CHEMISTRY COMMUNITY

Kate_Santoso_4F

If given reaction mechanisms, can you tell whether the reaction is exothermic? If so, how?

Kate_Santoso_4F

What is the purpose of calculating the pseudo equilibrium constant for a reaction profile?

Kate_Santoso_4F

There are two forms of the Nernst Equation given on the constants and formulas sheet. One is E(reaction) = E(standard) - (RT/nF)*lnQ and the other is E(reaction) = E(standard) - (0.05916V/n)*logQ. Can someone please explain what the difference is between these two forms of the equation and when you ...

Kate_Santoso_4F

One stage in the extraction of gold from rocks involves dissolving the metal from the rock with a basic solution of sodium cyanide that has been thoroughly aerated. This stage results in the formation of soluble Au(CN)2- ions. The next stage is to reduce gold to the metal by the addition of zinc dus...

Kate_Santoso_4F

Consider the conversion of C to D via a one-step mechanism. The activation energy of this conversion is 3 kcal/mol. The energy difference between D and the transition state of the reaction is 7 kcal.mol. Calculate delta H for the reaction C --> D. Could someone please explain how to do this problem?

Kate_Santoso_4F

An integrated rate law gives the concentration of reactants or products at any time after the start of the reaction. The instantaneous rate of the reaction is the slope of the tangent to the curve at a single instant. The average reaction rate in a particular interval is the change in molar concentr...

Kate_Santoso_4F

If a plot of 1/[A] against time is a straight line with a positive slope of k, the reaction is second order.

Kate_Santoso_4F

The rate of reaction of NO2 can be found by the change in concentration of NO2 divided by the change in time. We are given the initial and final concentrations of NO2 in the problem (450 mmol/L to 320 mmol/L) and the change in time (20s). Therefore, the rate of reaction of NO2 is -(320 mmol/L - 450 ...

Kate_Santoso_4F

a) Write balanced half-reactions for the redox reaction between sodium perchlorate and copper(I) nitrate in an acidic solution.
How do you know which one of these species is being reduced or oxidized and which one is at the cathode or anode? There is no indication in the problem.

Kate_Santoso_4F

Eo is an intensive property (the voltage difference is the same and does not depend on how many times the reaction occurs). It stays the same when the half reaction is balanced. However, when one of the half reactions must be reversed, the sign of Eo changes.

Kate_Santoso_4F

Write the half-reactions, the balanced equation for the cell reaction, and the cell diagram for each of the following skeletal equations: Part c) Cd(s) + 2Ni(OH)3 (s) --> Cd(OH)2 (s) + 2Ni(OH)2 (s) The cell diagram in the answer key is the following: Cd (s) | Cd(OH)2 (s) | KOH (aq) || Ni(OH)3 (s) | ...

Kate_Santoso_4F

I thought that one of the half reactions must be reversed to form a redox reaction. Why is it that for a majority of the homework problems, the standard reduction potential for the anode, does not change signs when calculating the standard reduction potential for the cell? For example, for part a fo...

Kate_Santoso_4F

You can determine which of the following compounds are stable with respect to decomposition into their elements by analyzing their standard free energies of formation. Compounds with a positive free energy of formation are unstable with respect to the elements. Since PCl5 (g) and SO2 (g) have negati...

Kate_Santoso_4F

A certain enzyme-catalyzed reaction in a biochemical cycle has an equilibrium constant that is 10 times the equilibrium constant of the next step in the cycle. If the standard Gibbs free energy of the first reaction is -200 kJ/mole, what is the standard Gibbs free energy of the second reaction? Can ...

Kate_Santoso_4F

Problem 9.89: Some entries for Sm in Appendix 2A are negative. What is common about these entries and why would the entropy be negative?
From what I see, the negative entries all correspond to aqueous ions. Why is this?

Kate_Santoso_4F

Are work and heat extensive or intensive properties?

Kate_Santoso_4F

Can someone please explain how we know to use Cp or Cv when calculating the entropy change for something that has a change in temperature? I know the problem should indicate constant pressure or constant volume but it doesn't always say so.

Kate_Santoso_4F

Can someone please explain what the difference is between statistical and residual entropy and if it is just dependent on the number of microstates?

