Search found 51 matches

by Katherine Jordak 1H
Thu Mar 15, 2018 11:38 pm
Forum: Zero Order Reactions
Topic: 15.99
Replies: 1
Views: 202

15.99

In 15.99 we are supposed to determine which of the following plots are linear. (f) intitial rate against [A] for a reaction that is first order in A; (g) half-life against [A] for a reaction that is zero order in A; (h) half-life against [A] for a reaction that is second order in A. Why are (f) and ...
by Katherine Jordak 1H
Thu Mar 15, 2018 10:41 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: 15.79 [ENDORSED]
Replies: 2
Views: 181

Re: 15.79 [ENDORSED]

Will we need to know that for the final?
by Katherine Jordak 1H
Thu Mar 15, 2018 10:39 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: 15.85
Replies: 1
Views: 111

15.85

In problem 15.85, we are given rate laws and asked to write the chemical equation for the reaction, determine its molecularity, and draw a proposed structure for the activated complex. How do you know what the proposed structure for the activated complex is and will we need to know this for the fina...
by Katherine Jordak 1H
Wed Mar 07, 2018 11:27 pm
Forum: General Rate Laws
Topic: Coefficients
Replies: 5
Views: 188

Re: Coefficients

No you wouldn't. I think the equations given are used as so regardless of the coefficients in the reaction equation.
by Katherine Jordak 1H
Wed Mar 07, 2018 11:09 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: Self-Test 15.4B
Replies: 1
Views: 203

Self-Test 15.4B

Hi. When I was doing 15.4B on page 263 of my textbook, one if the reactants' order is not an integer. What would the units of k be in that case?
by Katherine Jordak 1H
Wed Mar 07, 2018 8:47 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: 15.9 part c
Replies: 3
Views: 296

15.9 part c

In homework problem 15.9 part c, the answer bool finds the value of k twice. The first time it uses the information from experiment 4 and in thr second it uses experiment 3. Is this necessary to do on a test? Is it possible for them to not be equal? What do I do if they are unequal? Does that just m...
by Katherine Jordak 1H
Wed Feb 28, 2018 10:05 pm
Forum: First Order Reactions
Topic: Derivation
Replies: 8
Views: 311

Re: Derivation

I will probably learn them regardless. I think knowing the derivations helps to better understand what the equations mean, where they came from, and overall helps keep the equations straight in my head.
by Katherine Jordak 1H
Wed Feb 28, 2018 10:04 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: 15.9
Replies: 3
Views: 168

15.9

I'm trying to do problem 15.9, but can't follow the logic of the solutions manual. Can someone break it down for me? The question reads: Express the units for rate constants when the concentrations are in moles per liter and time is in seconds for (a) zero-order reactions; (b) first-order reactions;...
by Katherine Jordak 1H
Wed Feb 28, 2018 9:36 pm
Forum: Second Order Reactions
Topic: 15.17
Replies: 4
Views: 203

15.17

I'm confused about 15.17 part a. In the answer guide it says use experiments 1 and 4 to show that [C] is independent of the rate. Can someone explain to me how I can deduce [C] is independent of the rate?
by Katherine Jordak 1H
Sun Feb 25, 2018 10:46 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell Diagrams
Replies: 4
Views: 190

Re: Cell Diagrams

In a galvanic cell, Ecell is always greater than zero. When you are given two half equations, determine in which reaction the reactant is being oxidized and in which reaction the reactant is being reduced. In problem 14.13 part c in the first half reaction, Cl's oxidation number goes from 0 to 1-. T...
by Katherine Jordak 1H
Sun Feb 25, 2018 10:34 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Order of Same State Molecules
Replies: 4
Views: 171

Re: Order of Same State Molecules

I read somewhere that you list reactant then product. However, I heard that one of the TAs said in office hours that the answer book is inconsistent with how they list the molecules of the same state, so you can list them however you want.
by Katherine Jordak 1H
Wed Feb 21, 2018 7:47 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: TEXTBOOK 14.25
Replies: 2
Views: 150

Re: TEXTBOOK 14.25

Choosing reactions of the same structure only works in part a. How am I supposed to know what data to use when there isn't a reaction structure in common for all of the elements?
by Katherine Jordak 1H
Thu Feb 15, 2018 2:55 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Pt (s) [ENDORSED]
Replies: 4
Views: 218

Re: Pt (s) [ENDORSED]

In problem 13 c, they say an inert electrode such as Pt. Does that mean other elements can be used? Will we need to know/recognize those other elements?
by Katherine Jordak 1H
Wed Feb 14, 2018 10:22 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Test 1 question 1
Replies: 2
Views: 159

