## Search found 60 matches

Fri Mar 15, 2019 3:10 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Catalyst and Activation Energy
Replies: 2
Views: 141

### Re: Catalyst and Activation Energy

The catalyst provides a new pathway altogether for the reaction, which has a different reaction mechanism as well. The new pathway has a lower activation energy than the previous pathway, which is how the reaction is sped up.
Fri Mar 15, 2019 3:07 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Partial Pressure
Replies: 4
Views: 341

### Re: Partial Pressure

The equilibrium partial pressure expression should not include solids, as they do not have a partial pressure. In this case, the partial pressure should be equal to the Kp value because there is no other value in this expression.
Fri Mar 15, 2019 3:05 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Purpose of Arrhenius equation
Replies: 2
Views: 122

### Re: Purpose of Arrhenius equation

A, the frequency factor or pre exponential factor will give information about the number of collisions with correct orientations. Generally, the higher the frequency factor the higher the rate constant k and thus the rate of reaction.
Sun Mar 10, 2019 2:45 pm
Forum: First Order Reactions
Topic: Units for lnconc
Replies: 1
Views: 75

### Re: Units for lnconc

The time would generally be in seconds, but depends on the units that you are given. ln[A] has no units, because you can't take the natural log of something with units. This is why K, the slope, has units of 1/sec.
Sun Mar 10, 2019 2:40 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Molecularity
Replies: 3
Views: 180

### Re: Molecularity

Molecularity refers to the number of species in an elementary step. In a unimolecular reaction, there is only one species in the elementary step. The reaction can be unimolecular if there is a rearrangement of a single molecule that produces product.
Sun Mar 10, 2019 2:23 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: reaction intermediates
Replies: 2
Views: 98

### Re: reaction intermediates

The reaction intermediates are species not included in the reactants or products side. When you have different steps in the reaction, you have to determine which species aren't part of the overall reaction, and these are the intermediate species.
Thu Feb 28, 2019 7:03 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Including Electrode in Cell Diagram
Replies: 2
Views: 148

### Re: Including Electrode in Cell Diagram

If the chemical equation does not have a conducting solid then you would need Pt(s) in the cell diagram, as this acts as the conducting solid which allows electrons to transfer from cell to cell.
Thu Feb 28, 2019 7:01 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: H+ and OH- in cell diagrams
Replies: 1
Views: 80

### Re: H+ and OH- in cell diagrams

Yes, you generally include H+ and OH- to indicate either basic or acidic conditions. However, spectator ions do not need to be included.
Thu Feb 28, 2019 5:59 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Order of Aqueous
Replies: 2
Views: 120

### Re: Order of Aqueous

I don't think it matters as long as the phases of the reaction are separated by one line and the two halves of the reaction are separated by two lines.
Sun Feb 24, 2019 10:13 am
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Plugging in
Replies: 2
Views: 130

### Re: Plugging in

You can also think of this as the number of moles of electrons that are transferred during the reaction.
Sun Feb 24, 2019 10:09 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: inert conductor in cell diagrams
Replies: 3
Views: 128

### Re: inert conductor in cell diagrams

The inert conductor is added when there is no conducting solid, meaning that the reactants and products for that half reaction are aqueous in solution. The cell reaction leads to a transfer in electrons and this must be done through a conductor, which is usually Platinum if nothing else is given.
Sun Feb 24, 2019 10:05 am
Forum: Balancing Redox Reactions
Topic: Standard Cell Potential
Replies: 3
Views: 154

### Re: Standard Cell Potential

When you use the equation E(cell) = E(cathode) - E(anode) it is easy to confuse the positive and negative signs of the values because for this equation both values are positive and you find the difference. In the other equation, the anode reaction has a negative value for the reduction potential, so...
Sun Feb 17, 2019 11:07 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: HW for W7
Replies: 7
Views: 257

### Re: HW for W7

Dr. Lavelle said that homework from this week should be on Thermodynamics including Gibbs Free Energy.
Sun Feb 17, 2019 11:06 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Spontaneity
Replies: 4
Views: 166

