Search found 59 matches
- Sun Mar 15, 2020 5:54 am
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Electrode Mass
- Replies: 10
- Views: 4581
Re: Electrode Mass
The wording is key. if the concentration of one of the electrode solutions is increased, then the concentrations between the two cells are more different (i.e. further away from equilibrium). However, increasing the mass of the electrode does not necessarily increase the concentration, in fact, incr...
- Sun Mar 15, 2020 5:52 am
- Forum: First Order Reactions
- Topic: First order vs zero-order
- Replies: 4
- Views: 413
Re: First order vs zero-order
The first order and zero-order integrated rate laws are designed to create a linear plot, using a different y-axis depending on the order of the reaction. While the two graphs can look similar in that they are both decreasing lines, the clue to what order the reaction is is in the y-axis. If it is f...
- Sun Mar 15, 2020 5:48 am
- Forum: Method of Initial Rates (To Determine n and k)
- Topic: relationship of K and time
- Replies: 3
- Views: 351
Re: relationship of K and time
yes, the instantaneous rate is always its maximum value in the initial stages when you have your initial concentrations of each reactant and are ready to conduct the experiment. As the reaction approaches equilibrium, the instantaneous rate of the reaction decreases, and the rates of the forward and...
- Sun Mar 15, 2020 5:46 am
- Forum: General Rate Laws
- Topic: Hw 7A.13
- Replies: 9
- Views: 695
Re: Hw 7A.13
yes, since when both concentrations of both reactants are doubled, this results in a doubling of the overall rate, both reactants are first order independently. Thus, when adding together n and m from k[A]^n[B]^m, 1+1=2, so it is overall a second-order reaction.
- Sun Mar 15, 2020 5:44 am
- Forum: Method of Initial Rates (To Determine n and k)
- Topic: order of reaction
- Replies: 6
- Views: 591
Re: order of reaction
Within the scope of this class, we will be asked to find the order of reactions based on experimental data, which is the example with multiple experiments where the concentrations of each reactant varied between each experiment and this resulted in a differing rate of the overall reaction.
- Wed Mar 04, 2020 9:44 am
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Cell Diagram
- Replies: 3
- Views: 343
Re: Cell Diagram
If a substance is reduced or oxidized but does not change state (i.e. Fe3+(aq) reduced to Fe2+(aq) by gaining 1e-), then a solid Pt(s) conducted should be used. C(gr) could also be used.
- Wed Mar 04, 2020 9:42 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: 326
Re: Equilibrium Constant K (Q) Units
You can combine different values (i.e. pressure and concentration) because K is a unitless value. Therefore, if you're given concentration of some solution and pressure of a gas, you can use both to calculate Q, if they are involved in the equation for such calculation.
- Wed Mar 04, 2020 9:40 am
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: cell diagram order of phases
- Replies: 6
- Views: 458
Re: cell diagram order of phases
Liquid is placed in between s and g in the cell diagram.
(s)|(l)|(g)|(aq)||(aq)|(g)|(l)|(s)
(s)|(l)|(g)|(aq)||(aq)|(g)|(l)|(s)
- Wed Mar 04, 2020 9:39 am
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Pt(s)
- Replies: 3
- Views: 333
Re: Pt(s)
Pt should be used in the cell diagram when there is either the oxidation or reduction of some substance without a change in phase/state. (i.e. if Fe3+ is reduced into Fe2+ by gaining an electron, but both are in solution, a Pt electrode would be placed in the solution to conduct the electron into so...
- Wed Mar 04, 2020 9:37 am
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Units for G°
- Replies: 6
- Views: 434
Re: Units for G°
Standard Free energy change units are either Joules per mole or Kilojoules per mole.
- Sun Mar 01, 2020 3:51 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: 6L.7a
- Replies: 1
- Views: 224
Re: 6L.7a
You can derive these half-reactions by the change in oxidation states of both of the species in the reaction. You notice that in the reaction given, Br is neither oxidized nor reduced, and Ag is being both oxidized and reduced in the reaction. Therefore, Ag is both the oxidizing and reducing agents,...
