## Search found 62 matches

Fri Mar 15, 2019 10:13 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Test 2 Question 7
Replies: 3
Views: 308

### Test 2 Question 7

Can someone explain why cooling a hot cup of coffee after it was brewed spontaneous (delta G < 0) when melting ice is also spontaneous?
Mon Mar 11, 2019 10:36 pm
Forum: Administrative Questions and Class Announcements
Topic: Final Exam Topics
Replies: 8
Views: 322

### Re: Final Exam Topics

Whatever is on the syllabus and outline will be tested on.
Mon Mar 11, 2019 10:20 pm
Forum: Ideal Gases
Topic: ICE
Replies: 8
Views: 207

### Re: ICE

We can assume x is negligible unless stated otherwise.
Mon Mar 11, 2019 8:37 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Ideal Gas C
Replies: 5
Views: 426

### Re: Ideal Gas C

R is the gas constant and it is usually in the units of J/K/mol.
Sat Mar 09, 2019 11:27 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: k & K
Replies: 18
Views: 813

### Re: k & K

k is Boltzmann constant, which is equal to 1.38064852 × 10^-23 m2 kg s^-2 K^-1. K is the equilibrium constant of a reaction, which is calculated by the concentration of the products over concentration of the reactants.
Sat Mar 09, 2019 11:24 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Kp
Replies: 7
Views: 277

### Re: Kp

You can use either units for the Kp value, but you have to keep it consistent throughout your equation.
Sat Mar 09, 2019 11:21 pm
Forum: First Order Reactions
Topic: Half-Life 1st Order Reaction
Replies: 6
Views: 202

### Re: Half-Life 1st Order Reaction

The initial concentration gets cancelled out when you derive the equation. Thus you end up with the equation t1/2 = 0.693/k
Sat Mar 09, 2019 11:14 pm
Forum: Balancing Redox Reactions
Topic: Oxidation number?
Replies: 12
Views: 2587

### Re: Oxidation number?

Group 1 (alkali metals) elements will always have a +1 charge, Group 2 has a +2 charge, group 7 has a -1 charge.
Sat Mar 02, 2019 3:15 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Nernst
Replies: 4
Views: 156

### Re: Nernst

0.0592 comes from changing the equation from terms of natural log (ln) to log base ten.
Sat Mar 02, 2019 3:13 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Equations
Replies: 5
Views: 464

### Re: Equations

The Cv for diatonic molecules is Cv = 5/2 R. I know they gave the Cv for a monatomic molecule.
Sat Mar 02, 2019 3:06 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: E
Replies: 4
Views: 186

### Re: E

E is not a state function but through Gibb's free energy, which is a state function, can be broken down into multiple steps.
Sat Feb 23, 2019 11:59 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cathode vs. Anode
Replies: 9
Views: 297

### Re: Cathode vs. Anode

Cathodes will have electrons on its reactants side while anodes will have electrons on its products side when writing out the half reactions.
Sat Feb 23, 2019 11:53 pm
Forum: Van't Hoff Equation
Topic: Galvanic/Voltaic Cell
Replies: 2
Views: 129

### Re: Galvanic/Voltaic Cell

They are! They both mean the same thing. "Galvanic cell" was named after Luigi Galvani, and "voltaic" is named afterAlessandro Volta, but they are both electrochemical cells!
Sat Feb 23, 2019 11:50 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Replies: 4
Views: 215

Just to add on, charge = moles of electrons transferred times Faraday = nF
Mon Feb 11, 2019 2:44 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Question 8.39 (Sixth Edition)
Replies: 4
Views: 190

### Re: Question 8.39 (Sixth Edition)

You have to break this problem up into two steps:

1. Find m * Heat of fusion
2. Find m * C * delta T

When you find those two values, you add them up, and that is the total heat needed.
Mon Feb 11, 2019 2:35 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Question 8.53 (Sixth Edition)
Replies: 2
Views: 120

### Re: Question 8.53 (Sixth Edition)

As given, it says to balance the chemical equation first, and then use q = - m * delta T to get q because q reaction = -q calorimeter.

