## Search found 50 matches

Sat Mar 17, 2018 10:06 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: I-/I3-
Replies: 3
Views: 274

### Re: I-/I3-

First, you would have to balance the reaction, leading to 3I- arrow I3-. Now, there is a -3 charge on the on the left side and -1 charge on the right side. Then, you would add 2 electrons to the right side so the charges on both side would be -3, leading to this being an oxidation reaction.
Sat Mar 17, 2018 10:01 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Collision Theory
Replies: 5
Views: 212

### Re: Collision Theory

I would say that the most important thing we would need to know is that the collisions of a reaction must occur with the reactant molecules being at the correct orientation. Knowing this leads to connecting collision theory to the Arrhenius equation, with A being the collision frequency, which is ho...
Sat Mar 17, 2018 9:56 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Pseudo Equilibrium Constant
Replies: 1
Views: 188

### Re: Pseudo Equilibrium Constant

The pseudo equilibrium constant is the equilibrium constant of the transition state of a reaction, found in the reaction mechanism, whereas, a normal equilibrium constant is the equilibrium constant of the overall reaction. It is found by looking at the transition state reaction of a mechanism and u...
Mon Mar 12, 2018 12:29 am
Forum: General Rate Laws
Topic: Rate law constant
Replies: 4
Views: 129

### Re: Rate law constant

The rate law constant can never be negative, but it can be a slope of negative k on the graphs of zero order and first order reactions.
Mon Mar 12, 2018 12:27 am
Forum: Zero Order Reactions
Topic: Half life
Replies: 7
Views: 516

### Re: Half life

Yes you can. You can use the half life formulas and also plug in your values for time and concentration into the zero order and second order equations as well.
Mon Mar 12, 2018 12:22 am
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Problem 15.61
Replies: 5
Views: 179

### Re: Problem 15.61

I believe this equation was derived from the equation on the constants and equations sheet: k=A exp(-Ea/RT), where ln(k'/k) was used because of the reaction being first order and T being extracted from (-Ea/RT) to become Ea/r(1/T - 1/T'). I'm not entirely sure about this, but I hope this helps.
Sun Mar 04, 2018 8:19 pm
Forum: General Rate Laws
Topic: Half Life
Replies: 6
Views: 193

### Re: Half Life

A half-life reaction indicates how long it takes for the concentration of a reactant to decrease to half of its initial concentration. We would be interested because it is involved in many things, such as radioactive decay, which pertain to chemistry.
Sun Mar 04, 2018 7:55 pm
Forum: Balancing Redox Reactions
Topic: Test 2, Q5
Replies: 4
Views: 135

### Re: Test 2, Q5

These rankings are not based off the placement of the elements in the periodic table. They are based on the standard reduction potentials of each, given in the table provided on the test. Elements with a stronger reducing power will have a lower reduction potential, therefore; organize them based on...
Sat Mar 03, 2018 2:54 pm
Forum: Second Order Reactions
Topic: 15.35
Replies: 1
Views: 83

### 15.35

The solutions manual states that the equation for the half-life of a 2nd order reaction must be obtained, being [A]t=[A]0/1+[A]0*kt. How was this equation obtained/derived?
Sun Feb 25, 2018 9:58 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 14.13 part d
Replies: 2
Views: 102

### Re: 14.13 part d

One of the half reactions is flipped because one half reaction is the anode and the other is the cathode. Au goes to Au3+ because the standard reduction potential of that is lower than that of the other reaction, and whichever has the lower reduction potential is the anode. Therefore, to make it an ...
Sun Feb 25, 2018 9:54 pm
Forum: Balancing Redox Reactions
Topic: Half Reaction Order
Replies: 9
Views: 238

### Re: Half Reaction Order

The order does matter because the placement of the electron in the half reaction determines whether it is oxidation or reduction. If writing an oxidation reaction, you would write Zn+ arrow Zn2+ + e-, which means that that electrons are being lost, since it is oxidation. If writing a reduction react...
Mon Feb 19, 2018 10:52 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 14.15
Replies: 1
Views: 98

### 14.15

When an equilibrium reaction, how can you tell which reaction is the anode reaction and which is the cathode reaction? How do you know when to reverse the anode reaction?
Sun Feb 18, 2018 8:23 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Galvanic vs. Voltaic
Replies: 5
Views: 124

