Search found 54 matches
- Thu Mar 12, 2020 4:59 pm
- Forum: Balancing Redox Reactions
- Topic: Oxidizing and Reducing
- Replies: 5
- Views: 340
Re: Oxidizing and Reducing
Use the equation Ecell = E(cathode) - E(anode). Plug the cell potentials of the half-reactions so that Ecell > 0. When Ecell > 0, then you know what the reduction and oxidation half-reactions are by looking at the equation.
- Thu Mar 12, 2020 4:48 pm
- Forum: General Rate Laws
- Topic: 7A.9
- Replies: 4
- Views: 374
Re: 7A.9
The units of the rate is M/s^-1 (concentration/time). For a first-order reaction, rate = k[A]^1. To make the rate be in units of M/s^-1, k must be s^-1 (remember that the unit of [A] is M).
- Thu Mar 12, 2020 4:37 pm
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: Slow step of reaction?
- Replies: 5
- Views: 385
Slow step of reaction?
Is the slow step of an overall reaction determined experimentally? Can you know what the slow step is by looking at its chemical reaction?
- Thu Mar 12, 2020 4:17 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: Molecule names on the final
- Replies: 2
- Views: 215
Molecule names on the final
Are we supposed to know certain molecules and compounds for the final?
- Sun Mar 08, 2020 8:46 pm
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: Cell Diagram
- Replies: 21
- Views: 1065
Re: Cell Diagram
If the cell potential is not given, then assume the right is the cathode and the left is the anode. You might have to look up the cell potentials and add them up to give a positive standard cell potential to determine the anode and cathode.
- Sun Mar 08, 2020 8:38 pm
- Forum: Kinetics vs. Thermodynamics Controlling a Reaction
- Topic: Study Advice
- Replies: 73
- Views: 6565
Re: Study Advice
I read the textbook and take notes, then do sapling problems, and then do the textbook problems listed on the syllabus.
- Sun Mar 08, 2020 8:30 pm
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: Figuring out n
- Replies: 15
- Views: 910
Re: Figuring out n
n is the number of electrons transferred in the reaction. Unless the number of e- transferred are clear from the reaction, you can always find the number of e- by balancing the half-reactions.
- Sun Mar 08, 2020 8:27 pm
- Forum: Balancing Redox Reactions
- Topic: e- amount
- Replies: 9
- Views: 588
Re: e- amount
Multiply the reaction(s) so that the number of e- are the same.
- Sun Mar 08, 2020 8:25 pm
- Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
- Topic: calculating Q
- Replies: 12
- Views: 697
Re: calculating Q
Q is [Products]/[Reactants] so it depends on the chemical equation.
- Sun Mar 08, 2020 8:09 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Gibbs free energy and K
- Replies: 3
- Views: 231
Gibbs free energy and K
How does the Gibbs free energy relate to K and Q?
- Sun Mar 01, 2020 11:04 pm
- Forum: Kinetics vs. Thermodynamics Controlling a Reaction
- Topic: instantaneous rate
- Replies: 16
- Views: 888
Re: instantaneous rate
The instantaneous rate is for finding the entire area under the curve, while the average rate gives an approximation.
- Sun Mar 01, 2020 10:55 pm
- Forum: Balancing Redox Reactions
- Topic: 6K.5 part b
- Replies: 4
- Views: 679
Re: 6K.5 part b
Notice the Br2(l) is both the oxidizing and reducing agent. Therefore, you have two half-reactions: Br2(l) -> BrCO3-(aq) and Br2(l) -> Br-(aq). To balance Br2(l) -> Br-(aq), all you need to is balance Br-. For Br2(l) -> BrCO3-(aq), notice the oxygen. You need to add H2O and H+ to balance this half-r...
- Sun Mar 01, 2020 10:44 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Gibbs free energy equations
- Replies: 5
- Views: 392
Gibbs free energy equations
Can all the gibbs free energy equations be used for electrochemistry problems?
- Sun Mar 01, 2020 10:33 pm
- Forum: Kinetics vs. Thermodynamics Controlling a Reaction
- Topic: Kinetics in Test 2?
- Replies: 13
- Views: 720
Re: Kinetics in Test 2?