- Sun Mar 01, 2020 3:46 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Cathode and Anode of Electrolytic Cells
- Replies: 4
- Views: 292
Re: Cathode and Anode of Electrolytic Cells
The process of choosing which side the reaction will occupy in the cell diagram is the same regardless of the type of cell whether it is Galvanic or Electrolytic. However, conceptually, it is important to note that an input of energy will be needed for electrolytic cells regardless because they are ...
- Sun Mar 01, 2020 3:44 pm
- Forum: Administrative Questions and Class Announcements
- Topic: Chem community posts
- Replies: 3
- Views: 319
Re: Chem community posts
I believe it depends on who your TA is. If they are on Chem community often, they may check at certain weekly deadlines but others may just check to see if you met 50 posts at the end. The best advice would be to ask your TA in particular.
- Sun Mar 01, 2020 3:42 pm
- Forum: Kinetics vs. Thermodynamics Controlling a Reaction
- Topic: how can you tell
- Replies: 11
- Views: 792
Re: how can you tell
Reactions that are carried out quickly (i.e. those with short reaction times) are said to be kinetically controlled while those carried out over longer periods of time are said to be thermodynamically controlled.
- Sun Mar 01, 2020 3:40 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: cell diagram order
- Replies: 3
- Views: 241
Re: cell diagram order
It should be based on state, so it should be s|g|aq||aq|g|s
- Sun Feb 23, 2020 12:32 pm
- Forum: Balancing Redox Reactions
- Topic: Oxidation Numbers
- Replies: 9
- Views: 661
Re: Oxidation Numbers
Many of the compounds that we deal with in redox reactions contain oxygen, hydrogen, and/or a transition metal, as well as common group 1 elements. Memorizing that Oxygen is 2- and the group 1 elements are +1 can help you identify the oxidation states of the other elements in the compound.
- Sun Feb 23, 2020 12:29 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: Autoprotolysis
- Replies: 6
- Views: 1178
Re: Autoprotolysis
Usually, a compound that contains both hydrogen bonds and loan pairs can go through autoprotolysis, as this is the proton transfer between two of the same molecules.
- Sun Feb 23, 2020 12:26 pm
- Forum: Balancing Redox Reactions
- Topic: Cell Diagrams
- Replies: 6
- Views: 385
Re: Cell Diagrams
A single line between compounds on the same side of a double line indicates a change in the physical oxidation state of the compound. For example, solid Fe being oxidized into Fe^2+ in solution would be denoted as { Fe(s)|Fe^2+|| }.
- Sun Feb 23, 2020 12:22 pm
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: Coulomb Unit
- Replies: 4
- Views: 459
Re: Coulomb Unit
J/C is used to indicate the potential difference because a Columb is defined as the amount of charge in 6.24x10^18 electrons. Therefore, the potential difference is defined as the energy transferred between two compounds per Coulomb of charge.
- Sun Feb 23, 2020 12:18 pm
- Forum: Balancing Redox Reactions
- Topic: What is Being Reduced?
- Replies: 10
- Views: 581
Re: What is Being Reduced?
It would most likely be safer to indicate the oxidation state of the compound especially in the instance of dealing with metals.
- Thu Feb 13, 2020 8:47 am
- Forum: Calculating Work of Expansion
- Topic: Positive or negative work
- Replies: 15
- Views: 2170
Re: Positive or negative work
When work is done on the system, work is positive. This is due to the fact that the reaction's capacity to do work has INCREASED. The same can be said for a reaction where work is done on the surroundings and the sign is negative because the reaction has lost energy to its surroundings in the form o...
- Thu Feb 13, 2020 8:45 am
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: adiabatic
- Replies: 19
- Views: 1068
Re: adiabatic
An adiabatic process is one in which no heat is transferred between the reaction and the surroundings (i.e. q=0). This is not the same as an isothermal process, in which the change in temperature is 0. Simply because there is no change in temperature, this does not indicate that there was no heat tr...
- Thu Feb 13, 2020 8:42 am
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: change in Kc
- Replies: 5
- Views: 417
Re: change in Kc
Multiplying a reaction by some constant is the mathematical equivalent of raising the power of the Kc of said reaction to that same constant.
