1) A sample initially contains 8.0 moles of a radioactive isotope. How much of t
ID: 883422 • Letter: 1
Question
1)
A sample initially contains 8.0 moles of a radioactive isotope. How much of the sample remains after five half-lives?
Express your answer using two significant figures.
2)
Consider a reaction that has a positive H and a positive S. Which of the following statements is TRUE?
Consider a reaction that has a positive H and a positive S. Which of the following statements is TRUE?
It is not possible to determine without more information.
3)
Consider a reaction that has a positive H and a negative S. Which of the following statements is TRUE?
Consider a reaction that has a positive H and a negative S. Which of the following statements is TRUE?
It is not possible to determine without more information.
4)
Consider a reaction that has a negative H and a negative S. Which of the following statements is TRUE?
Consider a reaction that has a negative H and a negative S. Which of the following statements is TRUE?
It is not possible to determine without more information.
5)
For the following example, identify the following.
3O2(g) 2O3(g)
For the following example, identify the following.
3O2(g) 2O3(g)
It is not possible to determine without more information.
6)
Which statement is true regarding the sublimation of dry ice (solid CO2)?
Which statement is true regarding the sublimation of dry ice (solid )?
H is positive,S is negative, and G is positive at all temperatures.
7)
Use the standard half-cell potentials listed below to calculate the standard cell potential for the following reaction occurring in an electrochemical cell at 25°C. (The equation is balanced.)
Mg(s) + Cu2+(aq) Cu(s) + Mg2+(aq)
Mg2+(aq) + 2 e- Mg(s) E° = -2.38 V
Cu2+(aq) + 2 e- Cu(s) E° = +0.34 V
Use the standard half-cell potentials listed below to calculate the standard cell potential for the following reaction occurring in an electrochemical cell at 25°C. (The equation is balanced.)
Mg(s) + Cu2+(aq) Cu(s) + Mg2+(aq)
Mg2+(aq) + 2 e- Mg(s) E° = -2.38 V
Cu2+(aq) + 2 e- Cu(s) E° = +0.34 V
-2.04 V
8)
Which of the following redox reactions do you expect to occur spontaneously in the reverse direction? (Hint: The reactions are occurring under standard conditions (1 M for the aqueous ions).)
Check all that apply.
Check all that apply.
This reaction will be nonspontaneous at all temperatures. This reaction will be nonspontaneous only at high temperatures. This reaction will be spontaneous only at high temperatures. This reaction will be spontaneous at all temperatures.It is not possible to determine without more information.
3)
Consider a reaction that has a positive H and a negative S. Which of the following statements is TRUE?
Consider a reaction that has a positive H and a negative S. Which of the following statements is TRUE?
This reaction will be nonspontaneous only at high temperatures. This reaction will be spontaneous at all temperatures. This reaction will be spontaneous only at high temperatures. This reaction will be nonspontaneous at all temperatures.It is not possible to determine without more information.
4)
Consider a reaction that has a negative H and a negative S. Which of the following statements is TRUE?
Consider a reaction that has a negative H and a negative S. Which of the following statements is TRUE?
This reaction will be nonspontaneous only at high temperatures. This reaction will be spontaneous only at high temperatures. This reaction will be nonspontaneous at all temperatures. This reaction will be spontaneous at all temperatures.It is not possible to determine without more information.
5)
For the following example, identify the following.
3O2(g) 2O3(g)
For the following example, identify the following.
3O2(g) 2O3(g)
It is not possible to determine without more information.
6)
Which statement is true regarding the sublimation of dry ice (solid CO2)?
Which statement is true regarding the sublimation of dry ice (solid )?
H is positive, S is positive, and G is positive at low temperature and negative at high temperature. H is negative,S is positive, and G is negative at all temperatures. H is negative, S is negative, and G is negative at low temperature and positive at high temperature.H is positive,S is negative, and G is positive at all temperatures.
7)
Use the standard half-cell potentials listed below to calculate the standard cell potential for the following reaction occurring in an electrochemical cell at 25°C. (The equation is balanced.)
Mg(s) + Cu2+(aq) Cu(s) + Mg2+(aq)
Mg2+(aq) + 2 e- Mg(s) E° = -2.38 V
Cu2+(aq) + 2 e- Cu(s) E° = +0.34 V
Use the standard half-cell potentials listed below to calculate the standard cell potential for the following reaction occurring in an electrochemical cell at 25°C. (The equation is balanced.)
Mg(s) + Cu2+(aq) Cu(s) + Mg2+(aq)
Mg2+(aq) + 2 e- Mg(s) E° = -2.38 V
Cu2+(aq) + 2 e- Cu(s) E° = +0.34 V
-2.04 V
8)
Which of the following redox reactions do you expect to occur spontaneously in the reverse direction? (Hint: The reactions are occurring under standard conditions (1 M for the aqueous ions).)
Check all that apply.
Check all that apply.
Mg2+(aq)+Fe(s) Mg(s)+Fe2+(aq) 2Al(s)+3Pb2+(aq) 2Al3+(aq)+3Pb(s) 2Cu+(aq)+Co(s) 2Cu(s)+Co2+(s) Fe(s)+Cr3+(aq) Fe3+(aq)+Cr(s)Explanation / Answer
1) Initial moles = 8 moles
After first half life = 8/2 = 4moles
After second half life = 4/2= 2 moles
After third half life = 2/2 = 1moles
After fourth half life = 1/2= 0.5 moles
After fifth half life= 0.5/2= 0.25 moles
2) G0 = H0 - TS0
The reaction is spontaneous if G0 < 0 [negative] .
Now a reaction that has a positive H and a positive S, the G can be negative if TS0 > H0
This is possible at high temperatures
Answer: This reaction will be spontaneous only at high temperatures.
3)
G0 = H0 - TS0
The reaction is spontaneous if G0 < 0 [negative] .
Now a reaction that has a positive H and a negative S, the G can not be negative at any temperature
This reaction will be nonspontaneous at all temperatures
4)
G0 = H0 - TS0
The reaction is spontaneous if G0 < 0 [negative] .
Now a reaction that has a negative H and a negative S, the G can not be negative at low temperature
This reaction will be nonspontaneous only at high temperatures.
5) a positive H and a negative S
6) Dry ice
has a positive H and a positive S and G is positive at low temperature and negative at high temperature
7) E0cell = E0cathode - E0anode
E0cell = 0.34 - (-2.38) = +2.72 V
8) Mg2+(aq)+Fe(s) Mg(s)+Fe2+(aq)
E0cell should be negative to have the reaction non spontaneous and spontaneous in reverse direction
E0cell = E0cathode - E0anode < 0 so the reaction is spontaneous in reverse direction
2Al(s)+3Pb2+(aq) 2Al3+(aq)+3Pb(s)
E0cell = E0cathode - E0anode > 0 so the reaction is non spontaneous in reverse direction
2Cu+(aq)+Co(s) 2Cu(s)+Co2+(s)
E0cell = E0cathode - E0anode > 0 so the reaction is non spontaneous in reverse direction
Fe(s)+Cr3+(aq) Fe3+(aq)+Cr(s) <0 so the reaction is spontaneous in reverse direction
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