Kate_Santoso_4F

If a problem indicates constant volume in one way or another, do we always assume w=0?

Kate_Santoso_4F

Can someone please explain why isothermal, reversible processes do more work than their irreversible counterpart?

Kate_Santoso_4F

Can someone please explain why isothermal, reversible processes do more work than their irreversible counterpart?

Kate_Santoso_4F

C(gr) represents carbon as graphite. Graphite is the most stable form of carbon at normal temperatures. The standard enthalpy of formation of an element in its most stable form is zero. For instance, the standard enthalpy of formation of C(gr) is zero because C(gr) --> C(gr) is a "null formatio...

Kate_Santoso_4F

Enthalpy change (delta h) only applies to reactions done at constant pressure and it is the state of a system while it contains a certain amount of heat. Heat (q) is just the energy that causes those changes and is the energy transferred as a result of a temperature difference.

Kate_Santoso_4F

I'm not sure if we need to use calorimeters in any calculations but I think we should just know that calorimeters measure transfers of energy as heat by recording the change in temperature produced by a process taking place within it. Bomb calorimeters are used to measure heat transfers at constant ...

Kate_Santoso_4F

Heat, represented by q, is the transfer of energy as a result of a temperature difference. When energy enters a system as heat, q is positive. When energy leaves a system as heat, q is negative. The measurement of heat produced or absorbed by a process is used to monitor the delta U, or internal ene...

Kate_Santoso_4F

When calculating Kp, do the partial pressures have to be in either bar or atm?

Kate_Santoso_4F

Le Chatelier's Principle: When a stress is applied to a system in dynamic equilibrium, the equilibrium tends to adjust to minimize the effect of the stress.

Kate_Santoso_4F

The correct answer should be C. If the amount of NO2 is increased, the equlibrium will shift to the products, which will result in an increase in NO. If SO3 is removed by condensation, the equilibrium will shift to the products again, which will result in an increase in NO. If the pressure is triple...

Kate_Santoso_4F

A student added solid Na20 to a 200.0 mL volumetric flask, which was then filled with water, resulting in 200.0 mL of NaOH solution. 5.00 mL of the solution was then transferred to another volumetric flask and diluted to 500.0 mL. The pH of the diluted solution is 13.25. What is the concentration of...

Kate_Santoso_4F

The correct answer should be C. If you increase the amount of carbon monoxide, the equilibrium will shift towards reactants since change in concentration of a chemical reaction at equilibrium represents a fixed P/R ratio. Therefore, more reactant will form until the original P/R ratio is attained (s...

Kate_Santoso_4F

What is the effect of increasing or decreasing the partial pressure of a reactant or product in a chemical reaction? How will we know which direction the reaction will shift?

Kate_Santoso_4F

Le Chatelier's principle suggests a good way of ensuring that a reaction goes on generating a substance: simply remove products as they are formed. In the continuing hunt for equilibrium, the reaction generates more product.

Kate_Santoso_4F

Here is the rule based on the textbook: If a chemical equation can be expressed as the sum of two or more chemical equations: The equilibrium constant for the overall reaction is the product of the equilibrium constants for the component reactions. When you add the two reactions, Cl2 is present as a...

Kate_Santoso_4F

If the pressure of a reaction vessel is increased by adding an inert gas, then moles of reactant, product, and volume are constant. Therefore, there is no change in the reactant and product concentration and no effect on the reaction. Remember that an inert gas does not undergo chemical reactions un...

Kate_Santoso_4F

Part b asks you to calculate the equilibrium constant for the reaction. The formula to calculate the equilibrium constant is as follows: K=(PB)*(PC)^2/(PA)^2 The partial pressures in the graph they give us are in kPA. To use the K formula, I believe you need to have the partial pressures in atm or b...

Kate_Santoso_4F

Here is the rule based on the textbook: If a chemical equation can be expressed as the sum of two or more chemical equations: The equilibrium constant for the overall reaction is the product of the equilibrium constants for the component reactions. When you add the two reactions, Cl2 is present as a...

Kate_Santoso_4F

According to the textbook, chemical equilibrium is defined as the stage in a chemical reaction when there is no further tendency for the composition of the reaction mixture— the concentrations or partial pressures of the reactants and products— to change. So I believe composition does refer to conce...

