CHEMISTRY COMMUNITY

Jacey Yang 1F

If Q>K, then the products are greater and the reverse reaction is favored. If Q<K, then reactants are greater and the forward reaction is favored.

Jacey Yang 1F

The units for k in a zero order reaction is M/s.

Jacey Yang 1F

To find K, Ecell would equal 0 since the reaction is at equilibrium, so you would use the equation E naught = RT/nF lnK.

Jacey Yang 1F

You need to have Pt(s) for the cathode because there is no solid metal on that side.

Jacey Yang 1F

For 1d, the size of the anode has no effect on the cell potential. For 1e, more Ag+ is reduced to solid Ag on the cathode side, so the overall cell potential increases.

Jacey Yang 1F

Since the reaction is first-order, the rate increases in direct proportion to the concentrations of both reactants, so doubling the concentration of reactants will double the reaction rate.

Jacey Yang 1F

Integrated rate law provides an equation of the initial concentration and the measured concentration of one or more reactants after a given amount of time. Differential rate law provides an expression of the rate of concentration change over a specific time period.

Jacey Yang 1F

The reaction will favor the reactants if the anode has a larger value than the cathode, because the overall cell potential will be negative, so delta G will be positive.

Jacey Yang 1F

The cathode has the more positive cell potential, the anode has the more negative cell potential.

Jacey Yang 1F

E°is the cell potential under standard conditions, while E is under non-standard conditions.

Jacey Yang 1F

You use K when the concentrations of products and reactants are at equilibrium. Electron flow stops at equilibrium because the voltage drops down to 0.

Jacey Yang 1F

The E value for concentration cells will always be 0 because the standard cell potential for the cathode and the anode will cancel each other out.

Jacey Yang 1F

n is the moles of electrons transferred in the reaction, which is determined from writing the oxidation and reduction half-reactions.

Jacey Yang 1F

Electron flow can go in any direction.

Jacey Yang 1F

Max cell potential is related to gibbs free energy through the equation deltaG = -nFE

Jacey Yang 1F

The Van't hoff equation relates the change in the equilibrium constant K of a chemical reaction to the change in temperature. It is derived from combining the equations deltaG = deltaH - TdeltaS and delta G = -RTlnK.

Jacey Yang 1F

A comma used when the ions are in the same phase, and a line is used when they are not.

Jacey Yang 1F

Why is gibbs free energy equal to maximum work?

Jacey Yang 1F

When the halogen is split, heat is required to break the bond, so it is an endothermic reaction.

Jacey Yang 1F

Gibbs free energy also represents the maximum work from the energy that is released.

Jacey Yang 1F

We use the equation to relate the change in the equilibrium constant K in a chemical reaction to the change in temperature, given a standard enthalpy change.

Jacey Yang 1F

The equation is derived from the two equations deltaG = deltaH - TdeltaS and deltaG = -RTlnK set equal to each other. The equation is used to find out how the change in K of a chemical reaction relates to the change in temperature, given a standard enthalpy change.

Jacey Yang 1F

When the problem asks for G at any stage of the reaction, we use G = G* + RTlnQ. However, at equilibrium G = 0 and Q = K, so then we would use G* = -RTlnK.

Jacey Yang 1F

Entropy is a state function, so the change in entropy of the system is the same regardless of whether the path is reversible or irreversible.

Jacey Yang 1F

The value is given in Table 4C.1 in the textbook.

Jacey Yang 1F

An extensive property depends on the amount of substance, such as heat capacity. An intensive property doesn't depend on the amount of substance, such as specific heat or molar heat capacity.

Jacey Yang 1F

Based on the units given in the problem, it will determine which value of R to use.

Jacey Yang 1F

C-H bonds cancel out on both sides of the reactions in parts a and b, so you don't consider them when calculating the rxn enthalpy.

Jacey Yang 1F

298K is the most common temperature used in data for reaction enthalpies, so we just have to assume that when no temperature is stated.

Jacey Yang 1F

It requires much more energy to completely break the hydrogen bonding in water molecules to convert to the gas phase.

Jacey Yang 1F

The heat supplied will raise the temperature of copper and the temperature of water, so both values of q must be added together.

Jacey Yang 1F

This is more of a conceptual question that is based on the equation for internal energy, delta U = q + w. Given that this is an adiabatic process, this would mean that q, energy transferred as heat, equals 0. Delta U would also equal 0, but only under the conditions that no work is done.

Jacey Yang 1F

Use Table 4C.1 to find the enthalpy of fusion of water. Convert 80.0 grams of ice to moles and multiply by the enthalpy of fusion to get the heat needed to melt the ice. Then, use 80.0 g in the equation q= mCΔT to find the heat needed to raise the temperature from 0 to 25 degrees C.

Jacey Yang 1F

What is the difference between a reversible and irreversible process? How does it relate to the work of expansion?

Jacey Yang 1F

Table 4D.2 in the textbook gives the standard enthalpies of formation for each compound. O2 and N2 are in their most stable form so their enthalpy of formation is 0. The rxn releases 1/4 amount of energy per mole of TNT consumed.