Hope this helps!
Mon Feb 11, 2019 2:30 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: 3/2 R and 5/2 R
Replies: 3
Views: 158

### Re: 3/2 R and 5/2 R

Cv = 3/2 R This constant is for solving entropy of a system with constant volume
Cp = 5/2 R This constant is for solving entropy of a system with constant pressure
Mon Feb 04, 2019 3:14 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Types of enthalpy
Replies: 2
Views: 139

### Re: Types of enthalpy

Standard enthalpy of formation is the standard reaction enthalpy for the formation of 1 mole of substance from its elements in their most stable form and is measured in units of kJ/moles
Mon Feb 04, 2019 3:03 pm
Forum: Calculating Work of Expansion
Topic: Degeneracy
Replies: 6
Views: 294

### Re: Degeneracy

Degeneracy, W, is the number of possible ways of achieving a given energy state.
It is determined on the number of particles and the number of arrangements.
For example if N particles and each particle can be in one of two states:
W = 2^N
Mon Feb 04, 2019 2:59 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Bond Enthalpy
Replies: 2
Views: 107

### Re: Bond Enthalpy

Lewis structure will most likely not going to be given on the test since we were expected to know how to do it 14A, but the bond enthalpies are likely going to be given on the test.
Tue Jan 29, 2019 4:05 pm
Forum: Calculating Work of Expansion
Topic: value of R?
Replies: 4
Views: 187

### Re: value of R?

The values of constant R are different due to the different units shown in each equation.
Tue Jan 29, 2019 3:53 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Isolated systems
Replies: 10
Views: 258

### Re: Isolated systems

An isolated system is a system that has no contact with its surroundings, but it may or may not have a fixed volume, depending on its conditions.
Tue Jan 29, 2019 3:47 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Heat and work
Replies: 4
Views: 202

### Re: Heat and work

Heat is the transfer of energy between thermodynamical systems, while work is the transfer of energy other than work.

They are related in the equation: delta U = q +w
where U is the change in internal energy, q is the heat transferred in or out of the system, and w is work.
Mon Jan 21, 2019 2:07 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Le Chatelier's Principle
Replies: 4
Views: 162

### Re: Le Chatelier's Principle

Adding on to that, his principle applies to changing physical parameters Pressure and Temperature.

When pressure increases, the reaction favors the side with the least moles of gas.
Mon Jan 21, 2019 1:49 pm
Forum: Administrative Questions and Class Announcements
Replies: 179
Views: 12685

On #4a Worksheet 2, I keep getting pH=4.40, while the answer key says 4.30, when both using the quadratic formula and the shortcut way. I don't understand how to get the answer to
Mon Jan 21, 2019 1:46 pm
Forum: Administrative Questions and Class Announcements
Replies: 179
Views: 12685

For #3 on Worksheet 2, how can you find the Kb value? I'm not quite what is the first step or what the base is.
Mon Jan 14, 2019 8:11 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Kc, Kw, and pKw
Replies: 4
Views: 2050

### Re: Kc, Kw, and pKw

Kc is the equilibrium constant, which is measured using products and reactants in either the gaseous or aqueous state.
Kw is the autoprolysis constant of water at 25 degrees Celsius and is always equal to 1.0 x 10^-14.
pKw is the -log(Kw) as p is shorthand for -log.
Mon Jan 14, 2019 8:07 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: (aq) in calculating K
Replies: 9
Views: 223

### Re: (aq) in calculating K

Aqueous means that the substance is dissolved in water. It is counted when calculating concentrations and the equilibrium constant Kc.
Mon Jan 14, 2019 7:43 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Are Either Products or Reactants Favored?
Replies: 3
Views: 82

### Re: Are Either Products or Reactants Favored?

No, products are favored but they are not greatly favored. You are right when K>1 there are more more products than reactants at equilibrium.
Mon Jan 07, 2019 11:08 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Video Module Post Assessment Question 12
Replies: 3
Views: 90

### Re: Video Module Post Assessment Question 12

"12. For a chemical reaction that has reached equilibrium which statement is false?"
The question asked for you to select the false statement. You were correct that the forward reaction is the same as the reverse reaction rate, but that statement is not false.
Mon Jan 07, 2019 10:59 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 11.7C
Replies: 2
Views: 117

### Re: 11.7C

For every 1 molecule of X2, it decomposes to 2 molecules of X. That is why there is a coefficient of 2 in front of X.
Mon Jan 07, 2019 10:49 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 6th edition hw problem 11.7
Replies: 3
Views: 130

### Re: 6th edition hw problem 11.7

905084274 wrote:Thank you! How do you find the % decomposition? it says (6/11) x 100% but where does 6 come from?

You start out with 11 X2 molecules, and after the reaction reaches equilibrium, you are left with 5 X2 molecules. This means that 6 of the initial 11 X2 molecules decomposed to X.

Hope this helps!
Fri Dec 07, 2018 8:54 pm
Forum: Hybridization
Topic: lone pairs of e-
Replies: 4
Views: 203

### Re: lone pairs of e-

No. I think we need to find hybridizations of bonds and atoms only. I don't think we have done an example with the hybridizations of lone electrons yet.
Fri Dec 07, 2018 8:50 pm
Forum: Ionic & Covalent Bonds
Topic: Bond length
Replies: 2
Views: 157

### Re: Bond length

Ozone's bond lengths are the same because the bond lengths are the averages of the two bonds (the double and the single bond).

