Search found 52 matches

by Katie Lam 1B
Thu Mar 15, 2018 4:56 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: isolated system after time
Replies: 2
Views: 203

Re: isolated system after time

The change in internal energy (delta U) for an isolated system is always 0 because no work is done on/by the system and no heat leaves/enters the system.
by Katie Lam 1B
Thu Mar 15, 2018 4:50 pm
Forum: *Enzyme Kinetics
Topic: Catalysts and Intermediates
Replies: 5
Views: 424

Re: Catalysts and Intermediates

Catalysts are usually part of the original reactants. They are not formed in one of the reactions, like intermediates are.
by Katie Lam 1B
Thu Mar 15, 2018 4:45 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: 15.49
Replies: 4
Views: 146

Re: 15.49

The rate law for each individual step is just the rate constant times the reactant concentrations for the reactants (including intermediates) in that particular equation.
by Katie Lam 1B
Fri Mar 09, 2018 1:53 pm
Forum: Second Order Reactions
Topic: Units [ENDORSED]
Replies: 5
Views: 292

Re: Units [ENDORSED]

The units for the rate constant changes depending on the order of reaction, but the rate itself is always in mol/(L*s).
by Katie Lam 1B
Fri Mar 09, 2018 1:52 pm
Forum: General Rate Laws
Topic: 15.13
Replies: 4
Views: 130

Re: 15.13

Both gases are distributed throughout the 0.75 L container, so you use that volume for both H2 and I2.
by Katie Lam 1B
Fri Mar 09, 2018 1:50 pm
Forum: First Order Reactions
Topic: Help on 15.3
Replies: 7
Views: 299

Re: Help on 15.3

Rate is expressed as change in concentration over time, so the units are mol/(L*s).
by Katie Lam 1B
Thu Mar 01, 2018 1:57 am
Forum: Method of Initial Rates (To Determine n and k)
Topic: 15.9
Replies: 3
Views: 123

Re: 15.9

Rate is always expressed in mol/(L*s), so k changes units depending on the order of the reaction.
by Katie Lam 1B
Thu Mar 01, 2018 1:52 am
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: Overall order
Replies: 4
Views: 141

Re: Overall order

The overall order of a reaction can be different from the order of the individual reactants. For example, a reaction may be first order with respect to X and first order with respect to Y. Even though the reactions are first order with respect to individual reactants, the overall order is second ord...
by Katie Lam 1B
Thu Feb 22, 2018 6:33 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Galvanic vs. Electrolytic Cell
Replies: 3
Views: 108

Re: Galvanic vs. Electrolytic Cell

Galvanic cells have spontaneous reactions, while electrolytic cells have nonspontaneous reactions.
by Katie Lam 1B
Thu Feb 22, 2018 6:21 pm
Forum: Balancing Redox Reactions
Topic: Half Reaction Order
Replies: 9
Views: 203

Re: Half Reaction Order

The placement of the arrow indicates whether oxidation or reduction occurs, so it is important. If it is Zn2+ + 2e- --> Zn, it is reduction since the zinc cation gains electrons. If it is Zn --> Zn2+ + 2e-, it is oxidation since zinc loses electrons.
by Katie Lam 1B
Fri Feb 16, 2018 2:26 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Magnitude
Replies: 2
Views: 69

Re: Magnitude

Magnitude would refer to the distance from zero. For example, -5 and 5 are the same magnitude. However, -6 is a greater distance from 0 than +4, so the magnitude is greater.
by Katie Lam 1B
Fri Feb 16, 2018 2:24 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Water in cell diagram
Replies: 3
Views: 98

Re: Water in cell diagram

It is assumed that the cations and anions involved in the half reactions are in aqueous solution, so water doesn't need to be explicitly written.
by Katie Lam 1B
Fri Feb 16, 2018 2:12 pm
Forum: Balancing Redox Reactions
Topic: Balancing redox rxns [ENDORSED]
Replies: 7
Views: 205

Re: Balancing redox rxns [ENDORSED]

You just need to balance it so that the electrons that are transferred cancel out between the two half reactions.
by Katie Lam 1B
Thu Feb 08, 2018 10:26 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Temperature and Spontaneity
Replies: 2
Views: 96

