## Search found 51 matches

Sun Mar 15, 2020 1:36 pm
Forum: Administrative Questions and Class Announcements
Topic: Athena
Replies: 34
Views: 2150

### Re: Athena

*high five*
Fri Mar 13, 2020 10:32 am
Forum: Balancing Redox Reactions
Topic: OH vs H
Replies: 12
Views: 246

### Re: OH vs H

H+ is used to balance acidic solutions, OH- is used to balance basic solutions. One can't be used for the other because there is no concentration to use, and that form of the reaction is highly unlikely to happen.
Fri Mar 13, 2020 10:29 am
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Catalysis
Replies: 11
Views: 184

### Re: Catalysis

A catalyst is a reactant in the first step, and a product in the second step. It lowers activation energy, and speeds up a reaction.
Fri Mar 13, 2020 10:27 am
Forum: Second Order Reactions
Topic: Example Help (Second Order)
Replies: 2
Views: 132

### Re: Example Help (Second Order)

A second order reaction is one that either has two different reactants that change the rate of the reaction, or has two moles of the same reactant that changes the rate of the reaction. ex) (H+) + (OH-) --> H2O is a second order reaction because the rate of the reaction depends on both H+ and OH-. T...
Fri Mar 13, 2020 10:22 am
Forum: First Order Reactions
Topic: Difference between first and second order
Replies: 6
Views: 143

### Re: Difference between first and second order

There are many ways a reaction can become first or second order, but the main difference is how many reactants the rate depends upon. If the rate depends on one reactant, then it is first order. If the rate doesn't depend on a reactant (say it depends on a catalyst instead) then the reaction is zero...
Fri Mar 13, 2020 10:13 am
Forum: Second Order Reactions
Topic: 7.21 part H
Replies: 2
Views: 110

### Re: 7.21 part H

Yes, it is because you have to account for the fact that the rate = A^{2} . From this equation, you can get the half-life equation which is t_{1/2}= \frac{1}{k[A]_{0}} . From this equation you can clearly see that with respect to [A], the half-life has an inverse relationship, so the plot won't be ...
Sun Mar 08, 2020 3:39 pm
Forum: First Order Reactions
Topic: how to know actual order
Replies: 4
Views: 170

### Re: how to know actual order

Stoichiometric coefficients aren't used when determining rate order because experimentally, concentration and time are the only things being considered, so rate order is based on each reactant, not how many moles of that reactant are reacting.
Sun Mar 08, 2020 3:31 pm
Forum: Balancing Redox Reactions
Topic: spontaneous redox reactions
Replies: 4
Views: 114

### Re: spontaneous redox reactions

Being spontaneous means the reactants have more energy than the products, so there's energy to be released. If it was the other way around, then energy would have to be input for the reaction to start.
Sun Mar 08, 2020 3:28 pm
Forum: Zero Order Reactions
Topic: Rate of Reaction Independent of [A]o
Replies: 3
Views: 76

### Re: Rate of Reaction Independent of [A]o

When catalysts/enzymes are saturated they can only work so fast. Adding more reactant won't affect the reaction rate because the catalyst/enzyme is already working as fast as it can (at that temp/pressure/acidity/etc.) This means the reaction rate is independent of concentration of reactant and it i...
Sun Mar 08, 2020 3:24 pm
Forum: General Rate Laws
Topic: slow step
Replies: 9
Views: 171

### Re: slow step

If it is a multi-step reaction and one is significantly slower than the other, then we will always use that step to determine the rate-law.
Sun Mar 08, 2020 3:22 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Slow step
Replies: 4
Views: 104

### Re: Slow step

Most of the time it will tell you, but if it asks you to determine which step is the slow step, then it's the one the rate law is describing. This rate law can be derived from concentrations and time as well, so be ready to derive the slow step from a table of concentrations and times.
Fri Mar 06, 2020 11:43 am
Forum: First Order Reactions
Topic: order of reaction equations
Replies: 6
Views: 142

### Re: order of reaction equations

I think we should be ready for anything. We've spent a lot of time in class on derivations and integrations, so I wouldn't be surprised if he asks us to derive something at some point. It shows a true understanding of the material, and is something that could only be helpful to know!
Fri Mar 06, 2020 11:41 am
Forum: Method of Initial Rates (To Determine n and k)
Topic: Initial Rates
Replies: 3
Views: 113

