Search found 16462 matches

by Chem_Mod
Thu Feb 07, 2019 3:30 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Enthalpy of phase change
Replies: 4
Views: 22

Re: Enthalpy of phase change

Because it has two components, one the energy required to break the bonds and the other is the energy required to vaporize the Br
by Chem_Mod
Thu Feb 07, 2019 3:28 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Cv vs. Cp
Replies: 1
Views: 11

Re: Cv vs. Cp

For solids and liquids, there is not much difference in Cp and Cv, so we just use C to represent the specific heat capacity. For water vapor, the value given is Cp.
by Chem_Mod
Thu Feb 07, 2019 3:21 pm
Forum: Calculating Work of Expansion
Topic: Constant Pressure and Temperature
Replies: 1
Views: 18

Re: Constant Pressure and Temperature

The equation to calculate work will be different.
For constant pressure W=-p(V2-V1)
For constant temperature W= -nRTln(V2/V1)
by Chem_Mod
Thu Feb 07, 2019 3:20 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: standard temperature
Replies: 1
Views: 9

Re: standard temperature

If it is not given, usually it is valid to assume the reaction happens at 298K
by Chem_Mod
Thu Feb 07, 2019 3:16 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: problem 4D.3
Replies: 1
Views: 15

Re: problem 4D.3

1.4 g of CO is much less than 1mol and you have to calculate the reaction enthalpy if 1mol of CO is reacted.
by Chem_Mod
Thu Feb 07, 2019 3:14 pm
Forum: Bronsted Acids & Bases
Topic: Weak Acids
Replies: 1
Views: 12

Re: Weak Acids

I do not quite get what you are asking, can you give an example?
by Chem_Mod
Thu Feb 07, 2019 3:12 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Taking into account 10^-7 [H3O+]
Replies: 1
Views: 9

Re: Taking into account 10^-7 [H3O+]

If the H3O+ concentration you calculated is smaller or close to 10^-7, you have to take the 10^-7 into consideration as it is no longer negligible
by Chem_Mod
Thu Feb 07, 2019 3:09 pm
Forum: Environment, Fossil Fuels, Alternative Fuels
Topic: midterm
Replies: 3
Views: 41

Re: midterm

The combustion related materials are fair to show up but those that are not related to chemistry won't be on the test.
by Chem_Mod
Thu Feb 07, 2019 3:08 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Bomb calorimeters vs polystyrene cup calorimeters
Replies: 2
Views: 9

Re: Bomb calorimeters vs polystyrene cup calorimeters

Bomb calorimeters are considered as isolated system, where there is no heat transfer. Common calorimeters are closed systems
by Chem_Mod
Thu Feb 07, 2019 3:04 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Question 8.41
Replies: 1
Views: 8

Re: Question 8.41

The heat required to melt ice and increase the temperature of the melted ice is equal to the heat lost from the hot water. This is a equation that you can set up to solve for the final temperature.
by Chem_Mod
Thu Feb 07, 2019 3:01 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: 4C.3
Replies: 1
Views: 20

Re: 4C.3

Change in enthalpy is the same as heat transfer at constant pressure, so you can use nCp(T2-T1)
by Chem_Mod
Thu Feb 07, 2019 2:53 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: Entropy
Replies: 1
Views: 18

Re: Entropy

When temperature is close to 0K, you can ignore the thermal vibration and the entropy is mainly from the positional entropy.
by Chem_Mod
Thu Feb 07, 2019 1:09 pm
Forum: Calculating Work of Expansion
Topic: Self-Test 8.6B
Replies: 1
Views: 34

Re: Self-Test 8.6B

Your answer is the work and for the change in internal energy, you need to add the heat transferred into the system
by Chem_Mod
Thu Feb 07, 2019 1:07 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: 9.9 6th edition
Replies: 1
Views: 17

Re: 9.9 6th edition

Please specify your concerns, simply just pasting the question will not count for credit.
by Chem_Mod
Thu Feb 07, 2019 1:06 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: 6th edition 9.1
Replies: 1
Views: 22

