Search found 47 matches
- Wed Mar 13, 2019 10:37 am
- Forum: Student Social/Study Group
- Topic: Chemistry Community
- Replies: 8
- Views: 1291
Chemistry Community
I have a question regarding how the grading will be done for the online chemistry community. Are the points calculated per week or overall toward the end of the course?
- Wed Mar 13, 2019 10:30 am
- Forum: Second Order Reactions
- Topic: Final
- Replies: 32
- Views: 2283
Re: Final
Based on my understanding, Lavelle would be testing on concepts mostly past the the midterm especially kinetics and electrochemistry since that is what he has been teaching but it will be cumulative.
- Wed Mar 13, 2019 10:27 am
- Forum: Student Social/Study Group
- Topic: Final
- Replies: 5
- Views: 829
Re: Final
Something that I find useful is going over some practice problems from the howework since he usually changes the numbers and uses the same concepts. Regarding any TA review sessions you can always check the main chemistry page since Lavelle is hosting many of those as well as the TA's.
- Thu Mar 07, 2019 10:33 am
- Forum: First Order Reactions
- Topic: First Order Decay
- Replies: 2
- Views: 337
Re: First Order Decay
According to my understanding, radioactive decay is a first order process since the decay rate is dependent upon the number of radioactive atoms. Moreover, since it is a first order the rate of the reaction depends upon the concentration of one reactant and thus it is not affected by factors that al...
- Thu Mar 07, 2019 10:21 am
- Forum: Method of Initial Rates (To Determine n and k)
- Topic: Rate constant k
- Replies: 3
- Views: 453
Re: Rate constant k
According to my understanding, Factors that affect the rate constant include adding a catalyst/ enzyme which lowers the activation energy of the reaction by allowing it to proceed faster since it will organize the orientation of the particles in a specific manner that is easier for the reaction to p...
- Thu Mar 07, 2019 9:54 am
- Forum: Zero Order Reactions
- Topic: zero vs. first vs. second reactions
- Replies: 3
- Views: 317
Re: zero vs. first vs. second reactions
To my understanding I know that in a zero- order the concentration of reactants does not affect k. Rate= k. It is used for 0 mole of reactant. For the first order reaction, Rate= k[A] and used for 1 mole of reactant. For the second order reaction, rate= k[A][B] and used for 2 mole of reactant. A zer...
- Thu Feb 28, 2019 6:30 am
- Forum: Student Social/Study Group
- Topic: Electrochemistry Outline
- Replies: 1
- Views: 511
Re: Electrochemistry Outline
For week 8 homework you can do problems related to topics latter of nernst equation and kinetics since that is what we have focused in class.
- Thu Feb 28, 2019 4:31 am
- Forum: Balancing Redox Reactions
- Topic: Oxidation Numbers
- Replies: 3
- Views: 416
Re: Oxidation Numbers
Other helpful rules to remember include: 1. The oxidation number of an atom is zero in a neutral substance that contains atoms of only one element. Thus, the atoms in O2, O3, P4, S8, and aluminum metal all have an oxidation number of 0. 2. The oxidation number of simple ions is equal to the charge o...
- Thu Feb 28, 2019 4:22 am
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Exothermic and Endothermic Reactions
- Replies: 4
- Views: 864
Re: Exothermic and Endothermic Reactions
A system that releases heat to the surroundings, an exothermic reaction, has a negative ΔH because the enthalpy of the products is lower than the enthalpy of the reactants of the system.The enthalpies of these reactions are less than zero, and are therefore exothermic reactions. A system of reactant...
- Thu Feb 28, 2019 4:16 am
- Forum: Balancing Redox Reactions
- Topic: Oxidation Numbers
- Replies: 3
- Views: 1306
Re: Oxidation Numbers
The oxidation number of an atom is zero in a neutral substance that contains atoms of only one element. Thus, the atoms in O2, O3, P4, S8, and aluminum metal all have an oxidation number of 0.
- Thu Feb 28, 2019 4:13 am
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Cathode/Anode, +/-
- Replies: 2
- Views: 314
Re: Cathode/Anode, +/-
Voltaic cells are driven by a spontaneous chemical reaction that produces an electric current through an outside circuit which are important because they are the foundation in batteries. There is a cell that does work on a chemical system by driving an electric current through the system which are c...