From what I remember, only thermodynamics and electrochemistry.
- Sun Mar 01, 2020 10:22 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Test 2
- Replies: 4
- Views: 282
Re: Test 2
Unless the standard cell potential is given, we will probably need to look it up from a table. A lot of electrochemistry questions need the standard cell potential.
- Sun Mar 01, 2020 10:19 pm
- Forum: Balancing Redox Reactions
- Topic: half reaction
- Replies: 10
- Views: 616
Re: half reaction
In acidic solutions, balance the half equation with H+ and H20. For basic solutions, balance the half reaction with OH- and H20. For some cases, like the reaction (H+) + (OH-) -> H20, you might need to look for the reduction/oxidation potentials given in the book.
- Sun Feb 23, 2020 9:03 pm
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: Work
- Replies: 5
- Views: 314
Re: Work
Work is done in an electrochemical cell when electrons move across a circuit from the anode to the cathode.
- Sun Feb 23, 2020 8:53 pm
- Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
- Topic: Calculating pH using Nernst Equation
- Replies: 2
- Views: 313
Calculating pH using Nernst Equation
How do you find the pH of solution using the Nernst equation? I read the chapter on it, but it is unclear to me.
- Sun Feb 23, 2020 8:43 pm
- Forum: Balancing Redox Reactions
- Topic: Determining direction of flow
- Replies: 15
- Views: 723
Re: Determining direction of flow
The oxidation reaction (e.g. Zn ---> (Zn^2+) + (2 e^-) in the cell diagram Zn|Zn^2+||Cu^2+|Cu) in the anode releases electrons that flow via a circuit to the cathode where the reduction reaction ((Cu^2+) + (2 e^-) ---> Cu in the cell diagram Zn|Zn^2+||Cu^2+|Cu) takes place.
- Sun Feb 23, 2020 8:31 pm
- Forum: Balancing Redox Reactions
- Topic: Half Reactions
- Replies: 12
- Views: 800
Re: Half Reactions
The "redox" in "redox reaction" is short for reduction-oxidation. The half-reaction of a reduction-oxidation reaction is the reduction reaction and the other half-reaction is the oxidation reaction.
- Sun Feb 23, 2020 8:24 pm
- Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
- Topic: Standard vs Non
- Replies: 3
- Views: 238
Re: Standard vs Non
Standard conditions are when the gases involved are at 1 bar, the participating solutes are at 1 mol L^-1 (1 M), and the liquids and solids involved are pure. The temperature is usually 298K.
- Sun Feb 23, 2020 8:06 pm
- Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
- Topic: Reversible Reaction
- Replies: 6
- Views: 422
Re: Reversible Reaction
A reaction is reversible when there is an infinitely small change in a variable (e.g. pressure) that changes the reaction back to its original state.
- Sun Feb 23, 2020 7:55 pm
- Forum: Phase Changes & Related Calculations
- Topic: Van't Hoff Eq
- Replies: 8
- Views: 629
Re: Van't Hoff Eq
For this class, I don't think we really need to derive most equations since we haven't done so so far. However, for the van't Hoff equation we need understand it usage.
- Sun Feb 16, 2020 8:38 pm
- Forum: Calculating Work of Expansion
- Topic: Work without volume
- Replies: 5
- Views: 373
Re: Work without volume
The only types of work we need to know for thermodynamics are expansion work and non-expansion work, which involve volume change.
- Sun Feb 16, 2020 6:39 pm
- Forum: Biological Examples (*DNA Structural Transitions, etc.)
- Topic: organic reactions, and environmental and biological examples
- Replies: 4
- Views: 719
Re: organic reactions, and environmental and biological examples
Thermodynamics are relevant in biological processes that need to use energy, like photosynthesis (an endothermic reaction). There is also complicated research on entropy and its relationship to the evolution of life.
- Sun Feb 16, 2020 6:28 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: Autoprotolysis
- Replies: 6
- Views: 1124
Re: Autoprotolysis
Another example is the autoprotolysis of ammonia (NH3). The reaction is 2NH3 (l) <-> NH4+ (aq) + NH2- (aq)
- Sun Feb 16, 2020 6:22 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Meaning of q=-w
- Replies: 14
- Views: 2221
Re: Meaning of q=-w
The heat supplied to the system is equivalent to the energy leaving the system as work.
