Search found 49 matches
- Fri Mar 16, 2018 11:05 pm
- Forum: Arrhenius Equation, Activation Energies, Catalysts
- Topic: Transition States
- Replies: 1
- Views: 272
Re: Transition States
Transition states have partial bonds and are not defined as individual molecules.
- Fri Mar 16, 2018 11:02 pm
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: Slow Step Vs. Steady State Approximation
- Replies: 3
- Views: 586
Re: Slow Step Vs. Steady State Approximation
Using the steady step method will get you the same result as using the pre-equilibrium approach. Either way you will need to identify the slow step of the reaction as it is the rate determining step.
- Fri Mar 16, 2018 11:00 pm
- Forum: Arrhenius Equation, Activation Energies, Catalysts
- Topic: Catalysts
- Replies: 2
- Views: 332
Re: Catalysts
A catalyst provides an alternate pathway and that pathway has a lower activation energy than the original. It increases the number of successful collisions.
- Sun Mar 11, 2018 4:21 pm
- Forum: Student Social/Study Group
- Topic: Post All Chemistry Jokes Here
- Replies: 9651
- Views: 3000832
Re: Post All Chemistry Jokes Here
What do chemists call a benzene ring with iron atoms replacing the carbon atoms?
A ferrous wheel.
A ferrous wheel.
- Sun Mar 11, 2018 4:17 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Heat Required to Heat a Substance
- Replies: 5
- Views: 668
Re: Heat Required to Heat a Substance
More complex molecules generally have high heat capacities because they have more degrees of freedom and more ways to store energy. Materials with more atoms per unit volume will generally have higher heat capacities.
- Sun Mar 11, 2018 4:11 pm
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: Using pre-equilibrium approach
- Replies: 3
- Views: 358
Re: Using pre-equilibrium approach
The pre-equilibrium approach should be used on problems where the slow step is not the first step in the reaction and the reaction rate of the later step contains and intermediate. You could also try using the steady state approach, but this is much more complicated and difficult.
- Sun Mar 04, 2018 2:27 pm
- Forum: Student Social/Study Group
- Topic: Post All Chemistry Jokes Here
- Replies: 9651
- Views: 3000832
Re: Post All Chemistry Jokes Here
A photon checks into a hotel and is asked if he needs any help with his luggage. He says, "No, I'm traveling light."
- Sun Mar 04, 2018 2:24 pm
- Forum: First Order Reactions
- Topic: Integrated rate law for first order reaction
- Replies: 3
- Views: 461
Re: Integrated rate law for first order reaction
The integrated rate law for a first order reaction is ln[A]=ln[A]initial-kt. I am unsure what the other equation is that you are referring to.
- Sun Mar 04, 2018 2:21 pm
- Forum: Second Order Reactions
- Topic: Slope of second order reaction
- Replies: 3
- Views: 631
Re: Slope of second order reaction
The variable for a second order reaction that create a linear graph are 1/[A] over time while for a first order reaction it is ln[A] over time and for a zero order reaction it is [A] over time. The 1/[A] creates a positive slope because as the concentration of A decreases 1/[A] increases.
- Sun Feb 25, 2018 7:20 pm
- Forum: Student Social/Study Group
- Topic: Post All Chemistry Jokes Here
- Replies: 9651
- Views: 3000832
Re: Post All Chemistry Jokes Here
If you're not part of the solution, you're part of the precipitate.
- Sun Feb 25, 2018 7:16 pm
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: Dissolving metal in a solution
- Replies: 3
- Views: 472
Re: Dissolving metal in a solution
You will want to balance the equation with the solid metal on the reactants side and the aqueous dissociated ions on the product side. If the formation of the ions is favorable, the metal will dissolve in the solution.
- Sun Feb 25, 2018 7:10 pm
- Forum: Kinetics vs. Thermodynamics Controlling a Reaction
- Topic: Kinetics vs. Thermodynamics
- Replies: 2
- Views: 445
Re: Kinetics vs. Thermodynamics
The rate constant k, associated with kinetics, is related to the activation energy required for a reaction to occur and can tell you about the speed of a reaction and how quickly is reaches equilibrium. Thermodynamics is related to the free energy, ΔG, given off by a reaction and tells you about a r...
- Sun Feb 18, 2018 11:14 pm
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: Cell Diagram
- Replies: 3
- Views: 1042
Re: Cell Diagram
Don't forget to include phases for all of the elements. The Br ions would be (aq).