- Fri Feb 22, 2019 9:35 am
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Electron Transfer and Galvanic Cells
- Replies: 2
- Views: 300
Electron Transfer and Galvanic Cells
In Wednesday's lecture, Lavelle went over the concept of electron transfer between two beakers where he described the concept of reduction and oxidation and elaborating on cathode and anode. May someone clarify that concept for me. Thanks.
- Fri Feb 22, 2019 9:27 am
- Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
- Topic: Isochoric
- Replies: 3
- Views: 666
Re: Isochoric
An isochoric process is a thermodynamic process in which the volume remains constant. Since the volume is constant, the system does no work and W = 0.
- Fri Feb 22, 2019 9:18 am
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Gibbs Free energy
- Replies: 5
- Views: 574
Re: Gibbs Free energy
The standard temperature used is 298k.
- Fri Feb 22, 2019 9:17 am
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Delta G spontaneity
- Replies: 7
- Views: 1195
Re: Delta G spontaneity
When Delta G is given and you see the standard symbol it means standard temperature which is 298K. Also 1M and 1Atm is standard. Delta G is spontaneous when Delta H is positive and and Delta S is positive. Also, Delta G is spontaneous when both Delta H and Delta s are negative. Delta G is non-sponta...
- Fri Feb 15, 2019 4:17 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Gibbs free energy
- Replies: 7
- Views: 672
Re: Gibbs free energy
Delta G is spontaneous when Delta H and Delta S are positive at low or high temperatures. It's all spontaneous when Delta H is positive and Delta S is negative at all temperatures. Delta G is nonspontaneous when Delta H is positive and Delta S is negative at all temperatures. It may also be nonspont...
- Fri Feb 15, 2019 3:14 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Liquid and moles
- Replies: 8
- Views: 1086
Re: Liquid and moles
Solids and liquids are not included because any change would not be sufficient to cause a drastic impact in the concentration of reactants. It is like saying you remove .10 cents from your $1000 savings account and thus that amount is not significant.
- Fri Feb 15, 2019 1:05 pm
- Forum: Biological Examples (*DNA Structural Transitions, etc.)
- Topic: Structures of the Human Body and Systems
- Replies: 5
- Views: 1328
Re: Structures of the Human Body and Systems
The human body is an open system because an open system refers to both energy and matter getting in and out of the system. Various inputs such as food, oxygen and water go in whereas wastes and carbon dioxide go out. Energy can be transmitted in and out of the body such as when throwing a ball. The ...
- Fri Feb 15, 2019 12:46 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: work and Gibbs Free Energy
- Replies: 2
- Views: 276
Re: work and Gibbs Free Energy
Gibbs free energy is the amount of non-expansion work that can be taken from a thermodynamically closed system which can attained only in a reversible process. Delta G is positive in a non spontaneous process at all temperatures.
- Fri Feb 15, 2019 12:29 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Quick Conceptual question
- Replies: 7
- Views: 863
Re: Quick Conceptual question
Enthalpy refers to the measure of total heat content in a thermodynamic system under constant pressure and is denoted by the symbol H. Entropy refers to the measure of the level of disorder and is denoted by the symbol S. Entropy is calculated in terms of change Delta S = q/T where q is the heat con...
- Fri Feb 15, 2019 12:15 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Gibbs Free Energy and Equilibrium
- Replies: 5
- Views: 508
Re: Gibbs Free Energy and Equilibrium
Gibbs free energy is a measure of how much potential a reaction has left to do a "net" something . If the free energy is 0 that means the reaction has reached equilibrium and no work can be done.
- Thu Feb 07, 2019 5:11 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Enthalpy and Entropy
- Replies: 2
- Views: 1040
Re: Enthalpy and Entropy
Enthalpy, is denoted by he symbol 'H' and refers to the measure of total heat content in a thermodynamic system under constant pressure. It is calculated in terms of change, i.e., ∆H = ∆E + P∆V(where E is the internal energy). The SI unit of enthalpy is joules (J). It can be defined as the total ene...
- Thu Feb 07, 2019 12:05 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: constant volume
- Replies: 3
- Views: 342
Re: constant volume
An isochoric process is one in which the volume is held constant, meaning that the work done by the system will be zero. The only change will be that a gas gains internal energy. Sometimes reactions happen in a rigid, sealed container such as a bomb calorimeter. When no change in volume is possible,...
