## Search found 62 matches

Mon Mar 16, 2020 7:33 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Exothermic rxns and heat
Replies: 6
Views: 147

### Re: Exothermic rxns and heat

q is negative, indicating that it's released in an exothermic reaction. It's the opposite in an endothermic reaction.
Mon Mar 16, 2020 7:32 pm
Forum: Phase Changes & Related Calculations
Topic: state functions
Replies: 13
Views: 267

### Re: state functions

State functions are an intrinsic value that do not depend on the path taken to obtain, only on the current state.
State functions: gibb's(G), enthalpy (H), entropy (S), heat capacity, pressure, volume, density
Not state functions: work (w), heat (q)
Mon Mar 16, 2020 7:20 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: pH of acids
Replies: 13
Views: 419

### Re: pH of acids

Weak acids are only partially ionized, in comparison to the strong acid that is completely ionized. With a lower concentration of [H+] in the solution, the weak acid would have a higher pH. Conversely, the strong acid would have a higher concentration of [H+] in the solution, resulting in a lower pH.
Mon Mar 16, 2020 7:18 pm
Forum: General Rate Laws
Topic: rate laws
Replies: 8
Views: 180

### Re: rate laws

Yes, for most circumstances. However, in a pre-equilibrium approach question, the rate would depend on the equilibrium step that occurs before the slow step and the slow step itself.
Mon Mar 16, 2020 7:16 pm
Forum: *Free Energy of Activation vs Activation Energy
Topic: Temperature vs. activation energy
Replies: 5
Views: 445

### Re: Temperature vs. activation energy

As the temperature increases, the amount of energy in the system increases. This energy is then used to overcome the activation energy
Mon Mar 16, 2020 7:12 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Kelvin or Celsius?
Replies: 57
Views: 1308

### Re: Kelvin or Celsius?

It's always in Kelvin because the R constant uses units of Kelvin
Thu Mar 12, 2020 6:13 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Activation Energy and the Rate Constant
Replies: 4
Views: 74

### Re: Activation Energy and the Rate Constant

When the activation energy increases, the rate constant decreases, indicating that there is a larger energy barrier for the reaction to proceed. When the activation energy decreases, the rate constant increases, indicating a smaller energy barrier for the reaction to get past.
Thu Mar 12, 2020 5:59 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Pre-Equilibrium Method
Replies: 4
Views: 114

### Re: Pre-Equilibrium Method

The pre-equilibrium method can be used to determine the K value of the overall reaction when given the k-values of the elementary steps. This assumes that the fast step is followed by a slow step that creates a bottleneck effect. Therefore, the overall rate is dependent on the slow step. You use thi...
Thu Mar 12, 2020 5:30 pm
Forum: Ideal Gases
Topic: reversing reactions
Replies: 80
Views: 387

### Re: reversing reactions

The K of the reverse reaction will be the inverse of the K of the forward reaction
Kreverse = 1/Kforward

A + B -> C
Kforward = [C]/[A][B]
Kreverse = [A][B]/[C]
Thu Mar 12, 2020 5:26 pm
Forum: Ideal Gases
Topic: R Constant
Replies: 26
Views: 390

### Re: R Constant

When looking at the units, it's good to note which ones will cancel out, and to keep in mind the units that your answer is supposed to be in. For the ideal gas law, you will typically be using any value with a unit of pressure (atm, bar, Torr). When calculating anything related to energy, the values...
Thu Mar 12, 2020 5:14 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: U vs H
Replies: 15
Views: 364

### Re: U vs H

Moreover, we can find that deltaU = qv, which makes sense because the volume is constant (no expansion work is being done), so the change in internal energy must solely be a result of the increase of energy inputted into the system qv at a constant volume. On the other hand, deltaH = qp, which can ...
Thu Mar 12, 2020 5:01 pm
Forum: Calculating Work of Expansion
Topic: Choosing work equation
Replies: 10
Views: 299

### Re: Choosing work equation

For an irreversible expansion, use w=-P(deltaX). For a reversible expansion (isothermal), use w=-nRT(ln deltaV2/deltaV1). Would the reversibility/irreversibility of a system be given explicitly in a problem, or would that be something that we have to figure out for ourselves? If so, how would we de...
Thu Mar 12, 2020 4:56 pm
Forum: Calculating Work of Expansion
Topic: isobaric compression
Replies: 7
Views: 191

