## Search found 31 matches

Thu Mar 15, 2018 10:12 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: rate law
Replies: 5
Views: 496

### Re: rate law

After concentrations, rates, and orders are calculated from experimental data, k is calculated using the equation rate =k [R]^n
Thu Mar 15, 2018 10:08 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: Rate Constant Units
Replies: 9
Views: 679

### Re: Rate Constant Units

Also, when solving for k through the equations, the units should cancel out to the proper units anyway, but it is useful to know what the units are for different orders anyway.
Thu Mar 15, 2018 10:06 pm
Forum: General Rate Laws
Topic: graphs
Replies: 8
Views: 426

### Re: graphs

You will most likely need to interpret them, but not draw them. It will be useful knowing the sign of the slopes of the different orders
Wed Mar 07, 2018 1:49 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: Integrated Rate Law
Replies: 2
Views: 253

### Re: Integrated Rate Law

It is possible with products, but in this class, our primary focus is on the reactants in rate laws because if there are products present, the reverse reaction may occur, which would complicate the calculations of the rate of reaction.
Wed Mar 07, 2018 1:47 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: Initial Rate and Concentrations
Replies: 2
Views: 209

### Re: Initial Rate and Concentrations

In addition, the reason why we use reactants is so that the reverse reaction from products to reactants does not interfere with the rate.
Wed Mar 07, 2018 1:45 pm
Forum: First Order Reactions
Topic: Pseudo First Order Reactions
Replies: 2
Views: 197

### Re: Pseudo First Order Reactions

It would most likely have to be specified. Just know that all reactants will be in excess concentrations except for one. That can be an indication that a pseudo first order reaction is in play.
Wed Feb 28, 2018 1:01 pm
Forum: General Rate Laws
Topic: 15.3 C
Replies: 8
Views: 859

### Re: 15.3 C

The unique rate of the reaction is always given by this format (click on the link to see) https://i.ytimg.com/vi/ycXCSY7N3qc/maxresdefault.jpg So therefore, according to this equation, because NO2 has a coefficient, it's rate of consumption it must be divided by that coefficient to find the rate of ...
Wed Feb 28, 2018 12:56 pm
Forum: General Rate Laws
Topic: Negative Sign [ENDORSED]
Replies: 7
Views: 417

### Re: Negative Sign[ENDORSED]

The reason why we want rates to be positive is because it is the standard convention. It makes it easier to compare rates of formation and consumption to each other without the distraction of the negative sign. Another way to think about it is that we generally don't report our speed in daily life w...
Wed Feb 28, 2018 12:49 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: Textbook Problems 15.3 and 15.5
Replies: 7
Views: 653

### Re: Textbook Problems 15.3 and 15.5

Just remember that the rate of the reaction (unique rate of the reaction) is always the rate of either formation of a product or consumption of a reactant divided by the coefficient of that product or reactant in the balanced chemical equation. For calculating the rate of a formation, you simply div...
Wed Feb 21, 2018 1:56 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Calculating K
Replies: 3
Views: 187

### Re: Calculating K

Either of the first two equations can be used. Just be sure to choose the one that is simplest used based off of the variables provided. For galvanic cells, the equation involving cell potential will likely be the best equation to use.
Wed Feb 21, 2018 1:53 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell Diagram Order
Replies: 3
Views: 213

### Re: Cell Diagram Order

Anode components are written on the left and cathode is on the right. Any inert metal component of an electrode is written as the outermost component of that electrode.
Wed Feb 21, 2018 1:42 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: redox
Replies: 7
Views: 514

### Re: redox

An easy way to remember this is that an agent has to induce what it is for, so in the case of an OXIDIZING agent, it has to induce oxidation (the loss of electrons) in another molecule; it does this by being reduced (accepting electrons). A REDUCING agent has to induce reduction in another compound,...
Fri Feb 16, 2018 3:41 pm
Forum: Balancing Redox Reactions
Topic: Oxidation
Replies: 5
Views: 372

### Re: Oxidation

Oxidation number is called "oxidation number" because it describes the degree of oxidation (the loss of electrons) of an atom IN a chemical compound. It describes it through the hypothetical (because it assumes all other atoms in the compound are fully ionic) charge the atom would have in ...
Fri Feb 16, 2018 3:32 pm
Forum: Balancing Redox Reactions
Topic: Oxidized vs oxidizing agent
Replies: 5
Views: 273

### Re: Oxidized vs oxidizing agent

Oxidizing agents are reduced--they accept the electron from the molecule that is oxidized. Reducing agents are oxidized--they donate an electron to the molecule that is reduced.
Fri Feb 16, 2018 3:27 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: Molar entropies
Replies: 5
Views: 500

### Re: Molar entropies

okay, thanks, also, what is the difference between standard molar entropies and statistical entropies? I know that standard molar entropies are a measure that is absolute and definite at 25 Celsius. I believe that what you are referring to as statistical entropy is the ones calculated using degener...
Fri Feb 09, 2018 4:01 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Anode and cathode
Replies: 9
Views: 421

### Re: Anode and cathode

There isn't really a visual way to tell unless if you can identify the solutions or the electrodes. For example, if you can identify that there is zinc on one side and copper on the other, you know that zinc is on the anode side and the side with copper is the cathode. Also, if you can see the elect...
Fri Feb 09, 2018 3:59 pm
Forum: Balancing Redox Reactions
Topic: Salt Bridges?
Replies: 6
Views: 274

### Re: Salt Bridges?

The salt bridge is used to complete the circuit by allowing ions from the anode and cathode to transfer.
Fri Feb 09, 2018 3:15 pm
Forum: Balancing Redox Reactions
Topic: Anode vs cathode
Replies: 6
Views: 257