Re: 6th edition 9.1

Please specify your concerns, simply just pasting the question will not count for credit.
by Chem_Mod
Thu Feb 07, 2019 1:04 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: question on 9.11
Replies: 1
Views: 16

Re: question on 9.11

P1 is 15 and P2 is 0.5, make sure you did not switch these values.
by Chem_Mod
Thu Feb 07, 2019 12:58 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Entropy units
Replies: 3
Views: 10

Re: Entropy units

entropy unit is J/K, and there is usually no unit for degeneracy
by Chem_Mod
Thu Feb 07, 2019 12:57 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Question 8.31
Replies: 1
Views: 6

Re: Question 8.31

Kr is a monatomic gas and assuming ideal gas behavior, Cv is 3R/2 and Cp is 5R/2
by Chem_Mod
Thu Feb 07, 2019 12:55 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Number 31 Ch.8
Replies: 1
Views: 11

Re: Number 31 Ch.8

Q=n Cv (T2-T1) and n Cp (T2-T1), for constant volume and constant pressure processes respectively, the Cv and Cp are 3/2 R and 5/2R assuming ideal gas behavior
by Chem_Mod
Thu Feb 07, 2019 12:51 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 6th edition, 8.53
Replies: 2
Views: 14

Re: 6th edition, 8.53

The 1.4 g of CO is less than 1 mol, so you want to find the reaction enthalpy of using 1.4 g of CO and then figure out what the enthalpy is if 1 mol of CO is reacted.
by Chem_Mod
Thu Feb 07, 2019 12:47 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Question 7 Chapter 8 6th edition
Replies: 1
Views: 12

Re: Question 7 Chapter 8 6th edition

This is a first law related question, the change in internal energy is the sum of heat transfer and work. In this case, you can calculate the work by subtracting heat from the change in internal energy.
by Chem_Mod
Thu Feb 07, 2019 12:43 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: ΔH
Replies: 2
Views: 31

Re: ΔH

There are different ways to calculate the enthalpy change. For example, you can use bond energy and standard enthalpy of formation. They do not require the equation that you showed.
by Chem_Mod
Thu Feb 07, 2019 1:37 am
Forum: Administrative Questions and Class Announcements
Topic: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)
Replies: 110
Views: 2522

Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

For question 6 on worksheet 4, how exactly are we supposed to determine which volume we use to find the pressure for the work component of the internal energy change? To my understanding, the pressure was calculated using PV = nRT, with V = 998L, n = 31.9 mol, R = 0.08206 L * atm / mol * K, T = 311...
by Chem_Mod
Wed Feb 06, 2019 3:44 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Review session (equilibrium) worksheet
Replies: 1
Views: 134

Review session (equilibrium) worksheet

Hi all,

Attached please find the equilibrium review session worksheet. Will post the answer later :)

Good luck!

-Joyce
by Chem_Mod
Tue Feb 05, 2019 8:24 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Midterm [ENDORSED]
Replies: 47
Views: 438

Re: Midterm [ENDORSED]

Homework problems are the BEST preparation.
Also one of the eight questions will come directly from the homework.

This review session is confirmed:

Wed Feb 6, 2-2:50pm, Dodd 147, Joyce, Equilibrium

The rest I will announce Wednesday in class.
by Chem_Mod
Tue Feb 05, 2019 8:20 pm
Forum: Student Social/Study Group
Topic: review sessions
Replies: 2
Views: 29

Re: review sessions

This one is confirmed:

Wed Feb 6, 2-2:50pm, Dodd 147, Joyce, Equilibrium

The rest I will announce Wednesday in class.
by Chem_Mod
Mon Feb 04, 2019 4:09 pm
Forum: Calculating Work of Expansion
Topic: Isothermal expansions
Replies: 1
Views: 34