### Re: isobaric compression

It helps me to use the equations to remember how these operate. Using PV=nRT, when you decrease the volume through the compression, some value on the right side of the equation should also decrease. Since we're keeping the number of moles consistent and R never changes, it's safe to assume that the ...
Thu Mar 12, 2020 4:51 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Cell Diagram
Replies: 16
Views: 280

### Re: Cell Diagram

I encountered a question once where the cathode was on the left and the anode was on the right, opposite of the convention of typical cell diagrams. So while it's generally a safe assumption that the cathode is on the right and the anode is on the left, I would still verify this by checking where th...
Thu Mar 12, 2020 4:48 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Reduced/Oxidized based on Ecell
Replies: 6
Views: 160

### Re: Reduced/Oxidized based on Ecell

Since the Ecell values are given under standard conditions, you would also have to take into account other factors such as the concentrations of the cathode and anode, as well as the temperature. The anode (oxidation reaction) will occur at the lower concentration of substrates, while the cathode (r...
Thu Mar 12, 2020 4:44 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: finding moles
Replies: 6
Views: 170

### Re: finding moles

N is the number of moles of electrons (per mole of reaction) transferred from the cathode to the anode. You'll find this value in the balanced half-reactions and not necessarily the overall chemical reaction.
Thu Mar 12, 2020 4:42 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: n in NFE
Replies: 19
Views: 280

### Re: n in NFE

Since it's n is the number of moles of electrons in the reaction after both half-reactions are balanced, it's good to note that it doesn't matter which half-reaction you take this value from. This value should be the same in both half-reactions.
Thu Mar 12, 2020 4:38 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: dilutions and Ecell
Replies: 8
Views: 170

### Re: dilutions and Ecell

Does this apply to both galvanic and concentration cells? Do the differences between these two types of cells affect the way a dilution affects the Ecell?
Thu Mar 12, 2020 4:31 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Enaught in Concentration Cells
Replies: 4
Views: 122

### Re: Enaught in Concentration Cells

No, remember that to find the change in gibbs free energy, you need the cell potential. You calculate the cell potential through the equation E = E˚ - (RT/nF) lnQ. This equation incorporates your standard cell potential value but it is not the only value that determines the cell potential. Then you...
Thu Mar 12, 2020 4:24 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Downs Process
Replies: 4
Views: 124

### Re: Downs Process

Would it be beneficial to know this process? Because I'm also curious now
Thu Mar 12, 2020 4:22 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Applying La Chateliers
Replies: 4
Views: 78

### Re: Applying La Chateliers

You can also see this mathematically with the Nernst equation. Q is the ratio of products to reactants in a concentration cell. When you increase the concentration of the products, lnQ consequently decreases and Ecell becomes a more positive value. When you increase the concentration of the reactant...
Thu Mar 12, 2020 4:06 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Concentration Cell
Replies: 5
Views: 116

### Re: Concentration Cell

A concentration cell has the same compound as both anode and cathode. This makes the Enot equal to zero. This reaction is driven by the difference in concentrations of both the anode and cathode, with the anode being the side with the lower concentration Could you explain why the anode is the one w...
Tue Mar 10, 2020 10:46 pm
Forum: General Rate Laws
Topic: orders
Replies: 6
Views: 127

### Re: orders

For a problem with three species being consumed, you would keep all but one of the concentrations constant. You would use a ratio of the rates to compare and isolate an exponent that you're solving for. Using 7A.17 as an example, to determine the exponent of species A, you would use experiments 1 an...
Tue Mar 10, 2020 10:29 pm
Forum: General Rate Laws
Topic: Homework 7A.1
Replies: 4
Views: 111

### Re: Homework 7A.1

Your answer is dependent on the molecule being altered in order to reach the rate of the second molecule. For example in b, the NH3 is being altered in order to derive the rate of H2. In that case, there are 2NH3 formed for every 3H2 consumed. Therefore the rate of NH3 formation is 2/3 the rate of H...
Tue Mar 10, 2020 10:21 pm
Forum: General Rate Laws
Topic: pseudo rate laws
Replies: 5
Views: 87

### Re: pseudo rate laws

The rate constant k is denoted as a k prime to indicate that it's inclusive of the other rate constants from other steps (i.e. k1, k2, etc)
Tue Mar 10, 2020 10:19 pm
Forum: General Rate Laws
Topic: 7A.3
Replies: 6
Views: 116