### Re: Spontaneity

A reaction is spontaneous when the delta G value is negative. This indicates that the given reaction is favorable in that direction and will lead to a release in free energy, meaning that reactants have more free energy to do work than the products.
Sun Feb 17, 2019 11:02 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Endothermic and Exothermic Graphs
Replies: 3
Views: 276

### Re: Endothermic and Exothermic Graphs

In both graphs, the x axis should indicate progress of a reaction and the y axis should indicate the energy of a reaction. In an exothermic graph, the products are at a lower energy level than the reactants, because energy is released. In an endothermic graph, the products are at a higher energy lev...
Sun Feb 10, 2019 11:21 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Constant Vol.
Replies: 8
Views: 509

### Re: Constant Vol.

Constant volume means that work is zero because there is no change in the volume, so you know that there is no work of expansion being done within the system.
Sun Feb 10, 2019 11:19 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: q=mCdeltaT
Replies: 15
Views: 4618

### Re: q=mCdeltaT

Use either m or n depending on the units of the specific heat, C, that is given to you. That way your units can be consistent with one another and cancel out to give you a q value in terms of Joules.
Sun Feb 10, 2019 11:17 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Work
Replies: 2
Views: 109

### Re: Work

When the system does work on the surroundings, it loses energy – that is why the value of work is negative. When the surroundings do work on the system, the system gains energy and the value of work is positive.
Sun Feb 03, 2019 11:45 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: implications of open vs closed beakers
Replies: 2
Views: 122

### Re: implications of open vs closed beakers

An open beaker implies constant pressure because the volume can be changed. A closed system is where energy can transfer in and out of the system.
Sun Feb 03, 2019 11:30 pm
Forum: Calculating Work of Expansion
Topic: Different ways to derive work
Replies: 3
Views: 102

### Re: Different ways to derive work

W=FD is the equation from which the other equations are derived using substitution, but it is useful to know which other variables are substituted to get the W=PΔV equation. Also it would be good to know the various units that can go into the equation and how to convert from one to another.
Sun Feb 03, 2019 11:18 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Types of enthalpy
Replies: 2
Views: 153

### Re: Types of enthalpy

Standard enthalpy refers to when all reactants and products are in their standard state at 1 atm or 1 M. For an element, it is the most stable phase at 25°C. Most reactions are given in standard state. If the bond enthalpies aren't given then you should calculate standard enthalpy of the reaction.
Sun Jan 27, 2019 10:53 pm
Forum: Phase Changes & Related Calculations
Topic: Delta Hº versus delta H
Replies: 2
Views: 131

### Re: Delta Hº versus delta H

Delta H refers to the enthalpy of any reaction at any temperature, pressure, etc. Delta Hº refers to the enthalpy of a reaction when one mole of the compound is formed from the elements in their stable forms at 25ºC and 1 atm.
Sun Jan 27, 2019 10:48 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Hess's Law
Replies: 3
Views: 135

### Re: Hess's Law

If you are given the enthalpies of 2 separate reactions, you may be asked to use these values to find the net enthalpy change of the overall reaction.
Sun Jan 27, 2019 10:45 pm
Forum: Phase Changes & Related Calculations
Topic: State properties
Replies: 3
Views: 126

### Re: State properties

A state property is a value that is determined by the current state, and not dependent upon the path taken to obtain that state. For example, E, P, V, T, and Density are all things that could be considered state properties. These properties can also be added or subtracted. Examples of properties tha...
Sun Jan 20, 2019 10:43 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Q VS. K
Replies: 13
Views: 811

### Re: Q VS. K

Yes, Q and K are calculated in the same way. Q is compared to K to determine which way the reaction will shift. If Q < K then then the forward reaction is favored and if Q > K then the reverse reaction is favored.
Sun Jan 20, 2019 10:25 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: 5% rule
Replies: 12
Views: 396

### Re: 5% rule

Additionally, if X is less than 5% of the initial concentration then the approximation made by eliminating X will be valid.
Sun Jan 20, 2019 10:22 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Strong vs Weak Acids and Bases
Replies: 2
Views: 137

