All of the following substances have a standard free energy of zero EXCEPT
a.Hg(λ).
b.Cl2(g).
c.Br2(λ).
d.I2(g).
e.S8(s).
All of the following substances have a standard free energy of zero EXCEPT?
I believe the answer is:
e.S8.
Monday, May 24, 2010
A.C. vs fan ?
We have a on bedroom apartment and are trying to keep the electric bill down as well as electric usage for environmental reasons. We have central A.C. Is it cheaper to set the A.C. to a bearable temperature, such as 79 deg F, or keep a standard box fan on all the time?
A.C. vs fan ?
Fans do not cool, they circulate air (hot air). You get the sensation of cool because of moisture drying on your skin. A fan will be cheaper to run than a 110 volt AC. Central AC units are 220 volt and cheaper to run. Setting the temp at 78 will actually cool the rooms and probably be more comfortable than a few fans.
Reply:Do both,the fan will circulate the cool air and make the room cooler.I use my A/C with a fan all the time.Low cool and a fan is my theory.....
Reply:get an A.C. but put on the setting called Energy saver so it won't use as much.
Reply:Fan, even a couple of fans are cheaper than the ac!
Reply:Central air is much more efficient than dealing with fans. For one fans only move around hot air. You can set your AC to whatever temp you are comfortable with and it will maintain that temp. Frankly, 79 is a bit high. We set ours at 76. It keeps the moisture out of the air without freezing everyone out. We also have a 3300 sq. ft. home. We have not had a high electric bill yet.
rosemary
A.C. vs fan ?
Fans do not cool, they circulate air (hot air). You get the sensation of cool because of moisture drying on your skin. A fan will be cheaper to run than a 110 volt AC. Central AC units are 220 volt and cheaper to run. Setting the temp at 78 will actually cool the rooms and probably be more comfortable than a few fans.
Reply:Do both,the fan will circulate the cool air and make the room cooler.I use my A/C with a fan all the time.Low cool and a fan is my theory.....
Reply:get an A.C. but put on the setting called Energy saver so it won't use as much.
Reply:Fan, even a couple of fans are cheaper than the ac!
Reply:Central air is much more efficient than dealing with fans. For one fans only move around hot air. You can set your AC to whatever temp you are comfortable with and it will maintain that temp. Frankly, 79 is a bit high. We set ours at 76. It keeps the moisture out of the air without freezing everyone out. We also have a 3300 sq. ft. home. We have not had a high electric bill yet.
rosemary
Standard Reduction Principal?
Half Reaction Eo (V)
Zn2+(aq) + 2e- -%26gt; Zn(s) = –0.763
Tl+(aq) + e- -%26gt; Tl(s) = –0.336
Use the standard reduction potentials to find the standard
cell potential, E°, for the reaction;
Zn(s) + 2Tl+(aq) r Zn2+(aq) + 2Tl(s)
(A) 0.427 V (B) 0.091 V
(C) –0.091 V (D) –0.427 V
How would I solve this?
Standard Reduction Principal?
Zn2+(aq) + 2e- -%26gt; Zn(s) = –0.763
Tl+(aq) + e- -%26gt; Tl(s) = –0.336
Flip first equation
Zn(s) -%26gt; Zn2+(aq) + 2e- = +0.763
Tl+(aq) + e- -%26gt; Tl(s) = –0.336
Note sign change
Mult. 2nd equation by 2
Zn(s) -%26gt; Zn2+(aq) + 2e- = +0.763
2Tl+(aq) + 2e- -%26gt; 2Tl(s) = –0.336
Note that the voltage is unaffected.
Add equations and voltages together. Here is just the voltages:
+0.763 + (-0.336) = 0.427 V
Zn2+(aq) + 2e- -%26gt; Zn(s) = –0.763
Tl+(aq) + e- -%26gt; Tl(s) = –0.336
Use the standard reduction potentials to find the standard
cell potential, E°, for the reaction;
Zn(s) + 2Tl+(aq) r Zn2+(aq) + 2Tl(s)
(A) 0.427 V (B) 0.091 V
(C) –0.091 V (D) –0.427 V
How would I solve this?
Standard Reduction Principal?
Zn2+(aq) + 2e- -%26gt; Zn(s) = –0.763
Tl+(aq) + e- -%26gt; Tl(s) = –0.336
Flip first equation
Zn(s) -%26gt; Zn2+(aq) + 2e- = +0.763
Tl+(aq) + e- -%26gt; Tl(s) = –0.336
Note sign change
Mult. 2nd equation by 2
Zn(s) -%26gt; Zn2+(aq) + 2e- = +0.763
2Tl+(aq) + 2e- -%26gt; 2Tl(s) = –0.336
Note that the voltage is unaffected.
Add equations and voltages together. Here is just the voltages:
+0.763 + (-0.336) = 0.427 V
Standard Cell Potential?
Given the following,
Fe3+(aq) + e- ===%26gt; Fe2+(aq) (E° = +0.771 V) and
Pb2+(aq) + 2 e- ===%26gt; Pb(s) (E° = -0.126 V),
calculate the standard cell potential for the cell based on the reaction below and predict whether the reaction can occur spontaneously under standard conditions:
Pb2+(aq) + 2 Fe2+(aq) ===%26gt; 2Fe3+(aq) + Pb(s).
A. -0.897 V
B. +0.897 V
C. -0.645 V
D. +0.645 V
E. spontaneous.
F. nonspontaneous.
Standard Cell Potential?
