Search found 51 matches

Wed Mar 11, 2020 2:36 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: intergrated rate law
Replies: 9
Views: 149

Re: intergrated rate law

I think that since Dr. Lavelle went over the derivations in class it is important to understand the concept but they should all be on the equation sheet so I wouldn't worry about memorizing! It is more important to understand the differences and know which equation to use for different ordered react...
Wed Mar 11, 2020 2:21 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: rate constant
Replies: 5
Views: 65

Re: rate constant

Temperature and activation energy affect the rate constant. When temperature increases, more reactants collide and therefore k increases too. On the other hand, when Ea is high, there is a larger energy barrier and therefore k is smaller.
Wed Mar 11, 2020 2:11 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Rate Constant K
Replies: 4
Views: 68

Re: Rate Constant K

I was also confused on this! k is the rate constant, while k' is the rate constant for the reverse reaction. On the other hand, K (capital) is the equilibrium constant, from earlier in the quarter.
Tue Mar 10, 2020 3:31 pm
Forum: Zero Order Reactions
Topic: Elementary Reactions
Replies: 5
Views: 103

Re: Elementary Reactions

I believe that coefficients determine the order of reactants in the rate law when we are dealing with elementary reactions. Elementary reactions are when chemical species react directly to form products with a single reaction step and single transition state.
Tue Mar 10, 2020 2:39 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: thermo or kinetics?
Replies: 9
Views: 180

Re: thermo or kinetics?

I think a better mindset to have when considering a reaction is to think that thermodynamic analysis tells us whether the forward or reverse reaction is favored (spontaneous or not spontaneous). However, thermodynamics does not tell us about the pathway, which is where kinetics comes in. From kineti...
Tue Mar 10, 2020 10:11 am
Forum: Biological Examples
Replies: 4
Views: 76

Yes, I believe so. Adsorption is when reactants sit on the surface of a catalyst versus absorption, where you can think of water soaking into a sponge (reactant breaching surface of the catalyst).
Thu Mar 05, 2020 9:42 am
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: delta G equations
Replies: 3
Views: 68

Re: delta G equations

I think that all of the basics that we will need for the test will be covered on the test, but it might be necessary to use the Van't Hoff equation, which is derived from deltaGo = -RTlnK. The Van't Hoff equation is ln(K2/K1) = deltaHo/R * (1/T1 - 1/T2)
Wed Mar 04, 2020 8:06 pm
Forum: Interesting Applications: Rechargeable Batteries (Cell Phones, Notebooks, Cars), Fuel Cells (Space Shuttle), Photovoltaic Cells (Solar Panels), Electrolysis, Rust
Topic: Electrochemical Series
Replies: 6
Views: 141

Re: Electrochemical Series

I don't think we have to have it memorized or anything, but the electrochemical series is a way elements are arranged according to their standard reaction potentials. It is more important to understand the magnitude of reaction potentials can either make a half reaction more likely to reduce or oxid...
Wed Mar 04, 2020 2:40 pm
Forum: Balancing Redox Reactions
Topic: Acidic and Basic Redox Reactions
Replies: 9
Views: 77

Re: Acidic and Basic Redox Reactions

From what I have seen the problem will always tell us what kind of solution (basic or acidic) we are dealing with. There wouldn't really be a way to know which redox process otherwise so I would just worry about being able to know how to do the problems for the different solutions.
Wed Mar 04, 2020 2:30 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Units for delta G
Replies: 14
Views: 258

Re: Units for delta G

Elizabeth Harty 1A wrote:What is the difference between delta g naught and delta g?

The units when you are talking about delta G naught would be kilojoules per mole, whereas under nonstandard conditions the units for delta G would be just kilojoules.
Wed Mar 04, 2020 2:24 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: finding moles
Replies: 6
Views: 154

Re: finding moles

I was also confused on this! N in this sense is the moles (or amount) of electrons being transferred in the redox reaction. You must balance your reduction half-reactions and make sure there are the same amount of balanced electrons in each half-reaction, and this will be your N value to use in this...
Wed Mar 04, 2020 2:18 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell Diagram and Ecell [ENDORSED]
Replies: 10
Views: 39818

Re: Cell Diagram and Ecell[ENDORSED]

bloodorangefield wrote:How do you tell the difference between when it is an anode vs when it is cathode?

