. If the calculation was done for 1 mole, it would be kJ/mol, but otherwise report it in kJ.

Suchita 2I

Although reversible expansion allows you to calculate the maximum work that can be done, this is not practically possible as it would take an infinite amount of time. However, I guess one possible application is that it can be used to assess the efficiency of irreversible expansion.

Suchita 2I

Is there a difference between absolute and statistical entropy?

Suchita 2I

I'd assume that since it is an inert electrode and does not participate in the redox reaction, that one electrode can be carbon and the other can be platinum. However, this is not usually done and the same element is generally used.

Suchita 2I

The enthalpy of atomization basically refers to the enthalpy of sublimation, that is, the enthalpy of fusion+the enthalpy of vaporization. This is necessary because solid carbon needs to be converted to gaseous carbon in order to use bond enthalpies. Hope this helps!

Suchita 2I

Since enthalpy of formation by definition is the enthalpy change associated with the formation of 1 mole of a compound in its standard state from its ELEMENTS in their standard states, the equation you should be using is: C(s) + 2H2(g) + 1/2O2(g) = CH3OH (l) However, when calculating the enthalpy ch...

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Heat capacity tells you the amount of heat required to raise the temperature of a substance by 1 degree Celsius/1 Kelvin. A large heat capacity suggests that a large amount of energy is required to raise the temperature by 1 degree Celsius. Since heat capacity is an extensive property (depends on ma...

Suchita 2I

Although the enthalpy of formation deals with all reactants and products in their standard states, when the enthalpy change of a reaction is being calculated with bond enthalpies, all reactants and products must be in the gaseous state. So: enthalpy of formation= delta H of sublimation of Carbon (to...

Suchita 2I

The enthalpy of the reaction is using the same formula that you are, but it looks slightly confusing because the standard enthalpies of formation of the ions are being used as both the acid and salt are in aqueous state. So in the SSM, -153.89 is the enthalpy of formation of Zn2+, 2(-167.16) is the ...

Suchita 2I

During lecture today he said that everything in chapter 8 except for isothermal expansion is on the test, so I would assume that it is on the test and that he might cover it on Friday's lecture.

Suchita 2I

Even though we are not provided the data for the enthalpy of sublimation, this can be found by adding the enthalpy of fusion and the enthalpy of vaporization. However, the calculation would technically be the same as you are still adding the two enthalpies together.

Suchita 2I

Energy is generally hard to define, and its definition as the ability to do work is slightly vague and difficult to visualize. I guess one common link is that all forms of energy can be transferred and thus, they all have an association with movement.

Suchita 2I

If an ideal gas is undergoing isothermal expansion, or volume change at constant temperature, there is no potential energy as the kinetic theory states that ideal gas particles have no interaction. Since kinetic energy is related to temperature, gas particles will expand and spread apart while maint...

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The equipartition theorem is used to calculate the total average kinetic and potential energies at a specific temperature which can further be used to calculate the system's heat capacity.

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Although the Lewis structure of ozone is a resonance hybrid, the dipole moment is easier to understand if one single and one double bond are drawn from the central O atom. The calculation of formal charges shows that while the central O has a +1 charge, the O atom with the single bond has a -1 charg...

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Transition metals have variable oxidation states so this helps specify the oxidation state in that transition metal complex.

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What the textbook is trying to say is that all Bronsted acids are Lewis acids but not all Lewis acids are Bronsted acids. That is, there are Lewis acids that do not involve the transfer of a proton as seen with BF3 which can accept an electron pair but does not have a proton.

Suchita 2I

No gas actually behaves like an ideal gas, but noble gases come the closest as they do not have attractive forces between them. Gases behave more like ideal gases at high temperature and low pressure as these conditions further decrease the inter-particle forces of attraction.

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If a compound has a proton it can donate it can act as a Bronsted acid. For example, HCO3 - can donate a proton and form CO3 2-. A compound can act as a Bronsted base if it can accept a proton, which it can only do if it has a lone pair of electrons it can donate. For example, HC03- can accept a pro...

