CHEMISTRY COMMUNITY

Julie Steklof 1A

Both A and B were correct. A is right because bigger, more complex molecules have larger molar entropies than smaller molecules.

Julie Steklof 1A

Although the moles of gas of products and reactants are equivalent, the reaction produces 6 moles of liquid which is more "disordered" or "chaotic" than the solid that reacts so entropy increases in the reaction (is positive).

Julie Steklof 1A

A large number for oxidation power means that the compound is readily reduced and so will have a more positive reduction potential.

Julie Steklof 1A

The half lives of second order reactions depend upon the initial concentration of reactants whereas the half lives of first order reactions do not.

Julie Steklof 1A

Yes, an intermediate must be formed and consumed in a proposed reaction mechanism.

Julie Steklof 1A

Molecularity is the number of species involved in an elementary step. So yes, for example a termolecular elementary step would have to have three reactants colliding which is seen in a reaction in which the stoichiometric coefficients add up to three.

Julie Steklof 1A

Yes, temperature will cause a change in k because an increase in temperature will increase the force of the collisions between molecules which gives more molecules enough energy to overcome the energy barrier and therefore speed up the rate of production of products. k can never be negative.

Julie Steklof 1A

John Huang 1G wrote:Then what would it mean for a reaction to have a second order or zero order?

The rate of a zero order reaction does not depend on the concentration of reactant.

Julie Steklof 1A

It would need to have the 0 subscript to be [A] initial.

Julie Steklof 1A

The chlorine in Cl2 has an oxidation state of 0 and -1 in HCl. The hydrogen has an oxidation state of 0 in H2 and +1 in HCl.

Julie Steklof 1A

The order of a reaction is given by adding the exponents of the concentrations in the rate law.

Julie Steklof 1A

The O2 concentration increases half as fast as the NO2 concentration decreases. For these rates to be equal, d[O2]/dt must be multiplied by two so it equals -d[NO2]/dt.

Julie Steklof 1A

A salt bridge keeps the solutions in each cell neutral and allows the redox reaction to continue.

Julie Steklof 1A

melissa carey 1f wrote:Whats the relationship between free energy and max work - are they equal?

I wrote in my notes from 2/9 that maximum cell potential is directly related to the free energy difference between reactants and products in the cell/ redox reaction.

Julie Steklof 1A

After writing balanced half reactions, you will be able to see the moles of electrons involved in the redox reaction. This is the number you use for n.

Julie Steklof 1A

Does the anode always have to be drawn on the left and cathode on the right? Or is it necessary to know the solutions in order to tell which cell is which?

Julie Steklof 1A

In an irreversible reaction, infinitely small changes occur that allow the reaction to end at equilibrium. In a reversible reaction, finite changes occur, usually quickly, that result in no equilibrium within the system.

Julie Steklof 1A

A salt bridge serves to keep the charges between the two solutions to remain neutral and for the redox reaction to continue.

Julie Steklof 1A

Based on this website, there may be some correlation but no definitive consistency can be found for solids.

https://chem.libretexts.org/Core/Physic ... eqn-approx

Julie Steklof 1A

Reactions are considered spontaneous when the products are favored over the reactants.

Julie Steklof 1A

Endergonic means that energy is absorbed from the surroundings (in terms of Gibbs Free Energy) so deltaG is positive and exothermic means a negative deltaH. I think it's possible for this to occur only when the entropy change is negative and the temperature is high.

Julie Steklof 1A

Does this mean that the specific heat for all ideal monatomic gases is equal?

Julie Steklof 1A

I think one of the main points made was that like a "boulder on a hill" (in the enthalpy diagram) you would not expect it to start rolling up the hill without work being put in, naturally it would go to the lowest point. This is in contrast to entropy where you would not expect a system to...

Julie Steklof 1A

In the example that Dr. Lavelle gave today during lecture he said that when V2=2V1, each gas molecule has 2x positions available to it and that because of this the ratio of W2 to W1 was equal to 2. How do we know that each gas molecule has 2x positions available to it?

Julie Steklof 1A

Why does a system being at equilibrium mean that it is a reversible process?

Julie Steklof 1A

AlyssaPeckham1A wrote:Would adiabatic walls be almost the opposite of diathermic walls?