### Re: Galvanic vs. Voltaic

The cell that uses the electron current to drive a non-spontaneous reaction is called an electrolytic cell. This is the cell in which electrical energy is converted into chemical energy, while in galvanic cells, chemical energy is converted into electrical energy (spontaneous).
Sun Feb 18, 2018 8:21 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Galvanic vs. Voltaic
Replies: 5
Views: 124

### Re: Galvanic vs. Voltaic

Galvanic cell and voltaic cells are the same thing, just different names of the same electrochemical cell.
Sun Feb 18, 2018 8:18 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Work when pressure is constant
Replies: 6
Views: 369

### Re: Work when pressure is constant

Work can also be w=-nRT because PV=nRT, leading to P(delta V)=(delta n)RT, and you can substitute (delta n)RT into w=-P(delta V).
Sun Feb 11, 2018 10:12 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Work not a state function [ENDORSED]
Replies: 2
Views: 129

### Re: Work not a state function[ENDORSED]

Work done by a system is not a state function because it is dependent on the pathway that a reaction takes (path used to go from initial to final state); whereas for state functions, the values can be determined by the initial and final values for the reaction. Work is dependent on the pressure and ...
Sun Feb 11, 2018 10:07 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Entropy
Replies: 1
Views: 78

### Re: Entropy

Kb is not the same as the R constant in the entropy equation. Both are given on the Constants and Equations Sheet provided by Dr. Lavelle. Kb is 1.38 x 10^-23 J*K^-1, while R is 8.314 J*K^1*mol^-1.
Sun Feb 11, 2018 9:57 pm
Forum: Third Law of Thermodynamics (For a Unique Ground State (W=1): S -> 0 as T -> 0) and Calculations Using Boltzmann Equation for Entropy
Topic: change in entropy total
Replies: 2
Views: 160

### Re: change in entropy total

The total change of entropy is not always 0 because there is always disorder in a system. The only time that entropy is 0 is when the temperature in kelvin is going to 0 K.
Sun Feb 04, 2018 8:14 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: deltaS question
Replies: 7
Views: 231

### Re: deltaS question

The Cp (5/2R) and Cv (3/2R) are the specific heat capacities for ideal gases only. When an ideal gas is not involved in a problem, you would use the value of R.
Sun Feb 04, 2018 8:09 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: sign of q
Replies: 7
Views: 204

### Re: sign of q

When qrev is negative, it means that the system is losing heat, so the surroundings will gain heat and vice versa if qrev is positive. You can think of it in the context of exothermic and endothermic: if a system is endothermic (taking in heat), then qrev will be positive and if a system is exotherm...
Mon Jan 29, 2018 3:02 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Homework 9.5 [ENDORSED]
Replies: 11
Views: 399

### Homework 9.5[ENDORSED]

For question 9.5, why are we supposed to use the equation delta S=-q/T for the entropy at 800 K and the equation delta S=q/T for the entropy at 200 K? Why is there a negative in one equation and no negative in another?
Sun Jan 28, 2018 12:26 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: CV or CP
Replies: 5
Views: 175

### Re: CV or CP

Cp is when a reaction is occurring at constant pressure and Cv is when a reaction is occurring at constant volume. The molar heat capacities of an ideal gas can be found on the Constants and Equations sheet where Cp= 5/2R and Cv=3/2R.
Sun Jan 28, 2018 12:21 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Chapter 9, Question 7
Replies: 2
Views: 125

### Re: Chapter 9, Question 7

Both molar heat capacities (Cp= 5/2R and Cv=3/2R) are given constants that can be found on the Constants and Equations sheet that is found on Dr. Lavelle's website and given to us during tests. Also, the R in both constants is the gas constant 8.314 JK^-1mol^-1. For an ideal gas at constant pressure...
Sun Jan 28, 2018 12:09 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Homework Problem 9.13
Replies: 1
Views: 66

### Re: Homework Problem 9.13

For a problem like this one, you would take each change individually and add the two together in order to get the net change in entropy. You would be using the equations: delta S=nRln(V2/V1), which is for the change in volume, and delta S=nRln(T1/T2), for the change in temperature. Then, you would a...
Sun Jan 21, 2018 9:32 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.31
Replies: 3
Views: 159

### Re: 8.31

For this question, you would use the equation q=mol*c*delta T. You would convert the mass of Krypton in order to find the moles of Krypton. You already have the change in temperature, so the only thing we would need to find is the specific heat capacity of krypton, being an ideal gas, at constant pr...
Wed Jan 17, 2018 10:58 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: 8.31
Replies: 3
Views: 121

