## Search found 56 matches

Thu Mar 15, 2018 8:23 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Midterm #5
Replies: 1
Views: 121

### Midterm #5

A system undergoes a two-step process. In step one, it expands adiabatically from 1.00 L to 2.56L against an external pressure of 1.00 atm. In step 2, it releases 73J of heat at 1.00 atm as it returns to the original internal energy. Find the volume of the system. I understand that because the syste...
Wed Mar 14, 2018 10:35 am
Forum: General Rate Laws
Topic: rate law from elementary step
Replies: 2
Views: 201

### rate law from elementary step

Why can you use the equation for the slowest elementary step, i.e. the stoichiometric coefficients for order, when writing out that steps rate law?
Mon Mar 12, 2018 10:40 pm
Forum: *Enzyme Kinetics
Topic: Catalysis 15.69
Replies: 3
Views: 358

### Re: Catalysis 15.69

You need to solve for the ration if k catalyzed and k uncatalyzed. This ratio is given as 1000, so you set that equal to the Arrhenius equation of the catalyzed reaction divided by the Arrhenius equation of the uncatalyzed reaction. You then use algebra to get the equation Ea(cat) = Ea - RTln1000. W...
Mon Mar 12, 2018 10:32 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Distinguishing a Catalyst
Replies: 4
Views: 284

### Re: Distinguishing a Catalyst

A catalyst is consumed at the beginning of the reaction mechanism, but then reappears as a product at a different step. Reactants are just consumed and never reappear, and intermediates are produced and then later consumed again.
Mon Mar 12, 2018 10:28 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Question 15.51
Replies: 8
Views: 473

### Re: Question 15.51

In a reaction mechanism, it is only the slowest elementary step that determines the rate law of the formation of product. In this case, the slow step is NO + Br2 ---> NOBR2. Since this is an elementary reaction we can write the rate law using stoichiometric coefficients of only step 1, since that is...
Thu Mar 08, 2018 2:35 pm
Forum: General Rate Laws
Topic: integrated rate law to determine order
Replies: 2
Views: 200

### integrated rate law to determine order

In Dr. Lavelle's chemical kinetics outline, it says that we should "be able to use the appropriate integrated rate law to determine the order of a reaction." I understand how to do the opposite and find the rate law based on the order, but how do we find the order from the integrated rate ...
Tue Mar 06, 2018 10:28 pm
Forum: General Rate Laws
Topic: Specification of Reactant/Product
Replies: 3
Views: 141

### Re: Specification of Reactant/Product

Yes, it would be different for average reaction rate because it is change in concentration/change in time, so it depends on the species.
Tue Mar 06, 2018 10:22 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: Homework 15.23
Replies: 3
Views: 250

### Re: Homework 15.23

The initial concentration of A is .153. The question is asking for the rate constant expressed for the rate constant of A, so you convert .034M B into units of A by multiplying by the mol ratio, 2molA/1molB. This gives you that the change in concentration of A is .068M. To find the final concentrati...
Tue Mar 06, 2018 10:15 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: Increasing Concentration of Reactants
Replies: 5
Views: 401

### Re: Increasing Concentration of Reactants

Yes because rate=k(conc. R)^n, so rate is proportional to the concentration of the reactants. This means that is concentration increases, rate increases.
Sun Mar 04, 2018 3:14 pm
Forum: General Rate Laws
Topic: Rate Law and Initial concentration of Reactant
Replies: 5
Views: 298

### Re: Rate Law and Initial concentration of Reactant

It is because it's easier to evaluate the rate at the initial point when there are an insignificant amount of products present, so you only have to take into account the reactants. The rate law can be found at other points, but it is much more complicated as there will be both reactants and products...
Sun Mar 04, 2018 3:11 pm
Forum: General Rate Laws
Topic: 15.25 part b
Replies: 1
Views: 130

### Re: 15.25 part b

I think you may have misread the question, part b reads "If [N2O5]0 = 0.0567 mol L-1, what will be the concentration of N2O5 after 3.5h?" so therefore you use 3.5 hours converted into seconds for your time.
Sun Mar 04, 2018 3:04 pm
Forum: First Order Reactions
Topic: orders of a reaction
Replies: 3
Views: 202

### Re: orders of a reaction

The order of a reaction can only be found experimentally, so you can't determine it by only looking at the equation for a reaction. If you are given a chart with different reaction rates for different concentrations of reactants, you can find the ratio to determine the order.
Thu Feb 22, 2018 12:34 pm
Forum: Interesting Applications: Rechargeable Batteries (Cell Phones, Notebooks, Cars), Fuel Cells (Space Shuttle), Photovoltaic Cells (Solar Panels), Electrolysis, Rust
Topic: Reducing Agent/ Oxidizing Agent
Replies: 6
Views: 618