Re: Isothermal expansions

Reversible expansions work against incrementally smaller external pressures rather than a constant smaller pressure, and thus do more work over a longer period of time.
by Chem_Mod
Mon Feb 04, 2019 4:05 pm
Forum: Administrative Questions and Class Announcements
Topic: Chem 14 BL
Replies: 5
Views: 59

Re: Chem 14 BL

Chem 14BL does not need to be taken before or with 14C. 14BL has to do with topics learned in 14B while 14C deals with organic chemistry.
by Chem_Mod
Mon Feb 04, 2019 4:03 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Change of Temp. converting from C to K in Entropy Change Problem
Replies: 2
Views: 16

Re: 4F.7 (7th Ed) Change in Temperature

Please delineate the problem itself so Chem Community users don't have to reference the book.
by Chem_Mod
Sun Feb 03, 2019 5:46 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Molar Heat Capacities of Ideal Gases
Replies: 1
Views: 38

Re: Molar Heat Capacities of Ideal Gases

C{v} = \frac{3}{2}R C{p} = \frac{5}{2}R These are the constants for molar heat capacities that we use when we are working with ideal gases. In that problem, it stated to assume that krypton behaves as an ideal gas, and so it is safe to assume that we can use Cv and Cp. R is the gas constant 8.314 J...
by Chem_Mod
Sat Feb 02, 2019 11:01 pm
Forum: Phase Changes & Related Calculations
Topic: Week 4 Discussion Notes & Worksheet (2E, 2I, 2K)
Replies: 3
Views: 141

Week 4 Discussion Notes & Worksheet (2E, 2I, 2K)

Hi all,

Attached please find the notes and worksheet answer.

Have a great weekend!

- Joyce
by Chem_Mod
Sat Feb 02, 2019 6:43 pm
Forum: Administrative Questions and Class Announcements
Topic: Midterm Review
Replies: 14
Views: 89

Re: Midterm Review

I am organizing Many review sessions.

Takes time as it is hard to find and reserve large lecture halls, organize schedules, etc.

I will announce them soon (most likely Tuesday/Wednesday).
by Chem_Mod
Fri Feb 01, 2019 9:06 pm
Forum: Administrative Questions and Class Announcements
Topic: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)
Replies: 110
Views: 2522

Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

This week we will be going over the 1st law of thermodynamics. I will also cover 2 more equations that you will learn next week, so don't be alarmed if there are a problem or two you are struggling with in this worksheet. This is so that next week we will have more time doing review problems for the...
by Chem_Mod
Thu Jan 31, 2019 8:45 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Determining Internal Energy
Replies: 3
Views: 29

Re: Determining Internal Energy

Negative indicates the heat is released
by Chem_Mod
Thu Jan 31, 2019 8:43 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Finding Heat
Replies: 4
Views: 22

Re: Finding Heat

delta T for change in celsius and change in kelvin are the same because you are looking at the difference in temperature. Generally stick to the same units as your constant so that the units cancel.
by Chem_Mod
Thu Jan 31, 2019 8:42 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 4E.5 part a
Replies: 1
Views: 14

Re: 4E.5 part a

Yes, you are correct in that the bond energy of the resonance structure was used. Benzene has resonance, so the true bond length is somewhere between single and double bond length. It is more accurate to use the resonance bond enthalpy.
by Chem_Mod
Thu Jan 31, 2019 8:39 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 4C.3 Cp to (5/2 * R)
Replies: 1
Views: 11

Re: 4C.3 Cp to (5/2 * R)

5/2R is used for constant pressure while 3/2R is used for constant volume.
by Chem_Mod
Thu Jan 31, 2019 8:36 pm
Forum: Phase Changes & Related Calculations
Topic: 4C.13 7th Edition
Replies: 1
Views: 17

Re: 4C.13 7th Edition

We set them equal to each other because the change in heat of the ice cube is equal to the change in heat of the water. This is heat transfer where we assuming all heat is being transferred within our system. They are opposite in sign because whatever heat the cube gains is equal to the heat the wat...
by Chem_Mod
Thu Jan 31, 2019 8:31 pm
Forum: Ideal Gases
Topic: pV=nRT
Replies: 7
Views: 41