Re: Temperature and Spontaneity

If both delta H and delta S are negative, the reaction is only spontaneous at low temperatures since the T delta S part of the equation will be overall positive. In order for a reaction to be spontaneous, then, the negative delta H needs to be of larger magnitude than the positive T delta S so that ...
by Katie Lam 1B
Thu Feb 08, 2018 9:58 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: delta G formation
Replies: 2
Views: 116

Re: delta G formation

Since the hydrogen gas is still the same substance, the entropy will not change.
by Katie Lam 1B
Thu Feb 08, 2018 9:55 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: delta G=0
Replies: 6
Views: 157

Re: delta G=0

Either delta H and delta S are 0, indicating that no reaction occurred, or delta H = T delta S and they cancel out.
by Katie Lam 1B
Thu Feb 01, 2018 2:58 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: Entropy Change factors
Replies: 6
Views: 198

Re: Entropy Change factors

More complex molecules can occupy more microstates so the entropy values are higher.
by Katie Lam 1B
Thu Feb 01, 2018 2:56 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: DeltaS= q(rev)/T
Replies: 1
Views: 87

Re: DeltaS= q(rev)/T

Most biological processes are irreversible. In thermodynamics, though, systems are often approximated as reversible and the assumption that the pressure inside and outside the system is the same is made.
by Katie Lam 1B
Thu Feb 01, 2018 2:47 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: 9.23 Determining what has higher entropy state
Replies: 4
Views: 163

Re: 9.23 Determining what has higher entropy state

Because COF2 has more microstates, its degeneracy is higher. The different atoms in COF2 can take more positions than the identical atoms in BF3 so it is at a higher entropy state.
by Katie Lam 1B
Thu Jan 25, 2018 2:51 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Formation of a Cation from an Atom
Replies: 3
Views: 215

Re: Formation of a Cation from an Atom

It is endothermic because it takes energy to break bonds and remove electrons from the atom. Forming cations is always endothermic.
by Katie Lam 1B
Thu Jan 25, 2018 2:45 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Confusion about entropy formula
Replies: 6
Views: 117

Re: Confusion about entropy formula

Reversible reactions occur when a system is in thermodynamic equilibrium with its surroundings, while this is not true for irreversible reactions.
by Katie Lam 1B
Thu Jan 25, 2018 2:40 pm
Forum: Calculating Work of Expansion
Topic: Irreversible Expansion
Replies: 3
Views: 137

Re: Irreversible Expansion

Irreversible expansion is irreversible because pressure is reduced much more quickly than in a reversible reaction, where the pressure changes very slowly and maximum work is done. In irreversible processes, the system is not in thermodynamic equilibrium the entire time while in reversible processes...
by Katie Lam 1B
Fri Jan 19, 2018 1:39 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: q and delta H interchangeable in calculations?
Replies: 4
Views: 107

Re: q and delta H interchangeable in calculations?

They are equivalent only under certain conditions, in this case at constant pressure.
by Katie Lam 1B
Fri Jan 19, 2018 1:37 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Internal Energy
Replies: 4
Views: 154

Re: Internal Energy

However, when no expansion work is done, the change in internal energy is equal to the change in enthalpy.
by Katie Lam 1B
Fri Jan 19, 2018 1:27 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: W=-(Pex)(deltaV)
Replies: 5
Views: 199

Re: W=-(Pex)(deltaV)

As the volume increases and the system expands, energy is lost as work so there is a negative sign.
by Katie Lam 1B
Fri Jan 12, 2018 3:00 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: 8.25
Replies: 1
Views: 96

8.25

A constant-volume calorimeter was calibrated by carrying out a reaction known to release 3.50 kJ of heat in 0.200 L of solution in the calorimeter (q =3.50 kJ), resulting in a temperature rise of 7.32 'C. In a subsequent experiment, 100.0 mL of 0.200 m HBr(aq) and 100.0 mL of 0.200 m KOH(aq) were mi...
by Katie Lam 1B
Fri Jan 12, 2018 2:55 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Question 8.3
Replies: 2
Views: 92

Re: Question 8.3

Since the question noted that there was an inner diameter, you can assume that it is referring to a cylinder.
by Katie Lam 1B
Sat Dec 09, 2017 8:41 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: 12.23 [ENDORSED]
Replies: 7
Views: 367

Re: 12.23 [ENDORSED]