An anode represents the oxidation half-reaction and a cathode represents the reduction half-reaction. The anode is usually on the left and the cathode is on the right.
Wed Mar 04, 2020 9:03 am
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Equilibrium Constant K (Q) Units
Replies: 3
Views: 60

Re: Equilibrium Constant K (Q) Units

Since K is unitless, I think that is part of why using both partial pressures and concentrations is okay in the Nernst Equation. The redox equations in these cases have both gases with partial pressures and solutions with different concentrations, so we want to use all components of the reaction whe...
Wed Mar 04, 2020 8:42 am
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: 6L.7
Replies: 2
Views: 40

Re: 6L.7

In general, when looking at the overall redox reaction use the half reaction that will cancel what needs to be cancelled (since there are multiple half reactions for the same elements). A lot of time I think the problem will make it pretty clear which half reaction should be used based on the compon...
Wed Mar 04, 2020 8:38 am
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: 6N.1.b)
Replies: 4
Views: 75

Re: 6N.1.b)

I also got K = 107, maybe there is a mistake in the solutions for the textbook.
Wed Mar 04, 2020 8:35 am
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: concentration cells
Replies: 4
Views: 84

Re: concentration cells

Because cell potential is sensitive to [R] and [P], we can make concentration cells. Concentration cells have two half cells (like galvanic cells) with the same electrode and components but differing concentrations. In concentration cells the electron flow is caused by the difference in concentratio...
Wed Mar 04, 2020 8:30 am
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Nernst Equation Components
Replies: 2
Views: 39

Nernst Equation Components

How do we find n in the Nernst Equation? It says in the book that it is a pure number and signifies molar convention, but I am confused on how this changes for different redox reactions.
Fri Feb 21, 2020 4:17 pm
Forum: Balancing Redox Reactions
Topic: Oxidizing/reducing agent
Replies: 7
Views: 104

Re: Oxidizing/reducing agent

It is more simple to know that the reducing agent is what is being oxidized, and the oxidizing agent is what is being reduced. A reducing agent loses an electron (oxidizes), which reduces another compound in the reaction. An oxidizing agent gains an electron (reduces), which oxidizes the other compo...
Fri Feb 21, 2020 4:09 pm
Forum: Balancing Redox Reactions
Topic: combining redox reactions
Replies: 2
Views: 43

Re: combining redox reactions

Making sure your electrons are balanced and cancel out is the most important thing. Everything else should be fine to be included in the final equation.
Fri Feb 21, 2020 3:50 pm
Forum: Balancing Redox Reactions
Topic: Redox in Acid/ Basic Solutions
Replies: 8
Views: 100

Re: Redox in Acid/ Basic Solutions

I think that the process is the same for both redox reactions of acidic and basic solutions. The difference will come in balancing the equation and whether you are adding H+ (acidic reactions) or OH- (basic reactions).
Fri Feb 21, 2020 3:39 pm
Forum: Biological Examples (*DNA Structural Transitions, etc.)
Topic: Examples Expected to Know
Replies: 10
Views: 422

Re: Examples Expected to Know

I don't think there is a specific list to know or memorize. I think it is just important to understand the biological examples Dr. Lavelle mentions in class and on the homework problems. Usually the problems explain the biological concept too.
Tue Feb 11, 2020 8:33 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Change in entropy of an irreversible process.
Replies: 3
Views: 48

Re: Change in entropy of an irreversible process.

When calculating delta S(total) of an irreversible system, it will equal delta S(system). Since no work is done in free expansion, w = 0. And because delta U = 0, and delta U = w + w, q also = 0. With this, we know that no heat is transferred into the surroundings, so delta S(surroundings) = 0.
Tue Feb 11, 2020 8:21 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: 4I.9 Irreversible Expansion
Replies: 2
Views: 37

Re: 4I.9 Irreversible Expansion

Additionally, when you calculate delta S(total) for isothermal reversible expansion in this problem, the value ends up being 0 because delta S(surroundings) = -delta S(system). However, for isothermal irreversible expansion in this problem, the total entropy was equal to delta S(system), as no heat ...
Mon Feb 10, 2020 2:26 pm
Forum: Calculating Work of Expansion
Topic: Ideal Gas Internal Energy
Replies: 4
Views: 46