Yes, adiabatic walls do not allow heat transfer between a system and its surroundings.

Julie Steklof 1A

Yes, the surroundings (the cooling system) gain 947 kJ as heat meaning that the system must lose 947 kJ.

Julie Steklof 1A

During a phase change, why does the temperature of a sample remain constant even when heat is being supplied?

Julie Steklof 1A

All elements in their natural states have an enthalpy equal to zero because there is no change involved in their formation.

Julie Steklof 1A

Yes, reversing a reaction will result in a enthalpy of opposite sign. This is because enthalpy is a state function/property.

Julie Steklof 1A

Helen Shi 1B wrote:Can someone explain why BaO is basic and As2O3 and Bi2O3 amphoteric?

As and Bi are metalloids and can act as either acids or bases.

Julie Steklof 1A

Yes they are the same thing. When an acid is deprotonated it is the same thing as being ionized.

Julie Steklof 1A

Because the only thing changed in the problem is concentration and k is constant regardless of initial concentrations, more product must be formed in order to make the ratio of concentration of products to concentration of reactants (k) the same.

Julie Steklof 1A

You could draw Lewis structures and see if a molecule has an element with an open octet (for example Boron in BF3). This tells you that the molecule is a Lewis acid. Similarly, if you draw a Lewis structure and see that an element has an unshared pair of electrons to be able to donate. This would be...

Julie Steklof 1A

I know that when naming coordination compounds if the overall charge is negative we add -ate to the end of the transition metal name. Is there any rule for when the overall charge is positive?

Julie Steklof 1A

When naming coordination complexes, the ligands are listed alphabetically. I don't think the order when writing the chemical formula is significant because everything within the square brackets is directly bonded to the transition metal.

Julie Steklof 1A

Yes putting less than 109.5 degrees for bond angles will be fine because molecules with lone electron pairs have bond angles that are determined experimentally and differ from molecule to molecule even if both have the same VSEPR shape.

Julie Steklof 1A

The unhybridized 2p electrons are the ones forming the 3 pi bonds.

Julie Steklof 1A

Yes, three bonds and a lone pair of electrons on the central atom results in a trigonal pyramidal shape. However, in response to the above comment, three bonding pairs with no lone pair is trigonal planar, not trigonal pyramidal.

Julie Steklof 1A

VSEPR formulas are generalized formulas describing the molecular shape of a compound. A represents the central atom, X represents the bonded atom(s), and E represents the lone pair(s) of a molecule. For example, a trigonal pyramidal molecule would have the VSEPR formula: AX3E, one central atom bonde...

Julie Steklof 1A

I'm pretty sure bond length is determined experimentally.

Julie Steklof 1A

To add to the above response, atoms that are bonded are more stable and therefore have less energy than the free atoms which are more unstable.

Julie Steklof 1A

Why is it that elements with low ionization energy conduct electricity in their solid states?

Julie Steklof 1A

The above response is correct. Because each ion has the same amount of electrons, to determine size we need to look at the number of protons within the ion. Because Magnesium 2+ has the highest nuclear charge, and each ion in the series have the same number of electrons, it will have the smallest io...

Julie Steklof 1A

The energy required to ionize an electron is the same as the energy required to remove an electron.

Julie Steklof 1A

I have not seen any energy levels higher than n=9.

Julie Steklof 1A

In E=hv, the units for h are Joules*seconds and units of v are seconds^-1. Multiplying these gives you Joules which is an appropriate unit for energy. In E=1/2mv^2, mass is measured in kilograms and velocity in meters per second. Joules is technically "short" for units of kg*m^2/s^2 which ...

Julie Steklof 1A

ΔE is the energy change that occurs when an atom absorbs or emits a photon (atomic spectra experiment) whereas E is used to calculate the energy per photon when completely removing electrons from an atom (photoelectric effect).

Julie Steklof 1A

I thought percent change was always (final-intial)/initial x100%? This would make the equation (504.3-502.31)/502.31 x100% which gives you .396% and rounds to .40%. However the solutions manual shows dividing by 504.3. Does anyone know why this is?

Julie Steklof 1A

In class we were told that for rounding if the number ends in a 5 we should round to the nearest even number. So if the number was .065 we would simply round to .06 but if the number was .055 we would round up to .06.

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