### Re: Reducing Agent/ Oxidizing Agent

The more negative the standard reduction potential of a reaction, the stronger that compound is as a reducing agent. This is because a very negative reduction potential will translate to a very high oxidation potential when the equation is flipped, meaning the compound will be oxidized more strong, ...
Wed Feb 21, 2018 10:55 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 14.15c
Replies: 2
Views: 161

### Re: 14.15c

Sorry that wasn't my question, I was asking about the presence of KOH in the cell diagram.
Wed Feb 21, 2018 9:51 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 14.15c
Replies: 2
Views: 161

### 14.15c

In part c of number 15, why is KOH added to the anode side of the cell diagram? It is not present in the given reaction so I don't understand where it came from.
Wed Feb 14, 2018 10:40 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: confused about 2nd law !!! [ENDORSED]
Replies: 3
Views: 449

### confused about 2nd law !!![ENDORSED]

I know that the second law of thermodynamics states that the entropy of an isolated system has a tendency to increase, but how is this law related to the equation deltaS = qrev/T ?
Wed Feb 14, 2018 10:33 am
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: Zero Degeneracy
Replies: 2
Views: 311

### Re: Zero Degeneracy

No, the smallest value W can have is 1. Degeneracy is calculated by W=(# of orientations)^(#of particles). There must always be at least one orientation for a molecule/particle, and the smallest number of particles you would be dealing with would be 1, which would give you W=1^1=1.
Wed Feb 14, 2018 10:28 am
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: delta U for reversible [ENDORSED]
Replies: 2
Views: 221

### delta U for reversible[ENDORSED]

I understand that delta U is zero for an isothermal expansion, but what if it is reversible? Will delta U=0 in that case?
Wed Feb 14, 2018 10:15 am
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: State Properties
Replies: 5
Views: 487

### Re: State Properties

Heat capacity is the energy required to raise the temperature of a substance by 1 degree C, and it is an extensive property. Specific heat capacity is the energy required to raise one gram of substance by 1 degree C, and is an intensive property. The difference lies in that one in extensive and one ...
Sat Feb 10, 2018 7:55 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Calculating delta H
Replies: 1
Views: 131

### Calculating delta H

I understand that deltaH = q when pressure is constant, but how do you solve for deltaH when the pressure is changing? For example if I am given moles, temperature, and pressure change, how could I use that information to find the change in enthalpy?
Thu Feb 08, 2018 8:43 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Positive cell potentials
Replies: 2
Views: 115

### Re: Positive cell potentials

Yes so that we don't confuse it with negative ones.
Tue Feb 06, 2018 5:19 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: 9.21
Replies: 3
Views: 212

### Re: 9.21

In this case kb is Boltzmann's constant, 1.38x10^-23 J/K
Tue Feb 06, 2018 4:16 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Calculating deltaG
Replies: 2
Views: 150

### Re: Calculating deltaG

If you look at the information you are given in the problem and the equations for deltaG, you can match them up to find the best equation to use.
Tue Feb 06, 2018 4:07 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: hw9.59 standard reaction entropy
Replies: 3
Views: 227

### Re: hw9.59 standard reaction entropy

Yes, you should use the stoichiometric coefficients given in the balanced equations for reactions when finding delta S,G, and H.
Tue Jan 30, 2018 3:08 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: 9.19
Replies: 3
Views: 218

### Re: 9.19

I think in this question we are not concerned with the number of moles. The solutions manual uses the equation S=Cpln(T2/T1), with no n. If the number of moles isn't taken into account, then you will be left with moles in your units at the end.
Tue Jan 30, 2018 2:48 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Question from 1/24/18 Lecture
Replies: 2
Views: 146

### Re: Question from 1/24/18 Lecture

We can equate k to nR because by definition, k=R/N where N is Avogadro's number, in this case the number of gas molecules per mole (n) of gas.
Tue Jan 30, 2018 2:27 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: 9.13 [ENDORSED]
Replies: 6
Views: 525

### Re: 9.13[ENDORSED]

The solutions manual uses R instead of Cv (3/2)R. Why do we use just the R value instead of the whole Cv value?
Thu Jan 25, 2018 3:23 pm
Forum: Phase Changes & Related Calculations
Topic: enthalpy of fusion/vaporization
Replies: 3
Views: 197

### enthalpy of fusion/vaporization

When you are calculating the heat of a phase change from a vapor to a liquid or a liquid to a solid, do you take the negative of the enthalpy of fusion/vaporization? Or do you leave it positive as it would be if you are moving from a solid to a liquid or liquid to a vapor?
Thu Jan 25, 2018 11:07 am
Forum: Phase Changes & Related Calculations
Topic: 8.87
Replies: 2
Views: 135