The equilibrium constant K changes with temperature so Kw is 10^-14 only at 25 degrees Celsius.
by Katie Lam 1B
Sat Dec 09, 2017 8:00 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Relationship between pH, protanation and molarity
Replies: 5
Views: 203

Re: Relationship between pH, protanation and molarity

You use the molarity of H30+ and OH- to find the pH and pOH by taking the -log of each.
-log[H30+]=pH
-log[OH-]=pOH
by Katie Lam 1B
Sat Dec 09, 2017 7:56 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Direction of the equilibrium
Replies: 2
Views: 222

Re: Direction of the equilibrium

Usually only the reactants have concentrations since none of the products have been formed yet (Q=0) so the reaction proceeds to the products. If the initial product concentrations are also given, it's not a bad idea to check Q to see which direction the reaction proceeds.
by Katie Lam 1B
Sun Dec 03, 2017 10:28 pm
Forum: Bronsted Acids & Bases
Topic: Acid and base reactions in water
Replies: 1
Views: 107

Re: Acid and base reactions in water

Yes, because a Bronsted acid is a proton donor so water gains a proton.
by Katie Lam 1B
Fri Dec 01, 2017 10:23 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Table 11.2 [ENDORSED]
Replies: 1
Views: 225

Table 11.2 [ENDORSED]

In Table 11.2, it lists values of K and Kc for various chemical equilibrium reactions. For top half of the table, the values of K and Kc are the same for each reaction (ex: K=4.0x10^31 and Kc=4.0x10^31), but for the second half of the table, K and Kc are different for each reaction (ex: K=3.0x10^-11...
by Katie Lam 1B
Sun Nov 26, 2017 11:30 pm
Forum: Ideal Gases
Topic: 11.7 Part C
Replies: 2
Views: 194

Re: 11.7 Part C

They only gave the overall pressure of the flask so in order to determine the partial pressures of X2 and X, you need to figure out the percentage of the total pressure for X2 and X. This is done by counting the number of molecules of X2 and X. Out of the 17 molecules in the flask, 12 were X and 5 w...
by Katie Lam 1B
Sun Nov 26, 2017 11:26 pm
Forum: Naming
Topic: Oxidation Numbers
Replies: 2
Views: 144

Re: Oxidation Numbers

The oxidation number refers to the charge of the ion. You determine the oxidation number by comparing the overall charge of the compound to the charges of anions within the compound in order to determine the charge on the transition metal cation.
by Katie Lam 1B
Mon Nov 20, 2017 11:41 am
Forum: Naming
Topic: Q. 37C
Replies: 1
Views: 87

Q. 37C

With the help of Table 17.4, determine the coordination
number of the metal ion in each of the following complexes:
[PtCl2(en)2]2+

How do we know that en (ethylenediamine) is bidentate?
by Katie Lam 1B
Sun Nov 19, 2017 8:35 pm
Forum: Naming
Topic: Naming
Replies: 5
Views: 225

Re: Naming

It is named ferrate because it is an anion within a coordination compound.
by Katie Lam 1B
Sun Nov 19, 2017 8:31 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: 180degrees and lone pairs?
Replies: 4
Views: 149

Re: 180degrees and lone pairs?

It could be trigonal bipyramidal with 3 lone pairs and a 180 degree bond angle.
by Katie Lam 1B
Tue Nov 07, 2017 9:00 pm
Forum: Resonance Structures
Topic: Delocalized electrons
Replies: 4
Views: 206

Re: Delocalized electrons

Delocalization occurs when there is resonance. For example, if there are two resonance structures--one with a single bond between 2 atoms and one with a double bond between two atoms, there won't be exactly 2 or 4 electrons bonded in that area. The electrons aren't specifically associated with these...
by Katie Lam 1B
Tue Nov 07, 2017 8:26 pm
Forum: Lewis Structures
Topic: 3.97
Replies: 2
Views: 134

Re: 3.97

It has to be drawn this way since there is a tetrahedral structure to the molecule. Each phosphorus atom is connected to all 3 of the other phosphorus atoms, but this is hard to convey using a 2D Lewis structure.
by Katie Lam 1B
Sat Nov 04, 2017 11:02 am
Forum: Octet Exceptions
Topic: Exercise 3.59 - Question on Radicals
Replies: 3
Views: 259