- Sun Feb 16, 2020 6:12 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: K
- Replies: 12
- Views: 636
Re: K
For a gas (g) and solutes in solutions (aq), their activity is included for solving for K. For pure solids (s) and liquids (l), their activities are 1.
- Sun Feb 16, 2020 6:06 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Delta S
- Replies: 8
- Views: 614
Re: Delta S
Delta S (sys) is the entropy of the system, Delta S (surr) is the entropy of the surroundings. Delta S (sys) + Delta S (surr) = Delta S(total), where Delta S (total) is the total entropy of both the surroundings and the system.
- Sun Feb 09, 2020 10:35 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Specific Heat Capacity
- Replies: 5
- Views: 156
Re: Specific Heat Capacity
Specific heat capacity is needed because certain things require more energy to raise its temperature than other things.
- Sun Feb 09, 2020 9:58 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: equations
- Replies: 4
- Views: 141
Re: equations
You can write down the information given (e.g. m = 6782 g, T 53 K, q = 6783 J,...) and see what you can do with them to get to where the question is asking of you.
- Sun Feb 09, 2020 9:42 pm
- Forum: Calculating Work of Expansion
- Topic: Vacuum
- Replies: 3
- Views: 100
Re: Vacuum
Usually, the question will tell you that the reaction is happening in a vacuum. Other than that, a keyword for knowing that a system is a vacuum is if the system is outer space.
- Sun Feb 09, 2020 9:36 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: Ka Kb
- Replies: 11
- Views: 624
Re: Ka Kb
Ka is for acids, so the equation would have [H3O+]. Kb is for bases, so the equation would have [OH-].
- Sun Feb 09, 2020 9:19 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: problem 4A9
- Replies: 2
- Views: 242
Re: problem 4A9
You first set up the equation (heat lost by the copper) = -(heat gained by the water), which is q = -q. Therefore, you are solving m*C*(T(final) - T(initial)) = - m*C*(T(final) - T(initial)). You have all the values execpt T(final).
- Sun Feb 09, 2020 9:07 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Delta U
- Replies: 7
- Views: 386
Re: Delta U
delta U = 0 for isothermal expansion or compression of an ideal gas. delta U = 0, when q = 0 and w = 0 (since delta U = 0 + 0 = 0). q = -w when delta U = 0, then 0 = q + w, which is q = -w.
- Sun Feb 09, 2020 8:52 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: Second Law Thermodynamics
- Replies: 4
- Views: 227
Re: Second Law Thermodynamics
The total entropy of a system either increases or stays constant, but never decreases. Entropy is always increasing in the universe until thermodynamic equilibrium (look up "the heat death of the universe").
- Sun Feb 09, 2020 8:20 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Bond Enthalpies
- Replies: 6
- Views: 277
Re: Bond Enthalpies
You can list all bonds on the reactant's side and the product's side, and then see if there are bonds on the product side that are not featured in the reactant side (the bonds formed) and then see if there are bonds that appeared in the reactant side but no longer appear in the product side (the bon...
- Sun Feb 02, 2020 9:43 pm
- Forum: Phase Changes & Related Calculations
- Topic: Open vs Isolated System
- Replies: 15
- Views: 1241
Re: Open vs Isolated System
An open system allows matter and energy to leave (or enter). For example, a cup of tea would be an open system because matter is leaving (i.e. water in the form of gas) and energy is leaving (i.e. the heat is leaving from the tea into the surroundings). A closed system does not allow matter to leave...
- Sun Feb 02, 2020 9:24 pm
- Forum: Phase Changes & Related Calculations
- Topic: Phase changes
- Replies: 3
- Views: 156
Re: Phase changes
Phase changes are relevant for problems that want the enthalpy. That is because the energy needed to be supplied for a phase change in a substance is different depending on the current phase of a substance. For example, the energy needed to change a liquid to a gas (the enthalpy of vaporization) is ...