Re: pV=nRT

pV = nRT is the ideal gas law. This is incredibly useful in calculating an unknown (for example, if you are given pressure, volume, and temperature, you can use this law to find the number of moles). In practice problems, this is often the first step before doing other calculations (such as solving ...
by Chem_Mod
Thu Jan 31, 2019 8:29 pm
Forum: Calculating Work of Expansion
Topic: Problem 8.27
Replies: 2
Views: 22

Re: Problem 8.27

The problem does not explicitly give you the moles, which is why you can use PV=nRT to find the number of moles. From that, you can calculate work for isothermal, reversible expansion. You can use w= - (external pressure) delta V for irreversible work of expansion. You don't need number of moles for...
by Chem_Mod
Thu Jan 31, 2019 8:26 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: 7th edition, 4.15
Replies: 1
Views: 14

Re: 7th edition, 4.15

First step is to determine the enthalpy of the reaction. Writing our the reaction 2HCl + Zn --> ZnCl2 + H2, we could find the enthalpy using heat of formations in the appendix. Remember to convert HCl and Zinc into moles to find the limiting reactant, and from that, calculate the enthalpy of the rea...
by Chem_Mod
Thu Jan 31, 2019 4:18 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Reversible Processes
Replies: 2
Views: 28

Re: Reversible Processes

In a reversible process (using gas expansion as an example), the internal pressure and external pressure are equal, and the gas expands because the external pressure very slowly decreases (so that internal and external pressure are equal). The gas is doing work against the "maximum" extern...
by Chem_Mod
Thu Jan 31, 2019 4:08 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Different Kinds of Symptoms
Replies: 6
Views: 29

Re: Different Kinds of Symptoms

Open system is when both energy and matter can be exchanged between system and surroundings. Ex: heating up something on the stove in a pot (without lid) --> heat can be transferred from the stove to the food. It's an open system, so matter can also be exchanged (perhaps steam from the liquid). Clos...
by Chem_Mod
Thu Jan 31, 2019 4:03 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Work Done By vs. On
Replies: 4
Views: 32

Re: Work Done By vs. On

When a system does work, it is exerting its own energy to do work against the surroundings. For example, when gas is expanding, the gas must be doing work on the surroundings (and therefore internal energy is decreasing). When work is being done on the system, the surroundings is exerting its energy...
by Chem_Mod
Thu Jan 31, 2019 3:53 pm
Forum: Administrative Questions and Class Announcements
Topic: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)
Replies: 110
Views: 2522

Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

Sorry for the delay in last week's worksheet key! Got caught up in some of my own midterms.

Happy midterms season!
by Chem_Mod
Thu Jan 31, 2019 3:51 pm
Forum: Administrative Questions and Class Announcements
Topic: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)
Replies: 110
Views: 2522

Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

Kenan Kherallah 2C wrote:For question 5, do we have to have whole numbers in the balanced equation to use bond enthalpies or can we keep fractions in there (for this and other questions like this).


You can use fraction, since bond enthalpy is a number per mol.
by Chem_Mod
Thu Jan 31, 2019 1:55 pm
Forum: Phase Changes & Related Calculations
Topic: finding heat
Replies: 3
Views: 24

Re: finding heat

latent heat is used during a phase change process (temperature does not change when heat is applied) while specific heat is used when heat is used for non-phase change process.
by Chem_Mod
Thu Jan 31, 2019 1:53 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: 8.1 part c
Replies: 1
Views: 15

Re: 8.1 part c

A bomb calorimeter is considered an isolated system because it prevents any heat from the reaction inside from escaping to the surroundings, and is closed so that no matter from the surroundings can enter or leave the system.
by Chem_Mod
Thu Jan 31, 2019 1:34 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: What do do when moles are given
Replies: 5
Views: 32

Re: What do do when moles are given

The moles are used to find concentration, the exponent depends on the stoichiometric coefficient.
by Chem_Mod
Thu Jan 31, 2019 11:45 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 6th edition 8.73
Replies: 1
Views: 31

