## Search found 47 matches

Tue Mar 10, 2020 9:47 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Gibbs free energy and K
Replies: 3
Views: 25

### Re: Gibbs free energy and K

dG = dG0 + RTlnQ
Tue Mar 10, 2020 9:42 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Equations
Replies: 8
Views: 108

### Re: Equations

also G=-nFE
Tue Mar 10, 2020 9:38 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Calculating Gibbs Free Energy
Replies: 6
Views: 100

### Re: Calculating Gibbs Free Energy

005384106 wrote:In what situation would S(total) ever be = 0?

S can only be 0 for a molecule at 0K which is theoretically unacheivable. If is is 0 between reactants and products in a reaction, that is because they had the same entropy value with opposite signs (coincidence)
Tue Mar 10, 2020 9:35 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: delta g
Replies: 6
Views: 47

### Re: delta g

depends on what is given. if you know dG for both then the easiest way is to simply use those values. If they aren't given you are probably going to have to use enthalpy, temp, and entropy to find the dG values then subtract reactants from products
Tue Mar 10, 2020 9:33 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: H2O as a Gas
Replies: 12
Views: 188

### Re: H2O as a Gas

H2O(g) is included but it is not as a liquid because it is a solvent
Tue Mar 10, 2020 9:32 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Strong/weak acids & bases
Replies: 14
Views: 211

### Re: Strong/weak acids & bases

We are usually given weak acids and bases on exams and the dissociation values for those you don't need to remember, they should be given
Tue Mar 10, 2020 9:30 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Shifts
Replies: 6
Views: 134

### Re: Shifts

if K>Q the reaction shifts in favor of the products
if K<Q the reaction shifts in favor of the reactants
Tue Mar 10, 2020 9:27 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Ka Kb
Replies: 11
Views: 157

### Re: Ka Kb

Use Ka if you are solving for the concentration of an acid and Kb for a base
Tue Mar 10, 2020 9:26 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Calculating K
Replies: 6
Views: 57

### Re: Calculating K

K is a ratio, and ratios have no units
Tue Mar 10, 2020 9:25 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Calculating concentrations at equilibrium
Replies: 4
Views: 140

### Re: Calculating concentrations at equilibrium

so the reaction looks like its gonna be COBr2 <> CO(g) + Br2(g)
you have the final concentration of CO
solve using ICE table
Tue Mar 10, 2020 9:23 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Reasonable values for K
Replies: 7
Views: 82

### Re: Reasonable values for K

if K is greater than 1 then products are favored, less than 1 and reactants are favored
Tue Mar 10, 2020 9:22 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Reasonable values for K
Replies: 7
Views: 82

### Re: Reasonable values for K

as long as K is between 10^-3 and 10^3 it should be reasonable
Tue Mar 10, 2020 9:20 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: ICE table
Replies: 5
Views: 57

### Re: ICE table

if equilibrium constant K is less than 10^-3 then you can ignore x for the initial concentrations. Also if the calculated constant is less than 5% of the initial concentration you can neglect x in your calculation as well.
Tue Mar 10, 2020 9:00 pm
Forum: Phase Changes & Related Calculations
Topic: Equation Choice
Replies: 5
Views: 196

### Re: Equation Choice

the most common phase changes are melting/freezing (dHf) and evaporating/condensing (dHv)
Tue Mar 10, 2020 8:54 pm
Forum: Phase Changes & Related Calculations
Topic: Negative Work
Replies: 18
Views: 303

### Re: Negative Work

work is typically negative when work is done ON the system
Tue Mar 10, 2020 8:47 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Steps to solve calorimeter problem
Replies: 3
Views: 102

### Steps to solve calorimeter problem

In general, what is an outline of steps for solving a basic calorimetry problem?
Tue Mar 10, 2020 8:46 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: endo/exo and temp
Replies: 12
Views: 440

### Re: endo/exo and temp

in exothermic reactions, heat is a product. So when heat is added, it caused the reaction to shift in favor of reactants
Tue Mar 10, 2020 8:44 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: midterm Q6A
Replies: 2
Views: 107

### Re: midterm Q6A

since the dH for the reaction is negative, heat would be released when HCL is formed. Evolved would be if the reaction is endothermic
Tue Mar 10, 2020 8:40 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Delta H
Replies: 10
Views: 226

### Re: Delta H

dH = dU - PdV
Tue Mar 10, 2020 8:39 pm
Forum: Phase Changes & Related Calculations
Topic: change in entropy
Replies: 7
Views: 211