- Thu Feb 13, 2020 8:40 am
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Spontaneous
- Replies: 23
- Views: 1239
Re: Spontaneous
If the change in gibbs free energy is negative, the reaction is spontaneous. If it is positive, it is not. It the change in gibbs free energy is equal to 0, the reaction is in equilibrium.
- Thu Feb 13, 2020 8:39 am
- Forum: Student Social/Study Group
- Topic: Notes from 2.10.20
- Replies: 3
- Views: 254
Re: Notes from 2.10.20
We did not cover any new material on Monday. Lavelle decided to review 3 past exam questions in preparation for the midterm exam.
- Wed Feb 05, 2020 8:56 am
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Cv and Cp
- Replies: 3
- Views: 99
Re: Cv and Cp
Under constant pressure, some of the heat can go into doing work in order to expand or compress against the surroundings. Under constant volume, no work can be done.
- Wed Feb 05, 2020 8:54 am
- Forum: Calculating Work of Expansion
- Topic: Reversible and irreversible process
- Replies: 2
- Views: 117
Re: Reversible and irreversible process
Basically, a reversible process is one in which the pressure of the system is equal to that of the surroundings. THIS HAS IMPLICATIONS when we describe the system using thermodynamics. When pressure is equal in a system and its surroudings, any infinitesimally small change in either the internal or ...
- Wed Feb 05, 2020 8:50 am
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: 4D5
- Replies: 3
- Views: 123
Re: 4D5
Work done on a system by its surroundings is positive. Work done by the system on its surroundings is negative. This has to do with the fact that when a system does work, it loses energy (negative), and when work is done on a system, its energy increases (positive).
- Wed Feb 05, 2020 8:47 am
- 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: Ideal Gas Constant Hw 4B.5
- Replies: 2
- Views: 125
Re: Ideal Gas Constant Hw 4B.5
There is a constant on the equations sheet on Lavelle's class website that has the conversion between Joules and L.atm
- Wed Feb 05, 2020 8:40 am
- Forum: Calculating Work of Expansion
- Topic: Work on a system +/-
- Replies: 4
- Views: 151
Re: Work on a system +/-
When work is done on the surroundings, work is negative. The negative sign is used to indicate that the system is losing energy to the surroundings through doing work (you get tired when you constantly have to push against something that is pushing in on you). When work is done on a system by the su...
- Wed Jan 29, 2020 8:52 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Closed Systems
- Replies: 13
- Views: 718
Re: Closed Systems
Closed systems can be changed by changing either the temperature, pressure, or volume of the given closed system. No matter can flow in and/or out of a closed system, but energy can still be transfered between the system and its surroundings.
- Wed Jan 29, 2020 8:48 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: 4F
- Replies: 2
- Views: 111
Re: 4F
No, technically we are still talking about topics in the realm of thermochemistry, and 4f is focused on topics that lay in thermodynamics. So no, we have not covered the material necessary to complete those problems.
- Wed Jan 29, 2020 8:47 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Cpm and Cvm
- Replies: 2
- Views: 194
Re: Cpm and Cvm
These are considered to be fundamentally differnet constants, given and acquired through different sets of conditions. Cvm is under constant volume, while Cpm is under conditions of constant pressure.
- Wed Jan 29, 2020 8:46 pm
- Forum: Calculating Work of Expansion
- Topic: Sum Equation in Lecture
- Replies: 2
- Views: 87
Re: Sum Equation in Lecture
I feel that he used the integral as a conceptual device to be able to reveal the idea he was trying to portray with the sum of infinitesimal changes in volume. Under constant pressure, P can be pulled out of the integral as a constant, and the change in V will be left as the product of the integral ...
- Wed Jan 29, 2020 8:43 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Heat Capacity
- Replies: 3
- Views: 163
Re: Heat Capacity
Heat capacity is the amount of heat needed to change the temperature of a substance by 1 degree C. The specific heat capacity yields the heat needed to raise the temperature of 1g of a substance by 1 degree C.
- Thu Jan 23, 2020 4:30 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Shifting Forward or Reverse
- Replies: 7
- Views: 177
Re: Shifting Forward or Reverse
Reducing the reactant induces the reaction to produce more of the reaction in order to balance out the system and achieve the same ratio at equilibrium.