Kate_Santoso_4F

Some reactions in solution involve the solvent as a reactant or product. When the solution is very dilute, the change in solvent concentration due to the reaction is insignificant so the solvent can be treated as a pure substance just like a solid. Also, the activity of a pure solid or liquid is 1 s...

Kate_Santoso_4F

When calculating concentration in units of mol/m^3 and you are given a pressure in atm, a temperature in Kelvin, and an R value with units of m^3*atm/K*mol, you do not need to do any conversions because the units atm and K should cancel leaving you with a concentration in mol/m^3. Just plug in the R...

Kate_Santoso_4F

You must count the number of diatomic molecules in each of the flasks. It goes from 11 to 8 to 5 to 5 from left to right. Since there was no change after the third flask, equilibrium is reached there.

Kate_Santoso_4F

Would it be appropriate to say that all bent or angular moleculars are polar? Because even if the atoms are the same (such as in ozone, O3), the molecule is still polar, or is ozone just a special case?

Kate_Santoso_4F

According to the textbook, ionic bonds acquire more covalent character as the distortion of the electron cloud on the anion increases. What exactly does this mean?

Kate_Santoso_4F

Yes when drawinga dipole moment, arrows are used to show the polarity points from the positive areas to the negative areas. For example, in water, there is a higher electron density around the oxygen atom, giving it an overall negative charge and the hydrogen atoms overall positive charges. The arro...

Kate_Santoso_4F

Ligands are basically just the Lewis bases attached to the central metal atom or ion in a d-metal complex.

Kate_Santoso_4F

Taken from the textbook, a coordination compound is an electrically neutral compound in which at least one of the ions present is a complex. A complex is a species consisting of a central metal atom or ion to which a number of molecules or ions are attached by coordinate covalent bonds.

Kate_Santoso_4F

A good example of a nonpolar molecule with polar bonds is CO2. The central carbon will have a net positive charge and the two outer electrons will have a net negative charge. Since the shape of the molecule is linear, these two bond dipoles will cancel each other and the overall molecule will have z...

Kate_Santoso_4F

If dipole moments are equal and opposite of each other, they will cancel each other, which gives rise to a nonpolar molecule. Some completely non polar molecules can have polar individual bonds. If the dipole moments in a particular molecule do not cancel out, then you will have a polar molecule.

Kate_Santoso_4F

Bond dipole moment is used to measure the polarity of a chemical bond within a molecule. There is a dipole moment whenever there is a separation of positive and negative charges due to the unequal attraction that the two atoms have for the bonded electrons. The larger the difference in electronegati...

Kate_Santoso_4F

In general, an atom is more polarizable the larger it is and an atom has more polarizing power the smaller it is. Therefore, polarizability increases down a group because atomic size increases and larger electron clouds distort more easily. Polarizability would decrease across a period because of in...

Kate_Santoso_4F

If this is for the 6th Edition, heres an example. For part a for Problem 4.35, you should have drawn a trigonal planar arrangement for the molecule BF3 with three lone pairs on each of the fluorines and three regions of electron density around the boron atom. This would give you a hybridization of s...

Kate_Santoso_4F

Benzyne would be highly reactive because the two carbon atoms that are sp hybridized are constrained to have a very strained structure compared to what their hybridization would like to adopt (linear arrangment) with 180 degree angles at these C atoms. The formation of a diradical would allow the C ...

Kate_Santoso_4F

There can only be one sigma bond between two atoms while there can be zero, one, or two pi bonds between two atoms. In general, sigma bonds determine the shape of a molecule whereas pi bonds make atoms move closer together.

Kate_Santoso_4F

Remember exceptions to the octet rule. For example, Boron and Aluminum commonly fail to complete an octet and often form compounds in which they have 6 valence electrons. Remember which elements can have an expanded octet. The octet rule can be expanded by some elements by using the d orbitals found...

Kate_Santoso_4F

A cation's polarizing power refers to its ability to attract valence electrons from a nearby anion and polarizability refers to the anion's tendency to become polarized by the cation. Small cations with high positive charges are said to have more polarizing power because the positive charge is distr...