- Thu Feb 07, 2019 11:52 am
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: Reversible vs irreversible
- Replies: 3
- Views: 527
Re: Reversible vs irreversible
A reversible process in thermodynamics refer to a process than can turn back in a way that both the system and the surroundings return back to their original states with no change occurring in the universe. Both the system and surroundings are returned to their initial states at the end of the rever...
- Fri Feb 01, 2019 8:55 am
- Forum: Phase Changes & Related Calculations
- Topic: U and its relations to work
- Replies: 8
- Views: 784
Re: U and its relations to work
U, stands for the internal energy of a system which can be altered by heat flow and work. If heat flows into the system; work is done on the system, and its internal energy increases, ΔU > 0. If heat flows out of the system, work is done by the system, and its internal energy decreases, ΔU < 0 Hope ...
- Thu Jan 31, 2019 8:41 pm
- Forum: Calculating Work of Expansion
- Topic: Work
- Replies: 5
- Views: 523
Re: Work
According to my understanding In the first law of thermodynamics : Q +W ; W is positive if work is done by the system and negative if work is done on the system.
- Thu Jan 31, 2019 1:52 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: steam vs. water
- Replies: 5
- Views: 1341
Re: steam vs. water
Burns from steam cause more damage than hot water due to the latent heat of vaporization which is the amount of heat energy required to change a unit of mass liquid into vapor at atmospheric pressure at its boiling point. In other words, it is the amount of heat energy required to change the state o...
- Thu Jan 31, 2019 12:14 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Isolated systems
- Replies: 10
- Views: 734
Re: Isolated systems
An isolated system refers to a system that does not exchange matter, heat, or work with the surroundings. Thus, what remains constant as time progresses is the mass and total energy of the system.
- Thu Jan 31, 2019 11:58 am
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Surroundings
- Replies: 11
- Views: 899
Re: Surroundings
The system is the part of the universe that is being studied while the surroundings are the rest of the universe that interacts with the system. A system and its surroundings can be as large as the forests in South America and as small as the contents inside a beaker in a chemistry lab.
- Thu Jan 31, 2019 11:44 am
- Forum: Phase Changes & Related Calculations
- Topic: What Does U and q stand for?
- Replies: 9
- Views: 2250
Re: What Does U and q stand for?
The first law of thermodynamics: Delta U= Q + W states that the change in internal energy of a system (Delta U) equals the net heat transfer into the system Q, plus the net work done on the system W. ΔU: change in internal energy U of the system. Q : net heat transferred into the system Q: the sum o...
- Thu Jan 31, 2019 11:38 am
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Heat Capacity
- Replies: 5
- Views: 507
Re: Heat Capacity
Intensive properties do not depend on the amount of matter present. Such examples include density, boiling point, melting point and temperature. They are useful in identifying a sample because the characteristics don't depend on the quantity of the sample and do not change according to conditions. O...
- Thu Jan 24, 2019 3:27 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: State Properties
- Replies: 6
- Views: 451
Re: State Properties
One way to think why heat and work is using this analogy. Suppose that you and your friend are trying to reach a mountain elevation of 1100 m and are at the same initial starting point, lets say at 150 m elevation. You may decide to walk it while your friend opts to take a bus. Then you both compare...
- Thu Jan 24, 2019 2:35 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: Calculating Q
- Replies: 11
- Views: 3510
Re: Calculating Q
For Q, we can plug in the concentrations of reactants/products at any instant of time. By comparing Q with K, we can predict whether the reaction will move in the forward or reverse direction. If Q< K the reaction will proceed in the forward direction. If Q>K, the reaction will proceed in the revers...
- Thu Jan 24, 2019 2:24 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: heat capacity
- Replies: 7
- Views: 753
Re: heat capacity
Heat capacity refers to the ratio of the amount of heat energy added or removed from an object to the resulting increase its temperature. This makes it a state property because it does not matter how the heat was added but rather depends on the initial and final states.
- Thu Jan 24, 2019 1:43 pm
- Forum: Phase Changes & Related Calculations
- Topic: Elements in different states
- Replies: 2
- Views: 259
Re: Elements in different states
To my understanding, all matter can move from one state to another and the physical state changes can be largely dependent by its temperature and pressure. These phase changes occur when certain points are reached such as the element's freezing or melting point. To my understanding, helium, a noble ...