- Sun Feb 18, 2018 10:58 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Electrochemical Series Definition
- Replies: 4
- Views: 756
Re: Electrochemical Series Definition
An electrochemical series is a list of reduction half reactions listed in order of increasing E°values.
- Sun Feb 18, 2018 10:50 pm
- Forum: Balancing Redox Reactions
- Topic: Basic and Acidic conditions [ENDORSED]
- Replies: 11
- Views: 6931
Re: Basic and Acidic conditions [ENDORSED]
For acidic questions balance with H3O+ and water. For basic conditions use OH- and water.
- Sun Feb 11, 2018 8:22 pm
- Forum: Van't Hoff Equation
- Topic: Free Energy, pressure, and equilibrium constant
- Replies: 2
- Views: 511
Re: Free Energy, pressure, and equilibrium constant
Gibbs free energy is an extensive property that depends on the amount and concentration of substances.
- Sun Feb 11, 2018 8:20 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Positive cell potentials
- Replies: 2
- Views: 334
Re: Positive cell potentials
If you were to leave the + off of your answer on a test I am sure you would get full credit.
- Sun Feb 11, 2018 8:15 pm
- Forum: Balancing Redox Reactions
- Topic: Nature
- Replies: 5
- Views: 655
Re: Nature
Reduction and oxidation occur together. This is why they are called redox reactions.
- Sun Feb 04, 2018 10:28 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Open, closed, or isolated test 1 question
- Replies: 10
- Views: 1583
Re: Open, closed, or isolated test 1 question
This is an open system because it can freely exchange energy and matter with its surroundings.
- Sun Feb 04, 2018 10:27 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Heat Transfer Test 1 Concept Question
- Replies: 2
- Views: 434
Re: Heat Transfer Test 1 Concept Question
Heat is a measure of thermal energy being transferred and does not necessarily result in a change of temperature.
- Sun Feb 04, 2018 4:08 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Periodic Trends
- Replies: 4
- Views: 755
Re: Periodic Trends
Heat capacity is an extensive property and therefore depends on the amount of a substance. Specific heat capacities of elements are different depending on what state they are in. Therefore, it is difficult to measure the periodic trends.
- Sun Jan 28, 2018 7:55 pm
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: Entropy Change equation
- Replies: 1
- Views: 297
Re: Entropy Change equation
The heat capacity equation is Q = ncΔ T
Change in entropy can be calculated using different equations depending on the situation
Boltzmann' equation: S = kB ln W
for an isothermal process ∆S = qREV/T
for a reversible process: ∆S = nR lnV2/V1
at constant volume: ∆ST1 ---> T2= nC ln(T2/T1)
Change in entropy can be calculated using different equations depending on the situation
Boltzmann' equation: S = kB ln W
for an isothermal process ∆S = qREV/T
for a reversible process: ∆S = nR lnV2/V1
at constant volume: ∆ST1 ---> T2= nC ln(T2/T1)
- Sun Jan 28, 2018 7:39 pm
- Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
- Topic: work definition
- Replies: 5
- Views: 670
Re: work definition
Both have to do with a transfer of energy. Work is defined as the amount of energy transferred by a force acting through a distance. Heat is defined as the energy stored as random motion of molecules or atoms.
- Sun Jan 28, 2018 7:32 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Adiabatic vs. Isolated
- Replies: 3
- Views: 522
Re: Adiabatic vs. Isolated
In an adiabatic system there is no transfer of heat while in an isolated system there is no contact with the surroundings and therefore no exchange of energy or matter.
- Sun Jan 21, 2018 3:15 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Change in temperature,volume and pressure for different equations
- Replies: 2
- Views: 319
Re: Change in temperature,volume and pressure for different equations
For enthalpy, delta H, pressure is constant. For change in internal energy, delta U, volume is constant.
- Sun Jan 21, 2018 3:01 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: 8.31? Molar heat capacity of a monatomic idea gas at constant pressure?
- Replies: 1
- Views: 273
Re: 8.31? Molar heat capacity of a monatomic idea gas at constant pressure?
These numbers have to do with the equipartition of energy theorem which involves molecules' degrees of freedom. It depends on translational and rotational degrees of freedom. R is the gas constant.