Re: 6th edition 8.73

What is your question about this question?
by Chem_Mod
Thu Jan 31, 2019 11:44 am
Forum: Calculating Work of Expansion
Topic: calculation of work of irreversible and reversible expansion
Replies: 5
Views: 38

Re: calculation of work of irreversible and reversible expansion

Use the pressure that is being pushed against. If the system is expanding (say 2 atm initial pressure for the system) and pushing against a constant external pressure of 1 atm then use 1 atm. If the expansion or compression is reversible (equilibrium pathway) then use either external or internal pre...
by Chem_Mod
Thu Jan 31, 2019 11:37 am
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Applied Exercises 8.113
Replies: 1
Views: 24

Re: Applied Exercises 8.113

What is your question about this question?
by Chem_Mod
Thu Jan 31, 2019 11:36 am
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Applied Exercises 8.115
Replies: 1
Views: 30

Re: Applied Exercises 8.115

What is your question about this question?
by Chem_Mod
Thu Jan 31, 2019 11:04 am
Forum: Phase Changes & Related Calculations
Topic: What Does U and q stand for?
Replies: 9
Views: 61

Re: What Does U and q stand for?

U is the internal energy and q is the heat transfer
by Chem_Mod
Thu Jan 31, 2019 10:58 am
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Problem 4A.9) 7th edition of the textbook [ENDORSED]
Replies: 3
Views: 203

Re: Problem 4A.9) 7th edition of the textbook [ENDORSED]

This is because of significant figures. It will work when plugging in 25 °C. The -∆T for copper is 75 °C and the ∆T for water is 3 °C (notice this now has one sig fig). When you multiply by the masses and the heat capacities, you get 570 J for copper and 636.3864 J for water, which are both 600 J to...
by Chem_Mod
Tue Jan 29, 2019 8:14 pm
Forum: Phase Changes & Related Calculations
Topic: Phase changes
Replies: 14
Views: 65

Re: Phase changes

s --> l --> g Endothermic, meaning DeltaH is positive Increase in entropy, meaning DeltaS is positive DeltaG = DeltaH - T*DeltaS At low temperatures, DeltaG is positive and this is unfavorable At high temperatures, DeltaG is negative and this is favorable s <-- l <-- g (backwards) Exothermic, meanin...
by Chem_Mod
Tue Jan 29, 2019 10:08 am
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Calorimeter vacuums
Replies: 1
Views: 13

Re: Calorimeter vacuums

No, calorimeters are not vacuum. It may make more sense if you see it being setup on a YouTube video.
https://www.youtube.com/watch?v=rYwgsF_haAg
by Chem_Mod
Mon Jan 28, 2019 5:42 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: eq constant
Replies: 1
Views: 41

Re: eq constant

What do you mean by Gibbs minimization method?
by Chem_Mod
Mon Jan 28, 2019 5:38 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Constant Pressure of Krypton (4c.3 7th Edition)
Replies: 1
Views: 12

Re: Constant Pressure of Krypton (4c.3 7th Edition)

Krypton is a monatomic gas, so assuming it is an ideal gas, its heat capacity at constant volume will be 3 x \frac{1}{2} R. C P = C V + R for an ideal gas, so C P = \frac{3}{2} R + R = \frac{5}{2} R R = 8.3145 \frac{J}{mol K} This is because each translational degree of freedom contributes \frac{1}{...
by Chem_Mod
Mon Jan 28, 2019 4:14 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Surface area and heat capacity [ENDORSED]
Replies: 2
Views: 32

Re: Surface area and heat capacity [ENDORSED]

For heat capacities, we are not really talking about surface area. If you have one bread, it will take a shorter amount of energy to heat up than 2 breads. Thus, having more of one object will require more energy to heat up.
by Chem_Mod
Mon Jan 28, 2019 4:06 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Cv and Cp
Replies: 3
Views: 25