### Re: Initial Rates

They're going to give you enough to solve the problem. Most of the time it will be concentrations and rates, sometimes they might give you k and n and have you solve for something else, just be ready for anything.
Fri Mar 06, 2020 11:37 am
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: thermodynamically stable
Replies: 6
Views: 156

### Re: thermodynamically stable

Thermodynamic stability is determined by somethings Gº value. The lower its Gº, the more stable it is going to be. If it is a reactant in a reaction, then the lower its Gº, the less likely it is going to be a spontaneous reaction.
Fri Feb 21, 2020 12:04 am
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Delta G and delta Gr
Replies: 3
Views: 124

### Re: Delta G and delta Gr

If the book says its in molar form, then I'm pretty sure we would take deltaG and divide it by the number of electrons being transferred in the reaction. This would turn the energy from KJ into KJ/mol, however I'm not sure, could someone confirm?
Thu Feb 20, 2020 11:57 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Galvanic/Voltaic Cells
Replies: 2
Views: 74

### Re: Galvanic/Voltaic Cells

Galvanic and Voltaic cells are the same thing. They are related through the equation deltaGº = -nFEº, where n is number of moles of electrons being transferred by the reaction, and F is Faraday's constant, 9.6485X10^4 Colombs/mol.
Thu Feb 20, 2020 11:54 pm
Forum: Balancing Redox Reactions
Topic: oxidation numbers
Replies: 5
Views: 74

### Re: oxidation numbers

For the most part, with a bit of practice, it becomes easier to tell which is being oxidized and which is being reduced. We know O and H, all alkali metals, and all halogens will be unchanging for the most part, so we are looking for transition metals. Once we know the molecule with the transition m...
Thu Feb 20, 2020 11:50 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: cell potential equation
Replies: 5
Views: 113

### Re: cell potential equation

F is faraday's constant, for the most part we will be using 9.6485 X 10^4
Thu Feb 20, 2020 11:44 pm
Forum: Balancing Redox Reactions
Topic: Galvanic cells
Replies: 2
Views: 60

### Re: Galvanic cells

Electrons must be forced into the system in order for a galvanic cell to be reversed. We know this because we have to do it, it will not happen by itself. If we are looking for if a galvanic cell is working, we need to run the current through something and test it, such as a voltmeter or a lightbulb.
Fri Feb 14, 2020 6:36 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Irreversible reactions and temperature
Replies: 3
Views: 137

### Re: Irreversible reactions and temperature

An example of this would be solid vs liquid of the same material. Inputting energy into the system will make the solid turn to liquid, but they can be the same temperature.
Fri Feb 14, 2020 6:30 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Van't Hoff Equation
Replies: 3
Views: 77

### Re: Van't Hoff Equation

I think in real life examples it isn't realistic, but if something is constant in a problem, there will be some way for you to tell, whether they tell you or they tell you something about the system that hints at it.
Fri Feb 14, 2020 6:27 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: isolated system
Replies: 16
Views: 300

### Re: isolated system

Yes because there is no way for energy to flow through it, so deltaU is 0, but w and q are also 0 because there is no way for energy to enter or leave, so they can't be balanced either.
Fri Feb 14, 2020 6:24 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Electrochemical cell
Replies: 4
Views: 78

### Re: Electrochemical cell

Basically how a cell works is that it separates two materials that can create a redox reaction, but allows them to be connected by a material that can conduct electricity. When this connection is made, the two species are allowed to react, and electrons flow through the circuit, powering it. When th...
Fri Feb 14, 2020 6:17 pm
Forum: Balancing Redox Reactions
Topic: Redox reaction
Replies: 5
Views: 87

### Re: Redox reaction

For the most part, O will always be -1, halogens will always be -1, and H will always be +1. Once we assign values to these elements, then the rest we just add up the rest of the molecule to equal the total charge.
Sat Feb 08, 2020 11:26 pm
Forum: Calculating Work of Expansion
Topic: Isothermal expansion of an ideal gas
Replies: 2
Views: 46