### Re: 8.31

Both molar heat capacities (Cp= 5/2R and Cv=3/2R) are given constants that can be found on the Constants and Equations sheet that is found on Dr. Lavelle's website and given to us during tests. Also, the R in both constants is the gas constant 8.314 JK^-1mol^-1. Hope this helps :)
Wed Jan 17, 2018 4:16 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: 8.31
Replies: 3
Views: 121

### 8.31

How do you find the molar heat capacity of Kr at constant pressure and constant volume? I understand that the molar heat capacity at constant pressure is 5/2R and at constant volume is 3/2R, but how do you use those values in the calculations?
Sun Jan 14, 2018 9:48 pm
Forum: Phase Changes & Related Calculations
Topic: enthalpy definition
Replies: 3
Views: 160

### Re: enthalpy definition

Enthalpy is the heat that is released or absorbed in chemical reactions and physical changes, at constant pressure
Sun Jan 14, 2018 9:42 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Reversible process
Replies: 2
Views: 176

### Re: Reversible process

A reversible process does the most work because all of the heat is converted into work, instead of the energy being lost as heat.
Sun Jan 14, 2018 9:37 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: State Property
Replies: 3
Views: 162

### State Property

Can someone explain what exactly a state property is? How do you know the difference of something being a state property versus something not being a state property?
Sat Dec 09, 2017 9:47 pm
Forum: Conjugate Acids & Bases
Topic: Protanation
Replies: 2
Views: 261

### Re: Protanation

Acids go through deprotonation, in which the acid dissociates into an H3O+ ion and another ion, being the removal/transfer of the H+ proton from the acid. Bases go through protonation, in which an H+ proton gets added/transferred to the base.
Sat Dec 09, 2017 9:41 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Equilibrium partial pressures
Replies: 2
Views: 301

### Re: Equilibrium partial pressures

Since the question is asking for the equilibrium partial pressures, it would not be necessary to calculate the number of moles using PV=nRT. You would just have to use the pressure of HCl that is already given, do the ICE table, and use K, which would compute the partial pressures.
Sat Dec 09, 2017 9:36 pm
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: Strength of an acid
Replies: 14
Views: 491

### Re: Strength of an acid

Electronegativity affects the relative strength of an acid because the more electronegative an atom is, the more likely it wants to "hold on" to the hydrogen atom attached to it, therefore making it harder for the acid to deprotonate and for the H+ ion to detach from it. For example, compa...
Sat Dec 09, 2017 9:31 pm
Forum: Lewis Acids & Bases
Topic: 12.51 comparing strengths of acids
Replies: 1
Views: 152

### Re: 12.51 comparing strengths of acids

HClO2 is a stronger acid than HBrO2 because since Cl has a higher electronegativity, the resulting ClO2- is more stable than the resulting BrO2-. Since there are oxygens bonded to each of the central atoms in the instances of HBrO2 and HCl2, we need to take in account the formal charges present thro...
Sun Dec 03, 2017 10:58 pm
Forum: Amphoteric Compounds
Topic: Amphiprotic [ENDORSED]
Replies: 5
Views: 439

### Re: Amphiprotic[ENDORSED]

There are other molecules that are amphiprotic besides water, which include the hydrogen carbonate ion, hydrogen sulfate ion, and the dihydrogen phosphate ion.
Sun Dec 03, 2017 10:55 pm
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: Weak Acids / Strong Acids
Replies: 5
Views: 239

### Re: Weak Acids / Strong Acids

You determine whether a certain acid or base is considered weak or strong by looking looking at its dissociation properties. If the acid deprotonates (dissociate) completely in water, it is a strong acid and if it deprotonates incompletely, it is a weak acid. For a strong acid, the Ka is much higher...
Sun Nov 19, 2017 5:58 pm
Forum: Naming
Topic: Naming
Replies: 2
Views: 162

### Re: Naming

When pairing a ligand with a transition metal cation, you write the ligand based on which atom in the ligand is exactly donating electrons to the cation (whichever atom is electron rich). Therefore, you either write it forwards or backwards to emphasize which atom is donating electrons. You can thin...
Sun Nov 19, 2017 5:41 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: HW Question 4.27
Replies: 4
Views: 159

### Re: HW Question 4.27

The nitrogen atom is more electronegative than than the CH groups present in the rest of the molecule; thus, pulling the electrons shared between the nitrogen and the carbons it is bonded to, towards the nitrogen, having a different electronegativity difference than the difference between the carbon...
Sun Nov 12, 2017 11:33 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: lewis structure and vsepr
Replies: 3
Views: 167