Re: Cv and Cp

Unlike for constant volume, at constant pressure work isn't zero and that contributes an entire R unit more (Cp = Cv + R) using a derivation that we didn't explore in this class.
by Chem_Mod
Mon Jan 28, 2019 2:02 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Question 4C.15 (7th Edition)
Replies: 1
Views: 16

Re: Question 4C.15 (7th Edition)

If the graph is q vs. T, then the slope is the heat capacity and the length of flat lines is the heat of change for that phase change (vaporization for liquid to gas).
by Chem_Mod
Mon Jan 28, 2019 1:58 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: Question 4D 15 7th edition
Replies: 1
Views: 27

Re: Question 4D 15 7th edition

Will you provide the full question?
by Chem_Mod
Mon Jan 28, 2019 1:51 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Q v. Delta H
Replies: 1
Views: 17

Re: Q v. Delta H

Enthalpy is a measure of the energy of the system. The energy of the system can change when the system does work or gives off heat (or the opposites). So heat is a transfer of energy but not the only way energy can transfer. The amount of money in a bank account is a state function. The cash deposit...
by Chem_Mod
Fri Jan 25, 2019 11:06 pm
Forum: Administrative Questions and Class Announcements
Topic: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)
Replies: 110
Views: 2522

Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

Worksheet for Week 3 (1/27) session. There was not much material learned this week due to the holiday, so the session should be quick. If you can't make it, get notes/ full solutions from a classmate or friend that can attend. Full solutions are not posted because my work is messy and may cause unne...
by Chem_Mod
Fri Jan 25, 2019 5:11 pm
Forum: Phase Changes & Related Calculations
Topic: Due date for Discussion Questions
Replies: 8
Views: 69

Re: Due date for Discussion Questions

They are due every week when you go to discussion section.
The day/time of your weekly discussion section is when you hand in weekly homework.
by Chem_Mod
Thu Jan 24, 2019 10:44 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 5G1part d
Replies: 1
Views: 17

Re: 5G1part d

When you start with more stuff, you get more. The K will, however, be the same at equilibrium. No direction is favored at equilibrium.
by Chem_Mod
Thu Jan 24, 2019 10:39 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: problem 5H1 7th edition part c
Replies: 1
Views: 11

Re: problem 5H1 7th edition part c

The trick is to write the expression of K in both cases and you will see why you need to square
by Chem_Mod
Thu Jan 24, 2019 10:26 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: HW 12.69 Q about spectator ions
Replies: 1
Views: 23

Re: HW 12.69 Q about spectator ions

For AlCl3 the Cl- will completely dissociate, the Al3+, however, will make the solution acidic because it likes to attract OH- from the water and therefore produce H3O+
by Chem_Mod
Thu Jan 24, 2019 10:20 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: ICE problems
Replies: 5
Views: 36

Re: ICE problems

If the reaction is going forward, the reactants decrease (negative), and the products increase (positive).
by Chem_Mod
Thu Jan 24, 2019 10:18 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 5%
Replies: 10
Views: 48

Re: 5%

When you assume the change is small, you have to make sure that the answer you get is within 5% of the initial, so that the assumption is valid. Otherwise, you have to solve the quadratic equation.
by Chem_Mod
Thu Jan 24, 2019 10:16 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: question 5i.19
Replies: 3
Views: 15

Re: question 5i.19

Set up an ice table and the change is given (60% is reacted) you can find the equilibrium concentration for all the gas and calculate K
by Chem_Mod
Thu Jan 24, 2019 10:14 pm
Forum: Phase Changes & Related Calculations
Topic: Steam and Boiling water
Replies: 2
Views: 19

Re: Steam and Boiling water

When water goes from gas to liquid it is undergoing what is called a phase change. Phase changes require a lot more energy than just a temperature change. The energy required for water to go from a liquid to a gas is called the heat of vaporization. When steam (water in the gas phase) hits your skin...
by Chem_Mod
Thu Jan 24, 2019 10:05 pm
Forum: Phase Changes & Related Calculations
Topic: Heat and path taken
Replies: 1
Views: 19

