CHEMISTRY COMMUNITY

Vanadium Wang 4H

Rate constant k should always be positive. From the Arrhenius Equation, we know k = A x exp(-Ea/RT). "A" (frequency factor) will always be positive because (according to Google) there are no experimental cases where A is negative, and mathematically exp(-Ea/RT) can never be negative. If rx...

Vanadium Wang 4H

The molecularity of a reaction is defined as the number of molecules or ions that participate in the rate determining step, the slowest step in a chemical reaction.

Vanadium Wang 4H

"(b) A -> 2B + C, when [A]₀ = 0.15 mol*L^-1, for the concentration of B to increase to 0.19 mol*L^-1, given that k = 0.0035 L*mol^-1*min^-1 in the rate law for the loss of A."

Vanadium Wang 4H

The unit will include time because the rate of a reaction is measured in M/s or mol*L^-1*s^-1

Vanadium Wang 4H

A concentration cell is an electrolytic cell that is comprised of two half-cells with the same electrodes, but differing in concentrations. A concentration cell acts to dilute the more concentrated solution and concentrate the more dilute solution, creating a voltage as the cell reaches an equilibri...

Vanadium Wang 4H

The rate of a reaction is measured in terms of how fast the concentration of one of the reactants is falling. Its units are mol*L^-1*s^-1

The exponents m and n are called partial orders of the reaction which depend on the reaction mechanism and can be determined experimentally.

Vanadium Wang 4H

In principle, every reaction is on the continuum between pure kinetic control and pure thermodynamic control. These terms are with respect to a given temperature and time scale. A process approaches pure kinetic control at low temperature and short reaction time. At the other end of the continuum, t...

Vanadium Wang 4H

In principle, every reaction is on the continuum between pure kinetic control and pure thermodynamic control. These terms are with respect to a given temperature and time scale. A process approaches pure kinetic control at low temperature and short reaction time. At the other end of the continuum, t...

Vanadium Wang 4H

Electrolysis takes an electric current to drive an otherwise non-spontaneous chemical reaction.

Vanadium Wang 4H

Kinetics is the measurement of how quickly reactions occur. If changes in conditions affect the speed of reaction, we can learn something about how the reaction happens. Kinetic studies are important in understanding reactions, and they also have practical implications. By understanding how a reacti...

Vanadium Wang 4H

Typically yes because the reaction will require a greater buildup of energy to overcome the activation barrier. Take a look at the Arrhenius Equation:
k = Ae^-(E_A/RT)
A higher activation energy would result in a slower reaction.

Vanadium Wang 4H

Kinetics deals with the rate of a reaction and thermodynamics deals with whether the reaction is favorable or not. Kinetic stability basically occurs when the reactants react at a slower rate. The slower the reaction occurs, the greater the kinetic stability. Thermodynamic stability depends on wheth...

Vanadium Wang 4H

You have to break this problem up into two steps: 1. Find m * Heat of fusion 2. Find m * C * delta T When you find those two values, you add them up, and that is the total heat needed. Is it n*Heat of fusion or m* Heat of fusion? For the first part we use moles and the second part we use mass right...

Vanadium Wang 4H

An element's most stable form is most likely its standard elemental form, usually either in a monatomic or diatomic form

Vanadium Wang 4H

4.18 J refers to the specific heat capacity of water.
0.38 J refers to the specific heat capacity of copper.

Vanadium Wang 4H

Because q_system=-q_surroundings, the amount of heat given off by your body (the system) is the same amount of heat absorbed by the surroundings.

Vanadium Wang 4H

A calorimeter is an isolated system so no heat is lost to the surroundings. Any heat released from the reaction will be absorbed by the calorimeter. Therefore, q_calorimeter = -q_reaction

Vanadium Wang 4H

H₂O is a liquid so it would not be included in calculating the equilibrium constant. This is because solids and liquids do not affect the reactant amount at equilibrium in the reaction, so they are disregarded and kept at 1.