- Sun Jan 21, 2018 2:37 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: State Functions and Bond Enthalpies
- Replies: 2
- Views: 175
Re: State Functions and Bond Enthalpies
On the other hand, path functions do depend on the path taken from initial to final state. One way to think about state functions is if you had a bank account with $1,000 in it and you took out $100 at once or $25 on four separate occasions, you would have $900 left in your bank account either way a...
- Sun Jan 14, 2018 11:30 am
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Why isn't heat a state function?
- Replies: 2
- Views: 738
Re: Why isn't heat a state function?
Enthalpy is a state function meaning it does not matter what path was taken. It depends only on the initial and final states. Enthalpy requires constant pressure and measures the heat given off or taken up by a reaction. On the other hand, heat is a path function meaning it does depend on the path t...
- Sun Jan 14, 2018 11:21 am
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Extensive vs Intensive Property
- Replies: 3
- Views: 282
Re: Extensive vs Intensive Property
This relates to calorimetry because heat capacity is an extensive property that depends on the amount of the substance while specific heat is an intensive property that does not change based on the amount of the substance.
- Sun Jan 14, 2018 11:12 am
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Reaction Enthalpy vs. Enthalpy of Formation
- Replies: 2
- Views: 345
Re: Reaction Enthalpy vs. Enthalpy of Formation
The reaction enthalpy is the heat taken up or given off during a reaction which is the difference in enthalpies between the products and the reactants. The enthalpy of formation is the change in enthalpy between elements in their standard states to the compound they form.
- Tue Dec 05, 2017 4:17 pm
- Forum: Acidity & Basicity Constants and The Conjugate Seesaw
- Topic: High pKa
- Replies: 1
- Views: 616
Re: High pKa
pH tells you the concentration of hydronium while pKa tells you the substance's ability to give up protons. For both, a lower number means a stronger acid. However, the pH scale is not the same as pKa values. If a substance has a Pka value over 7 it does not mean it is a base.
- Tue Dec 05, 2017 4:04 pm
- Forum: Acidity & Basicity Constants and The Conjugate Seesaw
- Topic: HCOOH vs CH3COOH
- Replies: 2
- Views: 888
Re: HCOOH vs CH3COOH
HCOOH is a slightly stronger acid than CH3COOH because H is slightly more electronegative than the CH3 group. A stronger acid forms a more stable anion when it dissociates and HCOO is more stable than CH3COO.
- Sun Dec 03, 2017 12:00 pm
- Forum: Lewis Acids & Bases
- Topic: HW12.13
- Replies: 2
- Views: 374
Re: HW12.13
The definition of a Lewis acid is a substance than can accept a pair of electrons while a Lewis base is a substance that donates a pair of electrons. Cations, atoms with an incomplete octet, or molecules where the central atom can have an expanded octet can act as Lewis acids. An atom, ion, or molec...
- Wed Nov 29, 2017 4:56 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: 4.13 d
- Replies: 1
- Views: 346
Re: 4.13 d
You use the least electronegative atom as the central atom. Nitrogen is less electronegative than oxygen.
- Sun Nov 26, 2017 2:40 pm
- Forum: Sigma & Pi Bonds
- Topic: Sigma and Pi Bonds
- Replies: 5
- Views: 1038
Re: Sigma and Pi Bonds
A single bond is always a sigma bond. In a a double or triple bond the first bond is always a sigma bond, but any following bonds must be pi bonds.
- Sun Nov 26, 2017 2:37 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: S Character Influencing Bond Angles
- Replies: 2
- Views: 466
Re: S Character Influencing Bond Angles
You can determine the bond angle based on the hybridization. SP has 180 degree bond angle, SP2 has 120 degree bond angle, and SP3 has 109.5 degree bond angle usually. As the number of p orbitals increases the s character decreases as does the bond angle as seen with the given numbers.
- Sun Nov 26, 2017 2:31 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: partial pressure
- Replies: 3
- Views: 358
Re: partial pressure
If all of the species given are gases then partial pressure can be used to calculate the equilibrium constant. If you are given Kp you would also use partial pressure. If you are given Kc you would use concentration.
- Sun Nov 19, 2017 10:44 am
- Forum: Electron Configurations for Multi-Electron Atoms
- Topic: Valence Shell Electron Configuration
- Replies: 2
- Views: 2245
Re: Valence Shell Electron Configuration
Copper is also an exception because its electron configuration is [Ar]3d10 4s1 not [Ar] 3d9 4s2. This is because a half-filled or full d subshell is more stable.
