Question

The decomposition of hydrogen peroxide (H2O2) is a first order reaction with a rate constant 1.8×10-5 s -1 at 20°C.

(a) What is the half life (in hours) for the reaction at 20°C?

(b) What is the molarity of H2O2 after four half lives if the initial concentration is 0.30 M?

(c) How many hours will it take for the concentration to drop to 25% of its initial value?

*Help please!!!*

Answer #1

**a)**

**Given:**

**k = 1.8*10^-5 s-1**

**use relation between rate constant and half life of 1st
order reaction**

**t1/2 = (ln 2) / k**

**= 0.693/(k)**

**= 0.693/(1.8*10^-5)**

**= 3.85*10^4 s**

**= 3.85*10^4 / 3600 hr**

**= 10.7 hr**

**Answer: 10.7 hr**

**b)**

**after each half life concentration becomes
half**

**after n half life,**

**concentration = initial concentration *
(1/2)^n**

**= 0.30*(1/2)^4**

**= 0.30/16**

**= 0.01875 M**

**Answer: 0.01875 M**

**c)**

**let initial concentration = 100**

**final concentration = 25 % of initial concentration = 25
% of 100 = 25**

**use:**

**concentration = initial concentration *
(1/2)^n**

**25 = 100 * (1/2)^n**

**1/4 = (1/2)^n**

**n = 2**

**It will take 2 half lifes**

**time =2*10.7 hour = 21.4 hour**

**Answer: 21.4 hour**

the decomposition of hydrogen peroxide
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QUESTION 6
The first-order
decomposition of hydrogen peroxide occurs according to the
equation
2
H2O2(aq) --> 2 H2O(l) +
O2(g)
Using data from a
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[H2O2] versus time
[H2O2]2 versus time
1 /
[H2O2] versus time
ln[H2O2] versus time

1) The decomposition of hydrogen peroxide in dilute sodium
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H2O2(aq)H2O(l)
+ ½ O2(g)
is first order in
H2O2 with a rate constant of
1.10×10-3
min-1.
If the initial concentration of
H2O2 is
9.20×10-2 M, the concentration of
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Data for the decomposition of hydrogen peroxide at some set
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2 H2O2 ---> 2 H2O + O2
t (seconds)
0 ,
60 , 120 ,
180 , 240 , 360 , 420 ,
600
[H2O2] (M) 0.882, 0.697, 0.566 ,0.458, 0.372, 0.236, 0.188,
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In a study of the gas phase decomposition of hydrogen
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H2O2(g)H2O(g)
+ ½ O2(g)
the following data were obtained:
[H2O2], M
0.133
6.65×10-2
3.33×10-2
1.67×10-2
seconds
0
16.1
48.2
112
Hint: It is not necessary to graph these
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(1)
The observed half life for this reaction when the starting
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when the starting concentration is
6.65×10-2 M is
s.
(2)
The average (1/[H2O2]) / t
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H2O2 solution at 46°C over a period of 24.0
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:
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decreases to 0.600 M;
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[H2O2]t after 225 s and (c) find
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Suppose that you start with .0175M of N2O5
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Clear solution, thicker
After drop a potassium iodide,...

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