Search found 50 matches

Mon Mar 12, 2018 2:57 pm
Forum: Zero Order Reactions
Topic: Slope From
Replies: 5
Views: 306

Re: Slope From

By plotting the experimental data vs time, you would be able to identify the order of the reaction depending on whether [A] vs time, ln[A] vs time , or 1/[A] vs time gave you a straight line plot, where A is the reactant. Also, the slope would tell you what k is.
Mon Mar 12, 2018 2:25 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: types of systems
Replies: 3
Views: 394

Re: types of systems

An open system would be a beaker of water, where matter and energy can exchange with the surroundings. A closed system would be a sealed beaker of water, where only energy can exchange with the surroundings. In an isolated system, such as a bomb calorimeter, neither matter nor energy can exchange wi...
Mon Mar 12, 2018 2:19 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Calculating standard enthalpy [ENDORSED]
Replies: 3
Views: 332

Re: Calculating standard enthalpy[ENDORSED]

The bond strength between a given pair of atoms varies slightly from one compound to another because of the different electronegativities of the other atoms in the compound. When we use bond enthalpy values to calculate standard enthalpy, we are actually using the mean bond enthalpy which is the ave...
Sun Mar 11, 2018 1:41 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Collision theory and transition state theory?
Replies: 2
Views: 102

Re: Collision theory and transition state theory?

Also, the section in the textbook on collision theory discusses reaction profiles, which were also mentioned in class, so I think knowing/understanding those would be useful.
Sun Mar 11, 2018 1:38 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: 15.63
Replies: 2
Views: 143

Re: 15.63

Also, once you've solved for k2, if you plug it in to ln(k1/k2) you get -0.59. But if you plug k1 and k2 into ln(k2/k1) you get 0.59. So to answer your question, ln(k1/k2) doesn't equal 0.59, it equals -0.59.
Sun Mar 11, 2018 1:26 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: 15.65 c
Replies: 2
Views: 142

Re: 15.65 c

The higher the activation energy, the stronger the temperature dependance of the rate constant. In this reaction, the forward reaction has a higher activation than the reverse reaction, which is why k of the forward reaction will increase more than k of the reverse reaction.
Tue Feb 27, 2018 10:22 pm
Forum: General Rate Laws
Topic: Homework Help 15.1
Replies: 4
Views: 477

Re: Homework Help 15.1

For part b, the balanced equation shows that for every 2 moles of NH3 formed, 3 moles of H2 are consumed. This means that the rate of formation of NH3 would be 2/3 of the rate of consumption of H2. We do the same thing for part c. For every 2 moles of NH3 formed, 1 mole of N2 is consumed. This means...
Tue Feb 27, 2018 10:03 pm
Forum: General Rate Laws
Topic: 15.17
Replies: 4
Views: 202

Re: 15.17

The reaction is second order with respect to B because when the amount of B is doubled (increased by a factor of 2), the rate increases by a factor of 4, so instead of it being a 1:1 ratio, which would make it first order, it's a 1:2 ratio, which makes it second order.
Tue Feb 27, 2018 9:57 pm
Forum: General Rate Laws
Topic: Orders and units
Replies: 3
Views: 171

Re: Orders and units

The rate of the reaction has units mol*(L^-1)*(s^-1) For a zero order reaction, the rate = k*[A]^0= k, where k is the rate constant. In order for the rate to have units mol*(L^-1)*(s^-1) the units for k have to be mol*(L^-1)*(s^-1) For a first order reaction, the rate = k *[A]^1 and the units for [A...
Sun Feb 25, 2018 10:29 am
Forum: General Rate Laws
Topic: Rate Law
Replies: 2
Views: 137

Re: Rate Law

From my understanding of it, if your stoichiometric coefficient is now 1/a instead of a, you plug in 1/a to where you would plug in a. This leaves you with
(-1/(1/a))*(d[A]/dt) which simplifies to -a*(d[A]/dt)
Sun Feb 25, 2018 10:19 am
Forum: General Rate Laws
Replies: 6
Views: 1237

The concentration of the reactants will decrease over the reaction, so without the negative sign, the reaction rate for the reactants would be a negative number, as it is calculated from the change in concentration over the change in time. However, we want to work with positive reaction rates, so by...
Sun Feb 25, 2018 10:16 am
Forum: General Rate Laws
Topic: Reactants Rate Law
Replies: 2
Views: 138