Re: Test 1 question 1

Sorry, I meant to say why do we include bond enthalpy of H-H in part B?
by Katherine Jordak 1H
Tue Feb 13, 2018 10:33 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Test 1 question 1
Replies: 2
Views: 159

Test 1 question 1

Hi,
I'm confused why in part A, the delta H of H2 is not included in finding the standard delta H of the rxn, but it is used in part B. I understand that standard delta H of H2 is zero, so we do we include bond enthalpy of H-H in part B?
by Katherine Jordak 1H
Tue Feb 13, 2018 8:54 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: 9.57
Replies: 1
Views: 118

9.57

In 9.57 part b, the solutions manual shows two different ways of finding the standard delta gibbs free energy of the reaction. The first is by subtracting the standard delta gibba free energy of formation of the reactants from that of the products. This gives us -713.02 kJ/mol. The second way of fin...
by Katherine Jordak 1H
Sun Feb 11, 2018 10:33 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Entropy
Replies: 6
Views: 260

Entropy

How does being vibrationally active affect entropy? Why is there a difference in entropy for diatomic and monoatomic molecules and which one typically has more entropy?
by Katherine Jordak 1H
Sun Feb 11, 2018 10:27 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: 9.35
Replies: 2
Views: 217

Re: 9.35

Can someone why the entropies of container A and container C would be the same then?
by Katherine Jordak 1H
Fri Feb 09, 2018 1:13 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: 9.37
Replies: 3
Views: 172

Re: 9.37

How do we know when we need to use the standard entropy change or formation and when to use the standard entropy change of reaction?
by Katherine Jordak 1H
Sun Feb 04, 2018 9:20 pm
Forum: Calculating Work of Expansion
Topic: 8.93
Replies: 1
Views: 100

Re: 8.93

We know PV = nRT. We also know that PdV = dnRT. I guess they are two different variations of the same equations, so if PdV in some equation and you substitute it out, you must use dnRT.
by Katherine Jordak 1H
Sun Feb 04, 2018 9:16 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Types of Entropy
Replies: 1
Views: 99

Types of Entropy

Hi! Can someone please explain the difference between statistical entropy and residual entropy? I'm having a hard time grasping this concept. Thanks.
by Katherine Jordak 1H
Sun Feb 04, 2018 9:12 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Equations
Replies: 2
Views: 131

Equations

Hi! I'm having a hard time keeping all of these equations straight in my head. Some equations are only for reversible reactions, some can only be used when the pressure is constant, some when the temperature is constant. Does anyone have any suggestions for how to keep all the equations straight or ...
by Katherine Jordak 1H
Sun Jan 28, 2018 7:36 pm
Forum: Phase Changes & Related Calculations
Topic: Chapter 8 Homework #99
Replies: 2
Views: 192

Re: Chapter 8 Homework #99

If the substance is in its standard states you would just look up the enthalpies for each of the different bonds and add them together.
by Katherine Jordak 1H
Sun Jan 28, 2018 7:34 pm
Forum: Phase Changes & Related Calculations
Topic: HW 8.1
Replies: 3
Views: 157

Re: HW 8.1

Another way to look at this is that you know gasoline somehow continually enters the engine every time you fill up the tank in your car. It isn't a manual process with a separate reaction each time you do it. You know for sure matter is going into the engine constantly, so it cannot be a closed syst...
by Katherine Jordak 1H
Sun Jan 28, 2018 7:29 pm
Forum: Phase Changes & Related Calculations
Topic: 8.17
Replies: 2
Views: 151

Re: 8.17

Especially since in the problem it tells us that the phase change happens at a constant temperature, you immediately know that no work is being done on the system in the form of heat. In order for the substance to change phases, it must be doing work on the atmosphere.
by Katherine Jordak 1H
Sun Jan 21, 2018 7:33 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Isolated vs. Adiabatic system
Replies: 8
Views: 635

Re: Isolated vs. Adiabatic system

There are different types of calorimeters. I know a bomb calorimeter is a closed system.
by Katherine Jordak 1H
Sun Jan 21, 2018 7:23 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Heat capacity
Replies: 2
Views: 117

Heat capacity

Why do different phases of a substance have different heat capacities?
by Katherine Jordak 1H
Sun Jan 21, 2018 6:13 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: isolated sytems
Replies: 4
Views: 180

Re: isolated sytems

An isolated system cannot exchange energy or matter with its surroundings. I read somewhere that the universe is an isolated system, which I found pretty interesting.
by Katherine Jordak 1H
Mon Jan 15, 2018 8:18 am
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Gas molar heat capacity [ENDORSED]
Replies: 4
Views: 243

Re: Gas molar heat capacity [ENDORSED]

All I know is that one molar hear capacity is for when there is a constant volume and the other one is for when there is a constant pressure.
by Katherine Jordak 1H
Mon Jan 15, 2018 8:15 am
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: 8.27b - how to find n
Replies: 1
Views: 99