### Re: 7A.3

A rate is inherently a positive value, whether or not the molecule is being consumed or produced
Tue Mar 10, 2020 10:16 pm
Forum: General Rate Laws
Topic: Determining Rate Laws
Replies: 4
Views: 89

### Re: Determining Rate Laws

In the intermediate rate laws, only the reactants are used. Their coefficients are used as exponents in the intermediate rate law. However, for the overall rate law, it would depend on the slow step.
Sun Feb 23, 2020 1:01 am
Forum: Balancing Redox Reactions
Topic: writing redox equations
Replies: 3
Views: 52

### Re: writing redox equations

If you're given the cell diagram, the anode (oxidation reaction) is conventionally on the left, and the cathode (reduction reaction) is conventionally on the right. However if you're just given the half reactions and the cell potential for each reaction, you would want to make sure that the overall ...
Sun Feb 23, 2020 12:55 am
Forum: Balancing Redox Reactions
Topic: Oxidation Numbers
Replies: 3
Views: 77

### Re: Oxidation Numbers

I believe the formal charges are hypothetical oxidation numbers that an element can have (based on the periodic table). The oxidation number is the actual charge of an element in a given molecule.
Sun Feb 23, 2020 12:51 am
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: work and cell potential
Replies: 4
Views: 57

### Re: work and cell potential

Since the cell potential is in units of volts, this can be converted to J/C. Joules is the unit for work, and coulombs is the unit for charge. Since the battery is doing the work, then the amount of energy that leaves the system is -w Therefore, cell potential = -(work/charge) I don't know how Lavel...
Sun Feb 23, 2020 12:42 am
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: 6L.1
Replies: 4
Views: 48

### Re: 6L.1

Since they're the same number, you can use either one. It's a matter of preference at this point
Sun Feb 23, 2020 12:39 am
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Concentration
Replies: 2
Views: 50

### Re: Concentration

The Nernst equation is Cell potential = standard cell potential - (RT/nF)lnQ When products>reactants, Q>1. Therefore, lnQ is positive. When this occurs, the sign of the cell potential will be dependent on whether the standard cell potential is greater than or less than (RT/nF)lnQ. When products<reac...
Sun Feb 23, 2020 12:31 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Using Pt
Replies: 7
Views: 129

### Re: Using Pt

Are there other inert conductors that could be used? For example, in the homework for 6L.3B, C(gr) is used as a conductor. Is this an inert conductor because it's in its most stable form?
Sun Feb 23, 2020 12:25 am
Forum: Balancing Redox Reactions
Topic: 6K.3 D
Replies: 2
Views: 47

### Re: 6K.3 D

I'm not completely sure if it would be a typo, since HClO is a weak acid. Because of this, HClO is not a stable structure, which could explain why there is still Cl2 (g) in the products.
Sun Feb 23, 2020 12:18 am
Forum: Balancing Redox Reactions
Topic: Oxidation Numbers
Replies: 9
Views: 123

### Re: Oxidation Numbers

I would also break down the molecule, like someone said previously. By using the periodic table, you can determine the formal charges for the well-known elements. However, for the other elements that you don't know as well, you can find it based off of the other elements in the molecule. The overall...
Sun Feb 23, 2020 12:13 am
Forum: Balancing Redox Reactions
Topic: Reducing agent/oxidizing agent
Replies: 5
Views: 96

### Re: Reducing agent/oxidizing agent

I like using the acronym OIL RIG (Oxidation Is Losing electrons; Reduction is Gaining electrons).
If the oxidation number is increasing, it's losing electrons. This means that it's being oxidized.
If the oxidation number is decreasing, it's gaining electrons. This means that it's being reduced.
Sun Feb 09, 2020 5:38 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: delta U
Replies: 8
Views: 79

### Re: delta U

Conceptually speaking, would an adiabatic system always be an isolated system? Or is there a more specific definition?
Fri Jan 31, 2020 4:29 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: Calculating microstates
Replies: 3
Views: 61

### Re: Calculating microstates

To clarify, this us the total number of possible combinations of states of matter that the two particles can be in? Does that mean that the base of the equation is referring to the number of particles and the exponent is referring to the number of possible states they can be in?
Fri Jan 31, 2020 4:25 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: KbNa
Replies: 4
Views: 350

