CHEMISTRY COMMUNITY

Alma Flores 1D

A porous disk is a single line | as opposed to a salt bridge which is two lines ||. In a cell diagram, porous disks look the same as a phase change which is also indicated by a single line |.

Alma Flores 1D

H+ would be on whichever side of the redox reaction it is on. The redox reaction is the overall reaction found when you combine both half reactions.

Alma Flores 1D

Pt(s) is an inert conductor used as an electrode to transfer e- when a half reaction has no conducting solids.

Alma Flores 1D

I believe Dr. Lavelle expects us to determine the molecularity of an elementary step in order to determine the rate law.

Alma Flores 1D

The overall order of a reaction is determined by the sum of the exponents (the order of each reactant).

Alma Flores 1D

Can you be more specific? What was the question?

Alma Flores 1D

It is the reaction rate given the amount of moles provided. Question 15.11 is asking for the initial rate of decomposition of N2O5 given 3.45 g of N2O5.

Alma Flores 1D

The average rate is the average instantaneous reaction rate over a period of time during the reaction. The average rate of reaction can be calculated for any time interval. The instantaneous rate is the rate at a particular instant of time during the reaction represented by the instantaneous slope o...

Alma Flores 1D

Eº is the standard state cell potential. This means that it is under standard conditions (1 atm and 25°C).

Alma Flores 1D

Conceptually, a half reaction is either a reduction half reaction or a oxidation half reaction. A half reaction makes up one part of a redox reaction. The redox reaction is separated into two half reactions by identifying identify what is getting reduced and what is getting oxidized. Mathematically,...

Alma Flores 1D

Usually potassium chloride or sodium chloride are used because they are chemically inert.

Alma Flores 1D

The problem will usually specify if it is in an acidic or basic solution. From there you can decide whether to use H20 or OH-.

Alma Flores 1D

Gibbs free energy of reaction is the standard free energy of formation of products minus the standard free energy of formation of the reactants. It is modeled by the equation: ΔG(rxn)=∑ΔG(products)−∑ΔG(reactants). The standard free energies of formation can be used to calculate the free energy chang...

Alma Flores 1D

Enthalpy of fusion is the amount of heat energy required to change the state of a substance from a solid to a liquid, at its melting point. When a solid becomes a liquid, it's called melting or fusion.

Alma Flores 1D

The Van't Hoff Equation can be used to calculate K at a different temperature if the standard enthalpy is known.

Alma Flores 1D

Question 5: Sodium propionate (NaC3H5O2) is used as a food preservative. What is the pH of a 0.020 M solution of sodium propionate? The pKa of propionic acid (C3H6O2) is 4.88. C3H5O2-(aq) + H20(l) ⇌ C3H6O2(aq) + OH-(aq) I don't understand the steps that need to be done to answer this question. Can s...

Alma Flores 1D

Degeneracy(w) is the number of ways to achieve a given energy state. w = (#of microstates available)^n , n=# of particles present. This is the used in the equation deltaS = Kb ln w

Alma Flores 1D

All the different values for R should be on the constants and equations sheet provided.

Alma Flores 1D

Work is being done on the system by its surroundings when the system absorbs heat. This would be positive. When work is being done by the system on its surroundings then they system releases heat. This would be negative.

Alma Flores 1D

The reaction quotient, Q, is calculated when you need to determine which direction a non-equilibrium reaction will proceed.

Alma Flores 1D

They should be on the constants and equations sheet provided.

Alma Flores 1D

Adiabatic means that it is not permitting or accompanied by the passage of energy as heat.

Alma Flores 1D

If the reaction releases heat and the surroundings warm, then the reaction is exothermic and negative.
If the reaction requires heat and the surroundings cool, then the reaction is endothermic and positive.

Alma Flores 1D

Reversible processes are when you are able to convert all of the energy you put into a system into work. The second law of thermodynamics states that in a reversible process, the entropy of the universe is constant.

Alma Flores 1D

Yes, steam causes more severe burns because it has more energy, with a temperature of 40.7 kJ/mol, as opposed to liquid which has a temperature of 7.5 kJ/mol. This is demonstrated using the heating curve for water.

Alma Flores 1D

Enthalpy is the amount of heat released or absorbed at a constant pressure. Heat is the energy that causes those changes.

Alma Flores 1D

Combustion cannot be reversible. The products (carbon dioxide and water) cannot react to form the reactants (fuel and oxygen).

Alma Flores 1D

Salts are ionic compounds formed by a neutralization reaction between an acid an a base. They can either raise or lower the pH of a solution.

Alma Flores 1D

The concentration of a pure substance does not change in a reaction! Therefore solids and liquids are not included in K expression.

Alma Flores 1D

pKa is the negative base-10 log of Ka. Ka is the acid dissociation constant.The smaller the pKa, the stronger the acid. pKb is the negative base-10 log of Kb. Kb is the base dissociation constant. The smaller the pKb, the stronger the base. For this question we would just order then from increasing ...

Alma Flores 1D

To convert between partial pressure and concentration you would use the ideal gas law, PV=nRT.
To convert partial pressure to concentration, you would use the equation (n/V)=P/RT or conc.=P/RT
To convert concentration to partial pressure, you would use the equation P=(n/V)RT or P=(conc.)RT

Alma Flores 1D

Would it be the same as K=[products]/[reactants]?

Alma Flores 1D

Also, the reaction quotient, Q, is compared to the equilibrium constant, K, to determine which direction a reaction will proceed. Q, Qc, or Qp are calculated the same way as K.

Alma Flores 1D

For this question you are looking for molarity. You would start this problem by converting your grams of Li2CO3 to moles, then multiply that by 2mol Li2/1mol Li2CO3 to find the amount of Li2 in 1 mol of Li2CO3. After this, divide your amount of moles by 1.00L of water since molarity is mol/L.

