## Search found 40 matches

Sat Mar 17, 2018 7:53 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Practice Midterm W18 #3A
Replies: 1
Views: 299

### Practice Midterm W18 #3A

Can someone please explain how I would go about solving this problem? It reads: Lex Luthor finds a sealed box that has two compartments. He puts 9.00g of Helium gas in the first compartment, and 125g of Krypton gas in the second. The compartment with Krypton is 3 times the size of the compartment wi...
Thu Mar 15, 2018 9:27 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Heat Capacity of Water
Replies: 4
Views: 430

### Re: Heat Capacity of Water

You are correct. It takes a lot of energy to break the hydrogen bonds in water. Also water is slightly polar so energy is also needed to break the bonds between H2O molecules.
Wed Mar 14, 2018 10:07 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: I'm confused on the formula for calculating cell potential?
Replies: 1
Views: 198

### Re: I'm confused on the formula for calculating cell potential?

When you use the equation given on the equations sheet for tests, you always subtract E°cathode-E°anode leaving the numbers as they are given to you. Another way to solve for E°cell is to determine which is the cathode and which is the anode. Once you have determined which is the anode you change th...
Wed Mar 14, 2018 10:02 pm
Forum: General Rate Laws
Topic: Powers of Concentrations in Rate Law`
Replies: 2
Views: 186

### Re: Powers of Concentrations in Rate Law`

The order of a rate law is determined experimentally using the method of initial rates or by looking at the graphs. When the observed rate law is given along with the elementary steps of a reaction, you can use the pre-equilibrium approach to determine the slow step that determines the rate of the o...
Wed Mar 14, 2018 9:58 pm
Forum: Phase Changes & Related Calculations
Topic: Test 1 Question 7
Replies: 1
Views: 182

### Re: Test 1 Question 7

The equation to use here is q=mCΔT. The heat lost by the tea will be transferred to the ice , therefore q(ice)= -q(tea). However, the ice will melt as it heats up so the ΔH(fusion) of water must be added to the side with the q(ice). Plug in the values and leaving T(final) as x for both sides. Solve ...
Wed Mar 14, 2018 9:50 pm
Forum: Balancing Redox Reactions
Topic: Lecture 3/14
Replies: 3
Views: 309

### Re: Lecture 3/14

For a galvanic cell the over charge of the cell must be positive, so you determine which one to switch based on which one will make the charge positive.
Wed Mar 14, 2018 9:49 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Pre-Equilibrium Approach
Replies: 1
Views: 168

### Re: Pre-Equilibrium Approach

The problem will likely not tell you. You determine the slow step by finding the rates of every step starting in step 1. If the rate for step 1 does not match the overall rate law then it is not the slow step and you will have to check step 2. You go in order finding the rate laws of each elementary...
Wed Mar 14, 2018 9:47 pm
Forum: General Rate Laws
Topic: Rate Law
Replies: 6
Views: 671

### Re: Rate Law

The order of a rate law is determined experimentally and cannot be determined using the coefficients in the reaction. However, when using the pre-equilibrium approach you use the coefficient as the exponent, but this can only be done when the observed rate law is given and you are trying to determin...
Wed Mar 14, 2018 9:42 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: delta s surrounding and system
Replies: 3
Views: 1860

### Re: delta s surrounding and system

The equation for entropy is q rev/ T. The heat lost by the system will be gained by the surroundings and vice versa. So on the equations for entropy will have -q. Furthermore, when the system loses entropy, the surroundings gain it. Hope this helps!
Wed Mar 14, 2018 7:26 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: delta s surroundings
Replies: 3
Views: 371

### Re: delta s surroundings

This is because any heat lost by the system is gained by the surroundings and vise versa; therefore, q has opposite signs.
Tue Mar 13, 2018 9:09 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: catalysts and intermediates
Replies: 2
Views: 252

### Re: catalysts and intermediates

I believe catalysts are in the first step as a reactants and get cancelled out later in the mechanism. An intermediate is produced within the mechanism and then cancelled out. Both are cancelled, but a catalyst is a reactant in the beginning of the whole mechanism while an intermediate is made withi...
Tue Mar 13, 2018 9:08 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Question 15.47
Replies: 4
Views: 283