### Re: lewis structure and vsepr

Using the notation with (A= central atom, X= bonded atom, E= lone pair) is an alternative to drawing the lowest energy Lewis Structure because typically, molecules with the same AXE formula have the same general shape, so it may be helpful to understand which VSEPR shape coordinates to which AXE for...
Sun Nov 12, 2017 11:27 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Lone Pair Placement
Replies: 3
Views: 180

### Lone Pair Placement

How do you determine where exactly to put the lone pairs on a molecule that has an electron density greater than 4? For instance, on a seesaw, T-shaped, square pyramidal, or square planar molecule?
Sun Nov 05, 2017 8:36 pm
Forum: Ionic & Covalent Bonds
Topic: Ionic Bonds Having Covalent Character
Replies: 2
Views: 158

### Ionic Bonds Having Covalent Character

Can someone clarify why ionic bonds display covalent character and how high polarization relates to this?
Sun Nov 05, 2017 8:07 pm
Forum: Ionic & Covalent Bonds
Topic: 3.25
Replies: 6
Views: 348

### Re: 3.25

To find the chemical formula of the compounds, just take the value of the charge of one atom and make it the subscript of the other atom in the compound. For example, when writing the chemical formula for magnesium arsenide, the charge for Mg (magnesium) is +2, so 2 would be the subscript for As (ar...
Sun Oct 29, 2017 9:47 pm
Forum: Formal Charge and Oxidation Numbers
Topic: when to calculate formal charge [ENDORSED]
Replies: 3
Views: 244

### Re: when to calculate formal charge[ENDORSED]

We should calculate formal charge when there's several resonance structures for a molecule and we need to find which resonance structure is the most stable, being the optimal resonance structure. We should calculate formal charges and compare structures, again, in order to find the most stable lewis...
Sun Oct 29, 2017 9:34 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Atomic and Molecular Orbitals [ENDORSED]
Replies: 1
Views: 140

### Re: Atomic and Molecular Orbitals[ENDORSED]

Yes, atomic orbitals always form molecular orbitals when they overlap in bonding.
Sun Oct 22, 2017 4:10 pm
Forum: Trends in The Periodic Table
Topic: Atomic Size Trend [ENDORSED]
Replies: 4
Views: 214

### Re: Atomic Size Trend[ENDORSED]

Also, as you move right across a period, the increased nuclear charge of the atoms increases pulls the electrons closer to the nucleus, leading to a decreasing size across the period table. Since the number of protons increases across the period, it leads to an increased positive charge of the nucle...
Sun Oct 22, 2017 4:01 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: 3d Orbital [ENDORSED]
Replies: 2
Views: 129

### 3d Orbital[ENDORSED]

I understand that the 4s orbital is filled up before the 3d orbital, but why is the 4s orbital filled up before the 3d orbital?
Sun Oct 15, 2017 12:38 pm
Forum: Properties of Light
Topic: How to use the Rydberg Formula? [ENDORSED]
Replies: 6
Views: 355

### Re: How to use the Rydberg Formula?[ENDORSED]

You can also use the equation: En=-hR/n^2 to find the energy of a energy level and do that for the final and initial energy levels and subtract the initial energy from the final energy to find the energy difference between two energy levels. It is always final energy level - initial energy level.
Sun Oct 15, 2017 12:19 pm
Forum: Properties of Light
Topic: 1.3
Replies: 5
Views: 240

### Re: 1.3

From what I was told, since the frequency of electromagnetic radiation decreases, the wavelength of the radiation would increase because of the inverse relationship between wavelength and frequency. An increased (longer) wavelength of the radiation would cause a decreased amplitude, so the slope of ...
Fri Oct 06, 2017 1:02 am
Forum: Molarity, Solutions, Dilutions
Topic: G13
Replies: 2
Views: 203

### Re: G13

I started the problem by finding the concentration of the diluted solution, NH4NO3(aq), by first adding 3.0 L to 1.0 L (since 3.0 L of water is added to the original 1.0 L solution). Then, I divided 0.20 mol by 4.0 L. Hope this helps!
Fri Oct 06, 2017 12:52 am
Forum: Limiting Reactant Calculations
Topic: Determining Limiting Reactant
Replies: 6
Views: 481

### Re: Determining Limiting Reactant

When determining the molar mass of a reactant, you don't have to include the coefficient that was found when balancing the equation. You use the stoichiometric coefficient when using dimensional analysis to figure out how many moles of a certain reactant is equivalent to the moles of another reactan...