Re: Ideal Gas Internal Energy

Also, Dr. Lavelle mentioned in class today that we will be given those equations or the heat capacities for those specific molecules. I think we will mainly use this concept for monatomic molecules.
Mon Feb 10, 2020 2:18 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: irreversible vs reversible
Replies: 3
Views: 33

Re: irreversible vs reversible

That is such a helpful graphic for reversible versus irreversible reactions! Since reversible reactions use infinitesimal steps along the reaction pathway, it remains very close to equilibrium and therefore can be reversed easily. This also means that reversible reaction pathways require more work. ...
Mon Feb 10, 2020 2:15 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Useful Summary of Thermodynamic Definitions
Replies: 34
Views: 14790

Re: Useful Summary of Thermodynamic Definitions

Thank you, this is such a helpful summary! I didn't realize that when you divide two extensive properties it ends up being an intensive, but now that makes sense.
Thu Feb 06, 2020 9:40 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Heat Capacities
Replies: 2
Views: 61

Re: Heat Capacities

There is also a chart on page 266 of the 7th Edition textbook that explains the use of these ratios and shows the differences between them for atoms, linear molecules, and non-linear molecules.
Thu Feb 06, 2020 9:35 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: reversible vs irreversible work
Replies: 4
Views: 64

Re: reversible vs irreversible work

Also, reversible systems use infinitesimal steps to calculate change of variables. These small steps make it possible for it to be reversible, as it will always be close to equilibrium.
Thu Feb 06, 2020 9:31 pm
Forum: Phase Changes & Related Calculations
Topic: State functions
Replies: 7
Views: 93

Re: State functions

State functions and properties are important for use in thermochemistry problems because their value is determined by its current state and is not dependent on the path taken to obtain that state.
Thu Feb 06, 2020 8:46 pm
Forum: Phase Changes & Related Calculations
Replies: 8
Views: 81

The system is the part of the universe we are studying (ex: reaction, gas, closed, open, or isolated systems). The surroundings include everything else (universe) but usually we are just looking at particular surroundings.
Wed Jan 29, 2020 8:52 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: internal energy
Replies: 4
Views: 74

Re: internal energy

Internal energy, U, is a state property and functions from its final and initial states. For example, if a closed system is changed by heating (+q) and compression (+w) then the equation for internal energy is: delta U = q + w. If volume is constant, delta U = q(v).
Wed Jan 29, 2020 8:48 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Closed Systems
Replies: 13
Views: 114

Re: Closed Systems

Yes, a closed system can be changed by changing temperature (heating or cooling), pressure, or volume. For example if you have mercury in a thermometer, outside temperature will cause a change in energy of the system.
Wed Jan 29, 2020 8:40 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Reversible Reactions
Replies: 1
Views: 18

Re: Reversible Reactions

What section of the book or lecture is this from? I am also confused on the reasoning behind it.
Wed Jan 29, 2020 8:35 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Specific Heat Capacity, Molar Heat capacity, and the Third?
Replies: 3
Views: 34

Re: Specific Heat Capacity, Molar Heat capacity, and the Third?

The three things Dr. Lavelle was talking about are heat capacity, molar heat capacity, and specific heat capacity (also called specific heat). Heat capacity is the heat required to raise the temperature of any object by 1 degree Celsius and is a more general term than the others. Molar heat capacity...
Thu Jan 23, 2020 5:27 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Delta H
Replies: 10
Views: 373

Re: Delta H

The rule of thumb is that when delta H is positive, it is endothermic (it takes up heat and its' surroundings become cooler) and when delta H is negative, it is exothermic (it releases heat and its' surroundings become warmer).
Thu Jan 23, 2020 5:19 pm
Forum: Phase Changes & Related Calculations
Topic: Enthalpy Units
Replies: 3
Views: 30

Enthalpy Units

Since enthalpy is the amount of heat released or absorbed at a constant pressure, what are the units of measurement for this value? Is delta H always measured in Joules or are there other units as well?
Thu Jan 23, 2020 9:34 am
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Difference in PH between strong and weak acids
Replies: 11
Views: 147

Re: Difference in PH between strong and weak acids

Additionally, it is good to note that smaller pKa or pKb values mean that the acid or base is stronger, while smaller Ka or Kb values mean that the acid or base is weaker.
Thu Jan 23, 2020 9:34 am
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Difference in PH between strong and weak acids
Replies: 11
Views: 147