Jacey Yang 1F

Enthalpy only depends on the initial and final values of heat in a reaction, not the path it takes to get to the current state.

Jacey Yang 1F

The standard rxn enthalpy can be calculated by using the standard enthalpy of formation of all products and subtracting it by the standard enthalpy of formation of all reactants.

Jacey Yang 1F

Heat depends on the path taken to obtain the current state. Enthalpy is a state function because it only depends on the initial and final values of heat, so it doesn't depend on the path taken.

Jacey Yang 1F

Increasing the partial pressure of one element causes an increase in partial pressure on the other side of the reaction in order to minimize the effect of the change. This also applies when increasing the overall pressure, where the equilibrium shifts in the direction that decreases the number of mo...

Jacey Yang 1F

It depends on the units for pressure and volume given in the problem.

Jacey Yang 1F

Yes, you would use the equation to convert between concentration and partial pressure, depending on what the problem asks for.

Jacey Yang 1F

According to Le Chatelier's principle, when the amount of reactant or product is changed in a reaction, the equilibrium will shift to minimize the effect

Jacey Yang 1F

Solids and liquids do not affect equilibrium or the equilibrium constant because they are pure substances that don't change in a reaction.

Jacey Yang 1F

(c) Use your results from parts (a) and (b) to determine which is thermodynamically more stable relative to its atoms at 1000. K, Cl2 or F2.

Why is Cl2 more stable than F2?

Jacey Yang 1F

Yes, the partial pressures should always be in bar.

Jacey Yang 1F

The total pressure is the sum of the partial pressures of each gas in a mixture.

Jacey Yang 1F

You would convert the partial pressures to concentration using the ideal gas law equation.

Jacey Yang 1F

Increasing pressure results from decreasing volume, so there are more moles of gas in the reactants and the reaction shifts to the right.

Jacey Yang 1F

For reactions that have homogeneous equilibrium for a gas, we can use the ideal gas law to convert between partial pressure and concentration.

Jacey Yang 1F

Equilibrium rxns are affected by the amount of products and reactants. The equilibrium constant represents the P/R ratio at equilibrium, which is not affected by the higher pressure of reactant since the temperature is constant.

Jacey Yang 1F

A molecule is polar when the central atom has lone pairs and the atoms attached aren’t the same, so the dipoles don’t cancel.

Jacey Yang 1F

We won’t need to know Arrhenius acids and bases for the final, just know the Lewis/Bronsted definitions.

Jacey Yang 1F

For mini marshmallow 2c, why is the coordination number for K[Cu(en)2(CN)2] 6?

Jacey Yang 1F

Nikki Razal 4E wrote:for question 40c, how do you know whether o2 or o3 has the stronger bond and why?

o2 has double bonds that are shorter and therefore stronger than the o3 bonds, which is between a single and double bond due to resonance.

Jacey Yang 1F

Why do the nitrogens in thymine show amphiprotic behavior? I understand that it accepts protons due to the lone pairs, but how can it donate protons?

Jacey Yang 1F

Cl is more electronegative than Br, so it can withdraw electrons from the O-H bond and it becomes easier to remove H+.

Jacey Yang 1F

There would be no suffix, so the metal name would just be iron. The suffix -ate is added when the compound has a negative charge.

Jacey Yang 1F

Drawing out the lewis structure would help in determining which atoms on the ligand have lone pairs and can bind to the transition metal.

Jacey Yang 1F

When writing the formula from a coordination compound, does the order of the ligands matter?

Jacey Yang 1F

Why can CO3 2- be monodentate or bidentate? And why is oxalate bidentate? I'm confused because all the oxygens have lone pairs, so how do you determine which places on the ligand bind to a single metal center?

Jacey Yang 1F

You won't know which complex it is, since you don't know if the central transition metal atom has lone pairs or not.

Jacey Yang 1F

The number of hybrid orbitals is equal to the number of bonds and lone pairs around the central atom.

Jacey Yang 1F

Why are sigma bonds stronger than pi bonds?

Jacey Yang 1F

Can someone please explain the hybridization concept and why it occurs?

Jacey Yang 1F

Lone pairs on the central atom count toward the number of hybrid orbitals in a molecule, which then determines the hybridization.

Jacey Yang 1F

The electron pair geometry is based on the number of regions of electron density around the atom (parent shape), while molecular geometry is the actual shape that includes bonding pairs and lone pairs.

Jacey Yang 1F

What is the difference between molecular shape and electron geometry?

Jacey Yang 1F

The single unpaired electron on the central atom is treated as a region of high electron density, so it acts like a lone pair when determining the molecular shape.

Jacey Yang 1F

The square planar shape minimizes repulsion, so it has the lowest energy. The lone pairs on either side are farthest from each other and farthest from the atoms bonded to the central atom.

Jacey Yang 1F

The lone pair on Cl exerts strong repulsion on the O atoms, causing them to move closer together, which slightly decreases the bond angle.

Jacey Yang 1F

The lone pair on the central atom has a stronger repelling effect, pushing the bonding pairs closer together to create a bent shape.