Alma Flores 1D

There is always one sigma bond in any kind of bond, and additional bonds are pi bonds. A single bond is 1 sigma bond. A double bond is 1 sigma bond and 1 pi bond. A triple bond is 1 sigma bond and 2 pi bonds.

Alma Flores 1D

No we do not need to draw the VSEPR models, they are just used to visualize the 3D structure.

Alma Flores 1D

Dr. Lavelle replied to another student saying to write slightly less than 109.5 since students are not expected to know the exact (experimentally measured) bond angles for individual molecules.

Alma Flores 1D

Since you are taking into consideration the lone pairs, the molecule would not be trigonal bipyramidal.

Alma Flores 1D

The dashed and solid lines are used to show the 3D shape of the molecule. The solid lines are used as the backbone for the structure, here bonds exist on the plane of the paper. The solid wedges represent groups that are pointing out of the page, towards you, and dashed lines represent groups pointi...

Alma Flores 1D

The lewis structure for I3- has two iodines attached to the central iodine and three lone pairs on the central iodine. This gives you 5 regions of electron density around the central atom. This is a trigonal bipyramidal shape. The electron pairs repel each other to maximize their distance from one a...

Alma Flores 1D

Test 3 is on chapter 3 so just lewis structures. VSEPR is chapter 4.

Alma Flores 1D

We just need to know the general trends on the periodic table.

Alma Flores 1D

The ground state configuration for Te2- is [Xe] because it has gained 2 electrons. Xe has filled its orbitals meaning it has no unpaired electrons. The ground state configuration for Ag+ is [Kr]4d10 because it has lost one electron from the 4s orbital. Remember that the electron configuration for Ag...

Alma Flores 1D

Also, after drawing the Lewis structure and finding the total amount of valence electrons, if there is a radical you will notice that the central atom does not complete its octet. For 3.55 part B, CH3 has 7 valence electrons. Carbon will form 3 bonds with the hydrogens and will have one lone pair el...

Alma Flores 1D

At the end of lecture, the TA explaining this section started drawing the Lewis structure of NO with a double bond. I didn't hear what she said, but I believe a double bond would work. Also, this would not be resonance.

Alma Flores 1D

These elements are trying to lose electrons to obtain a noble gas configuration.

Alma Flores 1D

Paramagnetic means it has unpaired electrons. Diamagnetic means it has paired electrons.

Alma Flores 1D

The 4s orbital has higher energy then the 3d orbital. After the 4s is completely filled, 3d is lower in energy than 4s.

Alma Flores 1D

For your first question, electron configuration should be ordered primarily by increasing order of shells, the principle quantum number n. The ground state of scandium is [Ar] 3d¹ 4s² because 3 comes before 4. For your second question, [Ar] is present in the ground state because it is the last noble...

Alma Flores 1D

Yes, the pattern for mI will always be -I to +I. Count the values to get the number of orbitals.

Alma Flores 1D

The question is just asking for the orientation of the lobes, meaning what axis they are on. The Px orbital will have its lobes oriented along the x-axis, the Py orbitals will have its lobes oriented along the y-axis, and the Pz orbital will have its lobes oriented along the z-axis.

Alma Flores 1D

It would not be incorrect to use shorthand, but it is better to show the electron configurations because they provide more detail. For example, the shorthand for K+ is [Ar] but it is better to write it out as [Ne] 3s^2 3p^6.

Alma Flores 1D

The Lyman Series uses UV light which is stronger than visible light. It releases electrons to n=1, the lowest energy level.

Alma Flores 1D

The uncertainty (3.4x10^10 m/s) is greater than the speed of light (3.0x10^8 m/s). This makes it an unrealistic number.

Alma Flores 1D

There can be a maximum of two electrons in the same orbital. Their Spin Magnetic Quantum Number cannot be the same, since they have opposite spins. This is supported by the Pauli Exclusion Rule.

Alma Flores 1D

De Broglie's equation only applies to objects with mass. So, it does not apply to light because photons don't have a mass.

Alma Flores 1D

Dr. Lavelle said that de Broglie's Equation ( lambda=h/p) doesn't apply to light because it measures objects with mass and photons do not have mass.

Alma Flores 1D

I was also confused about 9.109x10^-31 being the mass of an electron. Did he briefly go over this during lecture because I don't remember this being mentioned.

Alma Flores 1D

In Friday's lecture, Dr. Lavelle mentioned that the energy of of the photon is equal to the sum of the threshold energy and the kinetic energy.

Alma Flores 1D

It depends on the information given in the problem. Equations can be rearranged or combined to form an equation that will fit the problem. For example, E=hv can be combined with c=lambda x v, to form the equation E=hc/lambda, when you are looking for the wavelength but are not given the frequency.

Alma Flores 1D

He did say 3.00x10^8 m/s is the speed in vacuum during Monday's lecture. By this I believe he means the speed of light in a vacuum, which is the constant 3.00x10^8 m/s., meaning the light is traveling through empty space where nothing else can travel through. If light is not traveling at c (constant...

Alma Flores 1D

Yes, you have to multiply by 2 to cancel out the fraction. The stoichiometric coefficients should be whole numbers, not fractions.

Alma Flores 1D

Yes, the ratio between atoms in a molecule is the empirical formula.

Alma Flores 1D

In this problem, we know that 12 moles of the product ClO2F is produced and 2 moles of the product Br2. Only 4 BrF3 were needed for the reaction, but it is carried out with 5 moles of BrF3. That is the excess reactant, so there is 1 mole of excess BrF3.

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