## Search found 35 matches

Sun Feb 16, 2020 9:00 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Spontaneous
Replies: 13
Views: 121

### 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: 114

### 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: 18
Views: 264

### 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: 204

### 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: 101

### 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: 45

### 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: 32

### 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: 107

### 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: 62

### 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
Replies: 3
Views: 32

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: 49

### 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: 53

### 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: 164

### 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: 69

### 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: 86

### 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: 140

### 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: 16

### 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: 36

### 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: 723

### 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: 38

### 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: 44

### 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: 40

### 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: 68

### 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: 57

### 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: 139

### 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: 199

### 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: 29

### 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: 17

### 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: 111

### 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: 35

### 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: 45

### 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: 627

### 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: 38

### 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: 36

### 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: 65

### 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.