### Re: Question 15.47

Chlorine is an intermediate because it is produced in step 1, but it is used as a reactant in step 2; therefore, they cancel out, and the overall reaction does not include it.
Tue Mar 13, 2018 9:01 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Coefficients in oxidation
Replies: 2
Views: 229

### Re: Coefficients in oxidation

Coefficients do not matter when determining oxidation states. They only matter when determining how many electrons were transferred.
Tue Mar 13, 2018 8:57 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Oxidizing and reducing agents
Replies: 2
Views: 255

### Re: Oxidizing and reducing agents

I do not fully understand your question, but the reducing agent gives electrons while the oxidizing agent receives electrons. Sometimes an element or compound can act as both.
Sun Mar 04, 2018 9:26 pm
Forum: Zero Order Reactions
Topic: Determining Reactions
Replies: 2
Views: 215

### Re: Determining Reactions

One way we have learned to determine the order of each reactant in a reaction is the method of initial rates. Using this method we run many experiments and determine the order of each reactant by seeing how a change in initial concentration of a reactant changes the initial rate of the reaction. Add...
Sun Mar 04, 2018 9:23 pm
Forum: General Rate Laws
Topic: Stoichiometry coefficients
Replies: 3
Views: 270

### Re: Stoichiometry coefficients

The rate law is determined experimentally; the stoichiometric coefficients are not enough to write a rate law and determine the order.
Sun Mar 04, 2018 8:03 pm
Forum: General Rate Laws
Topic: Half Life
Replies: 6
Views: 360

### Half Life

Can someone explain what the half life of a reaction is? And why would we be interested in a half life of a reaction?
Sun Mar 04, 2018 7:57 pm
Forum: Balancing Redox Reactions
Topic: Test 2, Q5
Replies: 4
Views: 321

### Re: Test 2, Q5

I believe their order is determined based on their standard reduction potentials. The ones with the smallest reduction potentials are the ones with the most reducing power.
Thu Mar 01, 2018 10:55 pm
Forum: General Rate Laws
Topic: Determining Order [ENDORSED]
Replies: 8
Views: 464

### Re: Determining Order[ENDORSED]

To determine the order of the overall reaction you add the orders of the reactants.
Mon Feb 26, 2018 1:04 am
Forum: Balancing Redox Reactions
Topic: Water in balancing reactions
Replies: 4
Views: 305

### Re: Water in balancing reactions

Yes, water is always necessary to balane the oxygen in both basic and acidic solutions. In basic solutions, water is also needed to balance out the hydrogen.
Sun Feb 25, 2018 10:46 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Midterm Q3A
Replies: 2
Views: 341

### Re: Midterm Q3A

To solve this problem you find the heat needed to raise the temperature of the pot to 100 degrees C and the heat required to raise the temperature of the water to 100 degrees C. You add the heat values to answer the first question. To find the percentage of heat used on the water, you divide the hea...
Sun Feb 25, 2018 10:43 pm
Forum: General Rate Laws
Topic: rate constants
Replies: 7
Views: 494

### Re: rate constants

A rate constant represents how fast a chemical reaction will take place based on the concentrations of the reactants and products. You find it by plugging in the molar concentrations into your rate equation with their respective order and equaling it to the rate of the reaction.
Sun Feb 18, 2018 6:30 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell Notation
Replies: 1
Views: 161

### Re: Cell Notation

Pt(s) is included in the outer portion of cell notation when it is being used as an electrode. Pt(s) is used as an electrode when there is no solid in the half reaction. It is needed to transport or receive electrons, but it does not react.
Sun Feb 18, 2018 6:19 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell diagrams
Replies: 1
Views: 116

### Re: Cell diagrams

It does not necessarily have to be like that, but people and textbooks usually put the anode on the left. However, on an exam it could be the other way around. Essentially it does not matter. You just have to make sure which is which by checking the half reactions.
Sun Feb 18, 2018 6:10 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 14.11
Replies: 2
Views: 240

### Re: 14.11

The anode half cell is where oxidation happens. The cathode part is where reduction happens. During oxidation there is a loss of electrins. Dheing reduction there is a gain of electrons.
Tue Feb 13, 2018 3:58 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: delta U [ENDORSED]
Replies: 10
Views: 2399

### Re: delta U[ENDORSED]

Can someone explain why delta U is 0 in the isothermal expansion of an ideal gas?
Sun Feb 11, 2018 11:09 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Midterm 2018W [ENDORSED]
Replies: 4
Views: 252

### Re: Midterm 2018W[ENDORSED]

Hello Diego!