### Re: Strong vs Weak Acids and Bases

Strong acids completely dissociate in solution. Strong acids usually include alkali metal oxides and hydroxides and alkaline metals oxides and hydroxides. For oxoacids, it should have more oxygens attached to the central atom, a more electronegative central atom, and a more stable conjugate base.
Sun Jan 13, 2019 11:48 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Pure Solids and Liquids
Replies: 2
Views: 69

### Re: Pure Solids and Liquids

Pure solids and liquids are not dissolved so the concentration doesn't change. All solids and liquids are considered pure.
Sun Jan 13, 2019 11:40 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Change in concentration
Replies: 3
Views: 46

### Re: Change in concentration

If you change the concentration, then the reaction is no longer at equilibrium. K itself doesn't change because the original equilibrium reaction doesn't change, but instead the reaction shifts to accommodate the change.
Sun Jan 13, 2019 11:35 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Q and K considered different
Replies: 2
Views: 99

### Re: Q and K considered different

The values should be more or less similar. I think in the context of the homework problems and test questions, these values will be the same to avoid ambiguity.
Fri Dec 07, 2018 8:26 pm
Forum: Lewis Acids & Bases
Topic: Lewis v Bronsted
Replies: 2
Views: 77

### Re: Lewis v Bronsted

The Lewis definition for an acid is more general, stating that an acid is anything that accepts and electron pair. The Bronsted definition of an acid that it is a proton donor. All Bronsted acids are Lewis acids as well, and drawing the lewis structure for a molecule can help you better conceptualiz...
Fri Dec 07, 2018 8:24 pm
Forum: General Science Questions
Topic: polyprotic
Replies: 1
Views: 355

### Re: polyprotic

Polyprotic molecules are capable of gaining or losing more than one proton. Some common polyprotic acids include H2CO3 and H3PO4.
Fri Dec 07, 2018 2:20 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: determining the strongest acid
Replies: 2
Views: 285

### Re: determining the strongest acid

For oxoacids, the textbook lists 2 rules. Firstly, if the oxoacids have the same central atom, then the oxoacid with the greater number of oxygens will be a stronger acid because the conjugate base is more stable. Secondly, if the # of oxygens is the same, the oxoacid with the more electronegative c...
Sun Dec 02, 2018 10:55 pm
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: Acid + Base Reaction
Replies: 1
Views: 103

### Re: Acid + Base Reaction

Neutralization is when an acid and a base combine to form a salt and water. A strong acid and a strong base will completely neutralize and have a pH of 7. If there is a strong acid and weak base the pH will be more acidic, and a strong base combined with a weak acid will be more basic.
Sun Dec 02, 2018 10:52 pm
Forum: Conjugate Acids & Bases
Topic: Clarification of Conjugate Acids and Bases
Replies: 4
Views: 245

### Re: Clarification of Conjugate Acids and Bases

In reference to the Bronsted Lowry theory, conjugates are an acid and base that differ from each other by a proton. For example, OH- is the conjugate base to the acid H2O because H2O donates a hydrogen ion to form the OH- base.
Sun Dec 02, 2018 10:48 pm
Forum: Naming
Topic: Coordination in Chemotherapy
Replies: 2
Views: 122

### Re: Coordination in Chemotherapy

Cisplatin is a well known chemotherapy drug and it forms a coordination complex with DNA, stopping cell division because the DNA can't be further replicated.
Sun Nov 25, 2018 11:02 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Trigonal Shape
Replies: 3
Views: 138

### Re: Trigonal Shape

Trigonal planar exists in one plane, and you think of this shape as flat with 3 electron density regions. Trigonal pyramidal, on the other hand, is like tetrahedral, where the shape is characterized by 4 electron density regions as far apart from one another as possible in a 3D aspect. Trigonal plan...
Sun Nov 25, 2018 10:56 pm
Forum: Electronegativity
Topic: The central atom
Replies: 3
Views: 367

### Re: The central atom

The central atom should have the lowest ionization energy, which refers to the energy required to remove an electron. Electronegativity refers to the ability of an atom to attract electrons.
Sun Nov 25, 2018 10:51 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: 4.5 Bond Angle
Replies: 2
Views: 82

