CHEMISTRY COMMUNITY

Cynthia Aragon 1B

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?

Cynthia Aragon 1B

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.

Cynthia Aragon 1B

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.

Cynthia Aragon 1B

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...

Cynthia Aragon 1B

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...

Cynthia Aragon 1B

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...

Cynthia Aragon 1B

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.

Cynthia Aragon 1B

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...

Cynthia Aragon 1B

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...

Cynthia Aragon 1B

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.

Cynthia Aragon 1B

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...

Cynthia Aragon 1B

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.

Cynthia Aragon 1B

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.

Cynthia Aragon 1B

The standard temperature used is 298k.

Cynthia Aragon 1B

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...

Cynthia Aragon 1B

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...

Cynthia Aragon 1B

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.

Cynthia Aragon 1B

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 ...

Cynthia Aragon 1B

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.

Cynthia Aragon 1B

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...

Cynthia Aragon 1B

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.

Cynthia Aragon 1B

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...

Cynthia Aragon 1B

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,...

Cynthia Aragon 1B

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...

Cynthia Aragon 1B

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 ...

Cynthia Aragon 1B

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.

Cynthia Aragon 1B

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...

Cynthia Aragon 1B

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.

Cynthia Aragon 1B

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.

Cynthia Aragon 1B

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...

Cynthia Aragon 1B

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...

Cynthia Aragon 1B

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...

Cynthia Aragon 1B

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...

Cynthia Aragon 1B

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.

Cynthia Aragon 1B

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 ...

Cynthia Aragon 1B

Qp in the enthalpy formula represents heat absorbed or released under constant pressure conditions; where Delta T represents the difference between reactants and products.

Cynthia Aragon 1B

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.

Cynthia Aragon 1B

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...

Cynthia Aragon 1B

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.

Cynthia Aragon 1B

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...

Cynthia Aragon 1B

An endothermic reaction absorbs energy from the surrounding and exothermic reaction releases/ produces heat.
Endothermic: delta H >0
Exothermic: delta H < 0

Cynthia Aragon 1B

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.

Cynthia Aragon 1B

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...

Cynthia Aragon 1B

Kp stands for the partial pressure equilibrium constant
Kc stands for the molar concentration equilibrium constant

Cynthia Aragon 1B

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.

Cynthia Aragon 1B

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...

Cynthia Aragon 1B

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...

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