Re: 8.27b - how to find n

For part B, the equation is:
w=-nRTln(V2/V1).
To find n, you need use the information in the equation and put it into the equation:
PV=nRT, so
n= PV/RT
n=((1.79 atm)(4.29 L))/((0.08206 L•atm•K^-1•mon^-1)(305 K))= 0.307 mol.
Plug this value of n into the first function to get the value of work.
by Katherine Jordak 1H
Fri Jan 12, 2018 3:42 pm
Forum: Phase Changes & Related Calculations
Topic: Boiling water vs. steam
Replies: 6
Views: 538

Boiling water vs. steam

I know Dr. Lavelle was talking a lot in class the other day about why steam will burn you more than boiling water. I was confused by his explanation. Could someone please explain again why that is the case?
by Katherine Jordak 1H
Mon Nov 27, 2017 9:23 am
Forum: Determining Molecular Shape (VSEPR)
Topic: 4.11d
Replies: 2
Views: 156

Re: 4.11d

When a molecule has 4 regions of electron density and one of them is a lone pair, the resulting molecular shape is no longer tetrahedral. It is trigonal pyramidal. We learned that the bond angles for a tetrahedral are 109.5 degrees. However, because the repulsion of a lone pair is stronger than if t...
by Katherine Jordak 1H
Mon Nov 27, 2017 9:17 am
Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
Topic: HW 4.75
Replies: 2
Views: 196

Re: HW 4.75

Yes. Polarity is cause by the uneven distribution of electrical charge. Because of the differences in electronegativity of the oxygen and hydrogen atoms, they do not all exert the same pull on the electrons they are sharing with the central carbon atom. If oxygen's electronegativity is higher than b...
by Katherine Jordak 1H
Mon Nov 27, 2017 9:12 am
Forum: Hybridization
Topic: Hybridization in Double and Triple bonds
Replies: 2
Views: 1359

Re: Hybridization in Double and Triple bonds

Just to clarify some more, region of electron density are where a single/double/triple bond is or where a lone pair is. When deciding the hybridization of an atom, there should be one orbital (an s or a p or a d) for each region of electron density. An atom with a triple bond and one lone pair has t...
by Katherine Jordak 1H
Mon Nov 27, 2017 9:03 am
Forum: Ideal Gases
Topic: Kp and Kc
Replies: 7
Views: 541

Re: Kp and Kc

Is it possible to use Kc when only gases are involved in the reaction? If so, how do you know when to use Kp and when to use Kc?
by Katherine Jordak 1H
Mon Nov 27, 2017 9:00 am
Forum: Ideal Gases
Topic: Kp and Kc
Replies: 7
Views: 541

Re: Kp and Kc

Is it possible to use Kc when only gases are involved in the reaction? If so, how do you know when to use Kp and when to use Kc?
by Katherine Jordak 1H
Sun Nov 19, 2017 10:06 pm
Forum: Bond Lengths & Energies
Topic: Bond Strength
Replies: 5
Views: 410

Re: Bond Strength

Also, the smaller the difference in electronegativity between the two bonded atoms, the shorter the bond. This usually happens closer to the right side of the periodic table amd creates covalent bonds. These bonds are stronger because the two atoms are "sharing" the electrons. Neither one ...
by Katherine Jordak 1H
Sun Nov 19, 2017 9:59 pm
Forum: Bond Lengths & Energies
Topic: Bond Length and Ionic Character
Replies: 2
Views: 704

Re: Bond Length and Ionic Character

You can also think of it in terms of ionic and covalent bonds. The bigger the difference in electronegativity, the more ionic a bond is, the longer the bond length and the weaker the bond strength. This makes sense because we don't think of ionic compounds as sharing electrons and ionic compounds di...
by Katherine Jordak 1H
Sun Nov 12, 2017 4:56 pm
Forum: Dipole Moments
Topic: Dipole Moments
Replies: 2
Views: 158

Re: Dipole Moments

Yeah. I this of the molecule being symmetric. If the atoms are the same and symmetric around the central arom, then dipole moments cancel.
by Katherine Jordak 1H
Sun Nov 12, 2017 4:54 pm
Forum: Dipole Moments
Topic: When do dipole moments occur?
Replies: 3
Views: 337

Re: When do dipole moments occur?