- Thu Jan 24, 2019 1:20 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: p in qp
- Replies: 1
- Views: 76
Re: p in qp
Qp in the enthalpy formula represents heat absorbed or released under constant pressure conditions; where Delta T represents the difference between reactants and products.
- Thu Jan 17, 2019 11:49 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Thermodynamic Stability HW 5I.13
- Replies: 2
- Views: 293
Re: Thermodynamic Stability HW 5I.13
Thermodynamic stability usually refers to a system that is at its lowest energy state. A reactive species most stable and preferred state is that of the products.
- Thu Jan 17, 2019 11:39 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Hemoglobin and Homeostasis
- Replies: 1
- Views: 129
Re: Hemoglobin and Homeostasis
How does partial pressure and concentration of oxygen affect hemoglobin and oxygen exchange? Partial pressure plays a significant role in the binding of oxygen and dissociation from heme which is a binding iron protein found in hemoglobin. The ability of an oxygen molecule to develop an affinity for...
- Wed Jan 16, 2019 3:15 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: % Ionization
- Replies: 3
- Views: 226
Re: % Ionization
Percent ionization is related to the amount of weak acid that exists as ions at a specific concentration.
Percent ionization formula : [H+] / [HA] x 100%
Hope this helps.
Percent ionization formula : [H+] / [HA] x 100%
Hope this helps.
- Wed Jan 16, 2019 3:06 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Le Chatelier's Principle
- Replies: 7
- Views: 456
Re: Le Chatelier's Principle
Le Chatelier's principle corresponds whenever a stress is placed on a situation at equilibrium, the equilibrium will shift to relieve that stress. Stresses include change in concentration, volume, temperature and pressure. For example when the concentration of a reactant or product is increased, the...
- Wed Jan 16, 2019 2:52 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Exothermic vs. Endothermic Reaction
- Replies: 9
- Views: 3165
Re: Exothermic vs. Endothermic Reaction
An endothermic reaction absorbs energy from the surrounding and exothermic reaction releases/ produces heat.
Endothermic: delta H >0
Exothermic: delta H < 0
Endothermic: delta H >0
Exothermic: delta H < 0
- Mon Jan 14, 2019 10:11 pm
- Forum: Ideal Gases
- Topic: Homework for week 2 [ENDORSED]
- Replies: 10
- Views: 2951
Re: Homework for week 2 [ENDORSED]
You can focus on either chemical equilibrium problems related to ICE tables and any problem related to the acids and bases chapter since that is what is currently being covered.
- Thu Jan 10, 2019 4:32 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Pure solids and liquids in eq. constants [ENDORSED]
- Replies: 4
- Views: 1890
Re: Pure solids and liquids in eq. constants [ENDORSED]
Pure solids and liquids are not included in the equilibrium expression since their concentrations remain constant throughout the reaction. The density of a pure solid or liquid is the same despite how much pure solid or liquid is present. For the liquids, it is insignificant because since there is a...
- Thu Jan 10, 2019 3:17 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: K, Kc and Kp
- Replies: 8
- Views: 536
Re: K, Kc and Kp
Kp stands for the partial pressure equilibrium constant
Kc stands for the molar concentration equilibrium constant
Kc stands for the molar concentration equilibrium constant
- Thu Jan 10, 2019 11:45 am
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: K=1
- Replies: 5
- Views: 358
Re: K=1
If K is about equal to 1, the reaction will reach equilibrium as reaction intermediate meaning that the amounts of products and reactants will be equal in amount.
- Thu Jan 10, 2019 11:03 am
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: K
- Replies: 4
- Views: 399
Re: K
Kp= partial pressure Equilibrium constant; used when it is in the gas phase Kc= molar concentration equilibrium constant; used in concentrations other than gas since gases do not have concentrations Keq= typically written to write an equilibrium expression The units of Keq are "dimessioness&quo...
- Thu Jan 10, 2019 10:10 am
- Forum: Ideal Gases
- Topic: Algebra
- Replies: 5
- Views: 313
Re: Algebra
For a gas we use its partial pressure (P). To convert between concentration and pressure you use the ideal gas law: PV= nRT To ultimately get concentration, first divide by "V" on both sides of the equation to get P=(n/V) RT n/V stands for mole/V or mol/L Then P= conc (RT) To get concentra...