Search found 35 matches
- Sun Feb 16, 2020 9:00 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Spontaneous
- Replies: 13
- Views: 832
Re: Spontaneous
If delta G (the measure of Gibb's free energy) is positive, the reaction is not spontaneous. If it is negative, the reaction is spontaneous and therefore favorable.
- Sun Feb 16, 2020 8:58 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Standard Enthalpies of Formation
- Replies: 10
- Views: 597
Re: Standard Enthalpies of Formation
The standard enthalpy of formation for elements in their standard, most stable state is zero.
- Sun Feb 16, 2020 8:56 pm
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: S = 0
- Replies: 21
- Views: 1223
Re: S = 0
When your system is isothermal and your reaction is reversible, s = 0 because the reaction is considered at equilibrium throughout.
- Sun Feb 16, 2020 8:53 pm
- Forum: Phase Changes & Related Calculations
- Topic: change in entropy
- Replies: 7
- Views: 688
Re: change in entropy
Because delta S is measures the change in disorder, a delta S value less than zero signifies a decrease in entropy for the whole system.
- Sun Feb 16, 2020 8:51 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: How to interpret reversible/irreversible graphs
- Replies: 6
- Views: 704
Re: How to interpret reversible/irreversible graphs
The temperature is constant for reversible reactions
- Sun Feb 09, 2020 11:00 pm
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: Gas v Liquids
- Replies: 4
- Views: 248
Re: Gas v Liquids
Gas has a higher entropy than liquid because the molecules can move more freely and therefore occupy many more states.
- Sun Feb 09, 2020 10:50 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: work on the system or by the system
- Replies: 4
- Views: 275
Re: work on the system or by the system
if work is done on the system, w is positive because the system is gaining heat. If work is done by the system, w is negative because it is giving heat.
- Sun Feb 09, 2020 10:45 pm
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: Intensive
- Replies: 8
- Views: 516
Re: Intensive
Entropy is an extensive property, meaning its value changes with the amount of the substance. An intensive property does not depend on the amount.
- Sun Feb 09, 2020 10:44 pm
- Forum: Van't Hoff Equation
- Topic: MIdterm
- Replies: 1
- Views: 210
Re: MIdterm
Hi Nick! It's all about truly understanding the material and simplifying what can be some tricky concepts and equations. Good luck on the midterm:)
- Sun Feb 09, 2020 10:36 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Sudden vs. Gradual
- Replies: 3
- Views: 270
Re: Sudden vs. Gradual
A sudden expansion occurs all at once, such as with the piston example. This represents an irreversible reaction. A gradual expansion occurs in infinitesimal increments and represents a reversible reaction.
- Thu Feb 06, 2020 11:02 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Work done on or by the system
- Replies: 4
- Views: 354
Re: Work done on or by the system
If work is done BY the system, w is negative. If work is done on the system, w is positive.
- Thu Feb 06, 2020 11:00 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: calculating entropy
- Replies: 4
- Views: 230
Re: calculating entropy
The -deltaS implies a non spontaneous reaction.
- Thu Feb 06, 2020 10:46 pm
- Forum: Calculating Work of Expansion
- Topic: Isothermal
- Replies: 17
- Views: 823
Re: Isothermal
Isothermal refers to the constant temperature of a system. No heat is added or lost to the environment.
- Thu Feb 06, 2020 10:43 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Question from Wednesday Lecture
- Replies: 3
- Views: 273
Re: Question from Wednesday Lecture
Since it is isothermal and reversible, the temperature of the system remains constant. Therefore, deltaU=0, so 0 = q+w, and q = -w.
- Thu Feb 06, 2020 10:41 pm
- Forum: Phase Changes & Related Calculations
- Topic: Heating Curve Phase Changes
- Replies: 11
- Views: 633
Re: Heating Curve Phase Changes
The substance can change phases at a constant temperature. This is why ice can melt into water at room temperature, and if you check on the ice at different times you will see the ratio of ice to water change.
- Sat Feb 01, 2020 5:01 pm
- Forum: Phase Changes & Related Calculations
- Topic: Phase Changes
- Replies: 17
- Views: 749
Re: Phase Changes
The temperature does not change during a phase change- for example, you can have both ice and water at the same temperature.
- Sat Feb 01, 2020 5:00 pm
- Forum: Calculating Work of Expansion
- Topic: When to Use the Integral
- Replies: 2
- Views: 179
Re: When to Use the Integral
You use the integral when P is not constant, and when it is, you can move it to the outside of the integral.