- Sun Feb 02, 2020 8:47 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Temperature
- Replies: 14
- Views: 504
Re: Temperature
Since deltaH = Hfinal - Hinitial and if the reaction is exothermic (heat is released into the surroundings), then Hfinal < Hinitial (e.g. 3 kJ/mol - 4 kj/mol = -1 kJ/mol) which would yield a negative deltaH.
- Sun Feb 02, 2020 8:36 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Pressure in an open beaker
- Replies: 12
- Views: 714
Re: Pressure in an open beaker
The pressure in an open beaker would be the pressure of the surroundings. The surroundings is typically at a constant pressure.
- Sun Feb 02, 2020 8:26 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: 4A.9
- Replies: 2
- Views: 83
Re: 4A.9
Plug the final temperature into the equation and if mCdeltaT = -mCdeltaT is true, then the final temperatures are the same.
- Sun Jan 26, 2020 10:27 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Gas Constant
- Replies: 13
- Views: 504
Re: Gas Constant
Use the constant that includes the unit that is the same as the P in PV=nRT (so units cancel out nicely).
- Sun Jan 26, 2020 10:06 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Weak acid/base
- Replies: 14
- Views: 617
Re: Weak acid/base
If the conjugate base of an acid is very stable, the reaction would favor the production of the conjugate base. If the conjugate base of an acid is not very stable, then the production of the conjugate base is not favored. This hints at the acid being weak. Same idea with bases and their conjugate a...
- Sun Jan 26, 2020 9:50 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Finding Ka from pH
- Replies: 5
- Views: 273
Re: Finding Ka from pH
Giving pH or pOH, then [H3O+] = 10^(-pH) and [OH-] = 10^(-pOH).
- Sun Jan 26, 2020 9:41 pm
- Forum: Phase Changes & Related Calculations
- Topic: Why does steam cause burns?
- Replies: 29
- Views: 1079
Re: Why does steam cause burns?
Steam causes burns worst than water because the phase change from liquid to gases requires more energy
- Sun Jan 26, 2020 8:58 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Meaning of State Function
- Replies: 8
- Views: 194
Re: Meaning of State Function
A state function is a property that does not depend on the path taken. An example of a state function is temperature. For example, a pot of boiling water at 212 F could be boiled for hours or minutes, in a microwave or an oven, etc., it would still be at 212 F. The path taken does not matter. You mo...
- Sun Jan 26, 2020 8:34 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Pressure & temperature in chemical equilibria
- Replies: 3
- Views: 79
Pressure & temperature in chemical equilibria
How does pressure and temperature shift a reaction?
- Sun Jan 26, 2020 8:31 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Exothermic and Endothermic
- Replies: 11
- Views: 708
Exothermic and Endothermic
Why is the value of an exothermic reaction negative and why is the value of an endothermic reaction positive?
- Sun Jan 19, 2020 8:01 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Test 1 Acids and Bases Topic
- Replies: 9
- Views: 478
Re: Test 1 Acids and Bases Topic
Will Test 1 include any questions on ideal gases?
- Sun Jan 19, 2020 7:53 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Acidity and Basicity
- Replies: 4
- Views: 157
Re: Acidity and Basicity
Acids and bases in solution are examples of chemical equilibria. pH and pOH are measures of the molar concentration of H3O+ and OH- in a solution respectively.
- Sun Jan 19, 2020 7:31 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: ice boc
- Replies: 7
- Views: 202
Re: ice boc
Professor Lavalle gave a great analogy about approximations. Basically, let's you have 1,000,000 dollars and you subtract it by x amount. If x is very small, like 10 dollars, then x is negligible because 1,000,000 - 10 = 999,990, which is almost the same as 1,000,000. In acids and bases, a weak acid...
- Sun Jan 19, 2020 7:17 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: reactants and products in dynamic equilibria
- Replies: 3
- Views: 196
reactants and products in dynamic equilibria
Why is it that in chemical equilibria there is typically a greater concentration (or partial pressure) on one side of the reaction?
- Wed Jan 15, 2020 7:05 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Water in Acid-Base Equilibria
- Replies: 3
- Views: 87
Water in Acid-Base Equilibria
In lecture, the professor went over a question involving the reaction and used the ICE table. Why is the intial value of H2O zero and not 10-7?