### Re: 8.87

You use the enthalpy of sublimation when something is changing from a solid directly into a vapor, skipping the liquid state. In this case, the ice is changing first to liquid and then to a vapor, so you have to use both the enthalpy of fusion and that of vaporization.
Thu Jan 18, 2018 1:17 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Isolated system
Replies: 8
Views: 472

### Re: Isolated system

No, you can't do work on an isolated system. Doing work changes the energy of the system, and since in an isolated system the internal energy remains constant, work cannot be done on it.
Wed Jan 17, 2018 7:48 pm
Forum: Phase Changes & Related Calculations
Topic: 8.31
Replies: 2
Views: 170

### Re: 8.31

Sections 8.9 and 8.10 in the textbook go through the derivations for these. They use the ideal gas law combined with the C=q/T to derive these formulas for heat capacity at constant pressure and volume.
Wed Jan 17, 2018 7:44 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: 8.19 heating water in a copper kettle
Replies: 3
Views: 272

### Re: 8.19 heating water in a copper kettle

I think we only need to do this when the container has a non-negligible heat capacity, like a copper pot. The copper will influence the problem because of its specific heat, whereas glass will not.
Wed Jan 17, 2018 3:00 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Energy Change in an Isolated System
Replies: 4
Views: 289

### Re: Energy Change in an Isolated System

Exactly, in order to change the internal energy of the system there must be a transfer of energy as heat, which cannot happen in with an isolated system.
Tue Jan 16, 2018 9:51 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Heat Capacity: U vs H
Replies: 2
Views: 137

### Re: Heat Capacity: U vs H

U is the internal energy of the system, and doesn't refer to heat capacity.
Tue Jan 16, 2018 5:18 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: 8.19
Replies: 2
Views: 189

### 8.19

Calculate the heat that must be supplied to a 500.0-g copper kettle containing 400.0 g of water to raise its temperature from 22.0 'C to the boiling point of water, 100.0 'C. Why does the solutions manual have you add the q of the copper and the q of the water instead of setting q copper = -q water ...
Thu Dec 07, 2017 4:09 pm
Forum: Lewis Acids & Bases
Topic: strong or weak
Replies: 3
Views: 275

### Re: strong or weak

To answer your second question, when ions get larger in an HX acid, the length of the bond between the hydrogen and the ion gets longer. Longer bonds are weaker and more easily broken, allowing more H+ ions to be broken off and released into the solution to create H3O+ ions. This gives a higher conc...
Thu Dec 07, 2017 12:15 pm
Forum: Sigma & Pi Bonds
Topic: Delocalized Pi-Bonding
Replies: 5
Views: 531

### Re: Delocalized Pi-Bonding

For clarification, delocalized pi bonding happens when there is a molecule who's structure has some double and some single bonds, so has a resonance hybrid where each bond has partial double bond character?
Wed Dec 06, 2017 10:41 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Stable Conjugate base
Replies: 1
Views: 223

### Re: Stable Conjugate base

A stable conjugate base means it has more electron-pulling atoms, such as oxygen atoms, to share the negative charge on the molecule. If the negative charge is shared among more atoms, it will have a smaller effect on any one individual atom, making it more stable. A stable conjugate base means its ...
Sat Dec 02, 2017 6:42 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Question 12.19
Replies: 3
Views: 480

### Re: Question 12.19

You are solving for the change in pH, so you need to do final-initial. pH final is .12[HCl] and the initial is [HCl], so your equation for the change in pH would be -log(.12[HCl]) - -log([HCl]). Because of the log rules, where subtracting two log equations is the same as the log of the quotient betw...
Fri Dec 01, 2017 2:45 pm
Forum: Acidity & Basicity Constants and The Conjugate Seesaw
Topic: Why is Kw value typically used at 25 degrees C [ENDORSED]
Replies: 6
Views: 820

### Re: Why is Kw value typically used at 25 degrees C[ENDORSED]

25 degrees Celsius is the standard room temperature value used for most equations and calculations in chemistry. It is just used to show that its not super hot or super cold.
Wed Nov 22, 2017 10:09 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: K and Kc
Replies: 7
Views: 468

### Re: K and Kc

Kc just specifies that you need to use concentrations to find K. If it just says K and the reactants and products are gasses, you use their partial pressures.
Wed Nov 22, 2017 10:06 am
Forum: Naming
Topic: 17.31 part D
Replies: 3
Views: 227

### Re: 17.31 part D

The ligands only have to be in alphabetical order when writing out the name, when writing the formula for the compound the order doesn't matter. You should always write OH2 in coordination compounds instead of H2O.
Tue Nov 21, 2017 9:15 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Homework 17.35
Replies: 1
Views: 126

### Re: Homework 17.35

a chelating complex means that two ligands bind to the same metal center to form a ring. diagrams a and c would form a ring only if the NH2 ligands formed bonds to two different metal centers, and this does not count and a chelate. In diagram b, the two ligand bind to the same metal center.
Tue Nov 21, 2017 8:57 pm
Forum: Naming
Topic: Naming
Replies: 1
Views: 109

