Chemistry (Science & Mathematics) - February 2007

This question pertains to heat capacity, phase change, and/or colligative properties. Please point out the differences and similarities (if any). Thank you.

2007-02-27 04:28:21 · 4 answers · asked by Philippe 3

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What makes popcorn pop?

2007-02-27 03:59:58 · 8 answers · asked by Anonymous

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standard enthalpy of formation for CO?

Why does the standard enthalpy of formation for CO cannot be obtained directly by measuring the enthaply of this reaction
C+1/2O2 -> CO?

And instead have to be calculated from Hess law:
2CO2 -> 2CO + 02 Enthalpy =566.0 kJ
C(graphite) + O2 -> CO2 Enthalpy = -393.5 kJ
2CO -> C(graphite) + CO2 Enthalpy = -172.5 kJ

By Hess Law, enthalpy of formation of CO = 1/2(2(-172.5) + 566.0) = -110.5 kJ

2007-02-27 03:43:55 · 3 answers · asked by sky_blue 1

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Calculating pH of a 0.1 M ammonia solution?

Calculate teh pH of a 0.1 M ammonia solution. The pKb of ammonia 4.73.

This is how I solved it, and it's close to the value using the pH meter. But I'm not sure if I solved it right or just coincidentally got the right answer...

Kb = 10^(-4.73) = 1.86 x 10^-5

Kb = ( [OH-][NH4]/[OH- NH4] ) = x^2/ .10-x = x^2/.10

x^2/.10 = 1.86 x 10^-5

x=00136M

pH = -log[.00136] = 11.1

And the value we got when we measured using the pH meter was 11.3.....

So was the way I calculated the problem correct?

2007-02-27 03:43:04 · 2 answers · asked by Anonymous

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titration - 10 points for the first correct answer and procedure!?

Estimate the mass of KHP (formula: KHC8H4O4) that will require 25mL of 0.10M NaOH to reach the equivalence point in a titration. Give the chemical equiation for the reaction.

2007-02-27 03:37:36 · 3 answers · asked by Anonymous

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Periodic Table of Elements?

Any clues on an easy way to memorize the periodic table of elements?

2007-02-27 03:16:49 · 11 answers · asked by Sam4Pres 2

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What effect does the presence of salt have on the boiling point of water and why?

2007-02-27 03:00:50 · 7 answers · asked by Rabbit38 1

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Which electron transitions will produce a photon of shortest wavelength in the Bohr Hydrogen atom?

a) n = 3 to n = 4
b) n = 4 to n = 1
c) n = 3 to n = 1
d) n = 2 to n = 1

2007-02-27 02:57:02 · 2 answers · asked by Anonymous

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any easy way to learn reactions...?

2007-02-27 02:46:29 · 4 answers · asked by flora 1

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How long does it take for the concentration to drop?

Cyclopropane isomerizes to propene when heated. Rate constants for the reaction,

cyclopropane ---> propene

are 1.10e-4 at 743 K and 1.02e-3 at 783 K

(a) What is the activation energy?

(b) At 773 K and [cyclopropane] = 0.10 M, how long does it take for the concetration to drop to 0.023 M?

Note: i got the first step (a), bu i am still confused with the second step.How can i figure it out.PLS explain step by step.....thanx

2007-02-27 02:27:15 · 1 answers · asked by Tommy 2

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can somebody help me with my project. i need a study for our research.. pls.. i need it so badly.?

i thought of using banana peelings for floorwax but i had a hard time on how to test it.. im looking for a better study, i cant graduate if i wil not be able to pass a study.. pld... help me!

2007-02-27 02:16:49 · 6 answers · asked by ais 1

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Which of the following results would you expect to occur based on the section of the electrochemical series?

Cl2 + 2e --> 2Cl- E= 1.36V
Fe3+ + e ---> Fe3+ E= 0.77V
Fe2+ + 2e --> Fe E= -0.41V

a. Fe3+ ions and Cl- ions will not react

b. Fe and Cl- will react to form Fe2+ and Cl2

c. Fe3+ and Cl2 will react to form Fe3+ and Cl- ions

d. Fe2+ ions will undergo a disproportionation reaction to form Fe and Fe3+ ions

2007-02-27 02:06:03 · 1 answers · asked by godrics 2

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