Vanadium Wang 4H

Depending on the question, the gas constant, R = 8.314 J*K^-1*mol^-1 = 8.206*10^-2 L*atm*K^-1*mol^-1 = 8.314*10^-2 L*bar*K^-1*mol^-1 = 62.364 L*Torr*K^-1*mol^-1

Vanadium Wang 4H

The average kinetic energy is obtained from the expression: average kinetic energy = $\frac{3}{2}$ *R*T. Using this equation you should get the answers: a)4103.2 J*mol^-1; b)4090.7 J*mol^-1; c)12.5 J*mol^-1

Vanadium Wang 4H

An isolated system and a closed system are two different types of systems. An isolated system has no contact with its surroundings, neither energy nor matter can interact with the system. A closed system has a fixed amount of matter but it can exchange energy with its surroundings.

Vanadium Wang 4H

The ideal gas law (Pv = nRT) can be rearranged to create the equation P = (n/v)RT. P represents pressure and n/v represents concentration while R and T are constants/given so you can convert between partial pressure and molar concentration based on the information given in the problem.

Vanadium Wang 4H

When asked for K_p, use partial pressure and when asked for K_c, use molar concentrations. Partial pressure can be converted into molar concentrations and vice versa using the ideal gas law (Pv = nRT).

Vanadium Wang 4H

When calculating pH and pOH, sig figs are calculated from the initial concentration and applied after the decimal of the pH/pOH

Vanadium Wang 4H

What conditions outside of the chemical equilibrium reaction affect the equilibrium constant?

Vanadium Wang 4H

How do we know whether products or reactants are favored based on the equilibrium constant?

Vanadium Wang 4H

The two way arrow is used for chemical reactions that are in equilibrium. However, when an arrow is only pointing in one direction, that indicates that the equilibrium is favoring either product or reactant.

Vanadium Wang 4H

Flask 3 is at equilibrium because there is an equal ratio of X₂ molecules and X atoms

Vanadium Wang 4H

If you are given initial concentrations and all of them are nonzero, calculate the reaction quotient Q. If Q<K, the reaction moves toward the products, so the ICE table would have +x on the product's side and -x on the reactant's side. If Q>K, the reaction moves toward the reactants, so the ICE tabl...

Vanadium Wang 4H

I believe this question is actually 11.7. To calculate the value of K you use the equation (P_x)²/P_X₂. Multiply the mole fraction of the reactant and product respectively by the initial pressure of 0.1 bar to get the partial pressures. Solve and you should get 0.17

Vanadium Wang 4H

After naming the ligands, name the central metal. If the complex ion is an anion, the name of the transition metal ends with the suffix "-ate." If the complex ion is a cation, the metal is named same as the element.

Vanadium Wang 4H

A Bronsted acid donates protons and a Bronsted base accepts protons. A Lewis acid accepts an electron pair and a Lewis base donates electron pairs. Also, a conjugate acid accepts protons and conjugate base donates protons.

Vanadium Wang 4H

HBr is a stronger acid than HF because Br is a larger atom than F meaning the bond length between H and F is closer than H and Br. That means HBr is more likely to dissociate and a strong acid more readily dissociates in water.

Vanadium Wang 4H

s-character is the contribution of sigma type bonds in a hybridization. e.g sp = 50% s-character, 50% p-character; sp2 = 33% s-character, 66% p-character; sp3 = 25% s-character, 75% p-character. The more s-character a bond has, the shorter and stronger the bond is.

Vanadium Wang 4H

Relative orientations would refer to how the molecule is arranged. For instance, the sp³ orbitals are oriented toward the corners of a tetrahedron (109.5^o apart)

Vanadium Wang 4H

Pi bonds are usually weaker than sigma bonds. Quantum mechanics says this is because the orbital paths are parallel so there is much less overlap between the p-orbitals.

Vanadium Wang 4H

Like the similar problem 4.45, the question asks you to find the sigma and pi bonds for the entire molecule.

Vanadium Wang 4H

There is a 2014 post where Chem_Mod states "No, there is no difference. You can use either "angular" or "bent" to refer to the molecular shape of AX2E or AX2E2 molecules."

Vanadium Wang 4H

When drawing Lewis structures for ionic compounds, you draw the separate ions in their own brackets to denote the "donating" and "receiving" of electrons between the two.