Kate_Santoso_4F

Schrodinger's wave function equation basically just uses a wave function to describe an electron in an atom. It uses the concept that an electron, with wavelike properties and indeterminacy in momentum and position, can be described by a mathematical wave function.

Kate_Santoso_4F

Oxygen has a smaller atomic radius than sulfur so oxygen electrons experience more repulsions between each other since the valence shell is held closer to the nucleus. When an external electron is introduced, energy is released (electron affinity) but at the same time energy is consumed due to insta...

Kate_Santoso_4F

Cu+ would have a total of 28 electrons since you are losing one electron and Cu normally has 29 electrons. Argon is the nearest noble gas to Cu for the shorthand notation. Half filled and fully-filled orbitals are more symmetrical than any other configuration and symmetry leads to greater stability....

Kate_Santoso_4F

The up arrow electron is positive 1/2 which indicates a counterclockwise spin and the down arrow electron is negative 1/2 which indicates a clockwise spin.

Kate_Santoso_4F

In regards to electron spin for unpaired electrons, how do we know if the electron is spinning clockwise or counterclockwise? Based on what I've seen in class, an unpaired electron has a counterclockwise spin with a magnetic spin quantum number of +1/2. Why is this so?

Kate_Santoso_4F

The Rydberg equation is as follows: frequency = -R((1/n(initial)^2)-(1/n(final)^2)). If you have a negative sign in front of the Rydberg equation, the first n in the equation has to be the starting level. If there is no negative sign in front of the Rydberg equation, the second n will be the startin...

Kate_Santoso_4F

I had the same issue. I ended up with n2 being approximately 3.2. Someone please advise thanks.

Kate_Santoso_4F

In short, the Pauli Exclusion Principle states that in an atom or molecule, no two electrons can have the same four quantum numbers. Because an orbital can only contain a maximum of two electrons, the two electrons must have opposing spins. The two spin states of an electron can be represented as cl...

Kate_Santoso_4F

Based on the textbook, psi squared is the probability density, which means that wherever psi squared is large, the particle has a high probability density and wherever psi squared is small, the particle has a low probability density. What do these statements mean qualitatively in relation to the wav...

Kate_Santoso_4F

I don't think those two were covered on the Quantum World Outline, so we probably don't need to know those for Test Two next week.

Kate_Santoso_4F

For question 1.21, the correct answer should be (d) the photoelectric effect. The photoelectric effect best supports the idea that electromagnetic radiation has the properties of particles because electromagnetic radiation consists of particles (or packets) of energy called photons, each photon havi...

Kate_Santoso_4F

In each of these series, the principal quantum number for the lower energy level involved is the same for each absorption line. Thus, for the Lyman Series, the lower energy level is n=1; for the Balmer series, n=2; for the Paschen Series, n=3; and for the Brackett series, n=4.

Kate_Santoso_4F

If electrons revolve around the nucleus of an atom due to electricity and magnetism, what type of path does an electron take when it absorbs energy and jumps from a ground state to an excited state? Does it jump in a straight line or more of a curved line from one lower energy level to one higher en...

Kate_Santoso_4F

We are asked to solve for the empirical or molecular formula of a more complex compound such as caffeine and given the molar mass and the amounts of each of its atoms in grams. After we finally solve for the molar ratios of each of the atoms for caffeine, how do we know what order in which the atoms...

Kate_Santoso_4F

A reaction vessel contains 5.77g of white phosphorus and 5.77g of oxygen. The first reaction to take place is the formation of phosphorus (III) oxide, P4O6: P4 (s) + 3O2 (g) --> P4O6 (s). If enough oxygen is present, the oxygen can react further with this oxide to produce phosphorus (V) oxide, P4O10...

Kate_Santoso_4F

The molar concentration is called the "molarity" and its formally known as the "amount of substance concentration." We use moles of solute and the volume of the solution to find the concentration, or molarity of a solution. Moles of solute are used to find the molarity of a solut...

Kate_Santoso_4F

I had a chem discussion this morning and my TA said the periodic table will be given on the tests given in discussion.

Kate_Santoso_4F

For problem F9, they are specifically asking you "in what atom ratios are the atoms present in vanillin." They are simply asking for the empirical formula of vanillin. Since the molecular weight was not given, you cannot determine what the molecular formula is. Using the mass percentage co...

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