Fe2+ %26gt;%26gt; Fe3+ + 1e- ( E° = - 0.771 V)
Pb2+ + 2e-%26gt;%26gt; Pb ( E° = - 0.126 V)
E = - 0.771 - 0.126 = - 0.897 V
non spontaneous
Fe3+(aq) + e- ===%26gt; Fe2+(aq) (E° = +0.771 V) and
Pb2+(aq) + 2 e- ===%26gt; Pb(s) (E° = -0.126 V),
calculate the standard cell potential for the cell based on the reaction below and predict whether the reaction can occur spontaneously under standard conditions:
Pb2+(aq) + 2 Fe2+(aq) ===%26gt; 2Fe3+(aq) + Pb(s).
A. -0.897 V
B. +0.897 V
C. -0.645 V
D. +0.645 V
E. spontaneous.
F. nonspontaneous.
Standard Cell Potential?
Fe2+ %26gt;%26gt; Fe3+ + 1e- ( E° = - 0.771 V)
Pb2+ + 2e-%26gt;%26gt; Pb ( E° = - 0.126 V)
E = - 0.771 - 0.126 = - 0.897 V
non spontaneous
Quadratic function in standard form from sets of points?
please help and explain! thanks youuu!
Find a quadratic function in standard form for each set of points.
1. (0, 3) (1. -4) (2, -9)
(all i know is that c=3, right?)
a. f(x)= x^2+27x + 3
b. f(x)= x^2 -27x + 3
c. f(x)= x^2 +8x -3
d. f(x)= x^2 -8x + 3
2. (0, -4) (1, 0) (2, 2)
a. f(x)= -2 x^2 +5x -4
b. f(x)= -x^2 -5x +4
c. f(x)= -x^2+5x -4
d. f(x)= -x^2 +5x +4
Quadratic function in standard form from sets of points?
They are multiple choice question, so you can substitute and check.
1. First points satisfies all euqtions
so check with (1, -4)
1 + 27 + 3 = 31 not equal to -4 so its not a
1 - 27 + 3 not equal to -4 so its not b
1 + 8 - 3 not equal to -4 so its not c
1 - 8 + 3 is equal to -4 so its d
So the answer is d. Now if you want you can chcek with the third point.
4 - 16 + 3 = -9 so now you are sure its d
2. substitue (0, -4) from this you know it cannot be b, d as they will result is f(0) = 4
so it has to be a, d
Substitute (1, 0) in a
-2 + 5 - 4 = -1 not equal to 0 so its not a
in c, -1 + 5 - 4 = 0 so its c
Answer is c
Find a quadratic function in standard form for each set of points.
1. (0, 3) (1. -4) (2, -9)
(all i know is that c=3, right?)
a. f(x)= x^2+27x + 3
b. f(x)= x^2 -27x + 3
c. f(x)= x^2 +8x -3
d. f(x)= x^2 -8x + 3
2. (0, -4) (1, 0) (2, 2)
a. f(x)= -2 x^2 +5x -4
b. f(x)= -x^2 -5x +4
c. f(x)= -x^2+5x -4
d. f(x)= -x^2 +5x +4
Quadratic function in standard form from sets of points?
They are multiple choice question, so you can substitute and check.
1. First points satisfies all euqtions
so check with (1, -4)
1 + 27 + 3 = 31 not equal to -4 so its not a
1 - 27 + 3 not equal to -4 so its not b
1 + 8 - 3 not equal to -4 so its not c
1 - 8 + 3 is equal to -4 so its d
So the answer is d. Now if you want you can chcek with the third point.
4 - 16 + 3 = -9 so now you are sure its d
2. substitue (0, -4) from this you know it cannot be b, d as they will result is f(0) = 4
so it has to be a, d
Substitute (1, 0) in a
-2 + 5 - 4 = -1 not equal to 0 so its not a
in c, -1 + 5 - 4 = 0 so its c
Answer is c
Standard Deviation?
A teacher gave a 25 multiple choice question test. After giving the tests, she computed a mean and standard deviation of the scores. The standard deviation was 0. Based on this info:
a) all the students had the same score
b) she must have made a mistake
c)about half the scores were above the mean.
please explain!
Standard Deviation?
Standard deviation provides the intervals for a standard bell curve, which would give you the percent of people which got a certain score.
If the intervals on the bell curve were 0, all students would have the same score. Because of that, half of the scores could not be above the mean, since they all are the mean score, and while it is possible a mistake was made, all students getting the same score would be the correct answer
Reply:A, but probably B. If the SD was zero, the teacher could just look at the scores and know that!
Reply:SD = 0 is possible only if all the scores are the same. So, a is correct (although quite possibly b is also correct :) )
wallflower
a) all the students had the same score
b) she must have made a mistake
c)about half the scores were above the mean.
please explain!
Standard Deviation?
Standard deviation provides the intervals for a standard bell curve, which would give you the percent of people which got a certain score.
If the intervals on the bell curve were 0, all students would have the same score. Because of that, half of the scores could not be above the mean, since they all are the mean score, and while it is possible a mistake was made, all students getting the same score would be the correct answer
Reply:A, but probably B. If the SD was zero, the teacher could just look at the scores and know that!
Reply:SD = 0 is possible only if all the scores are the same. So, a is correct (although quite possibly b is also correct :) )
wallflower
Standard potential of a battery?
A student was given a standard Fe(s) | Fe+2 (aq) half-cell and another half-cell containing an unknown metal M immersed in 1 M MNO3(aq). When these two half-cells were connected at 25 (degrees) C, the complete cell functioned as a galvanic cell with E = 1.24 V. The reaction was allowed to continue overnight and the two electrodes were weighted. The iron electrode was found to be lighter and the unknown metal electrode was heavier. What is the standard potential of the unknown M+/M couple?
Standard potential of a battery?
Look up the iron half cell potential and subtract.
Standard potential of a battery?
Look up the iron half cell potential and subtract.
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