### Re: 4.5 Bond Angle

The bond angle is going to be slightly less than 109 because of the lone pair repulsion. Because there are 4 regions of electron density, the electron geometry would be tetrahedral and 109.5 bond angles, but for the molecular geometry you have to take the lone pairs into account.
Mon Nov 19, 2018 12:13 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Pi bonds and sigma bonds
Replies: 5
Views: 176

### Re: Pi bonds and sigma bonds

When you draw them out, the bonds determine certain properties of a molecule. For example, you can see how the orbitals are placed in relation to one another and whether or not the bound atom is able to rotate (yes for sigma bonds but not for pi bonds).
Mon Nov 19, 2018 12:10 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Electron geometry vs molecular shape
Replies: 4
Views: 162

### Re: Electron geometry vs molecular shape

I think he briefly mentioned it but basically electron shape views a lone electron pair the same as any regular bonding pair. For example, SO2 would have a molecular shape of bent (2 bonding regions + 1 lone pair) but electron geometry of trigonal trigonal planar (3 regions of electron density).
Mon Nov 19, 2018 12:07 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Naming the Shape
Replies: 16
Views: 464

### Re: Naming the Shape

Generally, try to visualize the structure based on the number of bonded pairs and lone pairs. You can guess some structures from the name, eg. trigonal planar or trigonal pyramidal, but for the most part you should try to memorize the common ones. Here is a chart for your reference: https://images.t...
Sun Nov 11, 2018 11:34 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Molecular Shape
Replies: 4
Views: 181

### Re: Molecular Shape

In a molecule, you should pay attention to the number of electron bonding pairs and the number of lone electron pairs, generally around the central atom. This will help you determine, according to electron repulsion, how the shape of a molecule should be and why it is that way.
Sat Nov 10, 2018 4:19 pm
Forum: Ionic & Covalent Bonds
Topic: Polarizability
Replies: 4
Views: 211

### Re: Polarizability

Polarizability is a measure of how easily the electrons can be distorted around an atom, thus creating a dipole. This depends on the number of electrons that an atom has and the size of the molecule (ex. I2 is a bigger molecule than H2 and has more electrons, is more polarizable). Polarizing power r...
Fri Nov 09, 2018 3:17 pm
Forum: Dipole Moments
Topic: Melting points
Replies: 5
Views: 238

### Re: Melting points

The partial positive charge of the hydrogen and the partial negative charge of the electronegative atom creates a stronger attraction. You can compare the electronegativity of S as well, which is lower than that of O. More energy is needed to break this attraction, whereas, because the attraction be...
Sat Nov 03, 2018 9:34 pm
Forum: DeBroglie Equation
Topic: HW 1.33b
Replies: 2
Views: 353

### Re: HW 1.33b

Basically, because the electrons are simply ejected, it is reasonable to assume that the work function (energy only needed to remove an electron) is equal to the energy of the photon (E photon = hv). By setting these E photon = work function, you can substitute hv and solve from there for the energy...
Sat Nov 03, 2018 9:27 pm
Forum: Ionic & Covalent Bonds
Topic: Ionic character [ENDORSED]
Replies: 5
Views: 232

### Re: Ionic character[ENDORSED]

Fluorine is much more electronegative than Hydrogen is because Fluorine has a greater electron affinity (increases from left to right and down to up) and a higher ionization energy (energy needed to remove the most loosely attached electron). Because the electronegativity of Fluorine is greater comp...
Sat Nov 03, 2018 9:22 pm
Forum: Lewis Structures
Topic: Lewis Structures
Replies: 1
Views: 78

### Re: Lewis Structures

Generally, the atom in the center is going to be the one with the lowest ionization energy. This is because the lower the ionization energy, the easier it is for that atom to give away or share electrons with other atoms. However, you always want to draw structures such that there is a symmetrical n...
Sun Oct 28, 2018 10:29 pm
Forum: Trends in The Periodic Table
Replies: 4
Views: 186

### Re: Atomic Radius

An anion, an atom that gains an electron, would have an increased radius. While the nuclear charge is not changing, an electron is being added to the outer shell. There are now more electrons for the nucleus to attract, so the pull of the nucleus becomes slightly weaker than that of the neutral atom...
Sun Oct 28, 2018 10:22 pm
Forum: Trends in The Periodic Table
Topic: s-block and p-block reactivity?
Replies: 6
Views: 318

