## Search found 51 matches

Thu Mar 15, 2018 11:38 pm
Forum: Zero Order Reactions
Topic: 15.99
Replies: 1
Views: 267

### 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 ...
Thu Mar 15, 2018 10:41 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: 15.79 [ENDORSED]
Replies: 2
Views: 246

### Re: 15.79[ENDORSED]

Will we need to know that for the final?
Thu Mar 15, 2018 10:39 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: 15.85
Replies: 1
Views: 149

### 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...
Wed Mar 07, 2018 11:27 pm
Forum: General Rate Laws
Topic: Coefficients
Replies: 5
Views: 267

### Re: Coefficients

No you wouldn't. I think the equations given are used as so regardless of the coefficients in the reaction equation.
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: 274

### 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?
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: 376

### 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...
Wed Feb 28, 2018 10:05 pm
Forum: First Order Reactions
Topic: Derivation
Replies: 8
Views: 438

### 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.
Wed Feb 28, 2018 10:04 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: 15.9
Replies: 3
Views: 268

### 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;...
Wed Feb 28, 2018 9:36 pm
Forum: Second Order Reactions
Topic: 15.17
Replies: 4
Views: 314

### 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?
Sun Feb 25, 2018 10:46 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell Diagrams
Replies: 4
Views: 309

### 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...
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: 277

### 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.
Wed Feb 21, 2018 7:47 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: TEXTBOOK 14.25
Replies: 2
Views: 197

### 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?
Thu Feb 15, 2018 2:55 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Pt (s) [ENDORSED]
Replies: 4
Views: 292

### 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?
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: 211

### Re: Test 1 question 1

Sorry, I meant to say why do we include bond enthalpy of H-H in part B?
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: 211

### 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?
Tue Feb 13, 2018 8:54 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: 9.57
Replies: 1
Views: 171

### 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...
Sun Feb 11, 2018 10:33 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Entropy
Replies: 6
Views: 377

### 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?
Sun Feb 11, 2018 10:27 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: 9.35
Replies: 2
Views: 288

### Re: 9.35

Can someone why the entropies of container A and container C would be the same then?
Fri Feb 09, 2018 1:13 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: 9.37
Replies: 3
Views: 252

### 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?
Sun Feb 04, 2018 9:20 pm
Forum: Calculating Work of Expansion
Topic: 8.93
Replies: 1
Views: 145

### 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.
Sun Feb 04, 2018 9:16 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Types of Entropy
Replies: 1
Views: 142

### 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.
Sun Feb 04, 2018 9:12 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Equations
Replies: 2
Views: 193

### 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 ...
Sun Jan 28, 2018 7:36 pm
Forum: Phase Changes & Related Calculations
Topic: Chapter 8 Homework #99
Replies: 2
Views: 252

### 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.
Sun Jan 28, 2018 7:34 pm
Forum: Phase Changes & Related Calculations
Topic: HW 8.1
Replies: 3
Views: 236

### 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...
Sun Jan 28, 2018 7:29 pm
Forum: Phase Changes & Related Calculations
Topic: 8.17
Replies: 2
Views: 172

### 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.
Sun Jan 21, 2018 7:33 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Replies: 8
Views: 3845

### Re: Isolated vs. Adiabatic system

There are different types of calorimeters. I know a bomb calorimeter is a closed system.
Sun Jan 21, 2018 7:23 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Heat capacity
Replies: 2
Views: 145

### Heat capacity

Why do different phases of a substance have different heat capacities?
Sun Jan 21, 2018 6:13 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: isolated sytems
Replies: 4
Views: 236

### 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.
Mon Jan 15, 2018 8:18 am
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Gas molar heat capacity [ENDORSED]
Replies: 4
Views: 327

### 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.
Mon Jan 15, 2018 8:15 am
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: 8.27b - how to find n
Replies: 1
Views: 149

### 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.
Fri Jan 12, 2018 3:42 pm
Forum: Phase Changes & Related Calculations
Topic: Boiling water vs. steam
Replies: 6
Views: 690

### 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?
Mon Nov 27, 2017 9:23 am
Forum: Determining Molecular Shape (VSEPR)
Topic: 4.11d
Replies: 2
Views: 189

### 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...
Mon Nov 27, 2017 9:17 am
Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
Topic: HW 4.75
Replies: 2
Views: 235

### 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...
Mon Nov 27, 2017 9:12 am
Forum: Hybridization
Topic: Hybridization in Double and Triple bonds
Replies: 2
Views: 3523

### 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...
Mon Nov 27, 2017 9:03 am
Forum: Ideal Gases
Topic: Kp and Kc
Replies: 7
Views: 684

### 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?
Mon Nov 27, 2017 9:00 am
Forum: Ideal Gases
Topic: Kp and Kc
Replies: 7
Views: 684

### 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?
Sun Nov 19, 2017 10:06 pm
Forum: Bond Lengths & Energies
Topic: Bond Strength
Replies: 5
Views: 513

### 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 ...
Sun Nov 19, 2017 9:59 pm
Forum: Bond Lengths & Energies
Topic: Bond Length and Ionic Character
Replies: 2
Views: 1015

### 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...
Sun Nov 12, 2017 4:56 pm
Forum: Dipole Moments
Topic: Dipole Moments
Replies: 2
Views: 223

### 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.
Sun Nov 12, 2017 4:54 pm
Forum: Dipole Moments
Topic: When do dipole moments occur?
Replies: 3
Views: 512

### 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.
Fri Nov 03, 2017 9:52 am
Forum: Lewis Structures
Topic: 3.59
Replies: 3
Views: 311

### 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...
Fri Nov 03, 2017 9:42 am
Forum: Ionic & Covalent Bonds
Topic: Metallic Bond
Replies: 4
Views: 311

### 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 ...
Sun Oct 29, 2017 9:18 pm
Forum: Ionic & Covalent Bonds
Topic: Noble Gases
Replies: 6
Views: 548

### Re: Noble Gases

They actually can bond with each other (London forces), but these bonds are temporary and very weak.
Sun Oct 29, 2017 9:07 pm
Forum: Lewis Structures
Topic: Placement [ENDORSED]
Replies: 6
Views: 378

### 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 ...
Sun Oct 29, 2017 9:05 pm
Forum: Lewis Structures
Topic: Placement [ENDORSED]
Replies: 6
Views: 378

### 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 ...
Sun Oct 22, 2017 4:44 pm
Forum: Quantum Numbers and The H-Atom
Topic: Writing e- configurations of atoms
Replies: 2
Views: 365

### 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 ...
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: 396

### 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.
Sun Oct 15, 2017 3:03 pm
Forum: Photoelectric Effect
Topic: Work Function vs. Threshold Energy [ENDORSED]
Replies: 5
Views: 531

### 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.
Sun Oct 15, 2017 2:56 pm
Forum: Properties of Light
Topic: Problem 1.55 part A
Replies: 1
Views: 258

### 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 ...
Sat Oct 07, 2017 9:26 pm
Forum: SI Units, Unit Conversions
Topic: Significant Figures in relation to molar mass [ENDORSED]
Replies: 4
Views: 7145

### 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.
Sat Oct 07, 2017 9:01 pm
Forum: Balancing Chemical Reactions
Topic: Order of Elements to Balance [ENDORSED]
Replies: 5
Views: 785

### 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.