Also, there is a dipole moment if a molecule is on some way unsymetric. For example, if the central atom has a lone pair or if the atoms attached to the central atom are different, the moleule will be polar and have a dipole moment.
by Katherine Jordak 1H
Fri Nov 03, 2017 9:52 am
Forum: Lewis Structures
Topic: 3.59
Replies: 3
Views: 218

Re: 3.59

Your goal when drawing a Lewis structure is usually to get each element to have 8 valence electrons. You know whether to use a single or double bond usually based on how close each atom is to having a full outer shell. If you draw the Lewis structure for a molecule and then realize that both the cen...
by Katherine Jordak 1H
Fri Nov 03, 2017 9:42 am
Forum: Ionic & Covalent Bonds
Topic: Metallic Bond
Replies: 4
Views: 235

Re: Metallic Bond

In metallic bonds, the valence electrons of each atom delocalize and kind of float around all the positively charged nuclei. These delocalized electrons form the "sea of electrons". I think that is why metals are often a malleable material; the atoms are able to slide on top of each other ...
by Katherine Jordak 1H
Sun Oct 29, 2017 9:18 pm
Forum: Ionic & Covalent Bonds
Topic: Noble Gases
Replies: 6
Views: 421

Re: Noble Gases

They actually can bond with each other (London forces), but these bonds are temporary and very weak.
by Katherine Jordak 1H
Sun Oct 29, 2017 9:07 pm
Forum: Lewis Structures
Topic: Placement [ENDORSED]
Replies: 6
Views: 261

Re: Placement [ENDORSED]

The central atom is the atom with the lowest ionization energy, yes. That means it is usually the atom that is closest to having its outer orbitals half-filled (so there is plenty of space for bonds). If two atoms in the same compound are in the same family on the periodic table, then the lower one ...
by Katherine Jordak 1H
Sun Oct 29, 2017 9:05 pm
Forum: Lewis Structures
Topic: Placement [ENDORSED]
Replies: 6
Views: 261

Re: Placement [ENDORSED]

The central atom is the atom with the lowest ionization energy, yes. That means it is usually the atom that is closest to having its outer orbitals half-filled (so there is plenty of space for bonds). If two atoms in the same compound are in the same family on the periodic table, then the lower one ...
by Katherine Jordak 1H
Sun Oct 22, 2017 4:44 pm
Forum: Quantum Numbers and The H-Atom
Topic: Writing e- configurations of atoms
Replies: 2
Views: 286

Re: Writing e- configurations of atoms

As Davalanya said, copper and chromium are exceptions to the electron configuration. This is because the predicted copper electron configuration has the d subshell at 1 electron less than it needs to be half full. Therefore, the d subshell snags an electron from the s subshell. This happens because ...
by Katherine Jordak 1H
Sun Oct 22, 2017 4:36 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: expected electron configuration of chromium [ENDORSED]
Replies: 3
Views: 253

Re: expected electron configuration of chromium [ENDORSED]

For similar reasons, Copper is also an exception to that normal electron configuration rule. Its electron configuration is [Ar]4s1,3d10. A completely filled sub-shell will be more stable than a partially filled one.
by Katherine Jordak 1H
Sun Oct 15, 2017 3:03 pm
Forum: Photoelectric Effect
Topic: Work Function vs. Threshold Energy [ENDORSED]
Replies: 5
Views: 371

Re: Work Function vs. Threshold Energy [ENDORSED]

I think for our purposes the two terms can be used interchangeably. However, I believe work function describes the minimum amount of energy needed to eject an electron, and threshold energy is used when talking about the frequency required to eject an electron.
by Katherine Jordak 1H
Sun Oct 15, 2017 2:56 pm
Forum: Properties of Light
Topic: Problem 1.55 part A
Replies: 1
Views: 202

Problem 1.55 part A

Part A: If an absorption occurs in the infrared spectrum at 3600 cm^-1, what is the frequency of radiation that corresponds to that absorption? When I did this problem I used the equation wavelength x frequency = c I converted 3600 cm^-1 into meters before plugging it into the problem and got 1.1 x ...
by Katherine Jordak 1H
Sat Oct 07, 2017 9:26 pm
Forum: SI Units, Unit Conversions
Topic: Significant Figures in relation to molar mass [ENDORSED]
Replies: 4
Views: 4003

Re: Significant Figures in relation to molar mass [ENDORSED]

I always use a couple more numbers than the amount of significant figures in order to avoid rounding errors and then round to the correct number of sig figs at the end. You can also use the correct sig figs for the molar mass of the molecules. Either way, just show your work.
by Katherine Jordak 1H
Sat Oct 07, 2017 9:01 pm
Forum: Balancing Chemical Reactions
Topic: Order of Elements to Balance [ENDORSED]
Replies: 5
Views: 429

Re: Order of Elements to Balance [ENDORSED]

In combustion equations of molecules with no oxygen atoms, I usually balance the hydrogens first. If the coefficient is odd number (for the H2O), it's likely you'll have to double the molecule that is being combusted. Just makes balancing combustion equations faster.

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