Oxygen would have the strongest bond due to having a double bond length, which average is shorter than ozone's average (double + single bond).
Fri Dec 07, 2018 8:48 pm
Forum: Lewis Acids & Bases
Topic: thymine bonds
Replies: 1
Views: 78

### Re: thymine bonds

The Nitrogen atoms have a lone pair, which can accept protons.
Wed Nov 28, 2018 11:54 pm
Forum: Hybridization
Topic: Bond Strengths
Replies: 4
Views: 162

### Re: Bond Strengths

In a Carbon Carbon double bond, it consists of one pi bond and one sigma bond. Pi bonds are weaker than sigma bonds due to less overlap between the p-orbitals, so therefore, the double bond (1 pi bond and 1 sigma bond) is less than the sum of 2 sigma bonds.
Hope this helps!
Wed Nov 28, 2018 12:21 am
Forum: Interionic and Intermolecular Forces (Ion-Ion, Ion-Dipole, Dipole-Dipole, Dipole-Induced Dipole, Dispersion/Induced Dipole-Induced Dipole/London Forces, Hydrogen Bonding)
Topic: London forces vs. Dipole-Dipole Importance
Replies: 1
Views: 139

### Re: London forces vs. Dipole-Dipole Importance

When the elements are in the same group, the difference in electronegativity isn't that large, so the size of the molecule (London forces) is a more important factor.
Tue Nov 27, 2018 11:23 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Week 7 Step Up WS Question D
Replies: 1
Views: 75

### Week 7 Step Up WS Question D

On question D it tells us to draw the lewis structure of XeF2, name the shape, and list the bond angles. I got the Lewis structure to have two bond pairs and three lone pairs. The key says the molecular shape is linear, but why?
Fri Nov 23, 2018 12:15 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Bent - Lone Pairs
Replies: 8
Views: 374

### Re: Bent - Lone Pairs

Are the angles the same or different whether it is one lone pair or two lone pairs in the bent shape? I presume the bond angles will be different depending on how many lone pairs there are in a bent shape. For sure they are both less than 109.5 degrees, but the more lone pairs there are the smaller...
Fri Nov 23, 2018 12:01 pm
Forum: Dipole Moments
Topic: Bond Angles
Replies: 8
Views: 355

### Re: Bond Angles

For a tetrahedral shape (4 areas of electron density) with no lone pairs the bond angle is 109.5 degrees, and if there is a tetrahedral shape (4 areas of electron density) with one or more lone pairs, than the bond angle is less than 109.5.
Fri Nov 23, 2018 11:57 am
Forum: Hybridization
Topic: S-Character Bond Angle Trend
Replies: 3
Views: 78

### S-Character Bond Angle Trend

How come as the s-character of the hybrids increase, the bond angle between the two hybrid orbitals also increase?
Wed Nov 14, 2018 9:46 pm
Forum: Ionic & Covalent Bonds
Topic: Hydrogen Bond
Replies: 7
Views: 445

### Re: Hydrogen Bond

Yes! A molecule can have both hydrogen bonds and covalent bond. Hydrogen bonds are INTERmolecular while covalent bonds are INTRAmolecular.
Wed Nov 14, 2018 7:29 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Bond Angles
Replies: 8
Views: 567

### Re: Bond Angles

I also agree that there's no calculations to determine bond angle; however, knowing how many lone pairs and bonded pair electrons may aid you in knowing the shape of the compound and then the assumed bond angle.
Wed Nov 14, 2018 7:16 pm
Forum: Lewis Structures
Topic: Boron Trifluoride
Replies: 8
Views: 294

### Re: Boron Trifluoride

That's why it's shape is trigonal planar.
Wed Nov 07, 2018 1:03 pm
Forum: Lewis Structures
Topic: Formal Charge
Replies: 14
Views: 477

### Re: Formal Charge

I agree with Rachael. It depends on the electronegativity of the atom. Whatever element is the most electronegative in the compound should have the charge. It doesn't have to be specifically the central atom or the outer one.
Tue Nov 06, 2018 6:58 pm
Forum: Octet Exceptions
Topic: Octet rule vs. Formal charge
Replies: 7
Views: 387

### Re: Octet rule vs. Formal charge

Row three elements and below can hold more than an octet is because they have a d-orbital shell to expand on.
Tue Nov 06, 2018 6:36 pm
Forum: Electronegativity
Topic: Electron affinity
Replies: 5
Views: 231

### Re: Electron affinity

An exception to the trend is that the electron affinities of the elements in column 15 are lower than those of column 14.