### Re: change in entropy

entropy is a measure of disorder, so an entropy below 0 means the reaction proceeds in a manner that leads to more order
Tue Mar 10, 2020 8:35 pm
Forum: Phase Changes & Related Calculations
Topic: Fusion = Melting?
Replies: 7
Views: 138

### Re: Fusion = Melting?

Heat of fusion refers to melting or freezing. It is positive when melting and negative when freezing
Tue Mar 10, 2020 8:34 pm
Forum: Phase Changes & Related Calculations
Topic: Phase changes
Replies: 8
Views: 169

### Re: Phase changes

you know if there is a phase change if in the reaction the molecule at focus has gone from a liquid to a solid or gas, etc
Tue Mar 10, 2020 8:32 pm
Forum: Phase Changes & Related Calculations
Topic: Relation to entropy?
Replies: 4
Views: 107

### Re: Relation to entropy?

Entropy is a measure of disorder. Solids are compact and their atoms have little room to move around, so since they are organized they have low entropy. Gases have atoms that are spread apart and can move freely, so they have high disorder and high entropy.
Tue Mar 10, 2020 8:30 pm
Forum: Phase Changes & Related Calculations
Topic: Delta H Fusion
Replies: 9
Views: 205

### Re: Delta H Fusion

when dealing with phase changes, you have to account for the energy spent during the actual phase change itself. Say you have 1 mol of water that just got to 100C. It doesn't all evaporate at one instant, it takes x amount of time. In this situation you would apply Hvap
Tue Mar 10, 2020 8:27 pm
Forum: Phase Changes & Related Calculations
Topic: delta G0 versus delta G
Replies: 15
Views: 359

### Re: delta G0 versus delta G

G0 is at standard conditions (25 degrees C and 1 bar) whereas G can be calculated at conditions are than the ones I just listed.
Tue Mar 10, 2020 8:26 pm
Forum: Phase Changes & Related Calculations
Topic: Van't Hoff Eq
Replies: 8
Views: 193

### Re: Van't Hoff Eq

as long as you know what the vant hoff equation is used for and how its used you should be fine. He says in the outline that we dont need to know how to derive it.
Tue Mar 10, 2020 8:20 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: How to determine slow step?
Replies: 9
Views: 88

### Re: How to determine slow step?

the slow step is typically the given rate of the reaction
Mon Mar 09, 2020 10:10 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Question on Midterm
Replies: 4
Views: 100

### Re: Question on Midterm

The more concentrated the solutions are the more reactive they will be and give off the most energy
Mon Mar 09, 2020 10:09 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: enthalpy and entropy
Replies: 4
Views: 79

### Re: enthalpy and entropy

basically if dS is very negative (very disordered) and |TdS|>|dH| then the dG becomes positive
Mon Mar 09, 2020 10:07 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: endothermic reaction
Replies: 5
Views: 90

### endothermic reaction

say we have reaction A+B -> C + D and delta H is positive. Does that mean you add heat to the left or right side of the reaction?
Mon Mar 09, 2020 10:07 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: exothermic reaction
Replies: 4
Views: 76

### exothermic reaction

say we have reaction A+B -> C + D and delta H is negative. Does that mean you add heat to the left or right side of the reaction?
Mon Mar 09, 2020 10:04 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: midterm 6 b
Replies: 6
Views: 48

### midterm 6 b

For which process will dH and dG be expected to be the most similar?

a)2Al(s) + Fe2O3(s) -> 2Fe(s) +2Al2O3(s)
b) 2Na(s) + 2H2O(l) -> 2NaOH(aq) + H2(g)
c) 2NO2(g) -> N2O4(g)
d) 2H2(g) + O2(g) -> 2H2O(g)
Mon Mar 09, 2020 9:37 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: midterm q3d
Replies: 1
Views: 53

### midterm q3d

At pH 6 what is the net charge for acetic acid CH3COOH (pKa = 4.75)?