### Re: KbNa

Does this mean that the Boltzmann constant is only used for gases? If so, does this translate to the Boltzman equation only being used for gas and why?
Fri Jan 31, 2020 4:22 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: Boltzmann Equation
Replies: 2
Views: 62

### Re: Boltzmann Equation

Could someone display the steps he used to get the final equation?
Fri Jan 31, 2020 4:10 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Degeneracy
Replies: 9
Views: 128

### Re: Degeneracy

asannajust_1J wrote:Degeneracy is a way to quantify the possible number of positions a particular species can form. In relation to entropy, it can be seen as the number of Microstates/positions that are possible for a particular system.

How do you determine the number of positions/microstates?
Tue Jan 21, 2020 11:32 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: If [H3O+] < 10^-7
Replies: 2
Views: 43

### Re: If [H3O+] < 10^-7

I remember he related it back to autoprotolysis and how the concentration of H3O+ is 10^-7 for water. I don't remember the complete logic unfortunately. Hopefully this might jog someone's memory
Tue Jan 21, 2020 11:26 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: total pressure increase
Replies: 1
Views: 36

### Re: total pressure increase

If I'm reading it right, this is talking about increasing pressure by adding an inert (non reacting) gas to the vessel, as opposed to decreasing the volume through compression. In that case, the equilibrium doesn't shift to either side of the equation. To explain why it doesn't shift: If you use the...
Tue Jan 21, 2020 11:08 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: ice box approximation
Replies: 9
Views: 115

### Re: ice box approximation

Approximation is okay when the K value is less than 10^-3. To check if your approximation was appropriate at the end of the problem, you can calculate the percent ionization. If this percent is less than 5%, approximation was acceptable. Just in case you need the equation for percent ionization, it...
Tue Jan 21, 2020 11:03 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Practice Problem 5.35
Replies: 1
Views: 41

### Re: Practice Problem 5.35

I got the same answer as you. It's possible that it's an error, or we're both doing it wrong haha.
Tue Jan 21, 2020 10:48 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Le Chatelier's in relation to stability
Replies: 3
Views: 53

### Le Chatelier's in relation to stability

Are there ever any situations where I would have to compare the stability of bonds in the products vs the reactants to determine which way a reaction would shift? To phrase differently, would any stressors require me to look at bond stability?
Fri Jan 10, 2020 11:58 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Value of K
Replies: 4
Views: 60

### Re: Value of K

If you're looking for an absolute threshold for all reactions, K cannot be less than 0 and no greater than the concentrations of the reactants to the power of the respective coefficients. So yes, it's relative to the reaction that is taking place.
Fri Dec 06, 2019 3:14 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Structure
Replies: 1
Views: 38

### Re: Structure

A tetrahedral has 4 ligands bonded to the the central atom, while a square planar has 4 ligands AND 2 lone pairs of electrons bonded to the central atom.
Mon Nov 18, 2019 5:45 pm
Forum: Administrative Questions and Class Announcements
Topic: Worksheet for 1D/1F 10/16
Replies: 24
Views: 1497

### Re: Worksheet for 1D/1F 10/16

Chem_Mod wrote:Answer key for test 2 problems

For part D, why is the AXE nomenclature AX3 and not AX4?
There's 4 atoms (2H, 2Cl) bonded to C.
Sat Nov 16, 2019 4:26 pm
Forum: Dipole Moments
Topic: Cancelling dipole moments
Replies: 11
Views: 282

### Re: Cancelling dipole moments

You can first relate it to its structure, which is a tetrahedral. Since there are two chlorine atoms on opposite sides of each other, the two dipole moments will cancel each other out. However, since there is a third chlorine atom, that dipole moment will not be cancelled out, meaning that there is ...
Sat Nov 16, 2019 4:11 pm
Forum: Ionic & Covalent Bonds
Topic: Polarity
Replies: 6
Views: 90

### Re: Polarity

Adding onto the structural symmetry, a molecule can be symmetrical but still polar. It depends on where the dipole moments are located. EX: cis-dichlorethene vs trans-dichlorethene (both are C2H2Cl2) - in both molecules, the C-Cl bonds have dipole moments - cis-dichlorethene has both chlorine atoms ...
Sat Nov 16, 2019 4:01 pm
Forum: Dipole Moments
Topic: 2E.2 Determing strongest dipole moment between resonance structures
Replies: 2
Views: 46