Re: Reactants Rate Law

Also, don't forget, you need to use a negative sign when referring to the reactants. For example, if the reaction was aA + bB --> cC + dD,
rate = -(1/a)*(d[A]/dt) = -(1/b)*(d[B]/dt) = (1/c)*(d[C]/dt) = (1/d)*(d[D]/dt)
Sun Feb 18, 2018 12:20 pm
Forum: Balancing Redox Reactions
Topic: Test #2
Replies: 5
Views: 198

Re: Test #2

I believe it will be on electrochemistry and everything that we covered in chapter 14. The assigned homework problems from the electrochemistry section should cover all of the topics we need to know.
Sun Feb 18, 2018 12:15 pm
Forum: Balancing Redox Reactions
Topic: 14.1 Part D
Replies: 4
Views: 161

Re: 14.1 Part D

After obtaining the half-reactions, you have to multiply the oxidation half-reaction (part b) by 3 so that both half-reactions have the same number of electrons involved. Afterwards, you combine the two equations.
Sun Feb 18, 2018 12:07 pm
Forum: Balancing Redox Reactions
Topic: Balancing Half Reactions
Replies: 2
Views: 133

Re: Balancing Half Reactions

Also, because the problem specifies that the reaction occurs in an acidic solution, you know to add H+ and not OH-.
Sat Feb 10, 2018 6:58 pm
Forum: Van't Hoff Equation
Topic: Finding K
Replies: 5
Views: 579

Re: Finding K

I was told that we won't be using ICE tables in this class.
Sat Feb 10, 2018 6:56 pm
Forum: Van't Hoff Equation
Topic: Derivation
Replies: 9
Views: 461

Re: Derivation

I don't think it would hurt to know the derivations, especially because knowing/understanding them could potentially help with conceptual questions.
Sat Feb 10, 2018 6:54 pm
Forum: Van't Hoff Equation
Topic: How to calculate K [ENDORSED]
Replies: 3
Views: 329

Re: How to calculate K[ENDORSED]

If you are given ΔG°, you can calculate K by first isolating it. Once you have lnK = ΔG°/-RT you then get rid of the natural log in front of the K by using e. You end up with e^(lnK) = e^(ΔG°/-RT) and the e^ln cancels out, so K = e^(ΔG°/-RT).
Sat Feb 03, 2018 6:21 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: Homework 9.21
Replies: 3
Views: 161

Re: Homework 9.21

The problem asks us to calculate entropy and gives us the number of molecules and the number of arrangements. Using these 2 things, we an calculate the degeneracy(W). To calculate the degeneracy: (# of arrangements)^(# of molecules). For part (a), we know there are 64 molecules aligned in the same d...
Sat Feb 03, 2018 6:12 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: Phase change question demonstrated in Lecture
Replies: 4
Views: 217

Re: Phase change question demonstrated in Lecture

When delta H is positive, the reaction is endothermic and is only spontaneous at high temperatures (unless delta S is negative, in which case the reaction is not spontaneous at any temperature, but the reverse reaction is spontaneous). Because this reaction requires heat, it is not favorable, and th...
Sat Feb 03, 2018 6:04 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: formula for standard entropy
Replies: 5
Views: 260

Re: formula for standard entropy

Yes, they are similar because they are both state functions. To calculate the standard reaction entropy, you subtract the sum of the standard formation entropies of all of the reactants from the sum of the standard formation entropies of all of the products.
Sun Jan 28, 2018 3:01 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Internal energy as a state function
Replies: 3
Views: 174

Re: Internal energy as a state function

Internal energy (U) us a state property because changes in internal energy are a function of initial and final states. It doesn't depend on the path taken, it just depends on the initial and final state. (delta U = Ufinal - Uinitial)
Sun Jan 28, 2018 2:48 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: units for delta H
Replies: 4
Views: 214

Re: units for delta H

Reaction enthalpies are usually in kJ because we have to multiply either the formation enthalpies or the bond enthalpies (usually given in kJ/mol) by the number of moles, so moles would cancel out and you'd be left with kJ.
Sun Jan 28, 2018 2:41 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Open System
Replies: 7
Views: 398

Re: Open System

In order to increase the energy of an open system, you can add substance to the system, heat the system, or do work on the system. In order to increase the energy of a closed system, you can heat the system or do work on the system. The energy of an isolated system is constant because no matter or h...
Fri Jan 19, 2018 1:20 pm
Forum: Calculating Work of Expansion
Topic: units for calculating work
Replies: 6
Views: 147

Re: units for calculating work

I think that atm is best for pressure and L is best for volume because then you can just convert from L.atm to J (1 L.atm = 101.325 J).
Fri Jan 19, 2018 1:09 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Internal Energy/Open System
Replies: 2
Views: 135