Re: Difference in PH between strong and weak acids

Additionally, it is good to note that smaller pKa or pKb values mean that the acid or base is stronger, while smaller Ka or Kb values mean that the acid or base is weaker.
Thu Jan 23, 2020 9:30 am
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Exothermic vs. Endothermic reactions
Replies: 12
Views: 459

Re: Exothermic vs. Endothermic reactions

It is also good to note that when a reaction requires heat (endothermic) while forming product, then heating will favor product formation. When a reaction gives off heat (exothermic) while forming product, then heating will favor reactant formation.
Thu Jan 23, 2020 9:26 am
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Acids and Bases
Replies: 6
Views: 67

Re: Acids and Bases

It might be good to know what polyprotic acids are for the future but I don't think they are something to worry about for this test.
Thu Jan 16, 2020 2:14 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Protonation & Deprotonation
Replies: 9
Views: 118

Protonation & Deprotonation

What is protonation or deprotonation referring to when talking about acids and bases? How do we calculate percent protonation/deprotonation?
Thu Jan 16, 2020 2:12 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Approximation
Replies: 8
Views: 68

Re: Approximation

You can use approximation for weak acids and bases problems when the K value is less than 10^-3. This means it is small enough to not make a huge difference when calculating concentrations, so you wouldn't need to use the quadratic formula. The 5% rule refers to evaluating whether the approximation ...
Wed Jan 15, 2020 9:43 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Kw
Replies: 16
Views: 135

Re: Kw

Kw refers to the equilibrium constant for water and/or the ionization constant. Also as Dr. Lavelle discussed further today in class, for acids you can call it the acidity, ionization, or dissociation constant.
Wed Jan 15, 2020 9:39 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: 5J.9b
Replies: 8
Views: 56

Re: 5J.9b

Yes, when the partial pressure of NH3 is decreased in this reaction, the reverse reaction will be favored. This will cause and increase in partial pressure for O2 as it is part of the reactants and will increase when the reaction shifts to the left.
Wed Jan 15, 2020 9:39 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: 5J.9b
Replies: 8
Views: 56

Re: 5J.9b

Yes, when the partial pressure of NH3 is decreased in this reaction, the reverse reaction will be favored. This will cause and increase in partial pressure for O2 as it is part of the reactants and will increase when the reaction shifts to the left.
Wed Jan 15, 2020 9:13 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Homework 5J.1
Replies: 4
Views: 82

Re: Homework 5J.1

I was also curious about this question! Applying Le Chatelier's principle makes sense also for part B of this question. In part B, if the partial pressure of CO is decreased, then the partial pressure of CO2 will decrease because the reverse reaction will be favored and there will be less products.
Thu Jan 09, 2020 4:55 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Units
Replies: 4
Views: 45

Re: Units

K, being the equilibrium constant, itself does not have units but when writing in values for the concentration or pressure it is definitely good to add them in. For example it might be molar (M) for concentration or atmospheres (atm) for pressure.
Thu Jan 09, 2020 4:50 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: K
Replies: 3
Views: 40

Re: K

I'm not 100% sure but I think stick to one form, either concentration or pressure. Since pressure can be converted to concentration I think it is safe to use that form!
Thu Jan 09, 2020 2:50 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Value of Kc and Kp
Replies: 6
Views: 53

Re: Value of Kc and Kp

Kp and Kc are measuring different relationships within a reaction, but are both equilibrium constants. This is just dependent on the nature of the reactants and the products. The K constant in both cases will have no units anyway, so there isn't much to worry about there but more about the concept i...
Thu Jan 09, 2020 2:45 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Q versus K
Replies: 4
Views: 54

Re: Q versus K

An example of using Q in comparison to K we did as an example in class with the reaction: N2O4(g) == 2NO2(g). Partial pressures of the two gases were given, and the goal was to see if the system was at equilibrium at this specific point in the reaction. The Qp ended up being less than the Kp, meanin...
Thu Jan 09, 2020 10:21 am
Forum: Administrative Questions and Class Announcements
Topic: Advice from a Medical Student [ENDORSED]
Replies: 221
Views: 116162

Re: Advice from a Medical Student[ENDORSED]

Thanks so much for the advice! So nice to hear that these courses helped you with your career and path in medicine - and that there are so many helpful resources!