### 2E.2 Determing strongest dipole moment between resonance structures

I don't know how to add a picture into posts, or if it's even possible so here is the problem description. 2E.29 There are three isomers of dichlorobenzene, C6H4Cl2, which differ in the relative positions of the chlorine atoms on the benzene ring. (a) Which of the three forms are polar? (b) Which ha...
Wed Nov 13, 2019 12:50 pm
Forum: Ionic & Covalent Bonds
Topic: Ionization of Nitrogen vs Oxygen
Replies: 11
Views: 200

### Re: Ionization of Nitrogen vs Oxygen

I was wondering whether this goes for the ones below as well. I was a little confused whether these exceptions are for all of the ones that follow the same atom trend. This doesn't apply to the ones below, hence why it's an exception to the general IE trend. Possible explanation: In the other atoms...
Tue Nov 05, 2019 10:23 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Heisenberg Problem
Replies: 3
Views: 187

### Re: Heisenberg Problem

To find the uncertainty of position, you would use the equation ΔpΔx is greater than or equal to h/4pi 1) Rearrange the equation to isolate Δx (uncertainty of position) to get Δx is greater than or equal to h/(4pi Δp) 2) Find Δp. We're given the the speed from which we can calculate Δv and subsequen...
Tue Nov 05, 2019 10:11 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: 1 B27
Replies: 5
Views: 274

### Re: 1 B27

Yes we're supposed to use 10m/s as our uncertainty in velocity. I think it was just a little fumble in the other explanation. It's also good to know that the equation to use, to be more precise, is Δp=mΔv (just in case that might've confused someone)
Tue Nov 05, 2019 10:06 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Uncertainty in Position and Uncertainty in Momentum
Replies: 4
Views: 176

### Re: Uncertainty in Position and Uncertainty in Momentum

From what I understood in lecture, it's difficult to experimentally know/record both the momentum and position experimentally. It's possible to measure the position of an electron through the light detectors, but this would veer it off course because of the photons that hit it. From this position, y...
Tue Nov 05, 2019 9:52 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Solving with Heisenberg
Replies: 4
Views: 218

### Re: Solving with Heisenberg

I have a follow-up question. How do you apply Δv into the equation? In other words, what is Δv in terms of Δp?
Thu Oct 03, 2019 11:48 pm
Forum: Balancing Chemical Reactions
Topic: Fractions in Balancing Equations
Replies: 11
Views: 490

### Re: Fractions in Balancing Equations

The answer should never be in fractions, but also make sure that it's simplified! I've had times where I multiplied by 2 more often than I should, making my coefficients bigger than necessary
Thu Oct 03, 2019 11:39 pm
Forum: SI Units, Unit Conversions
Topic: 2.Mass Percentage and Decimal Rounding:
Replies: 10
Views: 168

### Re: 2.Mass Percentage and Decimal Rounding:

When finding my answer, I keep the answer to each step to the thousandths place, but I make sure that my final answer follows sig figs (based off of given).
Thu Oct 03, 2019 11:33 pm
Forum: SI Units, Unit Conversions
Topic: Formula Units
Replies: 3
Views: 92

### Formula Units

In multiple questions of part E, it asked us to find the formula units, along with the moles/molecules/molecular formula of a given mass of substance (e.g. E9, E21, E25). Are formula units something we need to be familiar with? And if so, what are they and how do we calculate them? E21. Calculate th...
Thu Oct 03, 2019 11:15 pm
Forum: Balancing Chemical Reactions
Topic: States of matter
Replies: 2
Views: 63

### Re: States of matter

States of matter don't affect balancing equations. When balancing equations, this deals with the amount of moles (which can sometimes translate to amount of molecules/atoms) present. The state of matter is simply just the energy level of these molecules/atoms.
Thu Oct 03, 2019 10:46 pm
Forum: Molarity, Solutions, Dilutions
Topic: E 27
Replies: 6
Views: 112

### Re: E 27

Ok so to answer part a, you want to start with the information they give you (1 molecule water) and you're trying to get to grams of H2O. To get there, you have to convert the 1 molecule of water to moles of water by dividing by Avogadro's number (6.022 x 10^23), since 1 mol = 6.022 x 10^23 molecule...