Re: Internal Energy/Open System

Conversely, you could also remove substance from the system, cool the system, or let the system do work on the surroundings.
Fri Jan 19, 2018 1:08 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Internal Energy
Replies: 3
Views: 237

Re: Internal Energy

In the diagram, I believe that the volume is area x displacement of the piston because we need to calculate the change in volume (delta V) not the volume of the entire system. And so in order to calculate the change in volume, we would multiply the area and the distance that the piston has been disp...
Wed Jan 10, 2018 3:36 pm
Forum: Phase Changes & Related Calculations
Topic: Endo and Exothermic Ways to Remember
Replies: 28
Views: 3481

Re: Endo and Exothermic Ways to Remember

I remember that endothermic reactions require/absorb energy because of the root (endo) and that they have a positive delta H because if they absorb energy, then the final product of the reaction will have more energy than the initial reactants (change = final - initial). Exothermic reactions release...
Wed Jan 10, 2018 3:14 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Change in Enthalpy of the Reverse Reaction
Replies: 5
Views: 280

Re: Change in Enthalpy of the Reverse Reaction

You would make it negative, because for fusion, the process is endothermic and delta H is positive, which means the reverse reaction, freezing, would be exothermic and have a negative delta H.
Wed Jan 10, 2018 3:09 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Bond Enthalpies
Replies: 5
Views: 229

Re: Bond Enthalpies

The reactants have positive enthalpies because the process of breaking the bonds in the reactants requires/absorbs heat/energy, which means it would be an endothermic reaction, which is why delta H is positive. The products have negative enthalpies because the process of forming the bonds for the pr...
Sat Dec 09, 2017 7:45 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: if Kc is Halved
Replies: 1
Views: 270

Re: if Kc is Halved

In that problem I don't think the concentrations are halved, it says that the stoichiometric coefficients are halved. And because the stoichiometric coefficients become the exponents, taking the square root would be the equivalent of multiplying them by 1/2.
Sat Dec 09, 2017 7:36 pm
Forum: Lewis Acids & Bases
Topic: Lewis Acids/Bases vs Bronsted Acids/Bases
Replies: 3
Views: 207

Re: Lewis Acids/Bases vs Bronsted Acids/Bases

For Lewis acids and bases, I remember that the Lewis acid is the lone pair electron acceptor because acid and acceptor both start with the letter A.
Thu Nov 30, 2017 7:58 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Monodentate vs Bidentate etc. [ENDORSED]
Replies: 7
Views: 1829

Re: Monodentate vs Bidentate etc.[ENDORSED]

I saw a chart in the textbook that specified some of the polydentate ligands, it's in chapter 17, table 17.4.
Thu Nov 30, 2017 7:52 am
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: change in temperature
Replies: 4
Views: 223

Re: change in temperature

In class, we learned that if a reaction requires heat (is endothermic) while forming product, then heating would favor product formation. I read something that explained this using equations: heat+6CO2(g)+6H2O(l)⇌C6H12O6(aq)+6O2(g) In endothermic reactions, heat is on the side of the reactants, so a...
Mon Nov 20, 2017 3:48 pm
Forum: Lewis Structures
Topic: Best way to start Lewis Structures
Replies: 12
Views: 545

Re: Best way to start Lewis Structures

I first find out what the central atom is, and then I draw a single bond between the central atom and each of the other atoms. I then fill in all of the remaining electrons with either bonds or lone pairs and try to keep the formal charge as close to 0 as possible.
Mon Nov 20, 2017 3:35 pm
Forum: Ideal Gases
Topic: PV=nRT [ENDORSED]
Replies: 4
Views: 259

Re: PV=nRT[ENDORSED]

As the reply above said, the constant (R) usually used in this class is 0.08206. This constant is used when pressure (P) is measured in atm, volume (V) is measured in liters (L), n is the moles of gas, and temperature (T) is measured in Kelvin (K).
Sun Nov 19, 2017 12:52 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Lone Pair Repulsion
Replies: 2
Views: 141

Re: Lone Pair Repulsion

An electron cloud of a lone pair can take up more space than an electron cloud of a bonding pair because it's less restrained because it's held in place by only 1 atom, not 2. This leads to greater repulsion.
Sun Nov 19, 2017 12:37 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Cis- & Trans-
Replies: 3
Views: 158

Re: Cis- & Trans-

Cis- isomers have 2 of the same functional groups on the same side of the double bond, while in trans- isomers they are on opposite sides of the double bond.
Fri Nov 10, 2017 2:56 pm
Forum: Dipole Moments
Topic: Dipole moments
Replies: 6
Views: 396