### Re: Anode vs cathode

You are correct. The anode is the oxidation side as it loses electrons, while the cathode is the reduction side as it releases electrons.
Thu Feb 01, 2018 9:00 pm
Forum: Calculating Work of Expansion
Topic: Irreversible Work Chart
Replies: 5
Views: 226

### Re: Irreversible Work Chart

The vertical brown line just shows that before the expansion, the external pressure was lowered to a certain amount, then the horizontal line afterward represents that the external pressure stayed constant at that amount.
Thu Feb 01, 2018 8:58 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Spontaneous
Replies: 14
Views: 821

### Re: Spontaneous

When delta G is negative, the reaction is spontaneous. Take a roaring bonfire, for example. This is a spontaneous process because entropy is increasing, and heat is given off by the combustion reactions of the fire. And overall, after the reactants are burned, the products have a lower amount of ene...
Thu Feb 01, 2018 8:54 pm
Forum: Calculating Work of Expansion
Topic: Expansion
Replies: 3
Views: 233

### Re: Expansion

It would depend on how the pressure and volume are changing. If the pressure is external, the surroundings are performing work on the surroundings. If you are referring to the internal pressure of the system, then if the pressures or volume increases, then the system is doing work. If the volume inc...
Sat Jan 27, 2018 9:24 am
Forum: Calculating Work of Expansion
Topic: Internal Energy Change in Adiabatic Reversible Expansion vs Adiabatic Irreversible Expansion
Replies: 2
Views: 209

### Re: Internal Energy Change in Adiabatic Reversible Expansion vs Adiabatic Irreversible Expansion

I know that work and heat are different, but what does that mean for the fact that ΔU = w in adiabatic processes. Because internal energy is a state property, it should be the same for both irreversible and reversible expansions, at least that is what the textbook says. So how can work be different ...
Fri Jan 26, 2018 3:37 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Entropy Question [ENDORSED]
Replies: 3
Views: 183

### Re: Entropy Question[ENDORSED]

Entropy is a measure related the number of possible configurations that a thermodynamic system, which also means it is a measure related to the number of states the system can be in. The specific relation is given by the Boltzmann equation, S = K b ln(W), but the main point is that it is a related m...
Fri Jan 26, 2018 3:30 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Replies: 8
Views: 3925

### Re: Isolated vs. Adiabatic system

To answer Diane's question, a normal (coffee cup calorimeter) is a closed system, while a bomb calorimeter is an isolated system. Unless if there is a heat source in the calorimeter (not including the reaction) the calorimeter is adiabatic so any heat generated will be from the material sample place...
Fri Jan 26, 2018 3:24 pm
Forum: Calculating Work of Expansion
Topic: Internal Energy Change in Adiabatic Reversible Expansion vs Adiabatic Irreversible Expansion
Replies: 2
Views: 209

### Internal Energy Change in Adiabatic Reversible Expansion vs Adiabatic Irreversible Expansion

In adiabatic reversible expansions, the amount of work done is greater than the amount of work done in an irreversible expansion as the gas is expanding against greater external pressures. Internal energy, in this case, is given by the equation ΔU = w, and because it is a state property, it should b...
Thu Jan 18, 2018 11:21 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Reversible, Irreversible
Replies: 4
Views: 308

### Re: Reversible, Irreversible

To elaborate on the point that reversible work does more work than irreversible work, the reason why that is is that because in a reversible processes, the system is performing work against a pressure always less than just an infinitesimal amount, the max work is being done. In an irreversible proce...
Thu Jan 18, 2018 11:17 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: open system
Replies: 6
Views: 379

### Re: open system

The way I see it is that as noted in the textbook, matter has internal energy (U) which includes the energy of an atom, its electrons, protons, neutrons, and the bonds it forms with other atoms. All of this is energy within the matter, so when it is removed, energy is subtracted
Thu Jan 18, 2018 11:13 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Why is using bond enthalpies the least accurate method of finding reaction enthalpies?
Replies: 5
Views: 4440

### Re: Why is using bond enthalpies the least accurate method of finding reaction enthalpies?

While formation enthalpies are very precise, bond enthalpies are calculated as the average of many bonds. Even if you take the bond C-H, there are many different ways it can be formed into in different molecules.
Fri Jan 12, 2018 3:35 pm
Forum: Phase Changes & Related Calculations
Topic: Intensive vs. Extensive
Replies: 5
Views: 608

### Re: Intensive vs. Extensive

This is probably best understood through examples. Say you have a cup of tea at 80 degrees Celsius. If you use a spoon to scoop up some of the tea from the cup, the tea in the spoon will still be 80 degrees Celcius, and if you used a spoon of a different size, the tea will still be 80 degrees Celciu...
Fri Jan 12, 2018 3:23 pm
Forum: Phase Changes & Related Calculations
Topic: Constant Temperature
Replies: 4
Views: 258

### Re: Constant Temperature

Just to put it as an example, say you heat up an ice cube, and it undergoes a phase change to water. During that phase change, the heat is being used to break up the hydrogen bonds between the water molecules. So, the heat energy transitions to break up these intermolecular forces before it is used ...
Wed Jan 10, 2018 9:52 pm
Forum: Phase Changes & Related Calculations
Topic: Exothermic Rxn
Replies: 6
Views: 471

### Re: Exothermic Rxn

Interesting question! I can actually pull in information I've learned in LS7A to explain this: as others mentioned, negative enthalpy or exothermic reactions don't necessarily indicate that the reaction is spontaneous, it is actually the sign of the change of Gibbs free energy that does (a negative ...