How do you find charge from these given values? My only guess was to subtract the two but I know its not that easy
Mon Mar 09, 2020 9:33 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: midterm q3c
Replies: 3
Views: 92

### midterm q3c

A buffer solution made with NH3 and NH4Cl has a pH of 10.1. Which procedure(s) could be used to lower the pH? 1) adding HCl 2)Adding NH3 3) adding NH4Cl A) 1 only B) 2 only C) 1 and 3 D) 2 and 3 To solve this did you need to write out the balanced equation? I put a originally but now I'm thinking it...
Mon Mar 09, 2020 9:28 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: HCl and NaOH producing dT
Replies: 4
Views: 142

### HCl and NaOH producing dT

Which of the following combinations of HCl and NaOH produce the largest dT?
a)50mL of 1M HCl and 50mL of 1M NaOH
b)50mL of 2M HCl and 50mL of 2M NaOH
c)100mL of 1M HCl and 50mL of 2M NaOH
d)100mL of 1M HCl and 100mL of 1M NaOH

is the answer b or c?
Mon Mar 09, 2020 9:23 pm
Forum: Ideal Gases
Topic: Liter to meter cubed?
Replies: 4
Views: 101

### Liter to meter cubed?

does anyone have an easy way to remember a conversion factor for dm^3 to m^3?
On the midterm we were given 1L=1dm^3 but the answer called for mol/m^3
Mon Mar 09, 2020 9:16 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: How does K change during compression/expansion?
Replies: 2
Views: 105

### Re: How does K change during compression/expansion?

This depends on how many moles of gas you have as reactants and as products. During compression the reaction will shift in favor of whichever side has less moles of gas to try to maintain its pressure level; during expansion the reaction will shift in favor of whichever side has more moles of gas si...
Mon Mar 09, 2020 9:13 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Going from pKa to pH
Replies: 10
Views: 167

### Re: Going from pKa to pH

The lower the pH, the higher the concentration of hydrogen ions [H+].
The lower the pKa, the stronger the acid and the greater its ability to donate protons.
Mon Mar 09, 2020 9:11 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Finding pOH of a solution given the pKb of a conjugate acid?
Replies: 3
Views: 47

### Finding pOH of a solution given the pKb of a conjugate acid?

"The pKb of the conjugate acid of chlorous acid is 12.08. A 0.15 M solution of chlorous acid was made to use as an inorganic acid in the synthesis of a new pharmaceutical. What is the pOH os this solution at equilibrium? HClO2(aq) + H20(l) <> HClO-(aq) + H3O+(aq) I wrote the ice table down corr...
Mon Mar 09, 2020 9:02 pm
Forum: Ideal Gases
Topic: Partial Pressure
Replies: 13
Views: 142

### Re: Partial Pressure

Decreasing the volume of a system is going to cause the pressure to rise. To negate the increase in pressure, the reaction is going to proceed in the direction which favors the least moles of gas. Since there is two moles of gas as products and 3 moles gas as reactants, the reaction is going to proc...
Mon Mar 09, 2020 8:57 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: What do we do when we are faced with a cubic equation?
Replies: 2
Views: 24

### Re: What do we do when we are faced with a cubic equation?

We won't be given a cubic equation for a chemical equilibrium problem. The 5 percent rule should apply and you can ignore the x values for reactants.
Tue Feb 11, 2020 7:30 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: pKa and pKb
Replies: 4
Views: 68

### Re: pKa and pKb

so mathematically if you say pKa = 1x10^-7, Ka will be 7, and vice versa. To find pKa from Ka you do 10^-(Ka)=10^-7. Say Ka is now 3. Then pKa becomes 1x10^-3. I hope you can see here that a larger Ka leads to a smaller pKa.
Tue Feb 11, 2020 10:23 am
Forum: Ideal Gases
Topic: reversing reactions
Replies: 14
Views: 181

### Re: reversing reactions

for the reverse reaction lets say Kr, Kr=1/K
Tue Feb 11, 2020 10:22 am
Forum: Ideal Gases
Topic: R Constant
Replies: 18
Views: 251

### Re: R Constant

when using pv=nrt r is usually 8.314 J/molK but its gonna be given on the exam
Tue Feb 11, 2020 10:20 am
Forum: Ideal Gases
Topic: PV=nRT
Replies: 12
Views: 161

### Re: PV=nRT

P=Pressure
V=Volume
n= #moles
R= gas constant
T= temp
Mon Feb 10, 2020 8:47 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: pH
Replies: 3
Views: 59

### Re: pH

also remember that p is an operation for the negative log of the concentration of hydrogen atoms. So as the concentration gets larger (more acidic) the negative log of that number is going to get smaller. So a lower pH value is more acidic.
Mon Jan 27, 2020 4:28 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Exothermic reaction
Replies: 18
Views: 249

### Re: Exothermic reaction

Since heat is released in exothermic reactions this means that heat could be considered a product. Increasing the temperature would then be increasing the amount of product, causing a leftward shift to reestablish equilibrium. If temperature is decreased then the forward reaction would occur to rees...