### Re: s-block and p-block reactivity?

Yes, having a lower ionization energy means that these atoms can more easily lose or gain an electron, and thus more easily form bonds with other atoms. This lower ionization energy translates to increased reactivity, because the atoms can form compounds with other atoms with greater ease.
Sun Oct 28, 2018 10:18 pm
Forum: Trends in The Periodic Table
Topic: Lewis Structures
Replies: 7
Views: 370

### Re: Lewis Structures

When drawing a Lewis structure, start by placing one dot on each of the 4 sides and continue around again, if needed. The number of unpaired electrons should be the same as the number of bonds that the electron can form.
Thu Oct 18, 2018 11:28 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Wave Functions
Replies: 2
Views: 73

### Re: Wave Functions

A wave function describes an electron in an atom. A wave function is defined to be a function describing the probability of a particle's quantum state as a function of position, momentum, time, and/or spin. Wave functions are represented by the variable Ψ. This is based on the fact that an electron,...
Thu Oct 18, 2018 10:59 pm
Forum: Einstein Equation
Topic: Homework Question 1.55 (6th edition)
Replies: 2
Views: 163

### Re: Homework Question 1.55 (6th edition)

Hi Shreya! So the question asks you to solve for the frequency of radiation that corresponds with that absorption. Because the energy is given in 3600 1/cm, it is easiest to set up an equation where 3600 1/cm = v/c, as given by the problem. To solve for v, simply rewrite the equation as v=3600 1/cm ...
Thu Oct 18, 2018 1:27 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Atomic Spectra Module #41
Replies: 3
Views: 133

### Atomic Spectra Module #41

The question that I had is from the Atomic Spectra Post Assessment Module. #41 states For the hydrogen atom which statement is true? A. The transition from n = 5 to n = 3 involves greater energy than one from n = 4 to n = 2. B. The transition from n = 4 to n = 2 emits radiation of longer wavelength ...
Sat Oct 13, 2018 6:59 pm
Forum: Properties of Electrons
Topic: Diffraction patterns
Replies: 9
Views: 474

### Re: Diffraction patterns

Waves don't exactly transition from constructive to destructive, as these are two separate types of wave interactions. In constructive interference, the peaks and troughs of waves line up and make an overall larger amplitude. Destructive interference is when the two waves are out of phase with one a...
Sat Oct 13, 2018 6:13 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Negative v. Positive when calculating energy
Replies: 8
Views: 326

### Re: Negative v. Positive when calculating energy

The negative sign means that the bound electron has a lower energy value that a free electron, and in the calculations the sign is negative because energy is released and decreasing as a result of the reaction. The distinction does matter and it is important to ensure that ΔE is calculated using the...
Sat Oct 13, 2018 5:49 pm
Forum: Properties of Light
Topic: Rydberg Equation
Replies: 3
Views: 100

### Re: Rydberg Equation

He said that we should use the other equations, En = - hv/n^2 and ΔE=hv, because this is simpler to understand and helps us visualize where the answer comes from. In terms of the Rydberg equation, I believe that this will always be an option because they all use the same variables, but it is more he...
Wed Oct 03, 2018 2:24 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 8200
Views: 1430742

### Re: Post All Chemistry Jokes Here

I would post something original, but all of the good chemistry jokes Argon.
Wed Oct 03, 2018 2:23 pm
Forum: SI Units, Unit Conversions
Topic: SI Units
Replies: 10
Views: 405

### Re: SI Units

The first test is going to take place starting Tuesday October 9 in your given discussion section. It will cover all of the review material from the lectures thus far and include homework concepts as well!
Wed Oct 03, 2018 2:15 pm
Forum: General Science Questions
Topic: Systematic vs random error?
Replies: 2
Views: 270

### Re: Systematic vs random error?

Hi! Random error refers to an occasional fluctuation or mess up in calculations or measurements. For example, if you were measuring something that weighed 17 g and you got 17.5 or 17.1 or 16.9 a couple of different times that would be a random error. This can usually be fixed by averaging out a larg...

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