- Thu Jan 23, 2020 4:28 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: pKa/pKb and Ka/Kb
- Replies: 5
- Views: 183
Re: pKa/pKb and Ka/Kb
Ka is the acidity constant, and Kb is the basicity constant.
pKa = -log(Ka)
pKb = -log(Kb)
pKa = -log(Ka)
pKb = -log(Kb)
- Thu Jan 23, 2020 4:26 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Exothermic vs. Endothermic reactions
- Replies: 12
- Views: 968
Re: Exothermic vs. Endothermic reactions
The problem given on the tests gives you the chemical equation and the delta H value (change in enthalpy) and you are asked whether the reaction is endothermic or exothermic. If delta H is negative, the reaction is exothermic, and the contrapositive is true.
- Thu Jan 23, 2020 4:24 pm
- Forum: Phase Changes & Related Calculations
- Topic: Order to Read Book
- Replies: 3
- Views: 94
Re: Order to Read Book
The best way to be prepared for his lectures is just to follow the readings he assigned on the syllabus. Lavelle was explaining that the order in which he is going to teach us thermochemistry and thermodynamics differs from the order that the topics come in, in the book
- Thu Jan 23, 2020 4:23 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Prep for Test 1
- Replies: 16
- Views: 677
Re: Prep for Test 1
No, Ka and Kb values will be provided. It may be wise however, to be comfortable writing out chemical equations for the dissociation of acids and bases in water.
- Thu Jan 16, 2020 5:53 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Negative pH
- Replies: 6
- Views: 258
Re: Negative pH
The conventional scale of ph being between 0 and 14 is dewrvied from reactions with water at room temperature.
- Thu Jan 16, 2020 5:49 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: weak acids and weak bases
- Replies: 3
- Views: 164
Re: weak acids and weak bases
I am saying that the function for giving ka is set up the same way as kc or kp. However, you are correct in that you need to set up an ICE chart to be able to represent the function for ka as a quadratic function solving for x.
- Thu Jan 16, 2020 5:47 pm
- Forum: Ideal Gases
- Topic: ph
- Replies: 10
- Views: 513
Re: ph
THe scale is not restricted between 0 and 14 for pH or pOH. However, at room temperature, this scale is restricted. This is because the value of kw (autoprolysis of water) is 10^-14 and thus, the maximum valuue is set to be 14, with the lowest value being 0. In many of the cases, we are assuming tha...
- Thu Jan 16, 2020 5:45 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: change in temp
- Replies: 4
- Views: 124
Re: change in temp
A reaction that is endothermic requires heat to occur. Therefore, if we were to heat this reaction, it would favor the production of the reactions products, as sufficient heat is being applied to the system in order to elicit a reaction.
- Thu Jan 16, 2020 5:43 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: weak acids and weak bases
- Replies: 3
- Views: 164
Re: weak acids and weak bases
You will want to try and idenitfy ka or kb depending on whether the substance is a acid or base. ka is calculated the same way that kc or kp would be calculated, ([P]/[R] excluding liquids or solids). And there are a few important equations associated with ka and kb. - (ka)(kb) = 1.0 x 10^-14 - pka ...
- Mon Jan 13, 2020 4:56 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: Reaction Quotient
- Replies: 11
- Views: 322
Re: Reaction Quotient
The Reaction quotient Q is a number representative of what stage a reaction is at relative to its equilibrium conditions. Q can be used as a checkpoint in such a manner and will allow us to make predictions about which direction the reaction will tend to proceed. In order to do this, K will usually ...
- Mon Jan 13, 2020 4:54 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: Calculating for Pressure
- Replies: 5
- Views: 206
Re: Calculating for Pressure
In the scope of this class, when asked to calculate the pressure of a substance, you will be given a temperature and a relative concentration of this substance and will be expected to know how to manipulate the Ideal Gas LAw equation in order to solve the relation between concentration and pressure ...