Re: Heat and path taken

Heat is the energy transferred between the system and the surroundings during some process. The amount that transfers does depend on how the process happens and is therefore not a state function.
by Chem_Mod
Thu Jan 24, 2019 10:04 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Pressure and gas equilibria
Replies: 2
Views: 17

Re: Pressure and gas equilibria

Depends on how you change the pressure, pumping inert gas will not affect gas equilibria, but change the volume will (basically it is changing the concentration).
by Chem_Mod
Thu Jan 24, 2019 10:01 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: 6th Edition Problem 69 part B
Replies: 1
Views: 28

Re: 6th Edition Problem 69 part B

The extra 3 are used to get H3O+ from H+
by Chem_Mod
Thu Jan 24, 2019 9:59 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Acids and Bases (weak or strong)
Replies: 3
Views: 22

Re: Acids and Bases (weak or strong)

It is more convenient to remember all the strong ones and the rest will be weak. See the following for strong acids and strong bases.
HI HBr HClO4 HCl HClO3 H2SO4 HNO3
NaOH KOH LiOH RbOH CsOH Ca(OH)2 Ba(OH)2 Sr(OH)2
by Chem_Mod
Thu Jan 24, 2019 9:53 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Forming hydronium or hydroxide
Replies: 1
Views: 13

Re: Forming hydronium or hydroxide

Depends if it is an acid or a base, an acid will generate hydronium and a base will generate hydroxide
by Chem_Mod
Thu Jan 24, 2019 9:41 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Change in Pressure caused by Volume
Replies: 3
Views: 40

Re: Change in Pressure caused by Volume

Yes. The concentration of products will increase. If you calculate the Q, you would see Q < K at that moment.
by Chem_Mod
Thu Jan 24, 2019 2:22 pm
Forum: Phase Changes & Related Calculations
Topic: Reversible and Irreversible Processes
Replies: 1
Views: 23

Re: Reversible and Irreversible Processes

The process in which the system and surroundings can be restored to the initial state from the final state without producing any changes in the thermodynamics properties of the universe is called a reversible process. In the irreversible process the initial state of the system and surroundings canno...
by Chem_Mod
Thu Jan 24, 2019 2:19 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: q vs. qp
Replies: 2
Views: 22

Re: q vs. qp

q is the heat transfer, but sometimes a subscript p indicates that the process happens at constant pressure.
by Chem_Mod
Thu Jan 24, 2019 2:17 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Heat and Work Not State Properties
Replies: 1
Views: 12

Re: Heat and Work Not State Properties

Work is not a state function because it depends on the path. For same start and end point, different paths will lead to different work. Heat is not a state function, it is not an intrinsic property of a system. Heat is the energy transferred between the system and the surroundings during some proces...
by Chem_Mod
Thu Jan 24, 2019 2:13 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: 6B.3
Replies: 1
Views: 16

Re: 6B.3

HCl is a strong acid so the key is the find the concentration of H3O+. You can find the moles first and divide by the real volume of the container.
by Chem_Mod
Wed Jan 23, 2019 1:45 am
Forum: Administrative Questions and Class Announcements
Topic: Week 3 Sun/Mon/Tues UA Sessions
Replies: 1
Views: 324

Re: Week 3 Sun/Mon/Tues UA Sessions

Hope these were helpful.

See you in class. We start Thermochemistry!
by Chem_Mod
Tue Jan 22, 2019 10:08 am
Forum: Administrative Questions and Class Announcements
Topic: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)
Replies: 110
Views: 2522

Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

For number 7 on worksheet 1, why does high temperature favor the formation of bromine atoms if we don't know if the reaction is endothermic or exothermic? Breaking a Br2 atom into 2 atoms is energetically not favorable, so heat is required to be inputted. On Worksheet 2, why is the concentration of...
by Chem_Mod
Mon Jan 21, 2019 6:48 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Salt on Test 1
Replies: 5
Views: 62