Vanadium Wang 4H

Use the formula FC=V-(L+S) to determine the formal charge. The structure that has more atoms with a formal charge of 0 has lower energy. For part a) we can calculate the formal charge of the left molecule with the O to the left of Cl having a formal charge of 0 [6-(4+ \frac{1}{2} (2))], the Cl havi...

Vanadium Wang 4H

The solution manual identifies the element as phosphorus (P).

Vanadium Wang 4H

If you draw out the Lewis structure for ClO₂⁺, you will see that Cl is attached to one O by a double bond and the other by a single bond while Cl has a lone pair. The VSEPR formula for ClO₂⁺ is AX₂E₁ which has bond angles slightly <120^o

Vanadium Wang 4H

Using the Lewis structure, you can see how many electron pairs and lone electron pairs there are. From that you can write the VSEPR equation in the form AX_nE_n. From the VSEPR equation, you can refer to a chart for the molecular shape

Vanadium Wang 4H

taywebb wrote:I understand why H is an exception to the octet rule, but can someone explain why Hi, Le, and Be are as well?

Lithium and beryllium need to lose either one or two electrons, respectively, to attain an electron configuration of 1s^2 which is most stable.

Vanadium Wang 4H

Formal charge is the electric charge of an atom in a molecule assigned on the assumption that the bonding is nonpolar covalent. It is calculated by FC = number of valence electrons in the free atom - (number of lone-pair electrons + 1/2 * number of shared electrons). Stable charge refers to the form...

Vanadium Wang 4H

Degenerate means having the same energy. In the context of orbitals, degeneracy refers to all atomic orbitals in the same subshell

Vanadium Wang 4H

What are the possible sets of quantum numbers for a 3p orbital?

Vanadium Wang 4H

Degenerate means having the same energy. In the context of orbitals it is the number of atomic orbitals in the same subshell. Say the question is, how many degenerate 3p orbitals exist? (Remember: we need to see how many orbitals share the same n and l quantum numbers) If n = 3 and l = 1, ml could b...

Vanadium Wang 4H

Using the method given above ^ you should get 4.3 x 10^4 J/mol or 43 kJ/mol

Vanadium Wang 4H

I believe 28.9 is a typo, the correct number should be 28.3. In one ounce there are 28.3495 grams.

Vanadium Wang 4H

Yes, the diameter of the lead atom is given in the problem as 350 pm or 350 x 10^-12 m

Vanadium Wang 4H

The book defines photoelectric effect as "the emission of electrons from the surface of a metal when electromagnetic radiation strikes it."

Vanadium Wang 4H

On page 6 there is a paragraph that begins with, "As far as we know, ..." Within the paragraph there are a few examples of events corresponding to ultraviolet radiation and infrared radiation. However, like the other answers have suggested, the most important thing to know probably is what...

Vanadium Wang 4H

The electric field refers to the electromagnetic wave, more specifically its amplitude (height of wave). When frequency decreases, the wavelength (distance between peaks) broadens thus decreasing the change in the electrical field at any given point.

Vanadium Wang 4H

Unless it specifically asks you for the number of molecules, then you would need to take the moles and convert it to molecules by multiplying the number of moles with Avogadro's number. Otherwise, the problem just says find the number of moles so you're good where you're at

Vanadium Wang 4H

Once you've solved part a you'll end up with PCl5. To name the compound you start with the first element P (Phosphorus) and then you look at the second part of the compound Cl5 which translates to pentachoride (penta- denoting five and chloride is the naming structure for chlorine). Your answer woul...

Vanadium Wang 4H

Something else I've noticed is that compounds with more elements tend to have smaller values (1-3) so you could look to them to give you an idea on how to balance the equation

Vanadium Wang 4H

Yes, it is safe to round these ratio values into whole numbers. I believe that values can be off .1 and rounding would still produce a valid answer.

Vanadium Wang 4H

I believe you were looking at the second line when trying to copy the third line to balance. The textbook does say that the equation needed to be balanced is Fe3Br8 + Na2CO3 -> NaBr + CO2 + Fe3O4

Vanadium Wang 4H

I don't believe you need to find theoretical yield for limiting reactant problems. To find the limiting reactant, just take the information you're given and convert to moles (however needed). Once you have all the reactants in moles, compare to see which uses more moles quickly based on the given am...

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