Re: Dipole moments

Dipole moments can occur between ions in an ionic bond or atoms in a covalent bond. They occur when atoms in a molecule share electrons unequally, which occurs because one atom is more electronegative than the other. The more electronegative atom pulls more tightly on the shared electrons, creating ...
Fri Nov 10, 2017 2:51 pm
Forum: Dipole Moments
Topic: Dipole Moments and Electronegativity [ENDORSED]
Replies: 2
Views: 184

Re: Dipole Moments and Electronegativity[ENDORSED]

Dipole moments occur when atoms in a molecule share electrons unequally, which occurs when one atom is more electronegative than the other. The more electronegative atom will have a stronger pull on the electrons, creating a separation of charge. The greater the difference in electronegativity, the ...
Sat Nov 04, 2017 4:31 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Hund's Rule [ENDORSED]
Replies: 6
Views: 460

Re: Hund's Rule[ENDORSED]

To add on to the previous reply, Pauli Exclusion Principle states that there can be no more than 2 electrons per orbital and that if 2 electrons are in the same orbital then they spin paired.
Sat Nov 04, 2017 4:25 pm
Forum: Ionic & Covalent Bonds
Topic: Study Habits [ENDORSED]
Replies: 8
Views: 522

Re: Study Habits[ENDORSED]

I feel like the most important thing for me in terms of studying is doing all of the assigned homework problems, and making sure that I understand the concepts behind them. In terms of online resources, I really only use the video modules that Dr. Lavelle posted on the website.
Sun Oct 29, 2017 5:35 pm
Forum: Trends in The Periodic Table
Replies: 4
Views: 286

The atomic radius is the distance between the atomic nucleus and the outermost stable electron of a neutral atom (which is found by measuring the distance between the nuclei of 2 atoms that are touching, and halving that distance.) The ionic radius of an element is its share of the distance between ...
Sun Oct 29, 2017 5:20 pm
Forum: Ionic & Covalent Bonds
Topic: Test 3 preparation and date [ENDORSED]
Replies: 5
Views: 351

Re: Test 3 preparation and date[ENDORSED]

As test 2 covered the assigned homework problems 3-41 from chapter 1, for test 3 it would probably be a good idea to complete the rest of the assigned problems for chapter 1 as well as the assigned problems for chapter 2. And as mentioned above, the tests are in our discussion sections beginning Oct...
Sun Oct 22, 2017 4:18 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: ORBITALS, SHELLS ETC. [ENDORSED]
Replies: 6
Views: 381

Re: ORBITALS, SHELLS ETC.[ENDORSED]

Also, he mentioned in class that for electron configurations, we need to know the s-block, the p-block, and the first row d-block.
Sun Oct 22, 2017 4:11 pm
Forum: DeBroglie Equation
Topic: Wave vs Particle Properties of Light
Replies: 3
Views: 273

Re: Wave vs Particle Properties of Light

To add on to the last reply about matter, relatively large objects primarily exhibit particle properties, but to explain the behavior of very small objects, like electrons, both wave and particle properties must be considered.
Sun Oct 15, 2017 5:49 pm
Forum: Properties of Light
Topic: Converting Units [ENDORSED]
Replies: 11
Views: 579

Re: Converting Units[ENDORSED]

If you are trying to compare to other wavelengths, converting to nanometers would probably make things easier.
Sun Oct 15, 2017 5:40 pm
Forum: Properties of Light
Topic: Equation/Formula Clarification
Replies: 4
Views: 298

Re: Equation/Formula Clarification

You can use c = λ ν to find the wavelength when you are given the frequency, or vice versa. You can combine this formula with E = h ν to get E = hc/λ to solve for either the photon energy or the wavelength, as long as you know one of the 2 variables.
Sun Oct 08, 2017 11:28 am
Forum: Molarity, Solutions, Dilutions
Topic: Molarity and Dilution [ENDORSED]
Replies: 7
Views: 1016

Re: Molarity and Dilution[ENDORSED]

You could just use M = n/V, you just have to convert the grams of KCl to moles, and then use .125L as your final volume.
Sun Oct 08, 2017 11:23 am
Forum: SI Units, Unit Conversions
Topic: Formula Units
Replies: 7
Views: 384

Re: Formula Units

In ionic compounds, cations and anions are packed tightly in a crystal lattice pattern and form a giant structure, which is why we refer to them formula units as opposed to molecules.