For example, if we needed to rank C, N, O, F in order of increasing electron affinities, the order would be N<C<O<F.
Thu Nov 01, 2018 4:19 pm
Forum: Resonance Structures
Replies: 5
Views: 251

Because radicals have unpaired electrons, they are highly reactive and therefore cause a dangerous amount of damage.
Thu Nov 01, 2018 4:12 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Degeneracy
Replies: 4
Views: 466

### Re: Degeneracy

The number of degenerate orbitals of an orbital is equal to twice angular momentum plus one (# degenerate orbitals = 2l + 1), so the s-orbital will have 1 degenerate orbital, the p-orbital will have 3, the d-orbital will have 5, and the f-orbital will have 7.
Thu Nov 01, 2018 3:57 pm
Forum: DeBroglie Equation
Topic: De Broglie vs. speed of light/Einstein equation
Replies: 3
Views: 342

### De Broglie vs. speed of light/Einstein equation

When would you use De Broglie's equation (E=h/p) compared to using the Einstein equation (E=hc/lambda)?
Thu Oct 25, 2018 8:10 pm
Forum: Properties of Electrons
Topic: mass of electron
Replies: 5
Views: 300

### Re: mass of electron

The mass of the electron is given in the "Constants and Equations" sheet, although just realize when to switch from grams to kilograms when calculating equations calculating energy in general.
Thu Oct 25, 2018 8:07 pm
Forum: Einstein Equation
Topic: Units
Replies: 17
Views: 910

### Re: Units

105002507 wrote:When do we use kg?

We use kg when we are calculating energy, since the units are in jules (kg·m^2·s^-2)
Thu Oct 25, 2018 8:05 pm
Forum: DeBroglie Equation
Topic: Momentum
Replies: 10
Views: 782

### Re: Momentum

The mass and the velocity separately and make you multiply it together to be momentum (p = m x v), but other than that I'm sure the momentum will be given most of the time from the problems I did in the homework.
Fri Oct 19, 2018 4:05 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Electrostatic Potential Energy Example
Replies: 2
Views: 126

### Electrostatic Potential Energy Example

I am a bit confused with the example of today's lecture of the electrostatic potential energy example Lavelle did using carbon as one of the the q's. Can someone explain to me what he was trying to convey?
Fri Oct 19, 2018 3:37 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: 6th Edition 1.43
Replies: 2
Views: 59

### Re: 6th Edition 1.43

"h" is Plank's constant, and the constant you used for h was for the (h bar) x 1/2.
Fri Oct 19, 2018 3:33 pm
Forum: Properties of Light
Topic: Equations
Replies: 7
Views: 184

### Re: Equations

amogha_koka3I wrote:Will we be required to know how to derive De Broglie's Equation?

No, De Broglie's Equation is given on the "Constants and Equation" page, but it is not labeled as De Broglie's equation.
Thu Oct 11, 2018 10:56 pm
Forum: Einstein Equation
Topic: Question 9; 6th edition
Replies: 3
Views: 154

### Re: Question 9; 6th edition

For frequency, the standard unit is in s^-1 or Hertz (Hz). For wavelengths, meter is standard in calculations, however, you can change it to nanometers with conversions.
Thu Oct 11, 2018 10:38 pm
Forum: Properties of Light
Topic: speed of light
Replies: 8
Views: 345

### Re: speed of light

You can use 3.00 x 10^8 m/s, but you could use 2.998 x 10^8 or 2.99792 x 10^8 (in Lavelle's constants and equations sheet).
Thu Oct 11, 2018 10:18 pm
Forum: SI Units, Unit Conversions
Topic: TB 6th Edition E9 Part C
Replies: 1
Views: 146

### Re: TB 6th Edition E9 Part C

For every one mole of epson salt there is 7 moles of H2O, so the multiplication is to match the ratio.
Wed Oct 03, 2018 2:56 pm
Forum: Molarity, Solutions, Dilutions
Topic: Relationship between density and molarity
Replies: 2
Views: 895

### Re: Relationship between density and molarity

I'm assuming that you were given the mass of a substance (6.54 grams) and the density of the substance (0.7857 g/cm^3). Since the equation was D= m/V he substituted in D and m to find volume. I think he was trying to say like the C =n/V problems, you can find any variable of the D = m/V equation as ...
Wed Oct 03, 2018 2:38 pm
Forum: Molarity, Solutions, Dilutions
Topic: mixtures and separation terminology
Replies: 2
Views: 112

### Re: mixtures and separation terminology

We will encounter them in problems eventually, mostly when given a problem where you have to make an experiment or when an experiment is being done. Like the person above me said, it is best to understand them now.
Wed Oct 03, 2018 2:22 pm
Forum: Balancing Chemical Reactions
Topic: Combustion Reactions.
Replies: 8
Views: 958

### Re: Combustion Reactions.

Yes, Oxygen is always needed for a combustion reaction to occur, and the products will always have CO2 and H2O.