Re: Salt on Test 1

Salts have a cation and an anion.
E.g., NaCl
by Chem_Mod
Mon Jan 21, 2019 4:22 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: homework
Replies: 1
Views: 33

Re: homework

To solve you will want to set up and balance the reaction Na 2 O + H 2 O \rightarrow 2NaOH. Then this solution of NaOH is diluted by taking 5 mL or 0.005 L of the solution and diluting it to a final volume of 0.5 L. Using the given pH of this final solution to be 13.25 we can calculate the pOH by ta...
by Chem_Mod
Mon Jan 21, 2019 2:12 pm
Forum: Polyprotic Acids & Bases
Topic: Question 6E.3 7th edition
Replies: 2
Views: 26

Re: Question 6E.3 7th edition

The book states that the second deprotonation will always occur, but so long as the provided Ka2 is less than about Ka1/1000 then the second deprotonation will be so small that it will not affect the pH significantly and can thus be ignored.
by Chem_Mod
Mon Jan 21, 2019 2:07 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: homework
Replies: 2
Views: 20

Re: homework

You should be getting a negative number for pH, this is an extremely strong acid since the concentration of H 3 O + is on an order of magnitude that is greater than 10 -1 . This is when an acid will not follow the normal pH scale, where the pH is between 0 and 14, instead when you have whats called ...
by Chem_Mod
Mon Jan 21, 2019 1:59 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: 7th Edition 6B #9
Replies: 1
Views: 24

Re: 7th Edition 6B #9

The answer in the book is actually incorrect. You're answer is correct and the book is almost correct but they made a small mistake. If instead of using [H 3 O + ]* [OH - ] =1 x 10 -14 to find [OH - ], you first convert [H 3 O + ] into pH you would get the pH = -log[1.5]= -0.176. The book says pH=0....
by Chem_Mod
Sun Jan 20, 2019 10:46 pm
Forum: Administrative Questions and Class Announcements
Topic: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)
Replies: 110
Views: 2522

Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

Julia Lee wrote:Can someone please explain to me how number 4 part d and number 5 are solved for the the Chemical Equilibrium worksheet?


Hi Julia, can you please detail at which step you are stuck on? Or what concepts you think should be used?
by Chem_Mod
Sun Jan 20, 2019 10:43 pm
Forum: Administrative Questions and Class Announcements
Topic: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)
Replies: 110
Views: 2522

Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

Key for Week 2. Good luck on quizzes!

Corrections:

4a is 4.40, not 4.30
by Chem_Mod
Sat Jan 19, 2019 11:00 pm
Forum: Ideal Gases
Topic: ice
Replies: 4
Views: 49

Re: ice

For weak acids and bases the ICE tables are exactly the same as "regular" equilibrium problems. However, for strong acids and bases there are no ICE tables as the species dissociates 100%.
by Chem_Mod
Sat Jan 19, 2019 1:42 pm
Forum: Administrative Questions and Class Announcements
Topic: Week 3 Sun/Mon/Tues UA Sessions
Replies: 1
Views: 324

Week 3 Sun/Mon/Tues UA Sessions

Regarding UA schedule for week 3 due to Monday holiday. On Monday Week 3 (holiday), you may attend Ashley Van Belle, Step-up, 7-9pm in Covel 210 (switched with Lyndon for week 3 only) On Tuesday Week 3, you may attend Lyndon Bui, Workshop, 6-8pm in Covel 210 Students living off-campus can attend ses...
by Chem_Mod
Sat Jan 19, 2019 12:01 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Week 2 Discussion Notes (2E,2I,2K)
Replies: 1
Views: 163

Week 2 Discussion Notes (2E,2I,2K)

Hi all,

Attached please find this week discussion notes.

Have a great long weekend!

Best,
Joyce
by Chem_Mod
Fri Jan 18, 2019 9:29 pm
Forum: Administrative Questions and Class Announcements
Topic: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)
Replies: 110
Views: 2522

Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

Here is the worksheet for this Sunday's session covering acid and base calculations:

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