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: 621
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: 397
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: 379
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: 384
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: 715
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
- Topic: adsorbtion
- Replies: 6
- Views: 798
Re: adsorbtion
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: 296
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: 519
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: 526
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: 31
- Views: 1787
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: 439
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: 29
- Views: 112795
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: 302
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: 186
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: 278
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: 296
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: 176
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: 492
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: 161
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: 496
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: 15
- Views: 1780
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: 232
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: 88
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: 156
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: 167
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: 55
- Views: 18349
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: 219
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: 258
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: 432
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
- Topic: about system and surroundings
- Replies: 8
- Views: 347
Re: about system and surroundings
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: 178
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: 650
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: 87
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: 111
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: 727
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: 163
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: 478
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: 478
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: 914
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: 153
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: 323
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: 269
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: 362
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: 288
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: 288
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: 227
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: 139
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: 101
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: 177
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: 152
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: 297
- Views: 382642
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!