### Re: Isothermal expansion of an ideal gas

Assuming it's still the expansion of an ideal gas, heat will have to be entering the system. According to Charles law, we know the volume of a gas is inversely proportional to its temperature, so for a gas to increase in volume but stay the same temperature, heat energy must be entering it.
Sat Feb 08, 2020 11:17 pm
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: degeneracy
Replies: 2
Views: 25

### Re: degeneracy

Yes Exactly! To determine degeneracy we use # of states^ # of particles, so if there is a mol of something it would be ^6.022X10^23
Sat Feb 08, 2020 9:11 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: degeneracy relation to thermo
Replies: 5
Views: 78

### Re: degeneracy relation to thermo

Degeneracy in the case of thermo is relating to entropy. The more ways molecules can be ordered the more entropy it has, and the more entropy a species gains from a reaction, the more favorable that reaction is.
Sat Feb 08, 2020 9:06 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Spontaneous Reaction
Replies: 8
Views: 115

### Re: Spontaneous Reaction

Yes exactly, when ΔG is negative the reaction is favorable, and when it is positive it is unfavorable.
Sat Feb 08, 2020 9:02 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Irreversible Expansion
Replies: 2
Views: 38

### Re: Irreversible Expansion

If the temperature is constant, we have to use the equation S=nKln(V2/V1), reversible or irreversible. A reversible change can happen without a constant temperature, but if the pressure is constant, we have to use different equations depending on what is constant.
Sat Feb 08, 2020 8:56 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Reversible vs Irriversible
Replies: 3
Views: 69

### Re: Reversible vs Irriversible

If it happens slowly, tiny steps at a time, it is reversible. If it happens very quickly, and some of the energy is lost, it is irreversible.
Sun Feb 02, 2020 8:43 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Types of Systems
Replies: 3
Views: 61

### Re: Types of Systems

For the most part you will have to figure out if it is a closed open or isolated system, but there are some easy examples to know, anything open is open, anything with a cap on it is closed, and anything insulated and capped is isolated. A bomb calorimeter is also isolated. Hope this helped!
Sun Feb 02, 2020 8:40 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Identifying
Replies: 4
Views: 73

### Re: Identifying

It's necessary to identify this because we treat the systems differently. For example, in an open system, there will always be constant pressure, so we can treat q as deltaH, where as in a closed system or isolated system, this may be different.
Fri Jan 31, 2020 3:04 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Work
Replies: 6
Views: 71

### Re: Work

It all depends on what you set your system as. If you have a beaker and a piston and your system in just the piston, then the beaker would be losing energy and the piston is gaining energy, this means the beaker is putting positive work on the piston. If your system is the beaker AND the piston, the...
Fri Jan 31, 2020 2:58 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Increasing energy in an open system
Replies: 7
Views: 57

### Re: Increasing energy in an open system

Yes those are both ways to increase energy in an open system. Ways to increase or decrease energy only become more restricted as the system becomes more isolated. The more open a system is, the more ways there are to increase the energy of that system.
Fri Jan 31, 2020 2:55 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Work done by expansion
Replies: 8
Views: 64

### Re: Work done by expansion

All we know so far is that ΔU = q + w what we don't know yet is what q is when pressure is not constant.
Fri Jan 31, 2020 2:48 pm
Forum: Phase Changes & Related Calculations
Topic: energy of a system
Replies: 4
Views: 77

### Re: energy of a system

When the piston moves out, something has to push it out. Assuming nothing from the outside is pulling it out, something on the inside must be using energy to push it out, so the system must be losing energy.
Thu Jan 23, 2020 2:53 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: ice table
Replies: 13
Views: 129

### Re: ice table

No, solids and liquids are both put in as 1. The only things that can have value are aqueous (aq) and gas (g).
Thu Jan 23, 2020 2:52 pm
Forum: Phase Changes & Related Calculations
Topic: - and + H values
Replies: 5
Views: 62

### Re: - and + H values

H is calculated by taking final-initial, if the final has less H than the initial (-), then that energy had to go somewhere, it was released into the world, exothermic. If the final has greater H than the initial, then it needed energy from somewhere and was absorbing energy from the outside world (...
Thu Jan 23, 2020 2:46 pm
Forum: Phase Changes & Related Calculations
Topic: Enthalpy
Replies: 4
Views: 99