- Mon Jan 13, 2020 4:52 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: PV=nRT
- Replies: 9
- Views: 412
Re: PV=nRT
PV=nRT This equation is used to convert between partial pressure of a gvien substance and the concentration of this same substance. This would be useful if we were given Kc and the partial pressures of certain substances and asked to solve for the unknown concentration of some substance. This is now...
- Mon Jan 13, 2020 4:46 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: What is this?
- Replies: 23
- Views: 1474
Re: What is this?
This principle tries to minimize the effect of change by shifting the direction of the reaction in order to maintain equilibrium Just to clarify, it can shift either way right? Yes, if the concentration of products was increased, which could happen in the real world, the reaction would respond by f...
- Mon Jan 13, 2020 4:43 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Le Chatelier's Principle
- Replies: 5
- Views: 244
Re: Le Chatelier's Principle
The General Idea of Le Chatelier's principle is that a given system will respond to changes in the system so as to minimize the effects of said change. This entails a number of different characteristic responses to different types of changes in the system (Temperature, Volume, Concentration, etc.). ...
- Mon Jan 13, 2020 4:40 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: volume change with inert gas
- Replies: 9
- Views: 255
Re: volume change with inert gas
The answer to your question is found in the equation PV=nRT, which can be rewritten as P=(nRT)/V. n/V is the mathematical notation for concentration, therefore P = (concentration)(RT). Thus, the reason that concentration of a substance does not change in a beaker when the pressure is increased by ad...
- Mon Jan 13, 2020 4:35 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Changing Pressure
- Replies: 3
- Views: 121
Re: Changing Pressure
And it also may be worth noting that when dealing with changes in concentration of certain gases (pressures etc.), only increasing pressure by decreasing volume will have an effect on the concentration of the compound. If pressure is increased by adding an inert gas, as Professor Lavelle made note o...
- Fri Jan 10, 2020 5:22 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: K expression involving solids/liquids
- Replies: 7
- Views: 300
Re: K expression involving solids/liquids
The concentration of liquids (solutes) and solids are not included in the calculation of the equilibrium constant because of the inability to apply this characteristic to these phenomena and have it possess and plausible meaning. Solutes, in a reaction at equilibrium, have an insignificant change in...
- Fri Jan 10, 2020 5:19 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Activity of Substance Versus Coefficient
- Replies: 1
- Views: 93
Re: Activity of Substance Versus Coefficient
The activity of a substance, denoted as sub j, is the effective equilibrium concentraiton of that substance in a given reaction. The activity coefficient is the ratio of the activity and concentration of the substances in a given reaction.
- Wed Jan 08, 2020 12:26 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Comparing Q and K
- Replies: 3
- Views: 124
Re: Comparing Q and K
A way to think about Q is a checkpoint to check where the reaction is at in the process of nearing equilibrium. (i.e. if Q<K, there is still more reactant that is being reacted to form the product. if Q>K, there is more product than the reactant would produce at equilibrium and thus, the reaction wi...
- Wed Jan 08, 2020 12:24 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: Effect of High Initial Concentration of Reactant
- Replies: 5
- Views: 243
Re: Effect of High Initial Concentration of Reactant
Yes, if there is a high concentration of intitial reactants, the reaction will favor the production of the products in the reaction. It is also important to note that the value of the equilibrium constant (Kc or Kp) will not change, as the ratio of reactants to products will stay the same, despite t...
- Wed Jan 08, 2020 12:21 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: HW 5I.5
- Replies: 3
- Views: 175
Re: HW 5I.5
Bar is a unit used to denote the partial pressures of gases in a given reaction. Another possible unit to represent a homologous gaseous reaction could be atmospheres. (atm)
- Wed Jan 08, 2020 12:18 pm
- Forum: Ideal Gases
- Topic: Nitrogen gas
- Replies: 5
- Views: 673
Re: Nitrogen gas
Gases in which the molecules do not interacti with each other or take up any space are characteristic of ideal gases. If that helps.
- Tue Jan 07, 2020 10:14 am
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Accessing Sapling Plus [ENDORSED]
- Replies: 1
- Views: 185
Accessing Sapling Plus [ENDORSED]
How do we access Sapling plus if we bought the textbook package off of the UCLA bookstore and not the link that Professor Lavelle had provided?