- Sat Feb 01, 2020 4:59 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: Degeneracy
- Replies: 3
- Views: 220
Re: Degeneracy
The dog bones were all of the possible states that two atoms could be in and represented the degeneracy of the two atoms.
- Sat Feb 01, 2020 4:57 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Isolated vs Closed [ENDORSED]
- Replies: 34
- Views: 4415
Re: Isolated vs Closed [ENDORSED]
A closed system is sealed, but can still interact with the outside environment. An isolated system is sealed and insulated and cannot interact with the environment.
- Sat Feb 01, 2020 4:56 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Energy of Systems
- Replies: 4
- Views: 287
Re: Energy of Systems
Adding or removing substance in a system changes the energy of an open system, changing the temperature of a closed system will change its energy, and doing work on the system/letting the system do work on the environment changes the energy of a closed system
- Tue Jan 21, 2020 1:27 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: H2O in K Expressions
- Replies: 6
- Views: 330
Re: H2O in K Expressions
Yes, H2O gas is included in K expressions.
- Tue Jan 21, 2020 1:26 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Approximation
- Replies: 6
- Views: 255
Re: Approximation
I think it can also be equal to 10^-3
- Tue Jan 21, 2020 1:24 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Prepping for Test
- Replies: 6
- Views: 340
Re: Prepping for Test
The homework problems, learning outcomes, and step-up sessions are really helpful for me!
- Tue Jan 21, 2020 1:23 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: ICE table
- Replies: 5
- Views: 236
Re: ICE table
The "C" is determined by the number of moles of products and reactants created or decreased. The "C" column is filled with +x or -x multiplied by the stoichiometric coefficient of the product or reactant.
- Tue Jan 21, 2020 1:17 pm
- Forum: Ideal Gases
- Topic: Acid and Bases
- Replies: 16
- Views: 603
Re: Acid and Bases
The pH scale is from 0-14. A solution is considered acidic if it has a pH below 7, and basic if above 7.
- Tue Jan 21, 2020 1:15 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: exothermic reactions
- Replies: 19
- Views: 2135
Re: exothermic reactions
An exothermic reaction creates heat- therefore if heat is considered a "reactant," the reaction will lean to the product side as it can produce more products with the increase in heat.
- Tue Jan 21, 2020 1:12 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Checking the approximation of "x"
- Replies: 4
- Views: 158
Re: Checking the approximation of "x"
X is such a small value that it is not drastically affected by coefficients, so you can use an approximation.
- Tue Jan 21, 2020 1:10 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: partial pressure vs concentrations
- Replies: 3
- Views: 123
Re: partial pressure vs concentrations
Usually the problem should give you some initial or equilibrium condition either in mol or bar- if given moles or mol/L you use Kc, if given bar you use Kp
- Tue Jan 21, 2020 1:07 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Changing K
- Replies: 13
- Views: 541
Re: Changing K
Because K is a constant, the only factor that can change it is temperature, as certain reactions will go further toward completion when heat is added and vice versa.
- Tue Jan 21, 2020 1:06 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: expanding the volume
- Replies: 3
- Views: 139
Re: expanding the volume
When you expand the volume, you are decreasing the pressure, so the reaction shifts toward the side with more moles to minimize the impact of the decrease in pressure of the reaction.
- Sun Jan 12, 2020 5:07 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Kc
- Replies: 5
- Views: 239
Re: Kc
Kc denotes the equilibrium constant in terms of molar concentrations. Aqueous solutions have concentrations so they are included in the expression, but solids do not so they do not factor into the Kc expression.
- Sun Jan 12, 2020 5:05 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: What is this?
- Replies: 23
- Views: 1513
Re: What is this?
Le Chatelier's principle states that a system in equilibrium will shift in response to a change in pressure, temp, concentrations etc. in order to minimize its effects on the reaction.
- Sun Jan 12, 2020 4:51 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Units for Kc and Kp
- Replies: 3
- Views: 142
Re: Units for Kc and Kp
Brackets are used to denote molar concentrations, and parenthesis are used to denote partial pressure.
- Sun Jan 12, 2020 4:50 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: ICE vs Normal Concentrations
- Replies: 5
- Views: 187
Re: ICE vs Normal Concentrations
ICE boxes are used to calculate K given a set of initial conditions and their change, but not the equilibrium conditions. When you know the conditions at equilibrium, you can solve for K without ICE.
- Sun Jan 12, 2020 4:45 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Different types of K
- Replies: 9
- Views: 304
Re: Different types of K
K is the general notation for the equilibrium constant. Kc is used when we are specifically defining the ratio of the molar concentrations of products and reactants.