Search found 25 matches
- Sat Mar 18, 2017 10:04 am
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Winter 2014 Final Exam #1
- Replies: 1
- Views: 437
Winter 2014 Final Exam #1
For this problem, the given ΔH° values are 1533 kJ, 3009 kJ, -348 kJ, and 445 kJ. With regards to sigfigs, why is the final answer is 3692 kJ, as opposed to 3690 kJ? Thank you!
- Mon Mar 06, 2017 11:29 pm
- Forum: *Organic Reaction Mechanisms in General
- Topic: Question 4.37
- Replies: 2
- Views: 640
Re: Question 4.37
The standard Gibbs free energy of activation is equal to ΔH°++ - TΔS°++. Because the standard Gibbs free energy of activation is always positive, ΔH°++ must be greater than ΔS°++, thus the standard enthalpy of is usually much larger than the standard entropy of activation. I'm not 100% sure if this ...
- Thu Mar 02, 2017 7:37 pm
- Forum: Student Social/Study Group
- Topic: Post All Chemistry Jokes Here
- Replies: 9651
- Views: 4036495
- Thu Feb 23, 2017 10:34 am
- Forum: Arrhenius Equation, Activation Energies, Catalysts
- Topic: Effects of Temperature on Rate Constant
- Replies: 1
- Views: 517
Re: Effects of Temperature on Rate Constant
I believe that this concept has to do with the Arrhenius equation, which states that ln k = ln A - Ea / RT , or k = Ae^-^E^a^/^R^T . With this equation, increasing the temperature (T) will decrease the quantity Ea / RT , thus increasing the quantity Ae^-^E^a^/^R^T . Because e is an exponential funct...
- Fri Feb 17, 2017 10:21 am
- Forum: Student Social/Study Group
- Topic: Post All Chemistry Jokes Here
- Replies: 9651
- Views: 4036495
Re: Post All Chemistry Jokes Here
You shouldn't drink water when studying because adding water to your system decreases concentration!
- Tue Feb 07, 2017 2:17 pm
- Forum: Student Social/Study Group
- Topic: Post All Chemistry Jokes Here
- Replies: 9651
- Views: 4036495
- Wed Feb 01, 2017 12:16 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: isothermal
- Replies: 1
- Views: 503
Re: isothermal
Yes, isothermal processes always constitute a constant temperature! It follows that ΔU = 0 because for ideal gases, the change in internal energy is dependent upon temperature; if T is not changing, neither will ΔU. And ultimately, q = -w.
- Mon Jan 23, 2017 9:38 pm
- Forum: Calculating Work of Expansion
- Topic: How to Calculate the Change in Internal Energy
- Replies: 1
- Views: 94727
Re: How to Calculate the Change in Internal Energy
It depends on the context of the system, from the perspective of the system! If it helps, you can think of internal energy change as ALWAYS being the ADDITION of q and w, but with varying signs (positive or negative). Positive denotes a gain and negative denotes a loss. In other words: - If the syst...
- Thu Jan 19, 2017 12:24 am
- Forum: Calculating Work of Expansion
- Topic: Work Equation [ENDORSED]
- Replies: 1
- Views: 482
Re: Work Equation [ENDORSED]
Yes! When the volume of the gas increases, the gas itself is the thing that is doing the work (for example, pushing up against a piston). If you think of the system from the perspective of the gas molecules, the gas is doing work, so it uses (and therefore loses) energy, as represented by the negati...
- Wed Jan 18, 2017 11:49 pm
- Forum: Student Social/Study Group
- Topic: Post All Chemistry Jokes Here
- Replies: 9651
- Views: 4036495
- Mon Jan 09, 2017 11:33 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Chapter 8 #3
- Replies: 1
- Views: 578
Re: Chapter 8 #3
Before attempting the problem, it will be helpful to first convert all the given quantities into standard units! As such: • Diameter of pump (d) = 3 cm = 0.03 m. => Radius (r) = 0.015 m. • Distance compressed (x) = 20 cm = 0.2 m. • Pressure applied (P) = 2 atm = 2 x 1.0 x 10^5 Pa = 2.0 x 10^5 Pa. a)...
- Fri Dec 02, 2016 1:29 pm
- Forum: Student Social/Study Group
- Topic: Post All Chemistry Jokes Here
- Replies: 9651
- Views: 4036495
Re: Post All Chemistry Jokes Here
Q: Why does Nicki Minaj like NaOH?
A: It's a super base.
A: It's a super base.