### Re: Enthalpy

Enthalpy is just the measure of heat! Temperature and enthalpy are related but are different, as seen in heat curves. The x-axis is heat supplied and the y-axis is temperature How are heat and enthalpy different? Heat is more of a descriptor, we can feel heat and know what it is and how to describe...
Thu Jan 23, 2020 2:44 pm
Forum: Phase Changes & Related Calculations
Topic: Calories vs calories
Replies: 5
Views: 36

### Re: Calories vs calories

Calories are 1000 calories.
Thu Jan 23, 2020 2:42 pm
Forum: Phase Changes & Related Calculations
Topic: Steam?
Replies: 8
Views: 101

### Re: Steam?

When heating up a material, the energy can go into two places, increasing the temperature (specific heat), or changing the phase (heat of vaporization). Steam may not be more hot compared to boiling water if they are both 100ºC, but it will be carrying more energy because of the energy input in orde...
Sun Jan 19, 2020 7:42 pm
Forum: Ideal Gases
Topic: When does the Ideal Gas Law Fail?
Replies: 7
Views: 69

### Re: When does the Ideal Gas Law Fail?

The ideal gas law takes into account many assumptions. The most important ones are all collisions are elastic, the molecules themselves don't take up space, and there is no interaction between gas particles except for collisions. These assumptions work best at low pressure and at high temperatures. ...
Sun Jan 19, 2020 7:23 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: pH vs. pOH
Replies: 13
Views: 166

### Re: pH vs. pOH

p before anything means to take the -Log of that thing. pH and pOH are the -log of the H concentrations and the OH concentrations. We can use the K equation to solve for the concentrations. We know we're solving for pH or pOH depending on if the reaction we are using, whether its a weak base or weak...
Sun Jan 19, 2020 7:15 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: X was ignored
Replies: 27
Views: 304

### Re: X was ignored

This is called the X is small approximation. Relative to the initial concentration, the change is so small, less than 10^-3 smaller, so we can treat it as the same number before and after without significant change. This makes our math much, much easier.
Sun Jan 19, 2020 7:02 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Concentrations
Replies: 12
Views: 129

### Re: Concentrations

Concentrations don't effect the K value in itself, but can effect the direction of the reaction. Only temperature can change the K value.
Sun Jan 19, 2020 6:57 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Buffer
Replies: 6
Views: 62

### Re: Buffer

A buffer resists changes to pH, it is usually made out of a weak acid and a salt containing the weak acids anion.
Sun Jan 12, 2020 4:50 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Finding K: liquids and aqueous
Replies: 7
Views: 92

### Re: Finding K: liquids and aqueous

Liquids are pure substances and therefor cannot have a concentration. To have a concentration there needs to be a solute in a solvent, 2 substances, liquids are only 1 substance.
Sun Jan 12, 2020 4:46 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: K vs Q
Replies: 9
Views: 169

### Re: K vs Q

Q is just a method to determine which way the reaction is going to go. The equation has products over reactants, so when there are more products, Q is larger, when there are more reactants Q is smaller. If we let any reaction sit for a while, it will eventually reach K, this means that if Q>K, there...
Sun Jan 12, 2020 4:42 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Inert Gases and Equilibrium Constant
Replies: 4
Views: 73

### Re: Inert Gases and Equilibrium Constant

Pressure alone doesn't change the equilibrium constant. The reason there is a change when we "increase pressure" is actually due to the decrease in volume, and change in concentrations of those initial gases. Adding an inert gas that will have no effect on the reaction doesn't change the e...
Sun Jan 12, 2020 4:35 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: when to use Kc vs Kp
Replies: 11
Views: 96

### Re: when to use Kc vs Kp

The brackets represent molarity, and the P represents partial pressure. The only time to use P is when we are dealing with gasses, it should be (g) as a subscript in the chemical equation this calculates Kp. If it has an (aq) it is a solution with a concentration, and we can use the bracket, this ca...
Sun Jan 12, 2020 4:30 pm
Forum: Ideal Gases
Topic: Bars vs atmospheres
Replies: 13
Views: 98

### Re: Bars vs atmospheres

They are both units of pressure, so as long as all the units match up you should be good to go.