Re: Exercise 3.59 - Question on Radicals

It would make sense for the unpaired electron to be on the atom with lower electronegativity since the atom with higher electronegativity has a stronger pull on the electrons and is more likely to fulfill its octet.
by Katie Lam 1B
Sat Nov 04, 2017 10:56 am
Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
Topic: Sigma and Pi Bonds
Replies: 3
Views: 228

Re: Sigma and Pi Bonds

Sigma bonds are the first covalent bonds that atoms can make. Since it is a covalent bond, the electrons are shared. If two atoms have a single covalent bond, it's a sigma bond. When they have double bonds, there is a sigma and a pi bond, and both types of bonds share electrons between the atoms.
by Katie Lam 1B
Sun Oct 29, 2017 7:53 pm
Forum: Ionic & Covalent Bonds
Topic: Ionization Energy [ENDORSED]
Replies: 5
Views: 225

Re: Ionization Energy [ENDORSED]

The second ionization energy is also higher than the first because there is less shielding.
by Katie Lam 1B
Sun Oct 29, 2017 7:50 pm
Forum: Coordinate Covalent Bonds
Topic: Chapter 3 Question 51
Replies: 1
Views: 289

Chapter 3 Question 51

Hypochlorous acid, HClO, is found in white blood cells, where it helps to destroy bacteria. Write two Lewis structures with different atom arrangements for HClO and select the most likely structure by identifying the structure with formal charges closest to zero. Consider only structures with single...
by Katie Lam 1B
Sun Oct 22, 2017 7:28 pm
Forum: Ionic & Covalent Bonds
Topic: Chemical formula?
Replies: 5
Views: 294

Re: Chemical formula?

The Roman numerals refer to the charge on that atom. In this case, chromium has a +3 charge so you know how to write the formula for a neutral molecule.
by Katie Lam 1B
Sun Oct 22, 2017 7:16 pm
Forum: Ionic & Covalent Bonds
Topic: covalent bond
Replies: 7
Views: 470

Re: covalent bond

Yes, one bond can only involve two atoms. However, one atom can have more than two bonds.
by Katie Lam 1B
Fri Oct 13, 2017 5:31 pm
Forum: Properties of Light
Topic: Velocity [ENDORSED]
Replies: 13
Views: 615

Re: Velocity [ENDORSED]

I went to Dr. Lavelle's office hours today and learned that De Broglie's equation cannot be applied to light or electromagnetic radiation. It can only be applied to particles with rest mass, like electrons, so you can't use the speed of light in De Broglie's equation.
by Katie Lam 1B
Fri Oct 13, 2017 5:08 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Example Shown During Lecture
Replies: 2
Views: 163

Re: Example Shown During Lecture

You're allowed to use the Rydberg equation if you know how it works. Like Tess said, he showed us the other method because it is more easily explainable.
by Katie Lam 1B
Sun Oct 08, 2017 6:34 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Atomic Spectra Post-Assessment Q. 29 [ENDORSED]
Replies: 2
Views: 250

Atomic Spectra Post-Assessment Q. 29 [ENDORSED]

In 1.0 s, a 60 W bulb emits 11 J of energy in the form of infrared radiation (heat) of wavelength 1850 nm. What is the energy per photon of light emitted? How many photons of infrared radiation does the lamp generate in 1.0 s? I understand how to find the energy per photon (1.074 x 10-19 J), but how...
by Katie Lam 1B
Sun Oct 08, 2017 6:25 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Atomic Spectra Post-Module Assessment Q. 20 [ENDORSED]
Replies: 2
Views: 237

Re: Atomic Spectra Post-Module Assessment Q. 20 [ENDORSED]

Each photon excites an electron to a higher level, so 1 million photons excites 1 million electrons (there is more than one hydrogen atom in the sample).
by Katie Lam 1B
Thu Oct 05, 2017 11:25 am
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: E.29 part b HELP
Replies: 3
Views: 211

Re: E.29 part b HELP

The number of moles of Cl- ions is different than the moles of CuCl2, so you use a stoichiometric ratio (2 mol Cl-/1 mol CuCl2) to get the correct moles of Cl- ions.
by Katie Lam 1B
Tue Oct 03, 2017 11:17 pm
Forum: Balancing Chemical Reactions
Topic: Nitrogen
Replies: 5
Views: 279

Nitrogen

When a problem states that nitrogen is formed, can we always assume that the product is gaseous nitrogen (N2)?

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