Jacey Yang 1F

All molecules have van der Waals forces because their electrons are constantly moving around and creating temporary dipoles.

Jacey Yang 1F

Hydrogen bonds are always stronger because they have dipole-dipole interactions between a hydrogen atom and an electronegative atom, whereas london forces only have temporary dipoles that form weak attractions.

Jacey Yang 1F

The Xenon in the expanded lewis structures has a formal charge of 0 when you follow the equation FC = V - (L + S/2). It can't have a negative charge because it is a noble gas and its outer shell is full, so it can't attract more electrons.

Jacey Yang 1F

Particles with wavelengths less than 10^-15 m have mass that is too large for there to be detectable wavelike properties.

Jacey Yang 1F

Each value of l is a subshell, and within each subshell are orbitals. The magnetic quantum number ml labels individual orbitals.
For example, when l=2, ml= -2,-1,0,1,2 meaning there are 5 d-orbitals.

Jacey Yang 1F

Can someone please explain the concept of effective nuclear charge and how it relates to periodic trends?

Jacey Yang 1F

3p^3 is fine, I don't think we'll need to specify px, py, pz.

Jacey Yang 1F

Radicals are compounds with unpaired electrons. They have an odd number of valence electrons, so one of their atoms cannot form an octet.

Jacey Yang 1F

What is the relationship between bond strength and electronegativity?

Jacey Yang 1F

The midterm will cover bond lengths and energies, up to the end of Focus 2D in the textbook.

Jacey Yang 1F

You would count the valence electrons on the outermost shell, which in this case are the s and p orbitals. The d orbital has a lower energy level.

Jacey Yang 1F

The ground-state electron configuration is the arrangement of electrons with the lowest energy state possible.

Jacey Yang 1F

Ga loses 3 electrons to form Ga^3+, meaning it loses its valence 4s and 4p electrons on the outermost shell.

Jacey Yang 1F

The dipole moment refers to the difference between partial charges across a molecule. The atom with higher electronegativity in a covalent bond pulls electrons away from the other atom, creating a partial negative charge, and the other atom is surrounded by a partial positive charge.

Jacey Yang 1F

Do you mean part C? When n=2, it can have values of 0 and 1 for l, which translate to one s-orbital and three p-orbitals respectively.

Jacey Yang 1F

As Dr. Lavelle explained in lecture, the 4s state is higher in energy than 3d once the 4s state becomes occupied and the electron enters the 3d state.

Jacey Yang 1F

The problem will usually ask directly for the minimum uncertainty in the speed or position of an object.

Jacey Yang 1F

h/mv is used to find the wavelength of one moving particle with momentum p, in this case an electron. hc/E calculates the wavelength of the light needed to eject an electron.

Jacey Yang 1F

DeBroglie equation is used to calculate the wavelength of any moving particle with linear momentum p. All matter has wavelike properties, but it is only noticed for objects of extremely small mass such as electrons.

Jacey Yang 1F

A lamp rated at 32 W (1W = 1 J.s-1) emits violet light of wavelength 420 nm. How many photons of violet light can the lamp generate in 2.0 s? How many moles of photons are emitted in that time interval?

I'm not sure how to go about solving this problem. Can someone please explain?

Jacey Yang 1F

Increasing the wavelength of a light source will lower the frequency, which decreases the energy of each photon. If it goes below the threshold frequency, the light cannot eject electrons.

Jacey Yang 1F

We would use the equation λ = hc/E, which is derived from taking λv = c and rearranging it in terms of v, then plugging it into the Einstein equation E = hv.

Jacey Yang 1F

Yes, electrons and protons must be conserved because they contribute to the atomic mass. According to the law of conservation of mass, the mass of the left side of the equation must equal the mass on the right.

Jacey Yang 1F

I think you will be docked off a little since it is off in the 0.1 decimal place, which is far off and probably a result of rounding too early on in the problem. We need to be as precise as possible when solving chemistry problems, so only round to the correct number of sig figs when you reach the f...

Jacey Yang 1F

After you find the empirical formula of OsC4O4 in part a, find the molar mass of the empirical formula unit to get 302.27 g/mol. Divide the given molar mass of 907 g/mol by 302.27 g/mol to get a value of 3. Then multiply the coefficients in the empirical formula by the factor 3 to get the molecular ...

Jacey Yang 1F

I would suggest rounding to the correct amount of sig figs for the final answer and trying to keep the precise values on your calculator as you work through the problem, that way there is more accuracy.

Jacey Yang 1F

Ionic bonds are stronger than covalent bonds, but when dissolved in water, they become much weaker because ions separate and are surrounded by water molecules.

Jacey Yang 1F

I don't think naming compounds is something we will be tested on or actually have to know. However, you should be expected to remember the formulas of common compounds such as hydrochloric acid and calcium carbonate. In this case, PCL5 is a molecular compound, so the rule for this is replacing the e...

Jacey Yang 1F

For a, you would convert the given number of moles, 0.750 mol KNO3, into the number of molecules.
0.750 mol * 6.022*10^23 = 4.52*10^23 formula units.

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