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To determine whether a ligand is a polydentate ligand count the number of atoms that have lone pairs and can thus act as donor atoms. For example, if there are two donor atoms, it is a bidentate ligand like ethylenediamine and the oxalate ion. Since a chelating agent is a substance that can form two...

Suchita 2I

Kc and Kp are both equilibrium constants used for gas-phase mixtures. However while Kc uses molar concentration of the gases, Kp uses partial pressure of the gases involved.

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A coordinate compound need not only consist of a central metal ion bonded to 6 ligands. Coordination numbers range from 2 to 9. Generally, however, the coordination number 4 is observed leading to a square planar or tetrahedral shape and the coordination number 6 giving the octahedral shape.

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Adding an inert gas to a gas-phase equilibrium changes the total pressure, but does not change the partial pressures of the gases involved in the reaction. Since the total pressure does not affect the equilibrium constant, the equilibrium will remain the same. That is, if the volume and therefore co...

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Polar bear: Help! Help! I'm dissolving!
Brown bear: But bears are insoluble...
Polar bear: That's easy for you to say...You're not polar!

Suchita 2I

The correct Lewis structure involves drawing the atoms in the order HOCO and then drawing a single bond between H and O, a single bond between O and C and a double bond between C and O. Since the total number of valence electrons is 17, add in two lone pairs on each O to give them both an octet (can...

Suchita 2I

The main point of difference is that sigma bonds involve end-on overlapping of orbitals while pi bonds involve side-ways overlapping of orbitals. It might be easier to imagine it as sigma bonds having the electron density along the internuclear axis and pi bonds having their electron density above a...

Suchita 2I

Yeah, always look at the number of areas of electron density which is 4 here.

Suchita 2I

Yeah, even though you need resonance to draw the correct Lewis structure, resonance does not affect VSEPR and therefore, the shape of the molecule.

Suchita 2I

The CH2O molecule has C as the central atom with a single bond with each H atom and a double bond with the O atom. This gives 3 regions of electron density around the C atom and therefore, sp2 hybridization. This gives a triangular planar shape with 120 degree bond angles. There are 3 sigma bonds (2...

Suchita 2I

a) 1-2 dichlorobenzene and 1-3 dichlorobenzene are polar while 1-4 dichlorobenzene is non polar. This is because while 1-2 and 1-3 dichlorobenzene have a net dipole movement, there is no net dipole in 1-4 dichlorobenzene due to the symmetry of the molecule. b)1-2 dichlorobenzene has the largest dipo...

Suchita 2I

Elements from Period 3 and higher can have an expanded octet due to the d orbitals which can accommodate more electrons, but generally look out for Phosphorus and Sulfur, as in PCl5 and SF6.

Suchita 2I

Yeah, all we need is to correctly draw the bonding pairs and lone pairs of electrons, taking into account formal charge and resonance. Also, do not forget to include the charge on the molecule if there is one!

Suchita 2I

Electron penetration describes the ability of an electron to approach the nucleus. This ability depends of the attraction of an electron to the nucleus, so 2s electrons have a higher electron penetration than 2p electrons as they have a higher relative electron density near the nucleus. Since, this ...

Suchita 2I

The total valence electrons are calculated by adding the valence electrons for each element in the molecule and then adding electrons if the charge of the molecule is negative or subtracting electrons if the charge is positive. The number of electrons added or subtracted is based on the magnitude of...

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Yes, the orientation of the orbital (the magnetic spin quantum number) depends on the angular quantum number which specifies whether it is an s, p, d, or f sub-level. For example, the s sub level only has 1 orbital, while the p sub level has 3 orbitals (px, py, and pz) which differ in their spatial ...

Suchita 2I

Can we form a general study group for tests and homework?

Suchita 2I

Why do chemists learn about ammonia first?
...
It's pretty basic stuff.

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Scientist: I just boiled water
Me: solid
Scientist: no
Me: I just mean that's cool
Scientist: WRONG AGAIN

Suchita 2I

I got C2H6O as the empirical formula and the molecular formula. Did anyone else get this?

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