### Re: Naming

Yes, on the lecture outline for coordination compounds on Dr. Lavelle's website it says to be familiar with the rules for naming coordination compounds, so we will most likely be expected to know the rules.
Mon Nov 13, 2017 10:13 pm
Forum: Polarisability of Anions, The Polarizing Power of Cations
Topic: Cation & Anion Polarity
Replies: 3
Views: 1408

### Re: Cation & Anion Polarity

Yes! Large anions are highly polarizable because they have many electrons far from the nucleus that are easily distorted. On the other hand, small cations have a high polarizing power because they cause large distortions.
Mon Nov 13, 2017 10:09 pm
Forum: Polarisability of Anions, The Polarizing Power of Cations
Topic: Ionization energy
Replies: 2
Views: 372

### Re: Ionization energy

oxygen has a lower ionization energy than nitrogen because nitrogen is more stable. Nitrogen has one electron in each of its 2p-orbitals, while oxygen has 2 electrons in one 2p-orbital and one electron in each of the other two. This makes nitrogen more stable as its electrons are more evenly distrib...
Tue Nov 07, 2017 10:20 pm
Forum: Molarity, Solutions, Dilutions
Topic: Post Module Assessment Question
Replies: 1
Views: 180

### Re: Post Module Assessment Question

A is wrong bc when a solution is diluted, that means solute is added which changes the concentration, but the amount (moles) of solvent doesn't change. C is wrong for the same reason -- solute is added which will increase the volume of the solute. D is wrong because when you are diluting a solution ...
Tue Nov 07, 2017 10:12 pm
Forum: Ionic & Covalent Bonds
Topic: Homework 3.39
Replies: 3
Views: 261

### Re: Homework 3.39

Yeah, since he hasn't gone over nomenclature in class we aren't expected to know it, so the formulas will be given on the exam.
Mon Oct 30, 2017 4:41 pm
Forum: Trends in The Periodic Table
Topic: Electron Affinity
Replies: 4
Views: 367

### Re: Electron Affinity

Electron affinity does follow the periodic table! Electron affinity increases as you move left to right and increases as you go up. Flourine, being in the top right, has the highest electron affinity of any element.
Mon Oct 30, 2017 4:36 pm
Forum: Lewis Structures
Topic: Knowing compound formulas
Replies: 3
Views: 338

### Re: Knowing compound formulas

I think Dr. Lavelle said in class that since we haven't gone over nomenclature yet in class, we won't be expected to know it on the tests. So he will give us the formulas!
Fri Oct 20, 2017 3:00 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Aufbau Principle - Carbon
Replies: 2
Views: 741

### Re: Aufbau Principle - Carbon

Hi! To write an electron configuration you first need to know the number of electrons in the atom, which in this case is 6. You then fill the sub shells from lowest to highest, starting with 1s, to 2s, 2p, etc. For carbon, you would first fill the 1s sub shell which can fit 2 electrons, giving 1s^2....
Thu Oct 19, 2017 5:57 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: 2.17
Replies: 2
Views: 191

### Re: 2.17

Is that implying that ml is inside of l? I was confused on this question too, and I don't understand how the quantum numbers (n, l, ml) all relate to one another.
Thu Oct 12, 2017 10:40 pm
Forum: Properties of Light
Topic: Photons and Photoelectric effect
Replies: 3
Views: 219

### Re: Photons and Photoelectric effect

yeah! Protons have mass so you can use the momentum formula p=mv, using the mass and velocity of a proton.
Thu Oct 12, 2017 10:28 pm
Forum: Properties of Light
Topic: converting units ( keV )
Replies: 2
Views: 258

### Re: converting units ( keV )

you first convert Kev to ev, by making it 140.511x10^3. you then multiply that by 1.6022x10^-19 Js which is the conversion factor that gives you joules.
Thu Oct 05, 2017 12:10 pm
Forum: Empirical & Molecular Formulas
Topic: E29 Fundamentals
Replies: 3
Views: 305

### Re: E29 Fundamentals

For part b, you look at molar ratios to determine the moles of Cl ions present. From the molecular formula you can see that for every 1 mole of CuCl2 x 4H2O, there are 2 moles of Cl ions. So you just double the number you found in part a and that will give you the moles of Cl. For part d, you find t...
Thu Oct 05, 2017 12:00 pm
Forum: Limiting Reactant Calculations
Topic: L #39
Replies: 4
Views: 290

### Re: L #39

The Roman numeral refers to the charge on tin. I believe that some metals can have a few different charges, so the the IV is clarifying that this is tin with a charge of +4, creating the need for two oxygen atoms each with a charge of -2. Hope that helps !