- Fri Nov 25, 2016 10:00 am
- Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
- Topic: Strong Acids
- Replies: 3
- Views: 753
Re: Strong Acids
Thank you both!
- Mon Nov 21, 2016 10:41 pm
- Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
- Topic: Strong Acids
- Replies: 3
- Views: 753
Strong Acids
Out of curiosity, why are strong acids considered strong acids if they lose hydrogen ions so easily?
- Wed Nov 16, 2016 9:55 am
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Significant Figures [ENDORSED]
- Replies: 3
- Views: 909
Re: Significant Figures [ENDORSED]
Thank you to you both! (:
- Mon Nov 14, 2016 4:36 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Significant Figures [ENDORSED]
- Replies: 3
- Views: 909
Significant Figures [ENDORSED]
Will we have to consider sigfigs when performing calculations regarding equilibrium?
- Wed Nov 09, 2016 10:00 pm
- Forum: Ideal Gases
- Topic: PV=nRT
- Replies: 3
- Views: 942
Re: PV=nRT
I believe that with regards to the ideal gas law, when the gas constant (R) is involved, we would use atmospheres, but in terms of other equations, we calculate using pascals.
- Wed Nov 02, 2016 4:25 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Polar vs Nonpolar
- Replies: 2
- Views: 745
Re: Polar vs Nonpolar
Another approach would be to draw out the dipole moments (pointing toward the more electronegative atom in each case) and treat them like vectors. If all of the dipole moments have a corresponding equal and opposite one, then the molecule is nonpolar; if they do not, then the molecule is polar. It i...
- Fri Oct 28, 2016 11:17 pm
- Forum: Ionic & Covalent Bonds
- Topic: H2S and HCl
- Replies: 1
- Views: 3211
Re: H2S and HCl
HCl has more ionic bonds than H2S because there is a greater difference of electronegativity between the hydrogen and chlorine atoms than between the hydrogen and sulfur atoms. Additionally, because of this, the HCl molecule is also more polar than the H2S molecule.
- Sat Oct 22, 2016 1:28 am
- Forum: Student Social/Study Group
- Topic: Post All Chemistry Jokes Here
- Replies: 9651
- Views: 4036495
Re: Post All Chemistry Jokes Here
Q: What's the significance of "NaCl/NaOH" in the context of video games?
A: Your base is under a salt (assault)!
A: Your base is under a salt (assault)!
- Wed Oct 12, 2016 9:36 pm
- Forum: Limiting Reactant Calculations
- Topic: Fall 2015 Quiz #2 [ENDORSED]
- Replies: 3
- Views: 828
Re: Fall 2015 Quiz #2 [ENDORSED]
Thank you so much!
- Tue Oct 11, 2016 10:56 am
- Forum: Limiting Reactant Calculations
- Topic: Fall 2015 Quiz #2 [ENDORSED]
- Replies: 3
- Views: 828
Fall 2015 Quiz #2 [ENDORSED]
May someone explain the second part of #2 on the Fall 2015 practice quiz? I balanced the equation, converted the given quantities of Al and HCl to moles, and did some dimensional analysis, but I can't seem to get the correct answer. Thank you! * Update: Aluminum and hydrogen chloride, HCl, react to ...
- Fri Oct 07, 2016 11:41 pm
- Forum: DeBroglie Equation
- Topic: Diffraction Patterns and Interacting Waves
- Replies: 1
- Views: 509
Re: Diffraction Patterns and Interacting Waves
Diffraction patterns occur when a wave of light passes through multiple mediums / substances. Constructive interference occurs when the phase difference between two waves is a multiple of 2π (the peaks and troughs align), and destructive interference occurs when the phase difference between two wave...
- Fri Oct 07, 2016 11:32 pm
- Forum: Properties of Light
- Topic: Formulas need to know? [ENDORSED]
- Replies: 3
- Views: 927
Re: Formulas need to know? [ENDORSED]
My TA told me that we would be given just about all the necessary constants / formulas, and that we just need to make sure we know exactly when / how to use each one!
- Wed Sep 28, 2016 6:09 pm
- Forum: SI Units, Unit Conversions
- Topic: When do we know whether to use gram vs. kilogram, etc.? [ENDORSED]
- Replies: 4
- Views: 4024
Re: When do we know whether to use gram vs. kilogram, etc.? [ENDORSED]
I believe we use grams when the problem involves chemistry concepts (e.g. converting substances to moles) for the majority and kilograms when the problem involves physics concepts (e.g. kinetic energy in the photoelectric effect) for the majority.