- Sun Nov 19, 2017 10:41 am
- Forum: Electron Configurations for Multi-Electron Atoms
- Topic: 3.5 Give the ground state configuration expected for each of the following ions:
- Replies: 3
- Views: 2793
Re: 3.5 Give the ground state configuration expected for each of the following ions:
You always remove electrons from the outmost shell first. This is because the electrons in front of them are essentially blocking them from the pull of the nucleus.
- Sun Nov 12, 2017 10:19 am
- Forum: Trends in The Periodic Table
- Topic: Hydrogen Electronegativity
- Replies: 4
- Views: 5571
Re: Hydrogen Electronegativity
Hydrogen does not take a full octet. It has a half filled 1s orbital and only wants one more electron. Therefore it has high electronegativity.
- Sun Nov 12, 2017 10:06 am
- Forum: Properties of Light
- Topic: Atomic Spectra
- Replies: 2
- Views: 312
Re: Atomic Spectra
Knowing the series may also be helpful. The Balmer series is associated with energy changes where n=2 and exists in the visible light spectrum. The Lyman series is associated with energy changes where n=1and exists in the UV spectrum. These series are for Hydrogen only.
- Sun Nov 05, 2017 6:24 pm
- Forum: Trends in The Periodic Table
- Topic: electron affinities
- Replies: 2
- Views: 388
Re: electron affinities
The electron affinities are close to zero. Noble gases have complete octets and do not want any more electrons. The Alkaline metals also have very low electron affinity as they often form cations and prefer to give up electrons than gain them.
- Sun Nov 05, 2017 6:14 pm
- Forum: Wave Functions and s-, p-, d-, f- Orbitals
- Topic: Lower in Energy? [ENDORSED]
- Replies: 6
- Views: 843
Re: Lower in Energy? [ENDORSED]
The quantum number n gives the energy level while the angular momentum quantum number tells you the subshell of the electron. So use n as l does not give you information about the energy level. For potassium and Calcium 4s has lower energy than 3d which may seem counterintuitive, but for Scandium th...
- Sun Oct 29, 2017 9:34 pm
- Forum: Wave Functions and s-, p-, d-, f- Orbitals
- Topic: 4s and 3d orbitals
- Replies: 5
- Views: 1761
Re: 4s and 3d orbitals
The electrons in the 3d orbitals essentially shield electrons in the 4s orbital from the nucleus, so electrons in the 4s orbital are lost first during ionization.
- Sun Oct 29, 2017 6:48 pm
- Forum: Lewis Structures
- Topic: Sulfate Ion
- Replies: 4
- Views: 597
Re: Sulfate Ion
Sulfur can have an expanded octet by using the empty 3d orbitals to accommodate "extra" electrons.
- Sun Oct 22, 2017 5:59 pm
- Forum: Heisenberg Indeterminacy (Uncertainty) Equation
- Topic: heisenberg post-module question 21
- Replies: 1
- Views: 260
Re: heisenberg post-module question 21
I would just choose the answer choice that best fits the question and repeat the calculations without worrying about them being included in the given answers.
- Sat Oct 21, 2017 6:54 pm
- Forum: Electron Configurations for Multi-Electron Atoms
- Topic: 3d and 4s
- Replies: 3
- Views: 331
Re: 3d and 4s
For Potassium and Calcium, 4s is lower in energy than 3d. From Scandium on 3d is lower in energy
- Sat Oct 14, 2017 9:07 pm
- Forum: Properties of Light
- Topic: 1.15 [ENDORSED]
- Replies: 2
- Views: 290
Re: 1.15 [ENDORSED]
The wavelength of the emitted photon is 102.6 nm which is in the ultraviolet spectrum. This section of the emission spectra for Hydrogen is know as the Lyman series which always corresponds to n=1 as one of the principle energy levels.
- Tue Oct 10, 2017 8:08 pm
- Forum: Properties of Light
- Topic: Calculating the wavelength of light [ENDORSED]
- Replies: 5
- Views: 937
Re: Calculating the wavelength of light [ENDORSED]
This equation is used to calculate the energy of a photon when you are given the wavelength of the light. For example, you could use this equation on homework question 1.9 where you are given the wavelength 2.5 nm and asked for the frequency and energy of the photon.