Yes there will be lecture that day.
Sun Feb 11, 2018 9:25 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Different ways to calculate deltaG
Replies: 2
Views: 219

### Re: Different ways to calculate deltaG

We use an equation to calculate delta G based on the information we are given in the problem.
Sun Feb 11, 2018 9:20 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Maximum Potential
Replies: 2
Views: 286

### Maximum Potential

Can someone elaborate on what the max potential of a cell means?
Wed Feb 07, 2018 12:16 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Delta G
Replies: 3
Views: 233

### Delta G

What is the difference between ∆G and ∆G°?
Mon Jan 22, 2018 4:47 pm
Forum: Calculating Work of Expansion
Topic: expansion work
Replies: 2
Views: 191

### Re: expansion work

In expansion work the pressure is usually constant and given in the problem; therefore the equation is work=−PΔV.
Mon Jan 22, 2018 1:12 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Internal Energy and Enthalpy [ENDORSED]
Replies: 2
Views: 274

### Internal Energy and Enthalpy[ENDORSED]

Under what conditions if any is the change in internal energy and the change in enthalpy the same?
Sun Jan 21, 2018 11:33 pm
Forum: Phase Changes & Related Calculations
Topic: enthalpy vs. heat
Replies: 2
Views: 201

### Re: enthalpy vs. heat

Heat is a path function because the amount of heat a system has is based on how it went from one state to another; however, enthalpy only depedns on the final and initial states.
Sun Jan 21, 2018 11:23 pm
Forum: Student Social/Study Group
Topic: First Test Topics
Replies: 2
Views: 450

### Re: First Test Topics

Test 1 will not have calculations on work and internal energy. Only conceptual questions will appear on these topics. We do not have to read 8.18 and 8.20.
Sun Jan 21, 2018 11:14 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: the sign of q
Replies: 5
Views: 208

### Re: the sign of q

If it is said that system requires heat then the sign of q will be positive because the system is absorbing heat. You can tell the sign of q based on the wording. If a system cools down or gives off heat then the sign of q will be negative.
Fri Dec 08, 2017 12:21 am
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Equilibrium Shift
Replies: 2
Views: 177

### Re: Equilibrium Shift

Will there be any approximation chemical equilibrium problems on the final?
Sun Dec 03, 2017 8:57 pm
Forum: Sigma & Pi Bonds
Topic: What is a localized and delocalized Bond?
Replies: 5
Views: 23147

### Re: What is a localized and delocalized Bond?

Localized electrons stay in between two atoms. Delocalized electrons are not confined to any space and go outside their boundaries.
Wed Nov 29, 2017 9:06 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: 17.35 Chelating Complexes
Replies: 4
Views: 405

### 17.35 Chelating Complexes

Can someone explain chelating complexes to me, and why is 17.35 have B as the one to form a chelating complex?
Thu Nov 16, 2017 11:08 pm
Forum: Hybridization
Topic: Hybridization in Carbon
Replies: 3
Views: 196

### Re: Hybridization in Carbon

The double bond counts as one domain of electron density and when determining hybridization the type of bond does not matter. Only the number of electon domains, so it would be sp^2.
Thu Nov 16, 2017 4:31 pm
Forum: Hybridization
Topic: Hybridization and lone pairs
Replies: 2
Views: 268

### Re: Hybridization and lone pairs

Each pair of electrons occupies one sp^3 orbital. There is no different rule for hybridization of central atoms with lone pairs; therefore, the oxygen in water has 4 sp^3 orbitals.

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